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1. C My Folder My Program SedentexCT is incorrect because there are spaces between words in two folder names My Folder and My Program A few examples of a correct path C MyFolder MyProgram SedentexCT software C SedentexCT software C CBCT QC SedentexCT software Stack of images datasets Similar to the software datasets used in the software must be placed within folders which have no space in their names For example Path C My FolderDeviceName is incorrect The most convenient place for the datasets would be in a subfolder of the SedentexCT software You can create a first subfolder called datasets in the main folder of the software e g C SedentexCTsoftware datasets and create further subfolders showing the type of device the name of the imaging protocol FOV resolution mA the date of exposure etc for example C SedentexCTsoftware datasets Scanora 60x60_HR_8mA 2010_11_ 14 FE SEDENTEXCT D3 4 Report Appendix II User Manual Make sure there are no spaces in any of the folder names Also the stack of images must be placed on a writeable medium hard drive with at least 1 GB of free space Opening the images from CDs DVDs is not possible as the program will not be able to convert the images To load a stack of images click on File and then on Open set of images In the pop up window browse to the folder containing the dataset
2. LN N o LA 2 540 25 _ N 10 25 0 25 5 LN N CONTRAST RESOLUTION INSERT 5 PER SET Aluminium 2 70 g cc ox holes PEE 2 16 g cc mm Delrin 1 42 g cc 4 0 0 1mm 3 0 0 1mm LDPE 0 92 g cc SO a Air 1 0 0 1mm Water PMMA use blank insert re with 10mm sides ES centred in the cylinder e 10mm 231 5 0 25 PS 134 5 0 25 LN S Te amp ee q PMMA 1 50 25 17 00 25 1 5 0 25 1 5 0 25 M31 5 0 25 1 5 0 25 PIXEL INTENSITY INSERT 1 PER SET Aluminium 2 70 g cc PTFE 2 16 g cc Delrin 1 42 g cc LDPE 0 92 g cc Air Water PMMA Each disc is 3 3mm thick from aluminium at the base up to air at the top LEEDS TEST OBJECTS LTD MiRo House Becklands Close phone 44 0 1423 321102 Boroughbridge email Info leedstestobjects com North Yorkshire YO51 9UY web www leedstestobjects com United Kingdom EUROPEAN COMMISSION European Research Area HEE sEDENTEXCT D3 4 Report
3. Insert measurements Software measurements Contrast to noise ratio Use the dataset containing the pixel intensity value insert Scroll through the axial slices using the slider underneath the top window of the three small windows at the left Scroll until you have a clear view of the pixel intensity value insert Click and drag the left mouse button to create a selection window After releasing the left mouse button you can still change the position of each border by selecting the small squares in the middle of the borders and dragging them pa SEDENTEXCT D3 4 Report Appendix II User Manual Align the border of the selection with the border of the insert Do not align them with the small wedges you see at the top bottom left and right Align them as if the insert would be a perfect circle NO YES The most crucial borders are the top and left border The size of the selected region is not important as long as those two borders are aligned with the insert border Once the borders have been set in the axial view switch to either the coronal or sagittal view by clicking in the middle or bottom small window on the left side of the screen Scroll through the slices until you are at the position of the insert around slice nr 180 in the coronal view and nr 270 in the sagittal view Adjust the top border with the top of the insert The lower border is not important pe SEDENTEXCT D3 4 Report
4. A dosimeter such as a thimble ionisation chamber should be positioned at the isocentre of the X ray beam or at the surface of the detector If possible the scanner should be set to operate in service mode so that the X ray tube is stationary If this is not possible then alternatives should be considered such as the possible use of the scout mode Alternatively the scanner can be operated under normal conditions with care taken in setting up the dosemeter and the filters A typical protocol for measuring HVL should be followed in which the transmission through known thicknesses of high purity aluminium is assessed Using this HVL measurement and knowledge of the X ray tube design the total filtration can be estimated from look up tables 2 4 Radiation Field of View The field of view FOV of a dental CBCT scanner is usually defined at the isocentre The scanner should be set to operate in service mode and a film or a CR cassette can be placed at the isocentre and exposed to different field sizes The size of the film or the CR cassette should be chosen so as to extend over the nominal dimensions of the FOV The dimensions of the imaged field can be measured and compared to the nominal FOV as quoted by the manufacturers and the dimensions of the FOV measured at baseline If the manufacturers state that it is necessary to irradiate beyond the nominal FOV for the purposes of image reconstruction this should be taken into accou
5. Appendix II User Manual Select CNR from the insert list from the bottom and press Evaluate After some processing time the results will appear in a pop up screen Copy the CNR values into the QC form see below Metal artefacts In a dataset containing the metal artefacts inserts in the axial view scroll to the insert and position the selection box using the same criteria as for the CNR insert again the top and left borders are the ones that should be accurate rs SEDENTEXCT D3 4 Report Appendix II User Manual Switch to the coronal or sagittal view and align the top border of the selection with the top of the insert The lower border is not important as demonstrated Select Artefacts from the insert list and press Evaluate Copy the value from the pop up window into the form PMMA noise amp uniformity Es SEDENTEXCT D3 4 Report Appendix II User Manual In the dataset containing the PMMA portion of the phantom in the axial view scroll to the homogeneous PMMA section For large FOV devices place the selection box by putting all four corners of the box on the edge of the phantom For medium and small FOV devices make the box as large as possible without going outside the phantom Also be sure to avoid artifact regions at the border of the FOV as they will hamper the analysis Next switch to the coronal or sagittal view Align the top border of the selection with the
6. axis FOV off axis Figure 1 Measurement points for Index 1 HEER SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol FOV axis Phantom ANTERIOR Figure 2 Measurement points for Index 2 Such indices can be used to monitor the reproducibility of the dose distribution over time to relate to manufacturer s specification and national or international diagnostic reference levels if set using a dose index 3 1 3 Dose area product DAP The product of the dose in the beam multiplied by the area of the beam at that point is known as the dose area product DAP and is a dose index routinely used in general radiography and fluoroscopy DAP can readily be measured by the medical physics expert using either a calibrated ionisation chamber that integrates the dose across the primary beam DAP meter or by measuring dose and beam size at a fixed point Care should be taken on units where the beam size changes during the scan and a suitable DAP meter must be used for these units If a DAP reading is provided on the equipment readout the medical physics expert should confirm the accuracy of such a readout The readout may then be used by the dentist to audit and monitor dose and compare to any national or international audit levels see diagnostic reference levels If no DAP reading is provided the medical physics expert should provide the DAP readings for all standard settings of the equipment so the dentist can compare
7. April 2009 Samei E Badano A Chakraborty D Compton K Cornelius C Corrigan K Flynn MJ Hemminger B Hangiandreou N Johnson J Moxley M Pavlicek W Roehrig H Rutz L Shepard J Uzenoff R Wang J Willis C Assessment of Display Performance for Medical Imaging Systems Report of the American Association of Physicists in Medicine AAPM Task Group 18 Medical Physics Publishing Madison WI AAPM On Line Report No 03 April 2005 Scarfe WC Farman AG What is cone beam CT and how does it work Dent Clin North Am 2008 52 4 707 30 Scarfe WC Farman AG Sukovic P Clinical applications of cone beam computed tomography in dental practice J Can Dent Assoc 2002 72 1 75 80 Suess C Kalender WA Coman JM New low contrast resolution phantoms for computed tomography Med Phys 1999 26 2 296 302 Vassileva J Stoyanov D Quality control and patient dosimetry in dental cone beam CT Radiat Prot Dosimetry 2010 139 1 3 310 12 Watanabe H Honda E Kurabayashi T Modulation transfer function evaluation of cone beam computed tomography for dental use with the oversampling method Dentomaxillofac Radiol 2010 39 1 28 32 WF seDENTEXCT D3 4 Report Appendix I Generic QA Protocol Quality Control for Dental Cone Beam Computed Tomography CBCT Systems ME seDENTEXCT D3 4 Report Quality Control for Dental Cone Beam Computed Tomography CBCT Systems 1 Introduction A Quality Control Programme lays out the necessary testing
8. Deliverable 3 3 MM PP 9 3 Work in the Final Period Methodology ociosas 10 4 Work in the Final Period Results oooocccconnncccccccnccccnncnonnncccncnnnnnnnnnnnnnnnncnnos 11 4 1 Generic QA protocol lui A nenene 11 4 2 User manual for using the SEDENTEXCT phantom and software 12 5 Work in the Final Period ConcluSions ccccceeeeeeseeeeeceeeeeeeeeeeseeneeeeeeeeeees 13 5 1 CONCISO shat ERE ED Eee adada ae Ada 13 5 2 Implications for future work cintia a 13 6 Overall Work Package Conclusions stereo 14 6 1 SEDENTEXCT Guidelines ccoo crio 14 o o E a aaa aaan aana EE 14 A A 14 6 4 Future dissemInatio HM ceci 15 Ae Eo deeeceenpeeeseasetusecectcepientis 16 Appendix I Generic QA Protocol Quality Control for Dental Cone Beam Computed Tomography CBCT Systems cccccccccnnnccococcnnncncconannnnnnnnnnnnnncnnnnnnnnnnnnnnnnencnannnnnes 18 Appendix Il SEDENTEXCT User Manual Image Quality Scanning Protocol 34 Appendix Ill SEDENTEXCT Quality Control Phantom Specification Sheet 50 MA seDENTEXCT D3 4 Report 1 The Context 1 1 SEDENTEXCT aims and objectives The aim of this project is the acquisition of the key information necessary for sound and scientifically based clinical use of dental Cone Beam Computed Tomography CBCT In order that safety and efficacy are assured and enhanced in the real world the parallel aim is to use the information to develop
9. National guidance exists in some EU countries and the SEDENTEXCT project has developed phantoms to facilitate carrying out a wide range of measurements Some of the tests are straightforward and can be readily performed by the clinical staff using the CBCT equipment Other tests are more complex and the input of a medical physicist is required Routine quality control tests primarily involve comparison of results with those determined during commissioning Significant variation as indicated by pre determined action levels should be investigated either with the help of a medical physics expert MPE or the equipment service engineer Not all possible methods of assessment are considered essential It is important to perform enough tests to confirm that the equipment is operating as intended More complex tests do add extra information that is helpful in the optimisation process and they are detailed here for completeness However whether the more detailed tests MS SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol are undertaken will depend on the availability of expert support and the necessary resources The tests are summarised in the table at the end of the manual The recommendations of priority level of expertise frequency and action levels are based on published guidance and the experience of the SEDENTEXCT team in validating the use of the SEDENTEXCT QC test phantom This represents an initial assessment of what
10. PTFE PSF INSERT 1 PER SET 0 25mm diameter Stainless Steel Wire 31 5 0 25 e 34 5 0 25 E 225 0 0 25 S i N 20 26 0 01 PMMA 1 5 0 25 17 0 0 25 gt 54025 0 25mm recess 1 0mm depth M31 5 0 25 1 5 0 25 Thread to fit above 1 5 0 25 ARTEFACT BEAM HARDENING INSERT 2 per set Titanium inserts 31 5 0 25 gt 234 5 0 25 a 25 15 0 1 10mm 3 o N PMMA 1 5 0 25 17 0 0 25 1 5 0 25 1 5 0 25 M31 5 0 25 1520 25 SPATIAL RESOLUITION Z 1 PER SET 1 0 LP mm 1 7 LP mm 2 0 LP mm 2 5 LP mm 2 8 LP mm 4 0 LP mm 5 0 LP mm Q A LN N JAY o RA Si NE K 31 5 0 25 A NSZ e 34 5 0 25 dl S o N PMMA 1 540 25 o 17 00 25 1 5 0 25 11 1 0 25 1 5 0 25 M31 5 0 25 1520 25 Continued 1 02025 _ 3 298025 1020 25 3 292025 QO 11 0 M12 SPATIAL RESOLUTION INSERTXY RESOLUTION INSERT XY 1 x XY per set 1 0 LP mm 1 7 LP mm 2 0 LP mm 2 5 LP mm 2 8 LP mm 4 0 LP mm 5 0 LP mm LA N 12 5 O o N 34 5 0 25 A i i 24 0 0 25 gt 10 5 0 25 PMMA 11 1 0 25
11. Radiology Dentomaxillofac Radiol 2009 38 4 187 95 HPA RPD 065 Recommendations for the design of X ray facilities and quality assurance of dental Cone Beam CT Computed tomography systems JR Holroyd and A Walker Health Protection Agency 2010 IPEM Quality assurance in dental Radiology Report No 671995 IEC International Electrotechnical Commission 2008 Medical electrical equipment Part 1 3 General requirements for basic safety and essential performance Collateral Standard Radiation protection in diagnostic X ray equipment IEC publication 60601 1 3 IPEM Report 32 Measurement of the Performance characteristics of diagnostic X ray systems used in medicine Part III Computed Tomography X ray scanners 2 Ed IPEM 2003 IPEM Report 32 Measurement of the Performance characteristics of diagnostic X ray systems used in medicine Part VII Digital imaging system IPEM 2010 IPEM Report 91 Recommended standards for the routine performance testing of diagnostic X ray imaging systems IPEM 2005 Jaffray DA Siewerdsen JH Cone beam computed tomography with a flat panel imager initial performance characterization Med Phys 2000 27 6 1311 23 Katsumata A Hirukawa A Okumura S et al Relationship between density variability and imaging volume size in cone beam computerized tomographic scanning of the maxillofacial region an in vitro study Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009 107 3 420 25 Lagrav re MO Carey J Ben Zvi M
12. evidence based guidelines dealing with justification optimisation and referral criteria and to provide a means of dissemination and training for users of CBCT The objectives and methodology of the collaborative project are 1 To develop evidence based guidelines on use of CBCT in dentistry including referral criteria quality assurance guidelines and optimisation strategies Guideline development will use systematic review and established methodology involving stakeholder input 2 To determine the level of patient dose in dental CBCT paying special attention to paediatric dosimetry and personnel dose 3 To perform diagnostic accuracy studies for CBCT for key clinical applications in dentistry by use of in vitro and clinical studies 4 To develop a quality assurance programme including a tool tools for quality assurance work including a marketable quality assurance phantom and to define exposure protocols for specific clinical applications 5 To measure cost effectiveness of important clinical uses of CBCT compared with traditional methods 6 To conduct valorisation including dissemination and training activities via an open access website At all points stakeholder involvement will be intrinsic to study design 1 2 Work package 3 WP3 objectives The Quality Assurance QA process is vital in order to provide confidence in the suitability of an imaging technique for its intended purpose and to ensure its safe us
13. is sensible and achievable but it must be borne in mind that as experience of testing these units is obtained over a period of years these recommendations should be critically reviewed as new evidence becomes available Some manufacturers of dental CBCT systems provide a quality assurance phantom with their system which should come with recommendations on the tests that should be performed the best way to perform them how often they should be performed and how the results should be interpreted Some of these quality assurance phantoms are also provided with software that automatically performs analysis of the acquired image Where a phantom has been supplied the manufacturer s recommendations are likely to be broadly similar to those contained within this manual Where there are some tests that are included in the manufacturer s recommendations but not in this manual they should be performed as there may be a specific reason for its inclusion Where a test is included in this manual but not in the manufacturer s recommendations consideration should be given to performing the test Consult a medical physicist if necessary 2 X ray tube and generator The correct and reliable performance of the X ray tube and generator is crucial to the production of consistent images Both radiation output and tube kilovoltage should be regularly monitored whilst tube filtration and leakage should be performed as part of the equipment commissioning and shoul
14. speed has been significantly increased and that the measurements can be sufficiently reproducible for QC purposes The purpose of this work to produce a marketable QA phantom for dental CBCT with associated software is met as indicated by the presented marketing plans of the partner LTO where the acceptance of the final phantom and the associated software for commercial production is demonstrated A sEDENTEXCT D3 4 Report 3 Work in the Final Period Methodology Sections 3 4 and 5 of this deliverable report the work in WP3 in the last period The purpose of this work is to form a QA protocol for periodic QA tests in daily clinical practice and determine its implementation on CBCT units As reported in earlier deliverables the tools phantom and software were developed in three rounds during the project and tested by NKUA and KUL resulting in the construction of the final QA phantom and the accompanying software for semi automatic image evaluation of the phantom images The definitive phantom and inserts were scanned on a wide range of CBCT devices Depending on the field of view size the number of scans needed varied between different devices Validation of the associated software by five consortium partners was successful and a clear scanning procedure protocol for all measurements was established as part of D3 3 The methodology used in the previous deliverable D3 3 for the evaluation procedure carried out on the definitive phan
15. the levels to any national or international audit levels see diagnostic reference levels 3 2 Diagnostic reference levels The European Medical Exposures Directive requires that diagnostic reference levels are set and used as part of the optimisation process Exactly how this requirement is applied varies from country to country depending on how it has been implemented into national legislation However the overall aim is that patient dose is audited and the dose for a typical patient is compared to past levels and any national and international levels This will give the dentist A SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol confidence that doses in their practice are not unnecessarily drifting upwards and that they are in line with accepted levels Diagnostic reference levels may be set using a variety of dose indices The UK Health Protection Agency has recommended the use of dose area product DAP and has proposed setting reference levels for the UK for both adult and child procedures The adult level is for the clinical protocol for the placement of an upper first molar implant in a standard male patient and the child level is for the clinical protocol used to image a single impacted maxillary canine of a 12 year old male Based on current national audit data an initial achievable level of 250 mGy cm is proposed and further data is requested so that national reference levels for both adult and child can be set It i
16. this deliverable D3 4 will feed into the Guidelines as an essential chapter regarding safety and efficacy of CBCT in daily practice 6 2 Impact The outcome of WP3 QC phantom software and QA protocol is expected to have a great impact on several stakeholder groups Dentists and radiologists will benefit from following the QA protocol frequently and using the phantom and the software to ensure that their CBCT equipment operates efficiently in terms of output image quality Medical physicists may use the same phantom and software for advanced imaging performance tests on CBCT units The research community may use the phantom and the software for further studies on imaging characteristics Finally the CBCT unit manufacturers may use the phantom and the software for testing prototypes units their new equipment before delivery and any new features added to their units 6 3 Roadmap Less than a decade has passed since CBCT has been widely accepted in dental practice Therefore there is no information available on image quality issues for CBCT devices that have been in commission for several years X ray tube or detector degradation can lead to a progressive deterioration of image quality This topic can be addressed using the QC phantom and QA protocol as it allows for a long term assessment of image quality and can help to define clear and evidence based action levels for different image quality parameters The QC phantom can serve an addit
17. A protocol for periodic QA tests in daily clinical practice 1 3 Anticipated impact of the work This section describes the impact of the work in this Work Package as anticipated at the start of the project The outcome of the WP3 QC phantom software and QA protocol is expected to have a great impact on several stakeholder groups Dentists and radiologists will benefit from following the QA protocol frequently and using the phantom and the software ensures that their CBCT equipment operates efficiently in terms of output image quality Medical physicists may use the same phantom and software for advanced imaging performance tests on CBCT units The research community may use the phantom and the software for further studies on imaging characteristics Finally the CBCT unit manufacturers may use the phantom and the software for testing prototypes units their new equipment before delivery and any new features added to their units Stakeholder s Impact Radiologists follow QA protocol use phantom software Dentists to test CBCT equipment efficacy Medical physicists advanced imaging performance tests Research community studies on imaging characteristics CBCT unit manufacturers testing prototypes units and new equipment 1 4 Current state of the art Due to the increasing use of Cone Beam CT CBCT in dental practice and the large number of devices on the market there is a need for a quantified and objective an
18. DI is usually used This is a measurement of the dose integrated across the dose profile along the patient s length It is measured using a pencil detector either in air or in a perspex phantom Such a dose index has drawbacks for use in dental CBCT units due to the greater beam size and asymmetry of the dose distribution However if a CTDI is quoted by the manufacturers it is suggested that this be measured by the medical physics expert at commissioning for comparison with the specification 3 1 2 CBCT dose index The SEDENTEXCT project has investigated the use of a dose index obtained from measurements using a small volume dosemeter in a Perspex phantom This is measured at points across the X Y plane in the centre of the Z axis Measurements can be performed using an ion chamber or TLDs within a suitable PMMA phantom diameter 16cm is recommended Two CBCT dose indices are currently proposed Index 1 requires measurements along a diameter of the phantom Figure 1 and is calculated as the mean of the readings Index 2 involves measurements at the centre of the phantom and at points around the periphery Index 1 allows the measurement of an index for on axis and off axis exposures and full and partial dose distributions simply by rotating the phantom in such a way that the isocentre of the x ray beam lies on the measuring diameter as shown in Figure 1 Index 2 is only suitable for symmetrical dose distributions FOV at the central
19. EURATOM Project Deliverable Project number Project Acronym Project title 212246 SEDENTEXCT Safety and Efficacy of a New and Emerging Dental X ray Modality Instrument Activity code Collaborative Project Small or medium scale Fission 2007 3 2 01 focused research project Start date of project Duration 1 January 2008 42 months Title D3 4 QA Procedure Writing QA protocol Contractual Delivery date Actual Delivery date 1 January 2011 27 March 2011 Organisation name of lead beneficiary for this Document version Deliverable NKUA National Kapodistrian v1 0 University of Athens Dissemination level PU Public X PP Restricted to other programme participants including the Commission RE Restricted to a group defined by the consortium including the Commission CO Confidential only for members of the consortium including the Commission A seDENTEXCT D3 4 Report Authors organisations Kostas Tsiklakis NKUA WP3 Lead Harry C Stamatakis NKUA Ruben Pauwels KUL Anne Walker UNIMAN Adrian Walker LTO Abstract In order to develop tools for Quality Assurance on CBCT in terms of image quality evaluation successive prototype phantoms were constructed and tested using specifically designed software for the evaluation of image quality in three rounds during the project In the third round results from the prototype phant
20. F Spatial Z Spatial XY along peripheral holes Fill up remaining holes using PMMA inserts Rows 5 amp 6 Fill up all columns using PMMA inserts Scanning protocol Phantom and FOV positioning pe SEDENTEXCT D3 4 Report Appendix II User Manual The positioning of the phantom should be done with a tripod or stable platform ensuring that the phantom is level Having the phantom level is one of the key factors for accurate software measurements The positioning of the FOV depends on the size of the FOV When considering the number of columns obtained in once scan there are different possibilities e Large FOV 15cm diameter or larger scan all columns in one scan by placing phantom centrally in the FOV If there is considerable image quality loss at the border of the FOV streaks darkening affecting the peripheral inserts the FOV should be considered as Medium see below e Medium FOV 8 14cm diameter scan 2 or 3 columns per scan depending on the actual size of the FOV and the image quality near the border of the FOV If scanning 2 columns place the centre of the FOV isocentre in the mid point between the two columns If scanning 3 columns place the isocentre between the middle of the peripheral columns and the central column so you will actually be scanning 4 columns e Small FOV up to 6cm diameter scan 1 column per scan When considering the number of rows included in one scan the height of FOV
21. PMMA portion and the insert portion of the phantom Measure the length between the centre of two randomly chosen holes Calculate the deviation by subtracting the measured length with the actual length in the example above the actual length was 50mm For holes that are in line the distance is 10 mm per hole For other measurements use the Pythagorean Theorem to calculate the distance between the holes Perform at least 3 measurements using different angles and combinations of holes Calculate the average deviation and enter it into the form Do not enter the measurement itself the value entered in the form should be the difference between the measurements and the real distance This concludes the geometric accuracy measurement pe SEDENTEXCT D3 4 Report Appendix II User Manual SEDENTEXCT phantom QC form QC information User Date amp hour QC measurements Geometric accuracy Average deviation mm Contrast resolution Air rods visible Aluminium rods visible Delrin rods visible LDPE rods visible PTFE rods visible Contrast to noise ratio Air CNR Alunium Delrin LDPE PTFE Noise amp uniformity Noise Uniformity Artefacts ahi Spatial resolution X Y lines visible Z lines visible pe SEDENTEXCT D3 4 Report Appendix II User Manual Appendix Ill SEDENTEXCT Quality Control Phantom Specificati
22. Packota GV Major PW Effect of object location on the density measurement and Hounsfield conversion in a NewTom 3G cone beam computed tomography unit Dentomaxillofac Radiol 2008 37 6 305 08 Lascala CA Panella J Marques MM Analysis of the accuracy of linear measurements obtained by cone beam computed tomography CBCT NewTom Dentomaxillofac Radiol 2004 33 5 291 94 Loubele M Jacobs R Maes F et al Image quality vs radiation dose of four cone beam computed tomography scanners Dentomaxillofac Radiol 2008 37 6 309 18 Loubele M Maes F Schutyser F Marchal G Jacobs R Suetens P Assessment of bone segmentation quality of cone beam CT versus multislice spiral CT a pilot study Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006 102 2 225 34 HEER seDENTEXCT D3 4 Report McCann C Alasti H Comparative evaluation of image quality from three CT simulation scanners J Appl Clin Med Phys 2004 5 4 55 70 Marguet M Bodez V Quality control of a kV cone beam computed tomography imaging system Article in French Cancer Radiother 2009 13 5 345 52 Naitoh M Hirukawa A Katsumata A Ariji E Evaluation of voxel values in mandibular cancellous bone relationship between cone beam computed tomography and multislice helical computed tomography Clin Oral Implants Res 2009 20 5 503 06 NHS Breast Screening Programme Commissioning and routine testing of full field digital mammography systems NHSBSP equipment report 0604
23. alysis of the technical image quality and radiation dose to enable an optimal use for this imaging modality Horner et al 2009 Loubele et al 2008 Three different aspects have to be considered in the optimization of an X ray imaging modality quantifying the radiation dose and risk for patients assessment of technical image A seDENTEXCT D3 4 Report quality and assessment of diagnostic image quality By means of an appropriate test object the first and second aspect can be studied in one investigation process Ideally the development of test objects goes along with the formation of Quality Assurance QA protocols During these activities the diagnostic image quality must always be considered implying that dose measurements are to be reported in terms of diagnostic needs and technical image quality assessments need to be evaluated for their diagnostic relevance This is particularly the case for dental imaging as it involves a large variety of diagnostic indications requiring different imaging approaches Scarfe et al 2002 There is a lack of standardized tools for image quality analysis for dental CBCT To develop such a tool all available knowledge regarding image quality assessment on other 3D or pseudo 3D imaging modalities spiral CT tomosynthesis kV CBCT used in radiotherapy etc Du et al 2007 Daly et al 2006 McCann et al 2004 Suess et al 1999 needs to be combined with the existing knowledge of CBCT and previous stu
24. amme Commissioning and routine testing of full field digital mammography systems NHSBSP equipment report 0604 April 2009 HEE seDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol Summary Test Priority Level of Suggested Action levels expertise frequency X ray tube and Output repeatability 12 monthly Mean 10 generator Output reproducibility 12 monthly Baseline 10 Filtration Essential MPE When new if output lt 2 5mm aluminium of which 1 5mm changes or tube head should be permanent dismantled Tube potential 12 monthly gt 5 of intended kV Field size and alignment 12 monthly gt 10 expected field size Leakage Essential MPE When new and if damage gt 1000uUGy hr 1 at maximum tube suspected rating Quantitative image Image density values In house MPE Monthly gt 10 from baseline Quali Uniformity and artifacts Essential In house Monthly Visible artefacts on the image or uality gt 10 of the mean Noise Recommended In house MPE 12 monthly gt 10 from baseline Limiting resolution In house MPE 12 monthly gt 20 from baseline Contrast detail In house MPE 12 monthly Dependent on method used Geometrical accuracy In house MPE 12 monthly within 2mm and 22 Display specific General condition Essential In house Monthly Failure to resolve different contrasts in test pattern not consistent between monitors Monitor resolution Monthly Not consistent with baseline image Patient dose Patien
25. antom has six rows for insert placement numbered 1 bottom to 6 top Figure A1 Six phantom rows for insert placement There are seven columns one central six peripheral named A to G Figure A2 pe SEDENTEXCT D3 4 Report Appendix II User Manual Figure A2 Columns for insert placement The distribution of the inserts over the different rows is determined in a more or less strict way with limited user freedom There are a few other restrictions regarding the choice of columns Row 1 Place Artefacts Titanium inserts inside a column that enables the rods to be placed along the radius of the phantom i e perpendicular to the edge Place second Artefacts Titanium insert at a position which enables the rods to be placed approximately parallel to the edge of the phantom The two artefact inserts cannot be adjacent they should be separated by 2 peripheral columns Fill up other central and peripheral columns using PMMA inserts Row 2 Fill up all columns using PMMA inserts This row is used to separate the artifact inserts from all other inserts avoiding interference Row 3 Place the five Contrast Resolution inserts at peripheral positions The placement of these inserts is not crucial as long as the central hole is not used Place the Pixel Intensity Value insert in the remaining peripheral hole Use a PMMA insert for central hole Row 4 Distribute 4 remaining inserts LSF PS
26. click on any file within this folder and click on the Open button to start the loading process This process is divided into 7 steps Figure A3 It is possible to cancel the loading process during these steps except for Step 2 Converting files pa SEDENTEXCT D3 4 Report Appendix II User Manual A Sorting fles in selected folder e Step 1 of 7 amp Converting files SSC Cd Step 2 of 7 Cancel process W Creating axial view Adl Step 3 of 7 D Preparing sagital view A A Step 4 of 7 Figure A3 Seven consecutive steps in the dataset loading process p SEDENTEXCT D3 4 Report Appendix II User Manual Main control elements of the program On the left side there are three preview panels showing a slice of each of the three views axial coronal sagittal It is possible to change the view in main window by clicking on them or on the bookmarks which are placed on the top right side of program window On the preview panels there are also scroll bars to enable scrolling through the slices in all three directions Inserts menu manager To open the inserts menu manager click on Options and then on Insert menu manager It is possible to add change and remove inserts name and measurement file The software provided to the user will have implemented all required measurements normally the user does not have to add or change anything to this manager
27. cquire an image of the uniformity section of the same phantom using the same protocol as at baseline e Draw a region of interest in the centre of the test object as close in size and position to that at baseline as possible and record the average standard deviation across five consecutive axial slices Further analysis Consideration should be given to the calculation of a signal to noise ratio in addition to the noise measurements described above The information provided by signal to noise ratios can be useful in investigating potential problems with the system where they are suggested by noise measurements alone 4 5 Spatial Resolution Spatial resolution is a measure of the ability of the system to detect small high contrast detail 4 5 1 Limiting resolution This test measures the smallest high contrast detail that can be detected usually by using a phantom in which small lines get closer and closer together Method Place a suitable object made of a high contrast material on the detector and expose at clinically relevant exposure factors Magnify the reconstructed image of the test object and optimise the window level Score the number of resolvable groups of lines and convert to the corresponding resolution Be sure to use the same exposure factors as at baseline year on year 4 5 2 Modulation Transfer Function MTF Measurement of the limiting resolution will assess the system s ability to transfer the high frequencies fin
28. cts result in metal artifacts due to scatter beam hardening and photon starvation All of these considerations affect the design of a QC phantom Another limitation is the minimum FOV size of all currently available CBCT devices the phantom must be suitable for all CBCTs including those with a FOV of a few cubic centimeters The objective of the current study is to develop a quality control phantom which is suited for dental CBCT imaging can be used on any CBCT device and allows for the measurement of parameters which are relevant to dental imaging requirements As an initial evaluation of the phantom it was scanned using a variety of CBCT devices to evaluate the reproducibility and applicability of the evaluated parameters and to investigate CBCT imaging performance 1 5 Deliverable D3 4 Deliverable D3 4 is the final deliverable of SEDENTEXCT Work Package 3 The objects of deliverable D3 4 are e To summarise earlier work e To describe new work in this Work Package in the last period The purpose of this work is to form a QA protocol for periodic QA tests in daily clinical practice and determine its implementation on CBCT units e To describe the possible impact of work in this Work Package To outline dissemination plans and possible future work MA seDENTEXCT D3 4 Report 2 Earlier Work in WP3 2 1 Deliverable 3 1 The purposes of Deliverable 3 1 were e to provide a 1 prototype phantom together with inserts for the testing o
29. d be repeated if major repair work is carried out on the tube head 2 1 Radiation output This is assessed by measuring the absorbed dose in air at a fixed point in the X ray beam e g by using a small thimble ionisation chamber placed at the isocentre It should be noted that the ionisation chamber should have isotropic sensitivity 2 1 1 Radiation Output Repeatability This test monitors the consistency of the radiation output for a series of radiation exposures using constant exposure parameters Example Repeat five measurements using constant exposure parameters at a typical clinical setting MZ SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol 2 1 2 Radiation Output Reproducibility This test monitors the effect of the exposure parameters tube voltage and mAs on the radiation output Comparison should be made with the baseline values established at commissioning Example Measure at a range of tube voltages e g 70 80 90kV at a range of typical clinical mAs settings Note Many CBCT units do not allow a manual selection of tube voltages and mAs For these units the above exposures should be made at the automatically selected exposure settings 2 2 Tube potential The voltage applied to the X ray tube determines the energy of the X ray photons and is a major factor in determining the contrast in the image Assessment of the tube potential ensures that the delivered kV is close to that set on the unit by
30. dies on CBCT image quality Even though a large number of CBCT image quality studies have been published over the last few years most have focused on the diagnostic image quality However a number of studies have already assessed technical image quality for one or more CBCT devices using an existing commercial Quality Control QC phantom Jaffray et al 2000 Marguet et al 2009 a phantom provided by a CBCT manufacturer Loubele et al 2008 Watanabe et al 2010 a water phantom Jaffray et al 2000 Vassileva et al 2010 a customized test object Bryant et al 2008 Lascala et al 2004 Katsumata et al 2009 Lagravere et al 2008 or clinical data Loubele et al 2006 Naitoh et al 2009 Although these studies have provided useful insights regarding certain image quality aspects they also show the need for a standardized QC phantom which is suited for use on all CBCT devices and which provides results that are relevant to dental imaging and that can be compared between systems Commercial QC phantoms have been described for conventional CT but these are not applicable for dental CBCT due to the difference in performance for certain image quality aspects CT phantoms use soft tissue equivalent materials for gray value analysis which are not relevant for dental CBCT McCann et al 2004 Suess et al 1999 Furthermore dental imaging requires a high spatial resolution and a limitation of metal artifacts both of which are not assessed by conve
31. e in clinical use It is usually performed by using a test phantom in conjunction with software routines that help in the interpretation of the results Preliminary tests before the start of this project on the NewTom 3G CBCT unit showed that using a phantom designed for Quality Assurance on medical CT equipment results in images with worse low contrast resolution than the medical CT scan Furthermore discrimination between objects with different density was not always successful It is speculated that this is due to the fact that NewTom 3G and possibly all other dental CBCT units are optimized for imaging of hard tissues This is also related to the low dose delivered compared with medical CT Therefore the development of a specifically designed phantom with a size and densities resembling those of dental interest is necessary A variety of test objects would be MA seoentexcr D3 4 Report included in the phantom body as inserts for the testing of the imaging performance characteristics Software tools would be developed for the interpretation of the results and the evaluation of image quality The objectives of WP3 are the following e to develop design and test a phantom for QA tests on dental CBCT equipment e to develop software tools for the evaluation of image quality and for routine QA testing e to form an Image Quality testing protocol and determine its implementation on CBCT units e to form and implement a routine Q
32. ed scoring with phantom software is being used results should be compared with baselines MA seDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol Scoring test objects by eye is very subjective It should be ensured that where there are different personnel scoring the details they use a similar methodology 4 3 Uniformity and artefacts It is important that the entire detector is capable of producing a useful image and so it must be ensured that there are no significant areas of damage or problems with detector calibration that could lead to artefacts in acquired images Similarly it must be confirmed that damaged or dead pixels are appropriately corrected for in the final image 4 3 1 Where a QC phantom is available e Acquire an image of the uniformity section of the phantom This should be a large homogeneous area so that it can be assured that any deviations on the image are the result of the imaging system and not the phantom itself e A visual check of the uniformity of the image will reveal any significant uniformity problems e Where quantitative tools are available draw a region of interest in the centre of the test object and then four evenly spaced regions around the periphery and measure the mean pixel value in each Assess the image uniformity using the results 4 3 2 Where no QC phantom is available e Acquire an image with nothing in the beam Be aware that this could give odd images on some scanners if the rec
33. eleased in the coming years providing an initial assessment of imaging performance By using the QC phantom and evaluating technical image quality parameters in relation with radiation dose it can be ensured that new and upgraded CBCT devices are optimized for dental imaging The QC phantom can also be used as a research tool for various applications Algorithmic improvement of CBCT image quality can be investigated using raw data of the phantom Improvements of image reconstruction in terms of noise spatial and contrast resolution and metal artefacts can be evaluated this way Furthermore it can be used as a validation tool for a Monte Carlo simulation framework to verify if the imaging chain is modelled appropriately Subsequently a voxel model of the phantom can be used to optimise CBCT imaging through simulation MA sEDENTEXCT D3 4 Report 6 Overall Work Package Conclusions This section considers both the earlier work and the work in the final period to draw conclusions regarding the SEDENTEXCT Guidelines and the overall impact of the work and to summarise the implications for further work 6 1 SEDENTEXCT Guidelines A Quality Control Programme lays out the necessary testing to ensure that all parameters during the examination procedure are in accordance with the standard operating protocol thus resulting in images with diagnostic value without exposing the patient to unnecessary risk The resulting QA procedure protocol of
34. est details but it does not provide any indication on how other frequencies are transferred This can be assessed by measuring the modulation transfer function MTF of the system The MTF can be calculated by measuring the Point Spread Function PSF or the Edge Spread Function ESF The PSF can be measured directly by imaging a high contrast wire The wire is embedded in a suitable medium and placed perpendicular to the scan plane The PSF is obtained by plotting the pixel values across the image cross section of the image of the wire Resolution can be measured directly from the PSF by measuring the full width at half maximum FWHM The ESF is measured by imaging an edge of a block of material embedded in a suitable material with the face of the block perpendicular to the scanned plane HEER seDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol The ESF is obtained by plotting the pixel values across the image Differentiating the ESF will give the Line Spread Function LSF The LSF can be used to asses the spatial resolution of the system similar to the PSF The MTF can be calculated as the modulus of the Fourier transform of the PSF or the LSF The values quoted are the frequencies at which the modulation falls to 50 or 10 of its initial value A more detailed description of the MTF method is given in the IPEM Report 32 Part VII 4 6 Geometric Accuracy Where it may be clinically useful to perform measurements of dis
35. f the imaging performance characteristics e to provide results on the suitability of the phantom and the inserts for their intended purpose e to reveal the required changes and improvements to the design of the prototype e to test a preliminary version of the software tools that help in the interpretation of the results and the evaluation of the image quality 4st The evaluating procedures carried on the first prototype phantom and the results obtained by the first version of the software tools D3 1 lead to important conclusions regarding required improvements of the design of the prototype phantom and inserts at the next phase 2 prototype 2 2 Deliverable 3 2 The purposes of Deliverable 3 2 were e to provide a 2 prototype phantom together with inserts for the testing of the imaging performance characteristics e to provide results on the suitability of the phantom and the inserts for their intended purpose e to reveal the required changes and improvements to the design of the prototype for the development of the final phantom e to test the 2 beta version of the software that help in the interpretation of the results and the evaluation of the image quality using a beta test evaluation form The design changes that were implemented into the 2 prototype are found appropriate for both the phantom body and the inserts for the different image quality tests A final round of small design changes that will further improve the sui
36. hese rods using 1 axial slice but scroll through the slices this can help to determine whether or not the smallest rods are visible Repeat for all five inserts Spatial resolution analysis pe SEDENTEXCT D3 4 Report Appendix II User Manual There are two inserts for spatial resolution containing the same pattern but in a perpendicular X Y and Z orientation Open the dataset contain the spatial resolution insert s For this insert the window and level need to be adjusted for optimal contrast between the different lines in the pattern Also it is needed to zoom into the insert using the zoom tool of the software to make sure you can accurately count the number of lines Count the number of white lines that can be distinguished from the next NOTE a line can only be counted if the separation with the previous line but also with the next line can be identified Fill in the number of counted lines for the X Y and Z insert into the QC form This concludes the spatial resolution analysis Geometric accuracy linear measurements As this analysis requires some degree of visual interaction to enable accurate measurements the software and workstation provided by the manufacturer should preferably be used If this is not possible the SEDENTEXCT software package can be used FE SEDENTEXCT D3 4 Report Appendix II User Manual Adjust the window and level to enable optimal viewing of the hole pattern between the
37. ial if the image quality measurements are to be performed MPEs should normally have access to such phantoms and software and will be able to carry out these measurements Note that whilst most systems exhibit a linear relationship between image pixel value and object density within a single scan the use of histogram shifting by some units means that this is not always the case from scan to scan Care should be taken when comparing uncorrected data across scans or from unit to unit HEER seDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol 4 1 Image density values A Clinically useful image relies on the system s ability to distinguish between and clearly display the different materials in an image The accuracy with which a system can continue to do this over time can be determined quantitatively 4 1 1 Setting a baseline e Acquire an image of the image density value section of the phantom This should be an area in which there are many different materials clearly distinguished from one another e Draw a region of interest in each of the different materials and record the mean pixel value and standard deviation in each 4 1 2 Routine measurements e In future visits expose the same test object using the same protocol draw a region of interest in each of the different materials and record the mean pixel value and standard deviation in each e Compare the mean pixel value for each material with that measured on the first visi
38. imaging systems IPEM 2005 HPA RPD 065 Recommendations for the design of X ray facilities and quality assurance of dental Cone Beam CT Computed tomography systems JR Holroyd and A Walker Health Protection Agency 2010 v SEDENTEXCT http www sedentexct eu IPEM Quality assurance in dental Radiology Report No 671995 Cranley K 8 Fogarty G W A 1988 The measurement of total filtration of diagnostic X ray tubes BUR 61 viii IEC International Electrotechnical Commission 2008 Medical electrical equipment Part 1 3 General requirements for basic safety and essential performance Collateral Standard Radiation protection in diagnostic X ray equipment IEC publication 60601 1 3 IPEM Report 32 Measurement of the Performance characteristics of diagnostic X ray systems used in medicine Part III Computed Tomography X ray scanners 2 Ed IPEM 2003 IPEM Report 32 Measurement of the Performance characteristics of diagnostic X ray systems used in medicine Part VII Digital imaging system IPEM 2010 Samei E Badano A Chakraborty D Compton K Cornelius C Corrigan K Flynn MJ Hemminger B Hangiandreou N Johnson J Moxley M Pavlicek W Roehrig H Rutz L Shepard J Uzenoff R Wang J Willis C Assessment of Display Performance for Medical Imaging Systems Report of the American Association of Physicists in Medicine AAPM Task Group 18 Medical Physics Publishing Madison WI AAPM On Line Report No 03 April 2005 NHS Breast Screening Progr
39. interpreting the results due regard should be made to the effectiveness of the attenuation applied at the tube window If the movement of the tube head cannot be stopped securely fixing a lead block as close to the tube window as possible should still allow meaningful measurements of secondary radiation to be made at accessible points adjacent to the unit These results will give an indication of whether the leakage from part of the tube housing is higher than expected The use of film or computed radiography plates around the tube housing can also be useful in detecting small areas in which there is less shielding or where the shielding is absent altogether If detected measurements of secondary radiation can be focussed in these areas 3 Patient dose Knowledge of patient dose is essential for clinicians who are making the decision regarding the justification of the exposure It is also important to ensure that doses are optimised and in line with any national and international guidelines The dose quantity effective dose gives an indication of radiation risk and can be compared to doses from other radiation sources However effective dose cannot readily be measured and must be inferred from more easily measureable dose quantities HEE SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol 3 1 Dose measurement A variety of dose indices are used to characterise patient dose 3 1 1 CTDI For CT scanners the CT dose index CT
40. ional purpose as a research tool for optimisation enabling the accurate evaluation of the variability in image quality for different exposure settings and reconstruction algorithms MA seDENTEXCT D3 4 Report 6 4 Future dissemination WP task Topic Provisional Title Main journals conferences targeted responsible WP3 1 Phantom Development and applicability of a KUL NKUA Journal of Applied Clinical evaluation quality control phantom for Cone Medical Physics prototype 1 Beam CT WP3 2 Artefact Evaluation of metal artefacts on KUL NKUA Clinical Oral Implants Research analysis Cone Beam CT WP3 2 Image analysis Image quality evaluation of Cone KUL NKUA Dentomaxillofacial Radiology Beam CT part 1 contrast resolution or alternative noise and uniformit WP3 1 Phantom Stability and reproducibility of image KUL NKUA Unknown not yet decided evaluation quality parameters measured on a prototype 2 quality control phantom for Cone Image analysis Beam CT WP3 2 Image analysis Image quality evaluation of Cone KUL NKUA Dentomaxillofacial Radiology Beam CT part 2 spatial resolution or alternative MTF and geometric accuracy WP3 2 Image analysis Accuracy and stability of density KUL NKUA Dentomaxillofacial Radiology measurement with Cone Beam or alternative Computed Tomography WP3 3 Quality Development of a quality assurance UNIMAN NKUA Unknown not yet decided assurance protocol for den
41. ns on the phantom handling and positioning test inserts selection inserts placing in the phantom and using the software for specific image quality tests based on the knowledge acquired from the past deliverable D3 3 This is supplemented by the Leeds Test Objects specification sheet for the phantom Appendix III MA seDENTEXCT D3 4 Report 5 Work in the Final Period Conclusions 5 1 Conclusions In conclusion the SEDENTEXCT project has met the WP3 objective to develop a phantom associated software and a QA procedure protocol for CBCT QA analysis that will be used to inform the writing of the Guidelines WP1 5 2 Implications for future work The recommendations of priority level of expertise frequency and action levels are based on published guidance and the experience of the SEDENTEXCT team in validating the use of the SEDENTEXCT QC test phantom This represents an initial assessment of what is sensible and achievable but as experience of testing these units is obtained over a period of years these recommendations should be critically reviewed as new evidence becomes available Apart from the obvious future use of the QA protocol and QC phantom i e to be used in a long term assessment of CBCT performance the QC phantom can also be used as a tool for CBCT optimisation The phantom is applicable on all CBCT devices that are currently on the market Furthermore it can be applied to any new or upgraded devices that will be r
42. nt If the scanner cannot be operated at the service mode then the film or the CR cassette could be placed on the detector and exposed to the maximum and different FOVs If the distance of the focal spot to the detector is known then the dimensions of the nominal FOV on the detector can be calculated and compared to the imaged FOV Alternatively two sets of thermoluminescent dosimeters TLDs could be placed using holders at the isocentre with the first set placed vertical and the second set placed parallel to the z axis and exposed to one FOV at a time The number of TLDs should be chosen so as to extend over the nominal dimensions of the FOV The TLDs are read out and the dimensions of the irradiated FOV are compared with the dimensions of the nominal FOV In addition it should be confirmed that the X ray beam is contained within the detector A film or a CR cassette should be placed on the surface of the detector and the edges of the active area of the detector should be marked on the film or CR cassette and then exposed to radiation The radiation field should not extend beyond the marked edges on the film or the CR cassette 2 5 X ray beam alignment This test is to assess the coincidence of the centre of the radiation and imaged FOV with the isocentre as defined by the alignment lasers or the scout view HEE seDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol Any radiopaque object positioned at the isocentre allows fo
43. ntional CT phantoms A CBCT system uses a cone or similarly shaped X ray beam that rotates around an object and acquires two dimensional projections reconstructed into a three dimensional volume Scarfe et al 2008 There is a variety of CBCT devices available with large differences for a number of imaging parameters peak voltage amount of filtration quantity of X rays mAs pulsed versus continuous exposure beam geometry number of projections detector type field of view FOV size reconstruction algorithm reconstructed voxel size pre and post processing of raw and reconstructed data etc Designing a QC phantom requires a cross section of all available CBCT devices identifying common properties These properties most of which are intertwined are ordered from general to specific 1 CBCT images show very poor soft tissue differentiation as they are meant for the visualization of hard tissues bone teeth and air sinus and air cavities 2 spatial resolution is high voxel sizes are generally below 0 4 mm and nominally identical in all planes isotropic 3 most devices expose at a kVp below 100 and a low mAs 4 there is a relatively large degree of scattered radiation resulting in image noise and HE sEDENTEXCT D3 4 Report nonuniformity 5 voxel values are not standardized and cannot directly be used as quantitative CT numbers for use in bone mineral density BMD evaluation 6 high density tissues and metal obje
44. oms and versions of software were taken into account for the construction of the final QA phantom and the accompanying software for semi automatic image evaluation of the phantom images The definitive phantom consists of a cylindrical Poly methyl methacrylate PMMA holder 16cm diameter and a number of inserts 3 5cm diameter for evaluating different physical properties of the CBCT technique employing several CBCT units For the semi automatic evaluation of phantom images a specific software program was developed A Quality Assurance QA procedure protocol was formed comprising a generic part about the implementation of a QA programme in CBCT followed by a specific part on the SEDENTEXCT tools the phantom and the software used for running the respective tests described in the QA protocol The results lead to the conclusion that SEDENTEXCT has met the WP3 objective to develop a phantom software and a QA procedure protocol for CBCT QA analysis that will be used to inform the writing of the Guidelines WP1 HEE seDENTEXCT D3 4 Report Table of Contents A O ite ell ed a ceca 4 1 1 SEDENTEXCT aims and Objectives coooonoccccncnncccccnccononcccnncnnnnnnnnnnnnnnncnnnnnnnnn 4 1 2 Work package 3 WP3 objectives soii oi 4 1 3 Anticipated impact of the work secure 5 1 4 Current state of the art eric Ilo ii 5 1 5 Deliverable D3 4 A AER 7 2 Earlier Workin WP S 2 En asii 8 2 1 Deliverable 3 lps da 8 2 2 DCI e ed ld 8 2 3
45. on Sheet HEE seDENTEXCT D3 4 Report Leeds Test Objects SE DE NTEXCT www leedstestobjects com user manual Draft Summary PHANTOM HOUSING PMMA Holes A1 6 at 60 intervals on circle 104 8mm 10 0 mm gt 177 x G2 0 recesses 3 0mm depth in the body of the phantom centred 3 5mm below the base of the 7 holes Geometric Distortion 10 0 mm PHANTOM HOUSING PMMA HOUSING PMMA 176 75 E 170 75 PA i 165 0 Mille pie Jane ety SOA A OE Se ee ell IA i ee A eee ee eee eee eel T T 45 0 5 0 TAE S HORIZONTAL ENGRAVED LINE 6 lines labelling 6 x 20 0mm intervals through 140 0mm depth of holes VERTICAL ENGRAVED LINE Centred on each of 6 peripheral holes BLANK INSERT PMMA 30 PER SET O34 5 0 25 20 0 0 25 2 5 20 0 0 25 LSF INSERT 1 PER SET SC 0 0 0T Sc 04001 10 0 0 25 10 0 0 25 934 5 0 25 PMMA
46. onstruction relies on a head or equivalent phantom being present In these cases consider the use of a scout view e A visual check of the uniformity of the image will reveal any significant uniformity problems In this case some windowing of the image may be necessary to better assess uniformity e Where quantitative tools are available draw a region of interest in the centre of the test object and then four evenly spaced regions around the periphery and measure the mean pixel value in each Assess the image uniformity using the results 4 4 Noise There are many processes that could affect the quality of a clinical image including tube output detector efficiency and image processing A quantitative assessment of the noise in an image can identify any deterioration in image quality with time and help determine the cause of the deterioration 4 4 1 Setting a baseline e Acquire an image of the uniformity section of the phantom This should be a large homogeneous area so that it can be assured that any deviations on the image are the result of the imaging system and not the phantom itself e Draw a region of interest in the centre of the test object with diameter no greater than one fifth the diameter of the test object Record the standard deviation HEE SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol e Repeat for five consecutive axial slices and calculate the average standard deviation 4 4 2 Routine measurements e A
47. play monitors should also be performed as follows 5 1 General condition e A suitable test pattern such as an AAPM TG18 or SMPTE image should be installed on the computer and viewed on the monitor which should be clean e lt should be ensured that all distinct greyscale levels on the test pattern can be individually resolved The small black and white squares within the larger black and white squares should also be clearly resolved e Where two monitors are used for reporting it should be ensured that the perceived contrast of each of the distinct greyscale levels is consistent between the two BD SEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol 5 2 Monitor resolution e It should be ensured that all of the bars on each of the resolution patterns on the AAPM TG18 or SMPTE test image can be clearly resolved Version 4 26 1 11 HEE SEDENTEXCT 3 4 Report Appendix 1 Generic QA Protocol References Council Directive 97 43 Euratom of 30 June 1997 on health protection of individuals against the dangers of ionizing radiation in relation to medical exposure Official Journal of the European Communities No L 180 11 1997 Draft Euratom Basic Safety Standards Directive Version 24 February 2010 http ec europa eu energy nuclear radiation protection doc art31 2010 02 24 draft euratom basic sa fety standards directive pdf IPEM report 91 Recommended standards for the routine performance testing of diagnostic X ray
48. priate for dental CBCT looking at different aspects of the equipment and image display Some of the tests are straightforward and can be readily performed by the clinical staff using the CBCT equipment Other tests are more complex and the input of a medical physicist is required Therefore the expertise required for each test is indicated in the protocol Routine quality control tests primarily involve comparison of results with those determined during commissioning Significant variation as indicated by pre determined action levels should be investigated either with the help of a medical physics expert MPE or the equipment service engineer Not all possible methods of assessment are considered essential It is important to perform enough tests to confirm that the equipment is operating as intended More complex tests do add extra information that is helpful in the optimisation process and they are detailed here for completeness However whether the more detailed tests are undertaken will depend on the availability of expert support and the necessary resources The tests described in the generic part are summarised in the table at the end of the Appendix I SEDENTEXCT D3 4 Report 4 2 User manual for using the SEDENTEXCT phantom and software The user manual describing how to use the SEDENTEXCT tools the phantom and the software for running the respective image quality tests is provided in Appendix II There are detailed instructio
49. r a measurement of the distance between the imaged object and the centre of the imaged FOV using the measuring tool of the scanner s software Note that the accuracy of this measurement is reliant on the correct calibration of the measurement software see section xxx and the voxel size of the reconstructed image 2 6 Leakage Radiation is emitted from all directions from the focal spot not just in the direction of the primary X ray beam The tube housing is designed to attenuate the radiation outside the main beam so that patient and staff are not significantly exposed This source of secondary radiation is known as leakage On standard X ray equipment leakage is measured during commissioning usually by a medical physics expert to confirm that the tube head design and construction is adequate It should also be measured if physical damage to the tube head has occurred or the tube head has been dismantled during repair The measurement of leakage on a dental CBCT is problematic and can only reliably be achieved if the movement of the tube head can be stopped likely to be available in service mode only and the primary beam can be blocked either by the use of collimators or a lead block at least 1mm thick placed as close to the tube window as possible If this can be achieved standard methods for leakage measurement can be applied involving the identification of areas of leakage and the measurement of dose rate at these areas When
50. s recommended that clinical dose levels are determined in a practice by measurement of standard protocols or by patient dose audit if dose index readouts are provided by the equipment and compared to past results and any national and international levels when set Dose levels higher than these standards merit investigation as this would suggest that dose is not optimised 4 Quantitative image quality performance A range of image quality indicators can be measured using phantoms designed for such measurements A variety of different phantoms are available Phantoms such as the Catphan designed for use on CT scanners can be used for dental CBCT units but are difficult to position and tend to use soft tissue equivalent materials for the more accurate evaluation of grey scale accuracy Dental imaging has a few specific requirements e g hard tissue visualisation and sub millimetre spatial resolution which are not assessed by phantoms not specifically designed for the purpose Some manufacturers provide phantoms with their scanners and the SEDENTEXCT project has designed a phantom specifically with dental CBCT units in mind In addition software tools are required to analyse the images of the phantom These may be available as part of the image viewing software or may be separately provided with the phantom The SEDENTEXCT phantom is provided with standard software for image analysis Acquisition of such a phantom and software tools is essent
51. should be considered as well as image quality loss artifacts and FOV narrowing near the upper and lower edge of the FOV Use the minimum amount of scans without hampering image quality For the PMMA portion and geometric pattern at the border between the PMMA portion and the insert portion it is important not to position the FOV too low if using a tripod or other high density phantom support to avoid artifacts If possible place the phantom on rigid object of medium density another phantom if available papers books etc and not directly on a metal platform For medium and small FOVs scan the peripheral PMMA portion of the phantom as well as the central portion For large FOVs position the FOV centrally to scan the entire PMMA portion in one scan Exporting data Export only axial slices using the thinnest slice thickness and smallest slice interval Check the folder after exporting for any non DICOM files e g DICOMDIR and delete them as they will hamper the import of the dataset into the SEDENTEXCT software see below a SEDENTEXCT D3 4 Report Appendix II User Manual Software protocol final phantom Setting up the software No installation is required just download the file SedentexCT zip and unzip into a chosen folder To run the program run the executable file Sedentex exe NOTE The program must be placed within folders folders and subfolders which have no space in their names For example Path
52. t 4 2 Contrast detail assessment Assessing a system s ability to display details of known varying contrast can give important information as to the deterioration of image quality over time A phantom containing objects with a range of different sizes and or contrasts is required 4 2 1 Setting a baseline e Acquire an image of the contrast detail section of the phantom This should be an area in which there are various details of the same material that vary in diameter and depth or various details of different materials e The simplest check of contrast detail is counting the number of details that can be clearly resolved on a reporting monitor O It may be useful to derive a single value for contrast detail assessment for example the threshold detection index the image quality factor or the contrast to noise ratio Action levels will depend on the test object and scoring methodology used O Some phantoms may provide software that calculates contrast detail values after analysing images In these cases follow the instructions that come with the phantom 4 2 2 Routine measurements e Acquire an image of the contrast detail section of the same phantom using the same exposure protocol as at baseline e Count the number of details on the image using the same monitor as at baseline where possible O If a threshold detection index image quality factor or contrast to noise ratio is being used compare with the baseline results O If automat
53. t dose index Recommended MPE 12 monthly Outside 15 of manufacturer s specification Patient dose audit Essential In house MPE At least 3 yearly gt national or international reference level Notes Level of expertise MPE indicates that this test would normally require the input of a medical physics expert with sophisticated test equipment whereas in house indicates that the tests can normally be performed by clinic staff using standard phantoms Action level Results outside these levels should be investigated and action taken The advice of a medical physics expert or service engineer may be required N B This table represents initial guidance based on current experience of dental CBCT units It should be kept under critical review as experience is gained in testing such units HEER sEDENTEXCT D3 4 Report Appendix 1 Generic QA Protocol Appendix Il SEDENTEXCT User Manual Image Quality Scanning Protocol MA seDENTEXCT D3 4 Report SEDENTEXCT Image Quality Scanning Protocol This protocol provides specific instruction for performing CBCT scans of the SEDENTEXCT image quality phantom It is important to place some of the inserts in a specific way to avoid interference between inserts Furthermore the phantom should be scanned using an accurate and reproducible positioning as deviations in positioning may lead to variable results for a few image quality parameters Placement of inserts As seen in Figure A1 the ph
54. tability of the phantom for QC testing are recorded and will be implemented into the final version of the phantom The beta testing of the software revealed that the following should be implemented in the final version Compatibility with DICOM data from all available CBCTs Optimisation of viewing MPR scrolling window level adjustment Optimisation of insert selection Manual insert selection tool 3D selection Insert analysis implementation of all image analysis parameters Automatic report creation A seDENTEXCT D3 4 Report 2 3 Deliverable 3 3 The purposes of Deliverable 3 3 were e to provide the definitive phantom together with inserts for the testing of the imaging performance characteristics e to validate the readiness of the associated software including that o the software is able to open datasets from all available CBCT devices o the software allows for the measurement of all image quality parameters that are relevant for quality control o there is a sufficient agreement between repeated measurements by different observers or by the same observer The design changes that were implemented into the definitive phantom are found appropriate for both the body and the inserts for the different image quality tests Validation of the associated software by five consortium partners was successful A clear protocol for all measurements was established It was found that the final software is easy to work with that the working
55. tal Cone Beam CT KUL ME seDENTEXCT D3 4 Report 7 References The following reference list includes references from the QA Protocol Appendix 1 Bryant JA Drage NA Richmond S Study of the scan uniformity from an i CAT cone beam computed tomography dental imaging system Dentomaxillofac Radiol 2008 37 7 365 74 Council Directive 97 43 Euratom of 30 June 1997 on health protection of individuals against the dangers of ionizing radiation in relation to medical exposure Official Journal of the European Communities No L 180 11 1997 Cranley K Fogarty GW The measurement of total filtration of diagnostic X ray tubes Br J Radiol 1988 May 61 725 388 92 Daly MJ Siewerdsen JH Moseley DJ Jaffray DA Irish JC Intraoperative cone beam CT for guidance of head and neck surgery Assessment of dose and image quality using a C arm prototype Med Phys 2006 33 10 3767 80 Draft Euratom Basic Safety Standards Directive Version 24 February 2010 http ec europa eu energy nuclear radiation protection doc art31 2010 02 24 draft euratom basic safety standards directive pdf Du LY Umoh J Nikolov HN Pollmann SI Lee TY Holdsworth DW A quality assurance phantom for the performance evaluation of volumetric micro CT systems Phys Med Biol 2007 52 53 7087 108 Horner K Islam M Flygare L Tsiklakis K Whaites E Basic principles for use of dental cone beam CT consensus guidelines of the European Academy of Dental and Maxillofacial
56. tance or angle on an image it must be ensured that measurements made on a system accurately reflect true distances and angles A phantom is required that contains an area with objects at known distances and angles from one another e Acquire an image of the geometric accuracy section of the phantom e Where quantitative test tools are available measure distances and angles across a variety of the objects within the phantom e Compare the measured values with known distances and angles A more detailed analysis can be performed by calculating the aspect ratio and pixel pitch if required e Ensure the aspect ratio is correct by calculating measured x measured y for distances of the same intended length The ratio should be 1 0 04 e Ensure the pixel pitch is as stated by the manufacturer by calculating measured distance mm number of pixels covering the measured distance Measure the pixel pitch for various distances in the x and y axes 5 Display equipment Regardless of the quality of the x ray equipment with which an image is acquired a clinical image can only be digitally displayed as well as the monitor on which it is viewed is capable of It is essential therefore to ensure that any monitor that is used to report on clinical images is well set up and subject to regular QC The QC programme outlined in the report of the AAPM task group 18 or equivalent is an appropriate methodology for MPE tests Regular in house checking of the dis
57. the operator Poor agreement between the two would affect clinical image quality equipment radiation output and patient dose 2 2 1 kV accuracy The kV should be measured directly using a kV divider device at intervals of 10kV across the full range the unit is capable of producing 2 2 2 kV repeatability The consistency of the tube potential should be monitored by repeating five measurements at at least two clinically relevant kVp values where possible 2 2 3 kV reproducibility The reproducibility of the tube potential over time should be monitored by comparing the measured results for kVps at intervals of 10kV across the full range the unit can produce with those established as baseline values at commissioning 2 3 Filtration The filtration of an X ray tube absorbs the low energy photons that do not contribute to the image formation but do contribute to patient skin dose Having adequate filtration is essential to ensure that patient dose is controlled The total filtration should be marked on the X ray tube housing Total filtration can be estimated by measuring the Half Value Layer HVL The HVL is the thickness of the absorber required to reduce the intensity of the incident X ray beam by half The HVL is an estimate of the penetrating power of the X ray beam which means that the higher the HVL the more penetrating the X ray beam is HEE SEDENTEXCT 3 4 Report Appendix 1 Generic QA Protocol 2 3 1 How to measure HVL
58. to ensure that all parameters during the examination procedure are in accordance with the standard operating protocol thus resulting in images with diagnostic value without exposing the patient to unnecessary risk A programme of equipment tests for dental cone beam CT should consider the following aspects Performance of the X ray tube and generator Patient dose Quantitative assessment of image quality Display screen performance Such a programme is a requirement of the European Union Medical Exposures Directive as part of the optimisation process to ensure patient dose is as low as reasonably practicable whilst achieving clinically adequate image quality Any practice undertaking medical exposure should have access to the advice of a medical physics expert on such matters The Medical Exposures Directive is currently under revision and the role of the Medical Physics Expert is given higher prominence in the most recent draft Testing and patient dose assessment is carried out when the equipment is first installed as part of the commissioning process and then throughout the life of the equipment This protocol outlines those physical tests and measurements that are considered to be part of a standard quality control programme for a dental CBCT unit It does not cover quality assurance of the clinical image A range of tests are appropriate for dental CBCT looking at different aspects of the equipment and image display
59. tom with the use of the validated software formed the basis for the writing of the QA Procedure QA Protocol as part of the final deliverable D3 4 HEE seDENTEXCT D3 4 Report 4 Work in the Final Period Results A Quality Assurance QA procedure protocol comprises two parts The first is a generic part about the implementation of a QA programme in CBCT Appendix that was formed based on previous knowledge on QA programmes with special consideration of the particularities of the CBCT technology The generic part is followed by a specific part on how to use the SEDENTEXCT tools the phantom and the software for running the respective image quality tests Appendix II 4 1 Generic QA protocol The Quality Control Programme in general lays out the necessary testing to ensure that all parameters during the examination procedure are in accordance with the standard operating protocol thus resulting in images with diagnostic value without exposing the patient to unnecessary risk The programme of equipment tests for dental cone beam CT considers the following aspects Performance of the X ray tube and generator Patient dose Quantitative assessment of image quality Display screen performance This protocol outlines those physical tests and measurements that are considered to be part of a standard quality control programme for a dental CBCT unit It does not cover quality assurance of the clinical image A range of tests are appro
60. top border of the PMMA section so at the bottom border of the geometric pattern the small holes Select PMMA from the insert list and press Evaluate Copy the NOISE and UNI values into the form Visual analyses For all visual analyses the first choice should be to perform them using the workstation and software provided by the manufacturer of the CBCT device Visual Pe SEDENTEXCT D3 4 Report Appendix II User Manual assessments can be affected by the screen room conditions and software function so ideally this should be performed in clinical conditions If it is not possible to perform this analysis on the manufacturer s workstation the SEDENTEXCT software can be used providing that optimal viewing conditions are ensured All analyses require an optimal setting of the grey levels displayed by adapting the so called window number of grey values displayed and level grey value of the center of the window Any software use for image viewing should have a window level or brightness contrast tool Contrast resolution analysis Five inserts are used for this analysis each containing five rods of a certain material in PMMA surrounding Open a dataset containing the contrast resolution insert s and adjust the level and window for optimal viewing of the rods Then count the number of distinguishable rods for each insert and fill in the number of visible rods in the form below Do not count t

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