Lasers Med Sci (2007) 22: 4–9DOI 10.1007/s10103-006-0417-7

ORIGINAL ARTICLE

C. Ash . G. A. Town . G. R. Martin

Preliminary trial to investigate temperature of the iPulse™intense pulsed light (IPL) glass transmission blockduring treatment of Fitzpatrick II, IV, V, and VI skin types

Received: 6 May 2006 / Accepted: 30 August 2006 / Published online: 21 November 2006# Springer-Verlag London Limited 2006

Abstract The glass transmission block, a key componentof all intense pulsed light (IPL) devices, is responsible forthe delivery of IPL energy from the xenon discharge lampto hair and skin structures during treatment. The purpose ofthis study was to investigate the variation in temperatureof the quartz glass block used in the iPulse™ (CyDen,Swansea, UK) handset during typical hair removaltreatments of Asian and Afro-Caribbean skin types. Initialresults from four subjects indicated that the temperature ofthe glass transmission block did not exceed 45°C duringany of the treatments. Furthermore, the development of thetemperature measurement methodology described in thispaper will enable the comparison of data from different IPLsystems to be undertaken in a subsequent larger scale trial.

Keywords Hair removal . Intense pulsed light (IPL) .Glass transmission block . Temperature measurement

Introduction

An integral component of the handset applicator of allxenon intense pulsed light (IPL) devices used for hairreduction and the treatment of skin conditions is the quartzor sapphire glass transmission block, which deliversbroadband, intense pulsed light energy from the xenonlamp to the skin. The size, energy, and dischargespecifications of most IPL devices require a cooling circuitwhere deionized water is pumped around the flashlamp tocool the lamp, filter, and glass transmission blockassembly. Moreover, some IPL systems require additionalcooling of the glass transmission block (by means of acirculating coolant collar or thermoelectric Peltier coolingdevice) to keep the transmission block temperature at acomfortable level for the patient and to avoid any sideeffects from excessive heat buildup while in contact withthe skin.

A review of the literature on temperature measurementand burn response shows that diathermy and radiofrequency (RF) are well-established technologies in clin-ical medicine usually involving the delivery of RF currentto the tissue in a unipolar mode with the current returningto the generator source through a large dispersive electrode.Skin burns at the dispersive electrode site represent seriouscomplications of RF ablation procedures, which have led toa number of studies seeking ways to reduce the incidenceof dispersive-electrode-related burns [1–4]. However, sinceGoldman and Eckhouse [5] began developing a new IPL(PhotoDerm VL) in the early 1990s, most studies haveemphasized positive results with these devices, and therehave been relatively few published reports on burncomplications or how to avoid them, especially in darkerskin types. Miyake et al. [6] determined a predictivemethod for measuring the increase in temperature duringIPL applications to prevent cutaneous lesions duringpolychromatic light sclerotherapy.

The subject of this preliminary evaluation is a patentedtwin-flashlamp, constant-spectrum, low-temperature, air-cooled IPL system (iPulse™ CyDen, Swansea, UK), whichcontains neither a colored glass absorption filter nor a water

C. Ash (*)CyDen Ltd.,Technium 2, Kings Road,Swansea, SA1 8PH, Wales, UKe-mail: cash@cyden.co.ukTel.: +44-1792-485618Fax: +44-1792-485631

G. A. TownGCG Healthcare Ltd.,88 Noah’s Ark Lane,Haywards Heath, RH16 2LT, England, UKe-mail: godfreytown@csi.comTel.: +44-1444-484911Fax: +44-1444-484357

G. R. MartinRobb Farm,Tuxford Road, Egmanton,Nottingham, NG22 OHA, England, UKe-mail: rossmartin@talk21.comTel.: +44-115-9827033Fax: +44-115-9580044

cooling circuit. The twin xenon lamps have cerium-oxide-doped glass envelopes to filter out potentially harmful UVradiation below 400 nm, and the quartz glass transmissionblock has a dichroic reflectance filter coating to allow onlywavelengths above 530 nm to be delivered to the skin. Asdiscussed by Weiss and Weiss [7], the method ofapplication requires the use of a refrigerated (+4°C), clearultrasound gel to cool the skin surface and assist in lighttransmission through the stratum corneum to dermal andepidermal targets such as hair follicles, thread veins, andbenign pigmented lesions. iPulse™ utilizes “partial dis-charge” technology whereby computer software delivers asquare pulse electrical discharge to the lamp to ensureconstant spectral output for the entire duration of the pulse.

In common with many other users of IPL technology,who have employed systems with conventional coloredglass absorption filters, users in tropical climates such asthose in Southeast Asia, have preferentially used red filtersto reduce competitive absorption of shorter wavelengths oflight into the epidermal melanin component of darker skintypes commonly found in these areas. Therefore, whenintroduced to iPulse™ technology, some clinicians inSoutheast Asia have expressed concern that the clear quartzblock may reach high temperatures that could possiblyproduce side effects during the treatment of dark Asian skintypes that are prone to hyperpigmentation. Therefore, thepurpose of this preliminary trial was to investigate thevariation in temperature of the glass block used inthe iPulse™ handset during typical hair removal treatmentsof Asian and Afro-Caribbean skin types.

Several preliminary investigations have been carried outto evaluate the characteristics of the iPulse™ system. Thefirst examined whether different reflective materials used torepresent the skin surface being treated have an effect onthe temperature of the handset and ultimately the userreplaceable lamp (Ash 2005, personal communication).The white fluorocarbon-based polymer, polytetrafluoro-ethylene (PTFE), was shown to be a suitable laboratory testmaterial substitute for tests on human skin. It was alsodemonstrated that the temperature of the glass block fallsbecause the subject’s cooler skin surface conducts heataway from the glass block as it moves over the skin.

A second study evaluated temperature change of thehandset during testing of the iPulse™ i200 and i300systems (Ash 2005, personal communication). A substan-tial improvement in temperature reduction was observedusing the new iPulse™ i300 handset. In this study, the glasstransmission block under test reached an extremely hightemperature (170°C) due to the handset being fired againstPTFE with no movement or cooling gel applied. Thecurrent study described in this paper, although using onlyfour subjects, expands on a preliminary investigation oftreatment temperature of the iPulse™ handset glass block,which included only two subjects (both of skin type II)(Ash 2005, personal communication). The current study is,therefore, more representative of treatments carried out byestablishments whose clients often have widely differingskin types.

Additionally, developing a method to measure the heatbuildup, if any, in the glass transmission block may betterallow comparative data to be gathered for different IPLsystems and identify possible causes of unwanted sideeffects.

Materials and methods

Selection of subjects

The subjects used for this investigation were of variousskin types. measured using the Fitzpatrick Scale, I to VI.The skin treatment area on all subjects was tested using aChromoTest melanin measuring system (Dupleix, Den-mark) to confirm the skin type with a numerical grade(Fig. 1). The use of the ChromoTest system reduced therisk of human error in skin-type assessment, which couldresult in ineffective hair removal treatment throughincorrect choice of pulse and energy density values.

The Fitzpatrick skin type and profile of the four subjects(unpaid volunteers from Swansea University) are summa-rized in Table 1. Subject D with a skin type II was chosen asa comparison with the three darker skin types. Subjects A,C, and D had previously regularly shaved the area treatedin this study using standard wet shaving products. Threedays before the treatment measurements were performed,each subject had a test patch (three IPL shots) to ensuresuitability for IPL treatment. Before treatment, the subjectscompleted a case report form, highlighting their medicalhistory, and also signed a treatment consent form. Table 2shows the treatment information for each subject.

Equipment setup and data recording

An iPulse™ i300 IPL was used for the investigation, withthe base unit operated using the appropriate pulse durationsand energy density (fluence) levels for the skin types

Fig. 1 ChromoTest melanin measuring system (Dupleix, Denmark)for skin type assessment

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selected. A laptop connected to a small Pico temperaturedata logger (Pico Technology, St. Neots, UK), which hadbeen independently calibrated according to the industrystandard protocol immediately before this study, and athermocouple attached to the handset glass block were usedto record the temperature measurements (Fig. 2). Thethermocouple, which measured the temperature of the glassblock, was placed into a small, 3-mm-deep groove cut inthe corner of the glass block using a circular diamond saw.The position and depth of the thermocouple were decidedupon to represent the true thermal energy seen at thetreatment face without being in contact with the coldultrasound gel which would reduce the temperature of thethermocouple and distort the results. It can be seen from thecomputer simulation of the heat transfer through the fusedsilica glass treatment block (Fig. 3) that with a cut 5 mmfrom the front of the glass block and at a depth of 3 mm, thetemperature at the thermocouple is the same as that seen atthe treatment surface center, without having compromisedresults due to the cold ultrasound gel.

As in the previous study, the Pico data logger wassampled at 100 ms intervals, which exceed the Nyquistcriteria. However, by sampling at this rate, the heatabsorption of light directly onto the thermocouple wasseen as sharp transient spikes. These almost instantaneousspikes were ignored as they did not represent the temper-ature of the glass block but only a transient response of thethermocouple.

The iPulse™ IPL device under evaluation features twinparallel xenon lamps (patent applied for) with reverseorientation of anode and cathode of each lamp tocompensate for any concentration of energy emission at

Table 2 Treatment information for subjects A–D

Subject Bodyareatreated

Numberof shotsused

Pulse Energydensity(J/cm2)

Sideeffects

A Leg L 95 Triple 3×10 ms on20 ms off (withinpulse train)

10 ErythemaLeg R 94

B Back 27 Triple 3×10 ms on20 ms off (withinpulse train)

10 None

C Leg L 65 Single 40 ms 11 NoneLeg R 68

D Leg L 81 Single 30 ms 14 NoneLeg R 85

Fig. 2 iPulse™ IPL handset showing glass transmission block withattached thermocouple for temperature measurement

Table 1 Subject profile information

Subject Profile

Age Sex (M/F) Ethnic origin Smoker Skin type

A 23 F Afro-Caribbean Yes VIB 28 M Afro-Caribbean No VC 22 F Chinese No IVD 23 F White No II

Fig. 3 CAD simulation of heat transfer through an iPulsetransmission block illustrating homogeneity of energy distribution(where color change from red to blue denotes temperature gradient)

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the cathode. This feature produces a more homogenousenergy distribution across the glass transmission block.

To simulate the ambient temperature conditions likely tobe encountered during skin treatments in air-conditionedclinic rooms in a tropical climate such as south east Asia,room temperature was increased using central heating and agas fire to between 24 and 27°C.

Treatment procedure

All experimental procedures in this pilot study were carriedout in accordance with the standard treatment protocol(Martin 2005, personal communication) and under thesupervision of the clinical author who produced it. Whileformal ethics committee approval was not sought,informed consent was obtained from trial subjects tomake these measurements of glass block temperature undernormal treatment conditions, which did not involvemeasuring therapeutic efficacy or any unwanted treatmentside effects.

The handset was discharged against the patient’s skin(Fig. 4) using the standard treatment protocol for hairremoval (Martin 2005, personal communication). Care wastaken not to overlap any areas on the subjects’ skin. Thetreatment was undertaken as rapidly as possible to create a“worst-case” scenario of a patient’s treatment where theremight be a buildup of heat in the glass block from the rapidtreatment. The occurrence of any normal side effects suchas erythema (skin reddening) was recorded.

The iPulse™ i300 system has an automatic short coolingcycle (43 s) after 50 discharges of the consumable lamp,and the operator cannot discharge the handset during thistime while the system is cooling, so it was anticipated thatthis would create breaks in the data being recorded. Also,groupings of approximately 20 sets of data were expecteddue to a series of discharges along the length of a leg, then ashort break was taken by the operator to prepare the nextarea for treatment with coupling cooling gel.

Results and discussion

It can be seen that there are two lines on each of the graphspresented in this study (Fig. 5a–g). The red, almostconstantly horizontal line is the ambient room temperatureduring testing. From the data, it can be seen that thetemperature of the environment during treatment isconstantly in the range of 24 to 27°C. As anticipated,there were several gaps among the groupings of measure-ments (Fig. 5a,f, and g), because of the automatic shortcooling cycle after 50 discharges of the consumable lampduring which the operator could not continue dischargingthe lamp. The expected groupings of approximately 20 setsof readings due to a series of discharges along the length ofa leg, interrupted by a short break for the operator toprepare the next area for treatment with coupling coolinggel, were noted as a dip on the temperature curve.

From inspection of the graph data (Fig. 5), it can be seenthat the glass block temperature varies somewhat as it isapplied to the patient’s skin. This can be explained by thefact that as the handset is discharged against the patient’sskin, it heats both the patient’s skin and the coupling gel inthat area. The handset is then moved to an area where thepatient’s skin and the coupling gel are at a lowertemperature than the area that just had IPL treatment. Thecooler area of skin and gel absorbs some thermal energyfrom the glass block, thereby cooling the glass block.

The difference in the number of shots used on eachsubject (Table 1) was due to the difference in body sizebetween subjects, resulting in varying size of treatmentsurface area. Most notable was subject C who was ofshorter stature than subjects A and D and so required fewershots.

The average temperature of the glass block for allsubjects was approximately 43°C, which was only 6°higher than the core body temperature (the average wasevaluated visually from the graph data). Subjects did notfeel this average 43°C temperature directly due to thecoupling gel acting as a thermal barrier between the skinand the glass block surface.

During the treatment of the lower back of subject B(Fig. 5c), the glass block had an initial temperature of 19°C(due to evaporation cooling of the gel) and increased byless than 1°C with each successive discharge before itdecreased as the glass block cooled to the ambienttemperature. It is the authors’ understanding that the heatenergy absorbed is spread homogeneously through theglass block due to a constant distribution of light throughthe glass block from the twin lamps. Despite the increase inambient temperature of approximately 4–5°C in the presentstudy vs the earlier study (Ash 2005, personal commu-nication), the temperature of the glass block peaks atapproximately the same temperature in both studies. Thismay be explained by the greater absorption of light energyby the darker skin type than the lighter skinned subjects inthe earlier trial, with correspondingly less reflection ofenergy back into the handset body.

Subjects B, C, and D felt comfortable during thetreatment of hair removal with no post treatment erythemaFig. 4 Hair removal treatment procedure

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Fig. 5 a–g Temperature recordings of the iPulse™ quartz glass transmission block for subjects A–D. The red line is the ambient roomtemperature, while the blue line is the block temperature shown over time, which did not exceed 45°C

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(redness) or side effects. Subject A experienced slighterythema probably caused by overlapping of adjacentspots. These treatment-related observations would havehad no effect on the recorded results.

It is worth reflecting that, in the Miyake et al. study [6],while treatments were performed on 20 female subjects ofFitzpatrick skin types I–IV, the study used a conventional“free-discharge” IPL, with 515 nm cutoff filter, and a 6-mssingle short pulse output, parameters that are rarely used onskin types III and IV. Miyake also proposed shooting theIPL with the light guide removed from the skin surface asthis facilitated simultaneous temperature measurementusing his test method and resulted in a complete absenceof side effects including an absence of any pain sensation.Given the extremely high divergence angle of polychro-matic light emitted from a glass transmission block, it isalso likely that the light energy reaching the tissue wouldhave been ineffective in treating the target lesion.

In a comprehensive review of thermal thresholds fortissue damage from hyperthermia based on measuredsurface temperatures, Dewhirst et al. [8] observed verylittle cytotoxicity for up to 5 h of heating at 42°C in hamstermodels in vitro, while in human and porcine studies invivo, the time–temperature relationships to achieve eartissue necrosis are far lower for mouse ear than for the skinof human/pig. Activation energies gave breakpoints of47°C for man and pig and 42.5°C for mouse. Moritz andHenriques [9] also reported that heating of human skin to atemperature of 44°C for 5 h (600 CEM 43°C) resulted inonly mild hyperemia in two subjects. The authors of thecurrent study do not therefore consider the measuredmaximum temperature of 43°C to be of concern as theexposure time on any given area of 8.9 cm2 of skin (thearea of the glass IPL transmission block) would never belonger than 110 ms with a single pass treatment.

Conclusions

Using iPulse™ technology, brief temperature rises up toapproximately 43°C were measured within the glass

transmission block during treatments on skin types II, IV,V, and VI and that other than normal erythema, no sideeffects were recorded.

Based on these encouraging results, a larger scalecontrolled trial with higher treatment fluences andcomplete treatment courses should be undertaken tovalidate these initial findings and show that iPulse7™ istherefore safe to use on darker skin when used as describedin the iPulse treatment protocol.

The use of a digital thermal imaging camera could beused in subsequent studies to observe directly the temper-ature of the patients’ skin and the thermal dissipationproperties of the subjects’ skin.

References

1. Thiagalingam et al (2005) A thermochromic dispersive electrodecan measure the underlying skin temperature and prevent burnsduring radiofrequency ablation. J Cardiovasc Electrophysiol7:781–788

2. Steinke K, Gananadha S, King J, Zhao J, Morris DL (2003)Dispersive pad site burns with modern radio frequency ablationequipment. Surg Laporosc Endosc Percutan Tech 13:366–371

3. Aigner N, Fialka C, Fritz A, Wruhs O, Zoch G (1997)Complications in the use of diathermy. Burns 23:256–264

4. Neufeld GR, Foster KR (1985) Electrical impedance propertiesof the body and the problem of alternate-site burns duringelectrosurgery. Med Instrum 19:83–87

5. Goldman MP, Eckhouse S (1996) Photothermal sclerosis of legveins. ESC Medical Systems, PhotoDerm VL CooperativeStudy Group. Dermatol Surg 22:323–330

6. Miyake RK, Miyake H, Kauffman P (2001) Skin temperaturemeasurements during intense pulsed light emission. DermatolSurg 27:549–554

7. Weiss RA, Weiss MA (2001) Noncoherent filtered flashlampintense pulsed light device. In: Lyons K (ed) Lasers in aestheticsurgery. Thieme, New York, p 196

8. Dewhirst MW, Viglianti BL, Lora-Michiels M, Hanson M,Hoopes PJ (2003) Basic principles of thermal dosimetry andthermal thresholds of tissue damage from hyperthermia. Int JHyperthermia 19(3):267–294

9. Moritz A, Henriques F (1947) Studies of thermal injury II. Therelative importance of time and surface temperature in thecausation of thermal burns. Am J Pathol 23:695–720

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