The present invention further refers to a method for the treatment of tissue in vivo, especially of cutaneous tissue, with the energy of a laser beam, in order, for example, to eliminate skin imperfections.

State of the art Devices have long been known for the treatment of the cutaneous surface with the energy emitted by a laser source. Typically, Nd : YAG, alexandrite, dye, and other types of laser are used, for various applications.

Laser is used, for example, to perform incision, vaporization, surface abrasion, elimination of wrinkles and other imperfections due to skin ageing, elimination of unwanted hair by destroying hair follicles, treatment of angiomas, spots, acne vulgaris and also for more strictly therapeutical applications.

One of the drawbacks and disadvantages of this type of treatment stems from the thermal damage that the laser can cause to the skin. Indeed, to achieve an appreciable result in short time and with a limited number of treatment sessions, high energy levels shall be used. On the other hand, the energy of the laser beam causes thermal damages to the skin which appear some time after the treatment.

No effective systems are presently known to control the emission characteristics of the laser beam so as to achieve the best compromise between the protection of the tissue and the efficacy of the treatment.

Attempts have been made to cool the skin during the treatment. To this end systems are currently used, for example, in which a coolant is made to circulate through a plate resting onto the region to be treated and being transparent to the laser beam. These systems have the drawback that they substantially attenuate the laser beam and, therefore, reduce the efficiency of the treatment, owing to the incomplete trasparancy of the plate.

According to a furhter known technique, the area under treatment is cooled down by a jet of cryogenic gas directed toward the treated area. The nebulized cryogenic gas interferes with the laser beam and, also in this case, causes a reduction of the efficiency of the treatment and uncertainty of the results due to an alteration of the emission parameters with respect to the theoretical ones.

The treatment also mostly depends on the characteristics of the skin of the various subjects. According to the type of effect to be obtained by the laser, different wave lengths must be used to reach different depths of the cutaneous layer. For example, in order to eliminate unwanted hair it is necessary to reach the hair follicles present at a certain depth from the outer surface of the skin. The degree of penetration of the laser beam within the skin depends mostly on the type of pigmentation, that is, on the so-called phototype. The same phototype is able either to absorb or backscatter different amounts of energy at different wave lenghts that can be used according to the type of treatment.

Presently, there is no way of taking into account the effect of the phototype in a laser treatment, so that the latter is carried out in a substantially empirical manner, regardless of the subject's features and without adapting the treatment conditions thereto.

Objects and summary of the invention The object of the invention is to provide a laser device and a method for laser treatment of the epidermis or skin or other tissues, for various medical and/or aesthetical purposes, able to overcome the drawbacks of the traditional devices and methods.

More particularly, the object of the invention is to provide a device and a method capable of optimizing the treatment by reducing the duration thereof, increasing its efficacy and lowering or eliminating the risk for thermal damages to the in vivo tissue under treatment.

The invention, in general, can be used for the treatment of in vivo tissues of any type but, in some of its embodiments, it is particularly suitable for cutaneous treatment of cosmetic character, or even for medical purposes.

Essentially, the device according to the invention comprises, in addition to the laser source which generates the laser beam and the member to direct the laser beam onto the tissue under treatment, a means for determining the quantity of energy, transferred by said beam to the tissue under treatment, which is backscattered or refracted or otherwise given back and thus not absorbed by the tissue being treated. In this way, it is possible to determine the behaviour of the treated tissue, in particular of the skin, according to the phototype, by assessing the amount of energy actually absorbed and which represents the useful portion of the energy emitted by the laser.

The patient under treatment will absorb a higher or lower amount of energy depending on the type of his/her skin and on the wave length being used. The means for detecting the energy sent back makes it possible to operate retroactively on the laser emission in order to optimize it according to the subject's characteristics.

It is thus possible to reduce the amount of applied energy, should the patient present a high absorption of the wave lenght being used, whereas the applied energy will be increased in case the phototype absorbs little energy at such wave length.

According to a further improvement, the device is provided with a sensor for measuring the temperature of the portion of tissue under treatment, for example, the skin temperature. The temperature sensor may be advantageously an infrared thermometer, able to sense the temperature without contact. Instead of the infrared sensor, equivalent means may be used which allow a reading of the temperature without contact and thus without interference with the laser beam during the application.

The detection of the temperature allows the laser emission to be so controlled as not to reach nor exceed the threshold of thermal damage, that is the maximum temperature beyond which the tissue is thermally damaged.

For example, in case of skin treatment, the surface temperature of the latter is prefereably kept below 45°C. The device may be provided with a control system which, based on the temperature reading, either cuts off the emission of the laser beam or alters the characteristics thereof by reducing the length and/or the intensity of the pulses.

According to a further, advantageously improved embodiment of the invention, the device is provided with an air-operated cooling system that delivers a jet of cold air onto the area under treatment. Contrary to the traditional systems which use liquids or gases, the use of air overcomes the drawbacks of interference with the laser beam and, therefore, of alteration of the characteristics of the beam reaching the tissue under treatment. The air suitably cooled at a temperature, for example of about-20°C, is substantially dry thereby avoiding phenomena of condensation which could lead to the formation of mist wich might interfere with the laser beam.

The air-operated cooling provided by the present invention has therefore no negative influence upon the treatment conditions and does not introduce uncertainties over the selected parameters for the treatment itself.

Further advantageous features of the device and method according to the invention are set forth in the appended claims and will be described in greater detail herebelow with reference to one embodiment thereof.

Brief description of the drawings The invention will be best understood by a reading the following description reference being made to the accompanying drawing which shows a practical, non limiting example of the invention. In the drawing : Fig. 1 schematically shows the device according to the invention ; Figs. 2 and 3 are front and rear perspective views, respectively, of the hand piece for the application of the laser beam for cutaneous treatments ; Fig. 4 is a schematic side view of the hand piece ; and Figs. 5 to 9 indicate results of experimental measurements.

Detail description of the invention Shown very schematically in Fig. 1 is a block diagram representation of the device according to the invention. The device comprises a unit which includes two laser sources 3 and 5. One of the two sources, for example the one designated by numeral 3, is a source for the generation of a pointing laser beam, and thus a low energy beam, which is intended to produce a bright spot having no effect on the tissue under treatment and having the sole purpose of correctly orienting the hand piece, schematically indicated with 7, where end of the light guide is located which conveys the laser beam towards the tissue under treatment. Laser 5 is instead a power laser and is the source of the treatment beam.

The two laser sources 3 and 5 can be connected to a single light guide consisting, in this case, of a optical fiber 9, with the provision of a Y- shape connector 11. The possibility is not excluded of providing a dual light guide leading up to the hand piece. The light guide 9 may also be made up of a set of mirrors arranged in an assembly of tubes articulated to each other, as well known in the art, or of any other suitable system.

Connected to the hand piece 7 is a thermally isolated tube 13 into which cold air generated by a refrigerator unit 15 is introduced. The cold air may be at a temperature of-20°C, for example. Arranged inside the hand piece 7, shown in greater detail in Figs. 2 to 4, is a photometer or refractometer 17 and an infrared thermometric sensor 19. Arranged sideway of the photometer 17 and thermometric sensor 19 is the output end of the light guide 9, shown at 9A in Fig. 3, and a nozzle 13A making up the terminal part of the tube 13.

Also arranged on the hand piece 7 is a spacer 21 intended to keep said hand piece, and thus the output end 9A of the light guide and the other accessories mounted thereon, at a predetermined distance from the surface to be treated, such as the skin of a patient. The hand piece further includes a handle 7A with an operating push-button 7B by which the power laser 5 is actuated after the hand piece has been correctly positioned.

As can be seen in Figs. 2 and 4, the axes of the thermometric sensor 19 and of photometer 17, as well as of the laser beam (schematically shown at F in Figs. 1 and 4) and of the air jet generated via the nozzle 13A, converge to the same area under treatment.

Thermometric sensor 19 and photometer 17 are connected via line 23 to a single control unit 25 which thus receives an input temperature signal generated by the thermometric sensor 19, and a signal generated by the photometer 17 proportional to the energy reflected or anyway returned by the tissue under treatment. The latter information provides for, by difference, the energy absorbed by the tissue under treatment, the energy supplied by the power laser 5 being known.

The device roughly described above operates as follows. The hand piece 7 is moved, wiht the aid of the pointing laser 3, to the position where the tissue treatment, such as an epilation, is to be carried out. After correct positioning, by means of button 7B the operator can activate the power laser 5 and open a valve on the conduit 13 to start blowing the cold and dry air onto the surface to be treated. The activation of the jet of cold air could also be obtained by a different means, for example a pedal control or a button on the equipment. The wave length of the laser emission, the pulse frequency and the pulse duration are set in a manner known per se and with systems known in the art. Based on the type of treatment to be performed, a selection may be made over wave lenghts, frequency and duration of the pulses and, thereby, over the energy delivery. The latter value is known by the control system 25-which receives indications from the photometer 17 on how much energy conveyed onto the tissue under treatment is actually absorbed-after subtracting from the energy delivered by the laser source 5 the amount of energy given back and sensed by said photometer 17.

The temperature of the surface under treatment is constantly monitored via the infrared thermometric sensor 19. The control system 25 can thus both increase and decrease the energy supplied by the laser 5 as a function of the fraction of this energy which is sent back, and thus not absorbed, by the tissue. At the same time, in case the temperature of the tissue rises above a critical value, for example 40 or 50 °C, as detected by the thermometric sensor 19, the control system 25 will interrupt the emission of the laser 5. Should the tissue temperature, owing to a modest energy delivery or other reasons, go down below a minimum threshold, 4 °C for example, the control system 25 would cut off the stream of cold air via the conduit 13 by closing a suitable valve, for example.

Figs. 5 to 9 show experimental results obtained by the device according to the invention with the provision of a laser source of alexandrite type, model Photogenica LPIR produced by Cynosure, U. S. A.

The temperature was measured with an infrared thermometric sensor of a model operating in the range of 0 to 500°C with an accuracy of +1% and a response time of 150 milliseconds. The photometer uses a photodetector Hamatsu S1226 (Japan), suitably amplified and with a shield made up of a 20D (optical Density) neutral attuenuatorfilter.

The measurements were made by delivering a series of pulses of laser energy for a total of 20 Joule/cm2.

Shown in Fig. 5 is a diagram showing the temperature (Curve T) versus time and the value of the reflected or refracted energy (Curve E) versus time, as measured by the photometer. In this case, the laser beam was directed onto an inert material constisting of brown enameled porcelain.

The measurement was made in this case without air cooling.

As can be seen from the diagram, the temperature of the material onto which the laser beams is directed rises abruptly when a series of laser pulses is delivered thereto. The temperature shifts from the room temperature (20 °C) to 150 °C. Afterwards, a gradual cooling takes place due to natural convection.

The curve E has a peak in correspondence of the emission of the laser pulses This peak is proportional to the energy fed back by the material surface. On the y-axis the energy detected by the photometer in percent with respect to the incident energy is shown. Approximately 50% of the energy is absorbed.

Fig. 6 shows the results of the same measurements on an inert material having a ligth color, i. e. a white enameled porcelain. In this case, the temperature of the material is just over 50 °C, the incident energy being equal, since a much higher portion of the incident energy is reflected or refracted, as revealed by the reading of the photometer. The latter plots a peak of back energy equal to 80% of the incident one.

Fig. 7 shows the same diagram as plotted in Fig. 6 but with a different time scale for pointing out the energy contribution of the individual laser pulses (six in the example).

A comparison between Figs. 5 and 6, 7 provides an indication of the remarkable influence that the phototype of the patient under treatment may have on the amount of absorbed energy and, therefore, on the efficiency of the treatment, but also on the risk of thermal damage (owing to the increase of temperature).

Figs. 8 and 9 show the same curves of refracted or reflected energy and of temperature for measurements made on a subject. Fig. 8 refers to the case in which the patient's dermis is not cooled. It can be noted that, with a series of laser pulses, the dermis reaches a temperature of 75°C, which is above the tolerance limit.

By cooling with an air jet at-18 °C (Fig. 9), the temperature of the skin remains below the safety value of 40°C. To be precise, the skin is cooled t down to 4°C before radiating the laser energy. Under these conditions, and keeping the cooling steady during the treatment, the highest temperature reached is 32°C.

As indicated above, the diagrams of Figs. 8 and 9 refer to the same subject (same phototype). It has now been found, surprisingly, that the temperature of the skin has a substantial impact over the amount of absorbed energy. Indeed, the response of the photometer under the conditions of Fig. 8 is equal to 35%, that is, about 65% of the incident energy is absorbed by the dermis. Under the conditions of Fig. 9, on the other hand, the photometer response is of 50%, i. e. only 50% of the energy is absorbed.

The whole system for cooling, detecting temperature, and detecting reflected or refracted energy (and thus absorbed energy by subtraction) makes it possible to take into account the combination of unpredictable phenomena which affect the absorption conditions and thus to optimize the treatment.

In the foregoing reference is made to a device with a laser source which generates a fixed spot. It will be appreciated that the same inventive concept may be applied also to devices in which the laser is associated to a scanning system able to treat extended areas by a suitable movement of the laser beam as obtained, from example, with a galvanometer system.

It is understood that the drawing shows an exemplification given only as a practical demonstration of the invention, as the latter may vary in the shapes and dispositions without nevertheless departing from the scope of the concept on which the same invention is based. The presence of reference numbers in the appended claims has the purpose of facilitating the reading thereof with reference to the specification and drawing, and does not limit the protection represented by the same claims.