Measuring key parameters of intense pulsed light (IPL
Contents
1. 60825 is designed to protect individuals from laser by specialists in the optical radiation field It radiation in the wavelength range 180 nm to 1 mm identifies retinal thermal hazard and blue light by indicating safe working levels of laser radiation photochemical hazard as relevant in considering and introducing a system of classification of lasers the safe use of incoherent light sources However at according to their degree of hazard The Standard the time of submission of this study standards requires both user and manufacturer to establish which will deal specifically with IPL sources are still procedures and supply information so that proper only at draft stage 3 precautions can be adopted Medical lasers intended This means that there is no incentive to perform for irradiation of the human body require internal measurement and no standard procedures in place controls to measure radiation emission levels with an to help manufacturers IPL devices are being used error in measurement of no more than 20 given widely with limited accurate knowledge of their in SI units and instructions specifying a procedure performance characteristics Measurement of certain and schedule for calibration of the measurement key parameters could help reduce the risk of under system 1 No such requirement exists for intense or over treatment or burn injury to patients The Correspondence Godfrey Town 88 Noah s Ark Lane Lindfield West Sussex RH16 2LT2. UK Tel 44 1444 484295 Fax 44 1444 484357 E mail godfreytown csi com Received 26 April 2007 accepted 3 May 2007 ISSN 1476 4172 print ISSN 1476 4180 online 2007 Taylor amp Francis DOI 10 1080 14764170701435297 G Town et al absence of any published standards for IPL safety eyewear used by the patient and the operator increases the risk of eye injury 4 The issue of IPL safety was raised by experts at the ASLMS Joint International Laser Meeting in Edinburgh Scotland 21 23 September 2003 when Hode of the Swedish Laser Medical Society considered the hazards of IPL sources 5 Clarkson has also documented the hazards of non coherent light sources within the framework of IEC TR 60825 9 6 In England and Wales the Care Standards Act 2000 as amended by the Health and Social Care Act 2001 treats establishments using IPL devices in a similar way to users of Class 4 medical lasers The statutory definition of an IPL states an intense light being broadband non coherent light which is filtered to produce a specified range of wavelengths such filtered radiation being delivered to the body with the aim of causing thermal mechanical or chemical damage to structures such as hair follicles and skin blemishes while sparing surrounding tissues 7 It is therefore clear that such high power devices can cause tissue damage in a similar way to medical lasers and should be subject to equivalent standards to those
3. 3B and IV lasers must comply with the Essential Requirements of the European Medical Device Directive which requires a device specific CE mark certificate from a Notified Body Manufacturers who register IPL devices under this scheme issue a Declaration of Conformity to standards maintain a Quality Assurance monitoring system under ISO9000 and are obliged to report any accidents to the authorities A medical CE mark can be identified easily by the four digit number next to the official CE mark on the device identification label which denotes that the Notified Body that has independently evaluated the device Medical authorities in several non European countries including South Africa and Australia recognize the medical CE mark as a requirement for electro medical equipment Measuring IPL parameters Energy density measurement IPL energy density fluence is the amount of light energy delivered per unit area and is measured in Joules per centimetre squared For treatments utilizing selective photothermolysis the light energy is absorbed by chromophores in the skin such as melanin and oxyhaemoglobin and converted into heat energy As energy is absorbed the temperature of the chromophore increases and tissue goes through biological changes The ideal fluence will raise the temperature of the chromophore to a level that causes damage to the target but does not lead to adverse side effects such as burns or blisters Even the m
4. 4 40 x 16 30 000 Non Med Free user manual if not displayed on the IPL screen Figures 3 and 4 By measuring devices in routine daily use measurements were effectively taken at different stages in the manufacturers claimed warranty lifetime of the applicator or lamp filter assembly which allowed observation of the degree of deterioration in fluence against claimed values Using this test method 30 IPL applicators were measured at maximum fluence of which 11 were more than 20 below and eight were more than 10 above the fluence levels given on the device display or claimed in user manuals even where brand new lamps were tested Altogether nine IPL devices out of 18 had applicators that were outside of the standard for medical Class 4 lasers gt 20 The authors considered the accuracy of maximum fluence values to be of greatest importance owing to the risk of under or over treatment However if a manufacturer performs a different fluence test method than the method used in this study then it is likely that comparing our measured results to the stated values will show discrepancies It is not possible for us to definitely prove traceability to national standards so no conclusion can be drawn on the correct absolute fluence The energy density measurements are more valuable as consistency checks prevent lamp output dropping below toler ance levels Example lamp discharge duration Measured pulse and sub pulse durations u
5. and long term health risks The photo spectrometer apparatus was arranged to produce accurate results with minimal experi mental error The applicator of the IPL system was used to direct the optical discharge energy into an HR2000 spectrometer Ocean Optics Dunedin FL 34698 USA at a distance from the spectrometer probe of approximately 150 cm to avoid saturation of the apparatus The spectrometer probe was held with a retort clamp fixed to a laboratory stand to ensure no movement of the probe The spectral output was saved digitally and presented in a Microsoft Excel graph for later analysis Time resolved spectral output measurement It has been noted earlier that a free discharge capacitor will exhibit changes in current which will in turn affect the emitted spectrum We can test this assumption with time resolved spectral output mea surements The time resolved spectrum was produced using an Ocean Optics HR2000 spectrometer and its counterpart Spectra Suite software This software has the capability of sampling the spectrum of light with a minimum integration time of 1 ms This test is intended to demonstrate the stability and degree of efficiency of spectral output for free discharge versus square pulse systems in delivering their stored energy to the chromophore targets within the patient s skin Results and Discussion General information Example test measurements on 18 IPL devices including 36 applicators with dif
6. manufacturers claims to determine whether the discharge to the xenon lamp is constant square pulse or variable free discharge The input pulse energy pattern to the lamp is pivotal in determining the efficiency of the spectral output and determines output intensity 4 the average spectral output of the IPL to identify undesirable wavelengths as there is increased risk of retinal corneal and epidermal damage from IPL systems that deliver wave lengths below 500 nm Accuracy and effective ness of cut off filters and the distribution of light energy at different wavelengths could also influence certain treatment outcomes 5 the time resolved spectral output of the IPL across the entire pulse width to determine the extent of spectral shift and confirm that the optical output reflects the profile of the elec trical discharge claimed by the manufacturer The time resolved spectrum defines the effec tive pulse duration during which the desired wavelengths are delivered in the optimum intensity Materials and methods The 18 devices and 36 applicators tested included IPLs manufactured in the USA UK Israel Sweden Switzerland and Italy markings on IPL F sug gested that it was originally manufactured in China All of the data were gathered over a 6 month period by two of the authors All measurements were made on site in the IPL treatment rooms where the equipment was in daily use between scheduled patient a
7. ms 15 5 5 15 17 5 15 17 5 15 17 5 15 17 50 51 10 15 No data 10 50 10 51 ms 20 150 Missing pulses 20 151 Missing pulses 10 6 20 6 6 20 8 7 5 5 5 5 5 5 5 4 6 4 7 0 short 5 5 5 5 2 5 5 5 5 2 med 3 6 3 6 3 6 3 long 3 6 3 6 3 6 3 4 0 4 0 4 0 3 4 5 4 5 4 5 3 40 40 34 8 37 123 121 15 black 2 2 15 blonde 5 3 3 5 5 35 132 35 132 10 24 40 42 Not given No data Not given No data 30 40 50 30 40 50 30 40 50 30 40 50 Only 14 of 31 pulse duration measurements were within 20 of the manufacturers stated or system displayed values IPLs B and C stated single pulse durations of 5 ms which were measured at 15 17 ms across all programs and settings In one example IPL program for IPL F one sub pulse was found to be entirely missing which correlated with the low fluence measured for that program compared with others on the same device Such discrepancies are clearly unacceptable as they may lead to selecting incorrect fluence values and under or over treatment of the patient leading to either ineffective treatment or unwanted side effects Figure 5 Example lamp discharge profile In manufacturers advertisements and marketing materials it has become fashionable to promote a non typical xenon lamp pulse shape meaning the pulse of electrical energy discharged across the lamp as unique and desirable and it is often described using colourful artist s illustrations rather th
8. popular and the highest IPL settings For assurance of continuing reliability of the lamp and filter it is useful if these measurements can be repeated throughout the lamp s lifetime If output drifts significantly from the results recorded with a new lamp then procedures should be in place to replace the lamp or treatment head Detailed records should also be kept so that consistency between new lamps can be checked The described method used for energy density measurements was devised following discussions with several leading UK manufacturers see acknowledgements of IPL devices and is therefore similar to the quality assurance testing performed prior to despatching new or refurbished applicators to IPL users The skin contact surface area of the quartz glass or sapphire transmission block of each IPL was measured in mm using a Vernier gauge in order to calculate the energy density accurately Lamp discharge duration measurement The measurement of lamp discharge duration also known as pulse width or pulse duration is important because according to Anderson and Parrish 10 the optimum pulse width should be close to the thermal relaxation time Previous studies have confirmed this proving that higher clearance rates occur when the pulse duration is close to or higher than the thermal relaxation time 23 However if pulse duration is too long the heat diffuses to surrounding tissue increasing the risk of adverse side effec
9. provided for Class 4 medical lasers The purpose of this study is to identify the key IPL parameters that impact on safety and treatment efficacy providing results from preliminary measure ments carried out on 18 IPL devices Clarkson 8 9 describes methods for measuring pulse duration and pulse profile in a similar manner the methods described in this paper can be used as a simple guide for service technicians to follow It is acknowl edged that these methods will not provide absolute values in terms of traceability to national standards however they will serve as a useful diagnostic tool enabling performance to be checked regularly during device lifetime The primary purpose of IPL devices is to destroy target structures through controlled thermal absorp tion in specific skin chromophores such as melanin and haemoglobin resulting in the long term reduc tion of unwanted hair or the removal of benign vascular and pigmented lesions 10 17 IPLs may also be used to produce a photochemical effect alone or in conjunction with topically applied photosensi tive drugs such as 5 ALA 18 20 which is used to stimulate the production of naturally occurring porphyrins to destroy bacteria IPLs may also provide penetrating wavelengths of light to directly stimulate tissue regeneration through a wound healing response photobiomodulation or low level laser therapy at the mitochondrial level 21 22 It is therefore increasingly importan
10. stains with a noncoherent pulsed light source A retrospective study Arch Dermatol 1999 135 679 83 Bjerring P Christiansen K Intense pulsed light source for treatment of small melanocytic nevi and solar lentigines J Cutan Laser Ther 2000 2 177 81 Brazil J Owens P Long term clinical results of IPL photorejuvenation J Cosmet Laser Ther 2003 5 168 74 Chan H The use of lasers and intense pulsed light sources for the treatment of acquired pigmentary lesions in Asians J Cosmet Laser Ther 2003 5 198 200 Weiss RA Weiss MA Beasley KL Rejuvenation of photo aged skin 5 years results with intense pulsed light of the face neck and chest Dermatol Surg 2002 28 1115 19 Gilbert DJ Treatment of actinic keratoses with sequential combination of 5 fluorouracil and photodynamic therapy J Drugs Dermatol 2005 4 161 3 Clark C Bryden A Dawe R Moseley H Ferguson J Ibbotson SH Topical 5 aminolaevulinic acid photodynamic therapy for cutaneous lesions Outcome and comparison of light sources Photodermatol Photoimmunol Photomed 2003319 134 41 20 21 22 23 Dover JS Bhatia AC Stewart B Arndt KA Topical 5 aminolevulinic acid combined with intense pulsed light in the treatment of photoaging Arch Dermatol 2005 141 1247 52 Eells JT Wong Riley MTT VerHoeve J Henry M Buchman EV Kane MP et al Mitochondrial signal transduction in accelerated wound and retinal healing by near infrared light therapy
11. Fournal of Cosmetic and Laser Therapy 2007 1 13 iFirst article informa healthcare INDUSTRY REPORT Measuring key parameters of intense pulsed light IPL devices GODFREY TOWN CAERWYN ASH EWAN EADIE amp HARRY MOSELEY Independent Laser Protection Adviser Haywards Heath West Sussex UK School of Physical Sciences University of Wales Swansea Swansea Wales UK and The Photobiology Unit University of Dundee Dundee Scotland UK Abstract Background Unlike medical lasers intense pulsed light IPL devices are largely unregulated and unclassified as to degree of safety hazard With the exception of most of the USA the United Kingdom and parts of Europe the Far East and Australia the sale of IPLs is generally unrestricted with the majority being sold into the beauty therapy and spa markets Standards are only imposed on manufacturers for technical performance data and operating tolerances determined by CE compliance under electrical safety standards or the EU Medical Device Directive Currently there is no requirement for measurement of key IPL performance characteristics Objective To identify the key IPL parameters emphasize their importance in terms of safe and effective treatment and provide examples of preliminary measurement methods These measurements can highlight changes in an IPL device s performance improving patient safety and treatment efficacy Methods Five key parameters were identified as having an im
12. IPL as the xenon lamp reaches its maximum current density within approximately 200 us there is a shift in the spectral output shown by output decay particularly in the yellow red region of the spectrum compared with the blue green Energy output at the atomic lines remains virtually constant throughout the pulse Therefore much of the discharged energy is wasted due to uneven distribution of wavelengths In a later comparative 1 OE He 1 40E 04 1 20E 4 1 OOF S 00F 03 6 00E 0R 4 WEH 0 00E 00 S00 530 600 650 700 Wavelength nm Measuring IPL parameters 750 800 50 900 F50 1000 1050 1100 Figure 9 Example standardized spectral output measurement showing IPL E with a sharp cut off at 530 nm and typical xenon lamp spectral profile intensity is irrelevant study it is intended to show time resolved spectral output data for different devices to investigate the square pulse partial discharge versus free dis charge argument and the potential impact on clinical outcomes Figures 9 and 10 Conclusions Measurement of IPL devices is becoming an important issue but is still at a very early stage after being neglected for years because of commercial pressures and a lack of regulation However the popularity of IPL as a treatment is growing and there is now a definite need for measurement to help improve both safety and efficacy The measurements in this paper will give techni cia
13. Mitochondrion 2004 4 559 67 Hawkins DH Abrahamse H The role of laser fluence in cell viability proliferation and membrane integrity of wounded human skin fibroblasts following helium neon laser irradia tion Lasers Surg Med 2006 38 74 83 Cameron H Ibbotson SH Ferguson J Dawe RS Moseley H A randomised blinded controlled study of the clinical 24 25 26 Measuring IPL parameters relevance of matching pulse duration to thermal relaxation time when treating facial telangiectasia Lasers Med Sci 20053 20 117 21 Vaynberg B Panfil S Epshtein V Spectrum controlled IPL Proc Photonic Therapeutics Diagnostics 2005 SPIE 5686 119 25 Clement M Daniel G Trelles M Optimising the design of a broad band light source for the treatment of skin J Cosmet Laser Ther 2005 7 177 89 Clement M Kiernan M Ross Martin GD Town G Preliminary clinical outcomes using iPulse intense flash lamp technology and the relevance of constant spectral output with large spot size on tissue Australas J Cosmet Surg 20063 2 54 9
14. Non Med Free Cl 610 25 No data 7 5 50 x 15 200 000 Non Med Free D 650 20 16 3 6 4 40 x 16 30 000 Non Med Free D1 540 20 No data 6 4 40 x 16 30 000 Non Med Free E 530 20 20 4 8 9 33 x 27 10 000 Med CE Partial F 560 50 22 2 2 69 34 x 7 9 10 000 Non Med Free F1 690 37 12 4 2 69 34 x 7 9 10 000 Non Med Free G 420 30 19 6 7 7 52 x 14 9 50 000 Non Med Partial Gl 530 17 6 13 5 7 7 52 x 14 9 50 000 Non Med Partial G2 600 18 16 7 7 7 52 x 14 9 50 000 Non Med Partial H 560 45 44 4 2 72 34 x 8 12 000 Med CE Free H1 695 45 51 0 2 72 34 x 8 12 000 Med CE Free I 645 35 41 8 2 72 34 x 8 12 000 Med CE Free I 695 35 No data 2 72 34 x 8 12 000 Med CE Free I2 755 28 No data 2 72 34 x 8 12 000 Med CE Free J 600 23 1 21 1 5 0 50 x 10 50 000 Non Med Free K 600 50 50 0 2 0 10 x 20 10 000 Non Med Free L 650 34 39 7 5 0 50 x 10 20 000 Med CE Free Ll 585 34 38 4 5 0 50 x 10 20 000 Med CE Free M 610 45 34 6 5 0 50 x 10 10 000 Med CE Free M1 530 51 No data 5 0 50 x 10 10 000 Med CE Free N 400 10 11 6 12 1 55 x 22 2500 Non Med Free Nl 430 7 10 7 12 1 55 x 22 2500 Non Med Free N2 400 10 5 8 3 6 33 6 x 10 9 2500 Non Med Free O 560 32 37 3 6 75 15 x 45 300 000 Med CE Free O1 695 32 36 6 75 15 x 45 300 000 Med CE Free O2 515 32 36 6 75 15 x 45 300 000 Med CE Free P 590 38 13 7 5 25 35 x 15 12 000 Non Med Free P1 640 38 No data 12 5 50 x 25 12 000 Non Med Free Q 540 20 20 2 6 4 40 x 16 30 000 Non Med Free Ql 650 20 14 9 6
15. UK www energist internatio nal com Instinctive Technologies Ltd Bedford UK www instinctiveuk com and Lynton Lasers Ltd Cheshire UK www lynton co uk G Relative intensity Intensity Town et al More blue More recdIR More red IR Wasted energy a a e o E e a l a a a a a Constant current Pulse duration ms gyn one ye ee 1 i Time ims 180 Free discharge 1100 Intensity i lime ms Nis Partial discharge Figure 10 Above Schematic illustration of the difference in the spatial and temporal characteristics of a free discharge and partial discharge pulse to an IPL xenon lamp and below time resolved spectral measurements of example IPL devices free discharge IPL C and partial discharge IPL E References 1 Subchapter J British Standards BS EN 60825 1 1994 Safety of laser products Part 1 Equipment classification requirements and user s guide BS EN 60601 2 22 1993 International Electrotechnical Commission PD IEC TR 60825 14 2004 Safety of laser products Part 14 A user s guide Radiological Health Code of Federal Regulations In FDA CDRH Center for Devices and Radiological Health Food amp Drugs Title 21 Volume 8 Revised as of April 1 2005 CITE 21CFR1040 10 and 1040 11 Performance standards for light emitting products International Electrotechnical Commission IEC TR60825 9 1999 Part 9 Co
16. an shown as an actual oscilloscope trace It was apparent that almost all claims recorded in this study made in manufacturers literature for a square pulse were not reflected in our example oscilloscope measurements as the pulses were usually the typical xenon krypton discharge slope increasing decreas ing of a free discharge system Note most of the useful light output is generated during the decay phase of the free discharge waveform Figure 6 Only IPLs E Figure 7 and G exhibited a true single square pulse shape confirming that they used partial discharge capacitor technology although close pulse stacking in devices A and O effectively achieved the same pulse shape and device D showed a nearly square pulse shape Only a comparison of time resolved spectral output will demonstrate whether there is any spectral deteriora tion across the entire pulse duration when compar ing these devices G Town et al Program 7 10 Stated Fluence 2 of Stated Fluence Measured Fluence D hw amp A om a lt a 6 7 8 9 10 11 l 13 14 15 l 17 18 19 20 Fluence Jcm2 Figure 3 Example standardized energy density measurement showing IPL system E whose energy output is well within the accepted tolerance of 20 for Class 4 medical lasers EN 60825 Expected Fluence 0 Below Expected Fluence ical Fluence 0 5 Lt 5 20 2 a0 33 di 45 50 2 Stat
17. e train and time resolved spectral measurements produced by the tested IPL applicators The spectrum graphs of the entire output are useful as they give an indication of accuracy of cut off filter wavelengths and the presence of unwanted ultraviolet or infrared wave lengths Of the 30 applicators tested seven IPLs measured more than 1 and two measured more than 2 of unwanted UV output below 400 nm when cut off filters were set significantly higher Table II Figures 8 9 10 G Town et al Input A 1 38 a SOS 0 98 046V 10 ls r ii 0 52 1 02 1 32 58 ms 5 mai Datablock lingut 29 01 1996 5 meN Z 58 m 225 255 Maxamum 1 22 Y Miramum 0 04 Figure 7 Example standardized lamp discharge profile measurement showing IPL system FE discharge profile of a square pulse constant current discharge 72D pit a iniae laren ary Tin Wanmangih irri ol a i Wavetangih inmi Figure 8 Example standardized spectral output measurement showing left IPL F with applicators with cut off filters at 560 nm and 690 nm demonstrating poor shallow slope cut off profiles and inaccurate cut off 620 nm red rather than 690 nm as stated in the manufacturer s user manual and right IPL T with cut off filters at 645 nm 695 nm and 755 nm showing good but inaccurate steep slope cut off profiles compared with
18. ed Fluence Jem Figure 4 Example standardized energy density measurement showing IPL system F whose output energy is only ca 25 of the stated energy on the device screen display and which is well outside the accepted tolerance of 20 for Class 4 medical lasers EN 60825 ripet A 12 08 r 10 08 8 08 6 08 4 061 208 aog 1 92 392 z 71 6 m 10 mz Div Measuring IPL parameters E y Datablock rout A Date 01 07 1996 Time 20h4 42 Maximum 608 Minimum 24 Cursor Values ie Mme IS2 36 0m da 452m ii O00 O16Y 000 O40 O00 O24 Figure 5 Example standardized lamp discharge duration measurements showing IPL system F which is a triple pulse system with one pulse missing thus one third of the energy is lost System display values T1 3 ms T2 20 ms T3 4 5 ms T4 30 ms T5 4 5 ms T3 4 5 ms sub pulse missing It is assumed that this is due to an error when writing the system software or when calibrating the microprocessor control system Irput 30 0 250 20 0 15 0 10 044 4 0 0 0 6 0 7 100 me 2 mei Mamim 24 0 A Mirum 14 4 4 Figure 6 Example standardized lamp discharge profile measurement showing IPL system B discharge profile of a free discharge IPL system Example spectral output In this initial measurement study spectral output measurements included both an average value for the complete pulse or puls
19. f light to achieve the desired photo therapeu tic effect can be measured by two methods The current can be measured by inserting a 0 01Q2 resistor in series with the flashlamp inside the applicator handpiece The current flowing through the electrodes is measured across the 0 01 resistor using a digital oscilloscope and plotted against time to give a graphical representation of the current ionizing the xenon gas Alternatively the current waveform can be measured by the induced current through a hand turned cable of thin enamelled copper wire wound around the electrode wire and a ferrite core This method can be used when the applicator can be opened easily by a technician but cannot be physically altered in any way without the manufacturer s permission Spectral output measurement The chromophores in the skin which are important for many IPL treatments have individual absorption spectra This means that depending on the target chromophore certain wavelengths will be more effective at treating certain conditions than others Therefore each treatment will be best suited to a particular wavelength range The range used should take into account the absorption spectra of all chromophores because heating a non target chromophore can damage the skin Knowing the Measuring IPL parameters spectral output will also provide information on any unwanted wavelengths such as ultraviolet and infrared radiation which can present immediate
20. ferent cut off filters were made as described and data were collected using the above methods The data and measurements were recorded and are summarized in Tables I and II The authors gathered the general information from the manufacturer s user manual web site and or current literature In most cases manufacturers accurately quoted the size of the treatment area Only device N claimed the treatment area to be 15 larger and device J claimed the treatment area to be 5 larger than was measured by the authors with a vernier mm scale Eight devices carried the medical CE mark and 10 had only the standard CE mark Example energy density measurement Fluence results were plotted on graphs for the example 18 devices against the systems displayed fluence or manufacturers claimed fluence in the G Town et al Table I Information recorded from manufacturer s specification in the user manual and measurements of spot size and range maximum fluence Claimed Measured Free or partial IPL study Cut on maximum maximum Actual spot size Claimed shot square ref filter fluence J cm fluence Jicm cm mmxmm lifetime CE class discharge A 600 21 20 8 4 8 48 x 10 30 000 Med CE Free Al 600 22 24 5 4 8 48 x 10 30 000 Med CE Free A2 555 8 9 2 4 8 48 x 10 30 000 Med CE Free B 450 22 11 1 7 5 50 x 15 100 000 Non Med Free Bl 450 22 13 0 7 5 50 x 15 100 000 Non Med Free C 535 25 14 5 7 5 50 x 15 200 000
21. flat and horizontal on the absorber head glass aperture with no lateral tilting The angle of the handset applicator position is critical as the slightest movement can result in an 8 10 difference in energy readings As the whole of the output from the transmission block usually cannot be measured owing to the size limitation of the absorber head aperture the IPL glass transmis sion block was centred over the aperture to ensure that maximum output energy was measured from the centre of the lamp plasma phase Figure 1C Firm downward pressure was applied to eliminate air bubbles which will impede light passage by light scattering in the gel between the glass block and the energy meter absorber head Figure 1D Sufficient time was left between each lamp discharge to again prevent excess heat creating small bubbles in the G Town et al Figure 1 A Mask the absorber head with a white PTFE sheet with aperture exposed for energy collection B fix the applicator in place on the absorber head energy collection aperture using a laboratory retort clamp and stand C take fluence measurements with the applicator transmission block flat and central on the absorber head energy collection aperture D apply firm downward pressure to eliminate air bubbles and tighten clamp fixing ultrasound gel An average of 10 shots was measured and divided by the area of the head aperture to give the energy density Measurements were taken for the most
22. manufacturer s operators manual intensity is irrelevant Measurements on 29 applicators showed 19 65 5 with cut off filters that were inaccurate by more than 20 nm versus the claimed cut off value given by the manufacturer Only 10 applicators 34 5 were within 20 nm of the stated cut off Figure 8 As with the energy density measurements the intensity of the spectral output is not traceable to national standards This means that an accurate determination of the retinal thermal hazard cannot be made Most monochromators suffer from stray light which effectively means light of a particular wavelength could be recorded incorrectly at a different wavelength It is possible that this could be the case with the HR2000 spectrometer although the manufacturer claims a stray light level of less than 0 1 Therefore assuming an accurate wavelength calibration it is possible from this measurement procedure to identify the filter cut off wavelength and any unwanted radiation Until accurate traceability can be established the main value is in recording regular spectral output mea surements that allow changes in the spectrum or deterioration in the filter to be detected Recent studies report the theoretical consequen tial benefits resulting from a square pulse profile resulting in a constant spectral output across the entire pulse or sub pulse duration and leading to greater treatment efficiency 25 26 In a free discharge
23. mpilation of maximum permissible exposure to incoherent optical radiation lst ed Edition Geneva International Electrotechnical Commission 1999 10 Hode L Are lasers more dangerous than IPL instruments Lasers Med Sci 20033 18 suppl 1 Abstract no 0189 Clarkson DM Hazards of non coherent light sources as determined by the framework of IEC TR 60825 9 J Med Eng Technol 2004 28 125 31 Care Standards Act 2000 The Private and Voluntary Health Care England Regulations 2001 3 1 b Prescribed tech niques or technology Clarkson DM The role of measurement of pulse duration and pulse profile for lasers and intense pulsed light sources J Med Eng Technol 2004 28 132 6 Clarkson DM Determination of eye safety filter protection factors associated with retinal thermal hazard and blue light photochemical hazard for intense pulsed light sources Phys Med Biol 2006 51 N59 64 10 11 12 13 14 15 16 17 18 19 Anderson RR Parrish JA Selective photothermolysis Precise microsurgery by selective absorption of pulsed radiation Science 1983 220 524 7 Haedersdal M Wulf HC Evidence based review of hair removal using lasers and light sources J Eur Acad Dermatol Venerol 2006 20 9 20 Angermeier MC Treatment of facial vascular lesions with intense pulsed light J Cutan Laser Ther 1999 1 95 100 Raulin C Schroeter CA Weiss RA Keiner M Werner S Treatment of port wine
24. ns working with IPLs a useful tool for checking output consistency and diagnosing performance issues Discrepancies can be seen between measured parameters and manufacturer claims but caution must be exercised with this comparison because the techniques described in the paper are subject to on going development In particular traceability to national standards is a pre requisite to accurate absolute as opposed to relative measurements On the other hand comparing different devices is useful as discrepancies highlight the need for legislation to produce standard measurement procedures This study has determined easily reproducible test methods for key parameters of IPL devices and tested their validity on 18 example systems As mentioned further work is required if measurement results are to be made traceable to national standards It is also hoped that a homogeneity test can be developed to provide objective measurable values to ensure even distribution of energy across skin contact areas Further research is required and a second trial is now underway to evaluate and compare a larger number of popularly available IPL devices in use in the United Kingdom using the test methods described in this paper Acknowledgements The authors wish to thank the following companies for their contribution in reviewing the fluence test methodology used in this study Cyden Ltd Swansea Wales UK www cyden co uk Energist Ltd Swansea Wales
25. ost restrictive IPL devices will at least allow the user some control over energy density which makes reproducible measurement very important to ensure consistent output and prevent under or over treatment An isopropyl alcohol wipe and an optical cloth were used to thoroughly clean the IPL light guide and head aperture of the energy meter Ophir LaserStar Power Energy Monitor Ophir L40 150 A DB SH NS Absorber Head Ophir Optronics Ltd Jerusalem 91450 Israel The slightest frag ment of dirt or a thin layer of dried ultrasound gel residue can make a significant difference to the passage of light from the handset applicator to the energy meter absorber head Clear optical coupling ultrasound gel Henleys Medical Hertfordshire AL7 1AN UK was applied to the top of the energy meter IPL absorber unit glass without any air bubbles in the gel Figure 1A A 2 mm thick white poly tetra fluoro ethylene PTFE plastic mask spacer with a 4 84 cm 2 2 x 2 2 cm aperture was used to prevent burning of the surface paint around the energy absorber head and to fix the depth of gel between the absorber glass lens surface and the applicator glass coupling block 0 1mm The applicator handset was placed in a horizontal position above the absorber head using a laboratory retort clamp and stand Figure 1B The applicator handset glass transmission block was in direct contact with the PTFE white spacer on the energy meter absorber unit and perfectly
26. portant role to play in the way light interacts with the skin and therefore an important role in patient safety and effective treatment Simple methods were devised to measure the parameters which include fluence pulse duration pulse profile spectral output and time resolved spectral output Results The measurement methods permitted consistent and comparable measurements to be made by two of the authors at working clinic locations on 18 popular IPL devices and allowed assessment of output variations Results showed discrepancies between the measured IPL device outputs and those values displayed on the system or claimed by the manufacturers The importance of these discrepancies and their impact is discussed Conclusions This study of 18 popular devices in regular daily use in England and Wales provides example methods for measuring key IPL device parameters and highlights the need for regular measurement of at least those five key parameters measured in this study These methods can help service technicians to check performance and eliminate device malfunction Key words Energy density fluence optical hazard spectral output square pulse Introduction pulsed light IPL devices whether or not they l l comply with the European Medical Device In Europe medical lasers are governed by strict Directive Technical Report IEC TR60825 9 con safety standards 1 2 The European Standard EN l ee firms risk factors and measurement practices applied
27. ppointments Where available the following general information was recorded e device identity name model manufacturer serial number manufacturing date withheld and coded for the study maximum stated pulse energy and or maximum stated fluence e CE classification e g medical device or not labelling details e number of shots claimed in the company litera ture web site user manual or system software The following parameters were measured on up to 18 devices and 36 applicators in common use in UK clinics e fluence energy density for a range of popular programs and energy settings including maximum fluence this was compared with the claimed maximum fluence e accurate pulse durations for different treatment types settings e electrical discharge across the xenon lamp oscil loscope trace e spectral output e dimensions of glass transmission block CE mark for medical devices explanatory note The CE mark is a visible declaration by the manufacturer or his representative importer etc that the equipment which is marked conforms to the required regulatory standards for safety and envir onmental protection legislation under all of the applicable European Union EU directives The letters CE are initials for the French phrase Conformit Europ ene European Conformity IPL devices are normally classified as Class IIa b electro medical devices with medium risk Medical Class
28. sing a reversed biased photodiode were recorded as an oscilloscope trace to permit measurement of pulse and sub pulse durations and intra pulse delay times Table II This test also served to validate the number of sub pulses in a pulse train Using this method there was generally a poor correlation between manufacturers claims or system displayed values and the pulse durations measured The data measured for six of the eight medical CE marked IPLs were consistent with displayed values where given Measuring IPL parameters Table II User manual indicated pulse data and measured pulse durations showing an approximately 3 deviation from specification Study ref Cut off filter filter below 400 nm A 600 1 8 0 4 Al 555 8 5 0 5 600 2 0 B 450 8 4 1 5 450 8 4 1 5 C 535 31 1 6 610 52 1 6 D 650 13 4 2 2 540 5 4 0 2 E 530 2 1 0 F 560 8 5 0 2 690 45 1 0 G 420 0 3 0 530 0 1 0 600 0 No data H 560 1 6 0 695 16 8 0 I 645 4 6 0 695 15 7 0 755 21 8 0 J 600 21 6 0 1 K 600 19 6 0 L 650 5 1 0 585 17 1 0 610 No data 0 7 530 2 1 No data N 400 No data 0 1 430 0 3 3 6 400 No data 0 1 O 560 2 5 0 2 695 7 4 0 2 515 3 4 1 4 P 590 No data No data 640 No data No data Q 540 No data No data 650 No data No data deviation of cut off UV Measured pulse duration ms Stated pulse duration ms 30 3 sub pulses 18 3 sub pulses 14 1 14 5 1 2x 2 5 ms 15 2x3
29. t that the user can be assured of accurately measured and correctly distributed energy at the skin surface The pulse duration of delivered light and the associated spectrum of light produced also play a key role in correct targeting of key structures There is little objective evidence provided by manufacturers even in user and service manuals to validate claims for pulse features or stability of spectrum characteristics The authors identified the following five key parameters to measure 1 energy density fluence for various popularly used pulse patterns over the claimed lifetime of the lamp and filter assembly to establish whether there is any significant deviation or deterioration compared with established stan dards for medical lasers Clearly excessive energy density above stated values may result in burns to patients skin and low energy density may result in under treatment and patient dissatisfaction 2 pulse duration or durations of sub pulses in a pulse train of the intense light emitted from the xenon flashlamps The pulse duration can be critical in the efficacy of the type of treatment particularly where the pulse duration is to be matched to the thermal relaxation time of the target Overstated pulse duration may result in a more aggressive treatment than was intended by the operator with concomitant side effects 3 electrical discharge pulse shape recorded as an oscilloscope trace entering the lamp versus
30. ts Risk is also increased if the pulse duration is short and the fluence high The duration of the discharged pulse or sub pulses of intense white light was measured using a reversed biased photodiode acting as a light dependant switch Figure 2 The pulse duration was captured as an oscilloscope image using a Fluke 196 Scopemeter and its counterpart FlukeView version 4 software Optimum Energy Products Ltd Calgary T2 Z4M3 Canada The pulse duration can differ considerably between IPL systems from different manufacturers some use true single pulses but most utilize two or more sub pulses to extend pulse duration to allow intra pulse epidermal thermal relaxation and to help extend flashlamp lifespan Ideally the pulse dura tions should be adjustable as various chromophores have differing thermal relaxation times TRI and Figure 2 Test apparatus for pulse duration measurement using a reversed biased photodiode acting as a light dependent switch therefore the IPL should match such times to target the correct chromophore Lamp discharge profile measurement A constant current through the xenon flashlamp may be critically important in the treatment of skin conditions The spectrum of a flashlamp whose energy is supplied from a free discharge capacitor will change as the current follows a standard distribution curve 24 The current discharge profile through the xenon flashlamp which should produce a balanced spec trum o
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