Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B18/18—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves
  • A61B18/20—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves using laser
  • A61B18/203—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves using laser applying laser energy to the outside of the body
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B2018/00315—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body for treatment of particular body parts
  • A61B2018/00452—Skin
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B2018/00315—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body for treatment of particular body parts
  • A61B2018/00452—Skin
  • A61B2018/00476—Hair follicles

Definitions

• This invention relates to light delivery and in particular to a apparatus and method for delivery of a beam of light to a target area beneath the surface of the skin.
• this invention relates to an apparatus and method designed to improve the delivery of laser or other light to targets underneath the skin surface especially, but not solely, to assist in optical hair removal. That is, this invention relates to the use of optical based techniques in dermatology for the removal of unwanted stains, pigment, marks, hairs, or other sub-surface features.
• Lasers and, in some cases, other light sources have found increasing use in dermatology for the treatment or removal of sub- surface lesions. These techniques have largely been based on the concepts of selective photothermolysis . This implies that the laser wavelength is chosen to match a characteristic absorption associated with the target but not with the surrounding tissue. Thus, absorption of the laser light and the subsequent heating is largely restricted to that target.
• the process also involves choosing the duration of the laser pulse to maximise the temperature of the target before significant conduction to the surrounding tissue can take place. For example, a 30 nanosecond pulse from a Nd:YAG laser at l.O ⁇ m is strongly and selectively absorbed in the blue-black pigments of common tattoos. Since the tattoo pigments accumulate in granules of micron size, such a short pulse is almost wholly used to heat and fragment the granule before significant heating of the surroundings takes place .
• Nd:YAG laser similar to the one mentioned above is used. Since there is little or no natural selective absorption at this wavelength, an external chromophore must first be applied and persuaded to migrate down the hair shaft to the base to provide an appropriate target.
• a ruby laser at 0.694nm is used.
• the melanin content of the hair shaft provides the selectively absorbing chromophore.
• the ruby laser was introduced many years ago for removal of tattoos.
• the laser output was "Q-Switched" - that is, the energy was compressed to a pulse of only a few 10' s of nanoseconds.
• Such a pulse whilst ideal for tattoo granule fragmentation, is neither necessary nor desirable for the more thermal process of hair removal.
• the ruby laser is operated in its so-called "normal mode" wherein the pulse duration is extended to about 1 millisecond.
• the real target is not the hair itself.
• the overall process relies on the conduction of heat from the shaft to surrounding tissue, in particular to two zones, the first near the shaft base (papilla) ; and the second approximately a third of the way down the shaft, known as the bulge. Direct absorption into these zones is possible, and can contribute to their heating since they also contain an enhanced level of melanin. These zones are believed to contain the cells responsible for hair growth, and damage to them via this process of laser heating should lead to permanent hair removal or at least substantially delayed regrowth.
• a simple approach is to apply light with the required level of energy density to an area of skin.
• the level is chosen to give sufficient heating to destroy the target zones whilst leaving the surrounding tissue undamaged. In practice this required level lies between 10 and 50 J/cm 2 .
• an apparatus for delivery of a beam of light to a target area beneath the surface of the skin comprising means to deliver a collimated light beam, and light delivery means to increase the light energy density at said target area while minimising the light energy density at the surface of the skin.
• said means to improve delivery comprises means to improve effective light coupling into tissue.
• Said means to improve effective light coupling may comprise recovery means to recover light reflected on incidence with the skin.
• Said recovery means may comprise a reflective surface.
• the apparatus comprises means to thin the skin above the target area.
• Said means may stretch the skin.
• the apparatus comprises means to reduce local blood flow in the target area.
• the means to stretch the skin acts also to reduce the local blood flow.
• the apparatus comprises means to subject the area adjacent the target area to vacuum suction.
• Said means may comprise a member adapted to be sealed to the skin and to subject the area of skin surrounding the target area to a vacuum.
• said member has an annular channel .
• Said channel may be ring shaped or oval .
• Preferably said channel is adapted to be positioned with the channel opening in contact with the skin.
• the apparatus comprises means to increase light flux density at the depth of the target.
• Said means may redistribute an incident collimated beam prior to its incidence with the skin.
• Said redistribution means may comprise an array of lenses.
• said lenses are of short focal length.
• Preferably said array is selected to increase the flux density at a nominated depth.
• the apparatus comprises recovery means to recover light reflected on incidence with the skin; means to thin the skin above the target; and means to increase light flux at the depth of the target.
• the light beam is a laser light beam.
• the apparatus may further include known techniques such as tissue precooling and/or selective cooling of the epidermis and/or use of optical transmitting gels and/or convex shaped applicators and/or devices to draw folds of skin which may receive radiation from either side and/or other features already known.
• a method for delivery of a beam of light to a target area beneath the surface of the skin comprising the step of using an apparatus according to the first aspect of the invention.
• a method for delivery of a beam of light to a target area beneath the surface of the skin comprising the steps of directing a collimated light beam onto the surface of the skin, and using a light delivery means to increase the light energy density at said target area while minimising the light energy density at the surface of the skin.
• Figure 1 shows a apparatus in accordance with an aspect of the present invention.
• Figures 2a and 2b illustrate the effect on fluence at the skin surface and at a given depth beneath the surface, of increasing the area of surface illumination of the skin;
• Figures 2c and 2d also illustrate the effect on fluence at the skin surface and at a given depth beneath the surface, of increasing the area of surface illumination
• Figure 2e is a graphical representation of the rate of increase of the effective fluence at depth with increase of surface beam diameter
• FIGS. 3a and 3b show a beam focusing arrangements in accordance with an aspect of the present invention
• Figure 4 illustrates means for recapturing reflected light in accordance with an aspect of the present invention
• Figure 5 shows an annular ring in accordance with an aspect of the present invention.
• this apparatus generally designated 1 is designed to provide a combination of both optical and mechanical means of improvement of the sub-surface flux density of a beam delivered by a beam delivery system to the target areas.
• this apparatus has its origins in improvements related to beam delivery for hair removal, other optical processes requiring selective sub-surface damage may benefit.
• a beam delivery system normally comprises a light source and means for its delivery to a target area.
• a first improvement to this system is the provision of a sealed annular ring 4 as shown in Figure 5.
• This annular ring is placed adjacent the tissue surface 2 above the target.
• the region of surface skin in the annulus is subject to a vacuum by connection of a vacuum pump to vacuum outlet 8 and is thus drawn upwards to form raised areas 11.
• this is similar to proposals for obtaining a fold of tissue to allow transillumination .
• the instant configuration takes advantage of the fact that dermal blood is taken towards the region 11 under vacuum in the direction of arrows 10 and thus away from the central circular core area 12.
• the ruby laser wavelength corresponds to a minimum in the absorption spectrum of blood
• residual absorption of blood remains a competing unwanted factor in the utilisation of the laser light.
• reduction of local blood volume due to adjacent vacuum suction provides an important advantage.
• a second and more significant effect is that the drawing up into the annulus of a small amount of tissue 13 effectively stretches the skin 2 throughout the circular core 12. Even mild stretching of around 10% of the diameter - 2mm in Figure 5 where the central area has a diameter of 20mm - translates to a thinning of the epidermis and upper dermis of 20%. Since the reduction in light flux with depth into the skin is exponential this thinning provides an increase in flux density of as much as 80% at a depth of 3mm corresponding to the depth of the papilla. This effect, in conjunction with the reduction of the local blood volume, reduces the required incident flux density by a significant factor. These effects also improve the selectivity of the process.
• This aspect of the invention is thus directed principally at providing a physical means of reducing beneficially both the blood content of the tissue immediately below the exposed area, and the thickness through which light must penetrate to reach structures at depths of several millimetres.
• a handpiece incorporating such a ring 4 has its most immediate application in a process such as hair removal where selective damage to the follicles 2 -4mm deep is required.
• Other applications, for example the visualisation of dermal blood vessel anatomy for diagnostic purposes would also benefit.
• the influence of light scattering in tissue is to substantially increase the volume of tissue experiencing some of the light compared with the initially exposed area.
• This therapeutic fluence is determined by the absorption of light from lasers such as ruby and alexandrite into the melanin within and around the follicle.
• the epidermis and upper dermis contain the same absorbing chromophore as that present in the target. Since it is desirable to spare the epidermis and upper dermis from damage, and these occur nearer the surface, it is clear that any means by which the ratio of fluence at a depth compared with surface fluence can be increased offers an improvement in efficacy and safety.
• Figure 3b shows an arrangement which overcomes this disadvantage by passing the large area collimated beam 3 through an array 5 of small micro lenses 5a. These lenses are of short focal length. The focusing function of this array 5 is estimated to double the sub-surface flux at point 17. There is insufficient energy falling within the acceptance area of an individual lens 5a to present a safety hazard.
• a third aspect of the invention addresses the issue of light coupling into tissue.
• the use of a gel has been suggested as a way of improving light coupling. Since the tissue surface is microscopically uneven, applying a gel - and thus essentially smoothing the surface profile to one of near normal incidence to the beam - would indeed help to reduce the reflection losses associated with the refractive index difference between tissue and air. Unfortunately this technique does not really address the reason for the 'apparent' high reflectivity of tissue. The greater portion of the apparent reflected light is caused not by index mismatch but rather by transmission into the tissue followed by scattering into a backward direction and finally re-emergence.
• This aspect of the invention seeks to provide means of capturing this effectively reflected light by using a mirror surface 6 around the handpiece 7 and thus returning the light to the tissue surface 2 once more.
• the area of surface that is the source of this back scattered light is larger than the original illuminated area, and the emerging ray directions 18 are spread widely. Under these circumstances, only limited focusing of the light to be returned to the tissue is possible. This is achieved using a mirror surface 6 of a parabolic form.
• a simpler hemispherical shape or a conical section are alternatives which give adequate advantage. Irrespective of shape, the action of returning the back scattered light to the tissue surface effectively provides an increase in overall coupling, and thus a reduction in the applied energy required to reach a therapeutic level. This reduction is estimated to be around 20% and therefore an initial requirement of, for example, a fluence of 20 J/cm 2 at the surface 2 would be reduced to around 16 J/cm 2 .
• FIG. 1 shows an apparatus 1 incorporating a combination of the improvements outlined above.
• This apparatus 1 includes means 4 for drawing up an annulus of tissue, thereby both stretching and thinning the central zone above a target area.
• This central zone is illuminated with a collimated laser beam 3 passing through an array of micro lenses 5.
• these lenses may be 1mm in diameter and have a focal length of around 10mm.
• the delivery handpiece 7 is provided with a means 6 of reflecting back any scattered light returning from the tissue surface.
• tissue precooling For example, for stretching the skin, would be included in the general principles outlined here.
• the embodiment described above offers significant advantages to the process of hair removal with lasers or other optical means. Specifically these include a change in the distribution of light to increase the flux density at significant depths of, for example, between 1 and 3 millimetres, a reduction in the blood volume in the illuminated area and an increase in the effective light flux coupled to the skin. Thus selectivity is improved and the optical energy from the laser or other source is reduced.
• the embodiment shows specific means for achieving these advantages.

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• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Surgery (AREA)
• Optics & Photonics (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Molecular Biology (AREA)
• Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
• Electromagnetism (AREA)
• Biomedical Technology (AREA)
• Heart & Thoracic Surgery (AREA)
• Medical Informatics (AREA)
• Otolaryngology (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Radiation-Therapy Devices (AREA)
• Laser Surgery Devices (AREA)

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• 1997
  • 1997-05-23 GB GBGB9710562.1A patent/GB9710562D0/en active Pending
• 1998
  • 1998-05-26 EP EP98922974A patent/EP1011498A1/de not_active Ceased
  • 1998-05-26 AU AU75432/98A patent/AU7543298A/en not_active Abandoned
  • 1998-05-26 WO PCT/GB1998/001523 patent/WO1998052481A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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