APPARATUS FOR SURVEYING THE THERMAL TOPOGRAPHY OF A SURFACE, IN PARTICULAR OF HUMAN SKIN

Abstract: Method and apparatus for surveying the thermal topog­ raphy of a surface, in particular of human skin, wherein a layer (14) of liquid crystals having cholesteric properties is applied in contact relationship to the area to be surveyed. The area to be surveyed is then illuminated with a light (18) having a wavelength in the visible spectrum range, and of shooting with a photographic camera (1) a number of photograms taken at various wavelengths in the visible range. The camera (1) is mounted for adjustment with respect to the layer (14) of liquid crystals which covers the area to be surveyed, at least one filter (16) is interposable between the objective (3) of the camera (1) and the layer (14) of liquid crystals. The apparatus includes a light source (18) adapted for emitting either a monochromatic light or a discontinuous spectrum light in the visible range of the spectrum, which impinges on said layer (14) of liquid crystals.

Description: This invention relates to a method for flurveying the thermal topography of a surface, in particular of human skin, and an apparatus imnlerìenting tile method. It is knorm that the temperature of human skin is currently detected with the aid of mercury thermometers, thermocouples, and thermistors. All these instruments have the disadvantage of having a certain thermal capacity. moreover, through their use, only the temperature of a small skin region can be measured, instead of a sufficiently large skin surface, to detect minimal temperature differences between one point and another of said surface, such as skin areas overlying veins and arteries which are slightly warmer than the adjacent areas, or in the pathological cases of subcutaneous tumoural tissues, which exhibit slight temperature differential with respect to the adjoining ones To survey the temperature of larger areas, the use of cholesteric liquid crystals has already been proposed. As is lmown from the most authoritative studies,cholesteric liquid crystals may be represented as a superpositionof layers of oriented molecules,which are oriented in each layer along a preferential vector such as to result in a helical structure having a certain pitch dimension. Conventional temperature measuring methods exploit a phenomenon whereby the pitch of the helix dipends on temperature, thereby it becomes possible, by letting a light beam to impinge on the liquid crystals, to obtain a selective reflection which is directly related to temperature. Thus, by coating a surface rath a light reflective film of cholesteric liquid crystals, isochromatic zones (of same color) will appear on said surface at the isothermal zones (of same temperature). Also hnown is the use of mixtares of cholesteric liquid crystals of different nattires to obtainagood brilliance of the color. The application of the cholesteric substances is carried out either directly or indirectly following cladding or enca#sL1'ating in special supports. Conventional techniques have some substantial disadvantages which affect their effectiveness. First of all, they have shortcomings as regards the ouantitabive evaluation of temperature owing to the difficult achievement of a correlation between the reflected wavelength and temperature. Secondly, they provid#e no means of following the evolution of a thermal contour, and no detailed definition of the warm areas can be obtained, especially in the case of a tumoural nucleus0 This invention sets out to provide a method which enables the isothermal values of a surface, in particular a cutaneous one, to be determined quantitatively. Within that general aim, the invention further provides an apparatus implementing said method in a reliable manner and such that it can be carried out by operators lacking any specific training. According to one aspect of this invention, there is provided a method characterized in that it comprises the steps of applying in contact relationship to the area to be surveyed a layer of liquid crystals having cholesterieproperties, and of illuminating then the area to be surveyed with a light having a wavelength in the visible spectrum range, and of shooting a number of photograms taken at various wavelengths in the visible range. Advantageously, the application of the liquid crystal layer is preceded by the coating of the area vmth a black substratum effective to absorb the light component which has passed through the liquid crystals. The light that impinges on the layer of liquid crystals may be monochromatic or a suitably filtered discontinuous spectrum one. For best results of the method, one may proceed by first defining, for a given mixture of cholesteric liquid crystals, the dependence of the selectively reflected wavelength on the temperature. Thus, it becomes possible to identify a light which is reflected more strongly by a certain area owing to a given temperature which characterizes that area and univocally determines both the refractive index and the pitch of the helix of the liquid crystals. To determine the dependence of the reflected wavelength on temperature, one can resort to spectrophotometry. In practice, to obtain monochromatic light, monochromators or "lasers" may be employed. Advantageously, to remedy to the poor Luminous intensity of monochromators and avoid the high cost of "lasers', one can utilize discontinuous spectrum light, preferably a line spectrum light, for example the light to be obtained from mercury vapor lamps, or mercury-cadmium-zinc lamps, very rich in lines in the visible range (approximately 400-800nm), The separation of the various lines to obtain monochromatic light is effected by means of a series of interferential filters which have a maximum of transparency at the various wavelengths of the emission lines of the lamp being used. These filters may be placed in front of the film to be exposed in a progressive order with respect to the wavelengths with which one wishes to photograph the area to be surveyed, thereby, once the wavelength which is reflected by the liouid crystals covering the area being surveyed and which reaches the film through the filter is known, a reproduction is obtained of the isothermal contour of the area on the film, and a certain temperature may be attributed to the isochromatic image owing to the interrelation between the latter and the wavelength. The various photographs; as a whole and as obtained with the various filters, may constitute a thermotopometric map of the area, whether this happens to be human skin or any other thermally non-homogeneous surface. According to a further feature of this invention, the apparatus which implements the method just described comprises a photographic camera mounted for adjustment with respect to the layer of liquid crystals which covers the area to be surveyed, at last one filter interposable between the objective of the camera and the layer of liquid crystals, and a light source adapted for emitting either a monocsromatic light or a discontinuous spectrum light in the visible range of the spectrum, which impinges on said layer of liquid crystals. A preferr#d embodiment-is schematically illustrated in the accompanying drawing, where the one figure shows an apparatus which operates with light having a line spectrum. With reference to the draxving figure, the apparatus comprises a photographic camera, generally indicated at 1, which includes a visor 2, an objective 3 and a flange 4 supporting said objective. The flange 4 is provided with a pair of parallel rods 5 for adjusting the objective. The rods 5 are slidable in a supporting block 6, which is articulated at the lower end, on 2 horizontal axis, about a pivot pin 7 carried, c2ntilever-fashion, by a small base 8 attached to a plate 9. A specially provided lever 10, through a conventional threaded or cam type of locking device, positions the block 6 fixedly with respect to the plate 9, thus imparting to the camera the desired inclination. With the plate 9, there are also rigidly associated two parallel sleeves 11 in which are guided respective stems 12, which support at one end a frame 13. In the frame, there is inserted a plate 14 carrying the liquid crystals and being located in front of the objective 3 at an appropriate distance therefrom. The position of the frame is fixed by securing the stems 12 within the sleeves 11 by meons of screws 15. Between the objective 3 and plate 14, there can be interposed interferential filters 16 mounted on a disk 17 which is pivotable in an offset relationship to the camera 1 such that each filter can be rotated to reach a position exactly in front of the objective 3. The reference numeral 18 designates mercury vapor flash lamps which are secured to the flange 4, either around the objective or sidewards thereof. The whole apparatus is mounted on a column 19 which can be adjusted for height in a pedestal 20 equipped with caster wheels 21 for moving it around. The operation of the apparatus vrill be next described with reference to the surveying of the temperature of a mammalian region. The patient is placed in front of the plate 14 veth the region to be surveyed resting on said plate. Obviously, the mixture of liquid crystals will be selected as a function of the thermal range which includes the temperature of the mainmarian skin. In this specific case, that range extends over 20C on either side of an average value of 35or. The mixture of cholesteric liquid crystals may be, for example, a 60/ó R and 40t Ii mixture, as suggested by 3 Company (Instructions Liquid Crystal Kit Type 874), where R and L are standardized components. Then, some photographs are shot, while inter posing between the objective and plate a new interferential filter each time. The photographs will reveal isothermal contours which are progressively narrower the shorter is the wavelength and the higher the temperature. The actual numerical value of the temperature can be obtained from a graph where the temperature is plotted as a function of the wavelength. In practicing the invention, numerous variations and modifìcations are possible which fall within the scope of the appended Claims. The materials and components employed may be selected to suit individual application requirements. For example, the light source may be a mercury vapor lamp manufac turedbytheFirz#OSRAi## and screened with a glass bulb to eliminate the ultraviolet radiation. The mercury lamps may be associated with other xenon lamps which afford the possibility of providing an overall chromatic display of the region being surveyed. According to a preferred embodiment, the thermosensitive plate may be formed from a fabric for silk-screening (e.g. having a thickness dimension of 70 microns) onto which, by means of suitable mordants, there are anchored the black substratum or primer, with a water soluble pigments base, and a mixture comprising at least two micro clad ar microencapsulated cholesteric systems in appropriate ratios (e.g 50fez each, in the instance of two such systems). These systems have the peculiarity of covering different but adjacent temperature ranges, with the obvious advantage that two or more isotherms can be obtained with one filter (i.e., with a single shot). This results in practice in an extension of the thermal range, with attendant improvement of the measuring sensitiveness (up to 1/10 of degree centigrade).

Claims: CLAIMS 1. A method for surveying the thermal topography of a surface, in particular of human skin, characterized in that it comprises the steps of applying in contact relationship to the area to be surveyed a layer of liquid crystals having cholestericproperties, and of illuminating then the area to be surveyed vath a light having a wavelength in the visible spectrum range, and of shooting a number of photograms taken at various wavelengths in the visible range. 2. A method according to Claim 1, characterized in that said light is monochromatic. 3. A method according to Claim 1 characterized in that said light is a discontinuous spectrum light. 4. A method according to Claim 3, characterized in that said light is a line spectrum light, the separation of the various lines being accomplished by means of interferential filters having their maximum transparency at the wavelengths of the various emission lines. 5. A method according to any of the preceding claims, characterized in that prior to the application of the liquid crystal layer on the area to be surveyed, a black substratum is applied. 6. An apparatus implementing the method of the preceding claims, characterized in that it comprises a photographic camera (1) mounted for adjustment with respect to the layer (14)of liquid crystals which covers the area to be surveyed, at least one filter (16) iriterposable between the objec tive of the camera (1) and the layer ( of liquid crystals, and a light source adapted for emitting zither a monochromatic light or a discontinuous spectrum light in the visible range of the spectrum, which impinges on said layer of liquid crystals. 7. An apparatus according to Claim 6, character sized in that the liquid crystals are clad in a support 14) carried by a frame (13) located adjustably at a distance from the objective (3). 8. An apparatus according to Claims 6 or 7, characterized in that there are provided several interferential filters (16) mounted on a disk (17) pivotally supported such that the filters (16) can be brought in succession in frontof the objective (3). 9. An apparatus according to ary of Claims 6 to 8, characterized in that said light source comprises mercury vapor flash lamps (18). 10. An apparatus according to Claim 7 characterized in -that there are provided two systems of liquid crystals which are anchored, along with a black substratum withawater soluble pigments base, on a "Nylon" fabric for silk-screening, said systems being effective to cover different temperature ranges.

Inventors: STREMMENOS, CRISTOS, KOUI, MARIA
Applicants: KOUI, MARIA, STREMMENOS, CRISTOS
Application year: 1980
Main classification: A61B5
IPC codes: G01K11, A61B5