WO2005074830A2

WO2005074830A2 - Hair and lesion removal and treatment of cutaneous conditions

Info

Publication number: WO2005074830A2
Application number: PCT/GB2005/000285
Authority: WO
Inventors: Michael Noel Kiernan
Original assignee: Cyden Limited
Priority date: 2004-02-03
Filing date: 2005-01-28
Publication date: 2005-08-18
Also published as: GB2410690A; GB0402321D0; WO2005074830A3; GB0405327D0

Abstract

A method is proposed for achieving long-term or permanent hair reduction or removal is proposed, which uses low optical energy density levels, typically 5 Joules/cm 2 or less, which is possible by exploiting the differential in the thermal relaxation time of the hair shaft and surrounding melanin in the basal and epidermal layers, namely that the thermal relaxation time of the hair shaft is long compared to that of the individual melanin cells. Therefore, for a given temperature rise, the hair shaft will remain at an elevated temperature for longer than the melanin cells, because the heat diffusion rate is much slower. A sequence of optical pulses, the 'pulse train', is delivered to the treatment site, with ability being provided for the pulses of the pulse train to have a variable duration, intensity and duty cycle. The total optical energy delivered causes a temperature rise in the tissue dependant upon the wavelength, energy density, pulse duration and the tissue parameters of skin colour (which is determined by the melanin content of the skin), the presence of hair and other pigment-containing structures.

Description

Hair and Lesion Removal and Treatment of Cutaneous Conditions

This invention relates to a method and apparatus for safe and effective removal of hair and/or cutaneous lesions from an area of the human body and, more generally, to treatment of cutaneous conditions and, more particularly, to a method and apparatus for removal of hair in which a flashlamp emits a series of sequential pulses of incoherent light energy which are transmitted to the same area of skin through an optical delivery system.

Excessive hair growth on areas of the human body is a common problem and can be unsightly. The removal of excess hair can be achieved using a number of different methodologies, including cutting or shaving, waxing, sugaring and, more recently, with the use of optical energy. Traditional hair removal techniques result in hair-free periods of, say 2 — 4 weeks, whereas techniques employing optical energy can achieve hair-free periods of many months and, in some cases, permanent hair removal.

Hair can be removed permanently for cosmetic reasons by, for example, heating the hair and the hair follicle to a high enough temperature that results in their coagulation. It is known that blood is coagulated when heated to temperatures of the order of 70°C. Similarly, heating of the epidermis, the hair and the hair follicles to temperatures of the same order of magnitude will also cause their coagulation and will result in the permanent removal of the hair.

One common method of hair removal, often called electrolysis, is based on the use of "electric needles" that are applied to each individual hair. An electrical current is applied to each hair through the needle. The current heats the hair, causes its carbonisation and also causes coagulation of the tissue next to the hair and some coagulation of the micro- vessels that feed the hair follicle. While the electrical needle method described above can remove hair permanently, or at least for a relatively long period of time, its use is practically limited because the treatment is painful and the procedure is generally tedious and lengthy.

Light can also be used effectively to remove hair or cutaneous lesions and/or to treat cutaneous conditions. For example, prior art methods of hair removal exist which involve the application of pulsed light, generally from coherent sources such as lasers. However, major deficiencies of such methods include the fact that lasers are expensive and subject to stringent regulations.

Light (electromagnetic) energy used to remove hair must be such that sufficient energy will be absorbed by the hair and the hair follicle to raise the temperature to the desired value. However, if the light is applied to the surface of the skin other than at the precise location of the hair follicle, the light may also heat the skin to coagulation temperature and a induce a burn in the skin. Accordingly, it is desirable to be able to effectively heat multiple follicles, without burning the surrounding skin. It is further desired to be able to remove more than one hair at a time, preferably over a relatively wide area of the skin, using incoherent light (which is relatively inexpensive to provide and subject to much less stringent regulations than lasers and the like).

Flashlamps allow the removal of large areas of hair from almost any body area, including the face, arms, legs, breasts, hands, stomach, etc. Flashlamp treatment provides a low discomfort level to the patient, and hair removal may last for weeks or months on a treated body area, and may even be permanent. However, some known flashlamp methods of hair removal can produce unwanted side effects, such as burning of the skin, changes in skin pigmentation and permanent scarring.

Current cutaneous flashlamps work by delivering energy in the form of visible light which is absorbed by the cutaneous target, heating the target and thereby causing its destruction. Different skin structures have different colours, different surface-to- volume configurations, and other factors which cause differential rates of heat loss. All of the hair removal flash lamps work by application of the principle of selective photothermolysis, i.e. selective destruction due to heat caused by absorption of light. Visible light, which has a varied wavelength, is absorbed by a target which has a complementary specific colour for those wavelengths. This flashlamp target is called a chromophore. The usual chromophore for hair removal flashlamps is melanin, found in high concentration in brown and black hair, and is responsible for the colour of hair. The clinical problem is that melanin is also found in the epidermis, and is responsible for native skin colour and tan. Flashlamp energy is therefore also absorbed into the epidermis. The problem of hair removal by flashlamps, therefore, is to deliver flashlamp energy that heats the hair to a sufficient degree to cause permanent damage and hair loss, and yet spare the skin of any damage.

Nevertheless, the use of visible light in the range of 550nm to 900nm still appears to be an effective way to achieve permanent hair removal and, in order to achieve predictable permanency, it is necessary to achieve higher temperatures in the hair without heating the epidermis to the point where it is burned. US Patent No. 6,080,147 describes a method of hair and cutaneous lesion removal and treatment of cutaneous conditions, using a flashlamp, in which a series of short flashlamp energy pulses are provided to the target area, with short time delays between the pulses, so as to heat the hair follicle sufficiently to cause permanent damage to that hair follicle, and yet spare the skin from burning, thus providing a safe and permanent method of hair removal. The amplitude and duration of the energy pulses, and the time delay between them, is set prior to treatment, according to hair and skin colour of the patient.

We have now devised an improved arrangement.

In accordance with a first aspect of the present invention, there is provided a method of removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, using a flashlamp apparatus, the method comprising delivering a sequence of pulses of light energy from said flashlamp apparatus to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined levels, and varying at least one pulse parameter and/or the time interval between adjacent pulses in said sequence, wherein pulse parameters comprise at least energy density, pulse intensity, wavelength of light energy and pulse duration.

Also in accordance with the first aspect of the present invention, there is provided flashlamp apparatus for removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, the apparatus comprising means for delivering a sequence of pulses of light energy to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined levels, and means for varying at least one pulse parameter and or the time interval between adjacent pulses in said sequence, wherein pulse parameters comprise at least energy density, pulse intensity, wavelength of light energy and pulse duration.

Thus, the first aspect of the present invention enables the effectiveness of the method to be optimised with regard to the patient's specific skin colour and type, while the time taken to perform the treatment can be minimised, by varying the energy density and duration of the pulses in a sequence, and/or the time interval between the pulses.

In a preferred embodiment, the wavelength of the pulses may be varied, beneficially by varying the intensity thereof, and preferably the spot size of pulses in the sequence can be varied.

The wavelength of pulses is beneficially between 550 and 1200 nm, and the energy density of pulses is preferably, between 0.1 and 100 Joules/cm², more preferably between 0.1 and 50 Joules/cm², even more preferably between 0.1 and 30 Joules/cm², still more preferably between 0.1 and 20 Joules/cm², even more preferably between 0.1 and 10 Joules/cm², and most preferably at least some of the pulses in the sequence have an energy density of between 0.1 and 5 Joules/cm .

The pulse duration may be between 1 and 100 ms, more preferably between 1 and 90 ms, still more preferably between 1 and 50 ms, still more preferably between 1 and 30 ms, and most preferably between 1 and 10 ms, beneficially less than 8 ms.

The flashlamp apparatus may comprise at least two flashlamp devices which are independently operable, for delivering first and second sequences of pulses of light energy from respective first and second flashlamp devices, whereby a pulse parameter and/or the time interval between adjacent pulses of at least one of the sequences may be varied. The first and second sequences of pulses of light energy may be delivered to the target area of skin at substantially the same time. The flashlamp apparatus may comprise control means for manually varying the at least one pulse parameter and or the time interval between adjacent pulses. In addition, or alternatively, means may be provided for automatically varying the at least one pulse parameter and/or time interval between adjacent pulses in a sequence. Monitoring means may be provided for monitoring the target area of skin to determine if the at least one pulse parameter and/or time interval is required to be varied. A processor may be provided for receiving data from the monitoring means, which may comprise temperature measurement means, such as an infra-red temperature measurement means. In one exemplary embodiment, means may be provided for delivering an initial pulse of light energy, monitoring the target area of skin and determining the thermal reaction thereof to the initial pulse of light energy, prior to delivery of the sequence of pulses of light energy for hair removal.

In accordance with a second aspect of the present invention, there is provided a method of removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, using a flashlamp apparatus, said flashlamp apparatus comprising at least two flashlamp devices which are independently operable, the method comprising delivering first and sequences of pulses of light energy from respective first and second said flashlamp devices to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined threshold levels.

Also in accordance with the second aspect of the present invention, there is provided flashlamp apparatus for removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, the apparatus comprising at least two independently operable flashlamp devices, and means for delivering first and second sequences of pulses of light energy from respective first and second said flashlamp devices to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined threshold levels.

Thus, the second aspect of the present invention enables the delivery of two or more independent sequences of pulses of energy to enable better control of the thermal profile of the target skin area, and further increase the effectiveness of the apparatus, while reducing the potential for damage to the surrounding tissue.

At least one pulse parameter and/or the time interval between adjacent pulses of at least one of the sequences may be varied, and the first and second sequences of pulses may be delivered to the target area of skin at substantially the same time.

The wavelength and/or spot size of the pulses of at least one of the sequences delivered to the target area of skin may be varied.

It will be appreciated that "cutaneous lesions" include, for example, vascular lesions and pigmented lesions and that the improvement of the appearance of the surface of the skin may be in response to a reduction in the severity of a cutaneous condition, such as acne or psoriasis.

These and other aspects of the present invention will be apparent from, and elucidated with reference to, the embodiments described herein.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a graphical illustration of the thermal relaxation (TR) times of a melanin cell compared with a hair shaft;

Figure 2 is a schematic cross-sectional view of hair shafts within a region of skin tissue;

Figure 3 is a graphical representation of pulses of optical energy delivered for the purpose of hair removal using an arrangement according to the prior art;

Figure 4 is a schematic illustration of the heating and cooling of a hair shaft relative to surrounding melanin cells as a result of application of a series of pulses of optical energy thereto; Figure 5 is a schematic block diagram illustrating apparatus according to an exemplary embodiment of the present invention;

Figure 6 is a graphical representation of pulses of optical energy delivered for the purpose of hair removal using an arrangement according to an exemplary embodiment of the present invention;

Figure 7 is a schematic representation of the thermal profile of a hair shaft and surrounding melanin cells corresponding to a pulse train delivered in accordance with an exemplary embodiment of the present invention;

Figure 8 is a graphical representation of two independent pulse trains being delivered at the same time in accordance with an exemplary embodiment of the second aspect of the present invention;

Figure 9 is a graphical representation of two independent pulse trains being delivered at the same time in accordance with another exemplary embodiment of the second aspect of the present invention;

Figure 10 is a graphical illustration of the wavelength spectrum of a low intensity incident light pulse;

Figure 11 is a graphical illustration of the wavelength spectrum of a high intensity incident light pulse; and

Figure 12 is a schematic diagram illustrating the different absorption profiles in melanin of red and blue light.

Thus, the present invention is concerned with the application of optical energy to the skin, with optical parameters of wavelength, energy density and pulse duration, so as to achieve long term hair removal with little or no damage to the surrounding healthy skin. This technique generally is known, and selective photothermolysis is also well known and documented in the field. Essentially, optical energy is delivered to the target, namely a hair shaft, and a photothermal process is induced whereby the optical energy is converted to heat through absorption of the light in a suitable chromophore in the target. In the case of hair, the target chromophore is melanin which has an absorption band in the visible and near-infrared region of the electromagnetic spectrum. Provided that the wavelength, energy and duration of the light pulse is sufficient to induce a temperature rise in the hair, typically above the tissue damage threshold, the cells responsible for hair growth can be damaged or destroyed, leading to a delay in, or even cessation of, the regrowth cycle of the hair. The optical energy is absorbed in the melanin in the hair shaft and induced heat diffuses to the follicle wall, interacting with the cells that control the hair regrowth cycle, either in the hair bulb or in a region known as the bulge which is located below the entrance to the sebaceous gland.

As explained above, it is of critical importance that the heat generated in the target structure is confined to the hair follicle and does not diffuse into the surrounding healthy structures leading to non-specific tissue damage, and this can be achieved in accordance with an exemplary embodiment of the present invention by a combination of the correct wavelength, energy density and pulse duration.

The pulse duration required for inducing the necessary temperature rise is governed by the thermal relaxation (TR) time of the target structure. The TR of a given object is the time taken for the object to cool to 50% of its maximum temperature. In general, the smaller the object, the shorter will be the thermal relaxation time, and vice versa. Thus, for example, a blood vessel with a diameter of 15μm will have a TR time of 100 - 200 μsec, whilst a hair shaft of 300 μm will have a TR time in the region of 20 msec, and an individual melanin cell, which is of the order of 5μm or smaller, will have a TR time of 50 μsec or less, as illustrated graphically in Figure 1 of the drawings.

For the effective removal of hair and cutaneous lesions, and/or improvement of the appearance of the surface of the skin, optimal parameters have been found to be in the range: Wavelength: 530 to 1200 nm Pulse duration: 1 to 100 msec Energy density: up to 50 J/cm² The following table summarises optical devices which can be, or have been, utilised for hair removal:

Typically, the devices listed in the table above achieve hair removal with energy densities above 15 J/cm².

As explained above, the incident light energy on the skin can also be absorbed by the melanin located within the basal and epidermal layers of the skin, leading to possible skin damage. Thus, in prior art systems, it is often necessary to provide cooling to the surface of the skin before, during and after the application of the optical pulse, to minimise the risk of such thermal damage.

Referring to Figure 2 of the drawings, a plurality of hair shafts 12 project below the epidermis region 16 of skin area 14 and into the dermis region 18. Each hair shaft 12 extends down the follicle 20 and includes a sebaceous gland 22 and, which at the anagen stage of the hair cycle, further includes a follicular papilla 24 within the hair bulb 26 of hair shaft 12. The follicular papilla 24 is supplied with a plurality of small blood vessels 28 that provide the plurality of growing hair shafts 12 with nourishment. The follicular papilla 24 is an essential structure within the follicle matrix structure 30.

In order to ensure destruction of the follicular papilla 24 and permanent hair removal, a sufficient flashlamp energy level is required that destroys the hair but does not burn the skin. In addition, the depth of penetration of the series of flashlamp pulses must be sufficient to cause permanent removal of the hair shaft 12 from the epidermis and dermis regions 16, 18 of the patient's skin area 14. In the arrangement described in US Patent No. 6,080,147, a method of hair removal is described in which a flashlamp is arranged to provide a series of pulses with short pulse delays of between 1 ms to 10 ms between pulses. The preferred pulse delay time is less than 8 ms. The single flashlamp is arranged to have the capability of sequentially emitting a series of pulses 2 to 6 times on the same spot of the patient's skin 14. For example, three pulses may be emitted at 10 Joules/cm² per pulse, each pulse having a pulse width of 2.5 ms and a delay timer between the pulses of 8 ms, which allows the delivery of 30 Joules/cm² to the same spot in 23.5 ms, as illustrated schematically in Figure 3 of the drawings. Thus, the described method requires that a series of relatively low energy flashlamp pulses be delivered in rapid succession with short delays between pulses, to exactly the same area of the skin. The short delay between pulses is shorter than the thermal relaxation time of the hair being treated but around equal to the thermal relaxation time of the melanin cells of the surrounding skin, so the hair does not have time to cool off between the pulses but the melanin in the skin does, as illustrated schematically by Figure 4 of the drawings. Thus, sufficient energy is delivered to permanently remove the hair, without causing significant damage to the surrounding skin area.

Thus, US Patent No. 6,080,147 describes the use of pulses of optical energy, spaced in time, so as to build up the required thermal profile in the hair shaft, whilst allowing the surrounding tissues to cool between pulses. Also described are different, optimal pulse combinations for use on different respective skin types. However, all the pulses for a given pulsing regime have the same energy level, the same duration and the same interval between pulses. Thus, while the energy, duration and interval can be altered for different skin types, they remain constant during treatment of a given patient.

In accordance with an exemplary embodiment of the present invention, a similar method is proposed for achieving long-term or permanent hair reduction or removal is proposed, which uses low optical energy density levels, typically 5 Joules/cm² or less, which is possible by exploiting the above-mentioned differential in the thermal relaxation time of the hair shaft and surrounding melanin in the basal and epidermal layers, namely that the thermal relaxation time of the hair shaft is long compared to that of the individual melanin cells. Therefore, for a given temperature rise, the hair shaft will remain at an elevated temperature for longer than the melanin cells, because the heat diffusion rate is much slower.

However, contrary to prior art arrangements, in the present invention, a sequence of optical pulses, the "pulse train", is delivered to the treatment site, with ability being provided for the pulses of the pulse train to have a variable duration, intensity and duty cycle. As before, the total optical energy delivered causes a temperature rise in the tissue dependant upon the wavelength, energy density, pulse duration and the tissue parameters of skin colour (which is determined by the melanin content of the skin), the presence of hair and other pigment-containing structures.

Referring to Figure 5 of the drawings, a flashlamp apparatus 100 according to an exemplary embodiment of the present invention comprises a control box 102 connected to a hand-held delivery device 104 via an electrical cable 106. The delivery device houses a flashlamp device 107 therein, and a capacitor means 108 is provided in the control box 102 for discharging flashlamp light pulses, the delivery device 104 also being provided with a pulse firing button 112.

The flashlamp device 107, which may comprise one or more flashlamps, includes a flashlamp projector lens of a specific wavelength for producing an incoherent flashlamp beam having a diameter of a given width, the flashlamp device 107 being electrically connected to a processor 114, a programmable control panel 116 and an electrical panel box 118 having electrical circuitry therein, the processor 114, control panel 116 and panel box 1 18 being provided in the control box 102. The control box 102 further houses a power supply 120.

The flashlamp device 107 is adjustable to control the energy level (Joules/cm²), pulse width duration (ms), delay time between pulses (ms), spot size (mm) and wavelength (nm) both manually, via the control panel 1 16 and automatically, via the processor 114. For example, the operator may perform the adjustments manually, but alternatively, temperature measurement means (not shown) in the hand-held delivery device 104 may be used to monitor the temperature of the skin area being treated and transmit representative data to the processor, which may be arranged to process such data and cause the energy pulses to be adjusted if required. It will be appreciated by a person skilled in the art that the most effective wavelengths for permanent hair removal are in the range of 550 nm to 1200 mn when using the flashlamp device 107.

The processor 1 14 is used for, among other things, controlling the sequential pulsing of the flashlamp beam from the flashlamp device 107 and includes a micro-controller for controlling the flashlamp to sequentially emit a series of pulses of coherent light energy via the capacitor means 108 when the flashlamp operator depresses the pulse firing button 1 12 on the delivery device 104. The pulses are emitted in the form of incoherent energy from the delivery device 104 via the flashlamp projector lens.

The control panel 116 is used for controlling the various output functions of energy/power level (Joules/cm²), the irradiation pulse width duration (ms), the pulse delay (ms), the number of pulses, and the flashlamp beam diameter (mm) for the or each flashlamp element of the flashlamp device 107. The control panel 1 16 may include a keyboard, a display screen, one or more selection means and/or indicator means (not shown), as required.

In use, a pulse train is delivered to a target skin area via the hand-held delivery device 104, the pulse train comprising n pulses of incoherent light energy generated using the flashlamp device 107 and flashlamp projector lens. As shown in Figure 6 of the drawings, the parameters of each pulse in a pulse train may vary, and are determined by the required temperature rise in the target structure (in this case, the hair shaft and follicle) and the damage threshold of the surrounding tissues.

Referring to Figure 7 of the drawings, the initial pulse in the pulse train will heat the hair shaft and melanin in the skin, then on termination of the pulse, the skin will begin to cool at a different (greater) rate to the hair shaft, i.e. in general, the skin cools faster than the hair shaft. Sometime after the first pulse, the second pulse will be delivered, at which point the hair shaft will have a higher temperature than the skin, and the intensity and duration of the second pulse can be adjusted to induce a temperature rise in both the hair and the skin. Note that as the duration of a pulse increases, the ratio of dt _ai_r/dT compared to dt_Ski_n/dT will differ due to the fact that skin is cooling, or losing its heat, during delivery of the pulse. The pulse parameters can be optimised for the particular skin colour and type, to achieve the desired removal of the hair in the minimum amount of time, without causing any damage to the surrounding tissue. In other words, provided that the pulse parameters and interval between the pulses are optimised for the particular skin colour and type of the individual being treated, the temperature rise in the hair shaft and follicle can be raised to a sufficient level to induce hair growth suppression whilst maintaining the surrounding tissue temperature below the damage threshold.

It will be appreciated that the present invention permits real-time optimisation of the pulse train, because the parameters of each pulse, and the interval between them, can be adjusted during delivery of the pulse train. This may be achieved by real-time temperature measurement, i.e. by the provision of temperature measurement means which monitors the temperature of the tissue in the area being treated and either causes the pulse parameters or the time interval to be adjusted automatically, or provides information to the operator which indicates that manual adjustment of the pulse parameters and/or the interval between pulses is required. In one embodiment, the temperature measurement means may comprise an infra-red sensor or the like. The apparatus may be arranged to automatically shut down, and/or issue a warning signal, if the measured temperature exceeds some predetermined threshold.

In another embodiment, the treatment method may include the delivery of a single, initial, low energy diagnostic pulse to the treatment area and determination of the thermal reaction in response thereto, prior to commencing the treatment itself. Thus, an optimum pulse train may be determined prior to treatment.

In another exemplary embodiment of the present invention, the flashlamp device 107 may comprise a plurality of flashlamps, each being independently operable. As a result, it is possible, for example, to superimpose one pulse form or train onto another pulse form or train, as illustrated schematically in Figure 8 of the drawings, so as to give better control over the thermal profile generated in the target structure.

In one specific exemplary embodiment of the invention, a first sequence of pulses may be delivered to the target area, each pulse having a relatively low energy, so as to slowly raise the background temperature of the skin and hair, then after some predetermined period of time has elapsed, or when the target area reaches some predetermined temperature, a second sequence of pulses may be delivered to raise the hair temperature to the desired level for the desired period whilst maintaining the required (lower) temperature of the skin.

In an alternative embodiment, the apparatus may provide independent sequences of pulses firing at the same time at the same target area, which enables better control of the thermal profile of the skin, and further enables the energy density of each individual pulse to be relatively much lower than would otherwise be possible to achieve the desired result. In yet another embodiment, a first flashlamp device may deliver a long, low energy pulse, while another flashlamp device delivers much shorter, higher energy pulses, the parameters and duty cycle of which may vary, as illustrated schematically in Figure 9 of the drawings.

It will be appreciated in all cases that one of the pulse parameters which can be varied is intensity, which causes a corresponding shift in the wavelength spectrum of the output light energy. For example, if a relatively low current is applied to a flashlamp, the resultant wavelength spectrum may be as illustrated in Figure 10 of the drawings, giving an output light which is mostly red. However, if a relatively high current is applied to the flashlamp, the resultant wavelength spectrum is shifted to the right, as illustrated in Figure 11 of the drawings, giving an output light which is mostly blue.

Thus it will be appreciated that it is possible to vary the current or intensity of the flashlamp pulses so as to change the absorption wavelength, bearing in mind that a lower current gives a wavelength spectrum having less blue wavelengths and more red wavelengths, and a higher current gives a wavelength spectrum having less red wavelengths and more blue wavelengths.

Melanin exhibits a different absorption profile in respect of different respective wavelengths. Thus, referring to Figure 12 of the drawings, the different absorption profiles of blue and red light are illustrated schematically, with respect to thickness x of a layer of melanin. The intensity I(x) of light at any distance x is given by:

T e ^x where I₀ is the intensity of the incident light, μa is the absorption coefficient and μs is the scattering coefficient. Bearing in mind that both μa and μs are wavelength dependent, although there is an exponential delay in intensity over distance in the case of both blue and red incident lights, the absorption profile is much steeper for blue incident light than for red. Thus, consider the case where the distance "c" denotes the thickness of the layer of melanin in the skin, and "h" denotes the thickness of melanin in a hair, it will be appreciated that a negligible amount of light is absorbed by the melanin in the skin when the incident light is mostly red compared with case where the incident light is mostly blue, whereas in both cases a significant amount of light is absorbed by the melanin in the hair, even though less so in the case of mostly red incident light than in the case of mostly blue incident light.

Thus, the effect on absorption of light in melanin by switching from incident light in one wavelength band to another can be exploited in the present invention. For example, a pulse having mostly blue wavelengths can be used to kickstart the temperature rise (in the hair, as well as the inevitable temperature rise in the skin as well), following which, for example, a pulse having mostly red wavelengths can be used to cause a continuation in the temperature rise in the hair with negligible further temperature rise in the skin. This may be particularly useful in the embodiment described with reference to Figures 8 and 9 of the drawings, in which two sets of pulses can be applied to a target area; intermittent high intensity, mostly blue pulses to effect a relatively large temperature rise (in both the hair and the skin) and the lower intensity, mostly red pulses to "top up" the temperature rise in the hair with negligible effect on the temperature of the layer of melanin in the skin.

An embodiment of the present invention has been described above by way of example only, and it will be apparent to a person skilled in the art that modifications and variations can be made to the described embodiment without departing from the scope of the invention as defined by the appended claims. Further, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The term "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The terms "a" or " an" does not exclude a plurality. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that measures are recited in mutually different independent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

Claims:

1. A method of removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, using a flashlamp apparatus, the method comprising delivering a sequence of pulses of light energy from said flashlamp apparatus to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined levels, and varying at least one pulse parameter and/or the time interval between adjacent pulses in said sequence, wherein pulse parameters comprise at least energy density, pulse intensity, wavelength of light energy and pulse duration.

2. A method according to claim 1, wherein the wavelength of the pulses in said sequence can be varied.

3. A method according claim 1 or claim 2, wherein the spot size of a pulse of light energy in said sequence can be varied.

4. A method according to any one of claims 1 to 3, wherein the wavelength of the pulses is between 550 and 1200 nm.

5. A method according to any one of the preceding claims, wherein the energy density of the pulses is between 0.1 and 100 Joules/cm², more preferably between 0.1 and 50 Joules/cm², and still more preferably between 0.1 and 30 Joules/cm².

6. A method according to claim 5, wherein the energy density of the pulses is between 0.1 and 20 Joules/cm², and more preferably between 0.1 and 10 Joules/cm².

7. A method according to claim 6, wherein the energy density of at least some of the pulses in a sequence is between 0.1. and 5 Joules/cm².

8. A method according to any one of the preceding claims, wherein the pulse duration is between 1 and 100 ms, more preferably, between 1 and 30 ms.

9. A method according to any one of the preceding claims, wherein the time interval between two pulses in the sequence is between 1 and 10 ms, and more preferably less than 8 ms.

10. A method according to any one of the preceding claims, wherein the flashlamp apparatus comprises at least two flashlamp devices which are independently operable, the method comprising delivering first and second sequences of pulses of light energy from respective first and second said flashlamp devices, and varying the pulse parameter and/or the time interval between two pulses in at least one of said sequences, wherein pulse parameters comprise at least energy density, pulse intensity, wavelength of light energy and pulse duration.

11. A method according to claim 10, wherein said first and second sequences of pulses of light energy are delivered to said target area at substantially the same time.

12. Flashlamp apparatus for removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, the apparatus comprising means for delivering a sequence of pulses of light energy to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined levels, and means for varying at least one pulse parameter and/or the time interval between adjacent pulses in said sequence, wherein pulse parameters comprise at least energy density, pulse intensity, wavelength of light energy and pulse duration.

13. Apparatus according to claim 12, comprising control means for manually varying said at least one pulse parameter and/or said time interval.

14. Apparatus according to claim 12 or claim 13, comprising means for automatically varying said at least one pulse parameter and/or said time interval.

15. Apparatus according to any one of claims 12 to 14, comprising monitoring means for monitoring said target area of said skin to determine if said at least one pulse parameter and/or said time interval is required to be varied.

16. Apparatus according to claim 15, comprising processor means for receiving data from said monitoring means.

17. Apparatus according to claim 15 or claim 16, wherein said monitoring means comprises temperature measurement means for measuring the temperature of said target area of skin.

18. Apparatus according to claim 17, wherein said temperature measurement means comprises an infra-red temperature measurement means.

19. Apparatus according to any one of claims 15 to 18, arranged to deliver an initial pulse of light energy, monitor said target area of skin and determine the thermal reaction thereof to said initial pulse of light energy.

20. A method of removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, using a flashlamp apparatus, said flashlamp apparatus comprising at least two flashlamp devices which are independently operable to produce respective sequences of pulses of light energy, the method comprising delivering first and second sequences of pulses of light energy from respective first and second said flashlamp devices to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined levels.

21. A method according to claim 20, further comprising varying at least one pulse parameter and/or the time interval between adjacent pulses in at least one of said sequences, wherein pulse parameters comprise at least energy density, pulse intensity, wavelength of light energy and pulse duration.

22. A method according to claim 20 or claim 21, wherein said first and second sequences of pulses of light energy are delivered to said target area at substantially the same time.

23. A method according to any one of claims 20 to 22, wherein the wavelength of the pulses in at least one of said first and second sequences can be varied.

24. A method according to any one of claims 20 to 23, wherein the spot size of the pulses in at least one of said first and second sequences can be varied.

25. Flashlamp apparatus for removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient the apparatus comprising at least two independently operable flashlamp devices, and means for delivering first and second sequences of pulses of light energy from respective first and second flashlamp devices to a target area of said skin, so as to raise the temperature of said target area to one or more predetermined levels.

26. Flashlamp apparatus according to claim 25, comprising means for delivering said first and second sequences of pulses of light energy to said target area of skin at substantially the same time.

27. A method of removing hair or cutaneous lesions from the skin of a patient, and/or otherwise improving the appearance of the surface of the skin of a patient, the method being substantially as herein described with reference to the accompanying drawings.

28. Flashlamp apparatus substantially as herein described with reference to the accompanying drawings.