referring to fig1 there is shown a system 10 for in vivo diagnosis of dermatological tissues . the system 10 may be embodied in a handheld head 32 as shown in fig1 a and schematically in fig3 . referring more particularly to fig1 there is shown a system 10 ( or instrument ) which contains optics of the type which are used in optical data storage heads which are used in recording and reading optical disks . light from a laser diode , contained in a laser and collimator assembly 12 , is collimated by a diffraction limited lens in the assembly 12 and is incident at an oblique angle on a beam splitter assembly 14 . refraction at this oblique angle causes the elliptical laser diode beam to become circular in cross - section . the circular beam passes through the beam splitter assembly 14 and a quarter wave plate 16 and is focused into the tissue 22 via a contact window 20 ( a glass window plate ) spaced from the sample , specimen or tissue 22 being examined , preferably by an optical contact liquid 21 . in the event the sample is viscus or liquid , it may be located in a sample well ( not shown ). the circular beam which passes through the beam splitter assembly 14 and the quarter wave plate 16 is focused into the sample by a precision focusing lens 18 , which suitably has a numerical aperture of 0 . 5 and a focal length of 4 . 3 millimeters . these dimensions and parameters are exemplary and demonstrate that the optical system 10 may be miniaturized so as to be adapted to be handheld . the quarter wave plate 16 converts the incident linear polarization from the laser in assembly 12 to circular polarization , i . e ., the quarter wave plate is oriented 45 ° to the incident polarization . in other words , the beam from plate 16 is circularly polarized . the focusing lens 18 is movable both in a direction along its optical axis and laterally as indicated by the arrows 24 and 25 , respectively . position mechanical actuators 34 ( fig1 a ) may be used for moving the lens 18 , and thereby control position of the focus spot of beam in the sample . these actuators 34 may be similar to those used in optical disk systems . the lens 18 may be mounted on a pair of such mechanical actuators . the actuators 34 provide lateral and vertical scanning of the focused laser beam in the tissue sample . the focusing lens 18 also collects scattered light reflected from the sample . the amount of coherent light scattered back into the detection system ( which includes lens 18 , plate 16 and assembly 14 ) depends upon local variations of the refractive index and the absorption in the immediate neighborhood of the focus spot . this coherent light may be defined as the component of the reflected light having a circular polarization orthogonal to the polarization of the beam focused into the tissue sample . the scattered light is incident to plate 16 and then to beam splitter assembly 14 . the plate 16 converts the coherent component of the scattered light into linear polarization , where beam splitter assembly 14 directs by reflection ( or filters ) the coherent light component of the scattered light at the beam splitting surface 15 in the beam splitter assembly 14 . the reflected light passes through a relay lens 26 . the light from relay lens 26 may be reflected from a pair of fold mirrors 28 ( see also fig1 a ). these fold mirrors 28 may be part of the beam splitter assembly 14 . the relay lens 26 may also be part of this assembly 14 . the scanned light from the focus spot is reflected from the fold mirrors 28 to a pinhole photodetector assembly 30 , which may also be considered part of the detection system . the fold mirrors 28 are used to make the instrument more compact . a prism assembly may alternatively be used , which is part of the beam splitting assembly 14 , and allows the samples to be placed face down . this orientation allows gravity to assist in maintaining the sample in a stable viewing position . maintaining a stable viewing position is also enhanced by the use of the window 20 as shown in fig1 . a top view of the instrument is illustrated in fig1 a . typical dimensions are given in fig1 a to illustrate the compacted size of the confocal imaging head 32 . the elements in the head 32 may be located on a single board to provide unitized construction . the height of the head may be approximately two inches from the base to the nominal focal point of the focusing lens 18 . by scanning using the mechanical actuators 34 successive lines may be scanned at successive depths to provide images of vertical sections ( i . e ., along a vertical plane through the tissue sample ). if desired the images may be formed from horizontal sections ( i . e ., along a horizontal plane through the tissue sample ) as the lines are scanned horizontally . by tilting the sample , sections at desired angles to the surface of the sample ( i . e ., along a tilted or non - perpendicular plane ) may be formed , such sections may also be formed by moving the lens 18 via actuator 34 as desired angles . referring to fig2 there is shown a block diagram of the data acquisition and analysis system which is part of the imaging system 10 provided by the invention . the confocal head 32 is the head shown in fig1 and 1a . the output 36 from the head 32 is the output from the pinhole detector assembly 30 . this output 36 is the confocal detector signal . signals are also provided from sensors 38 , namely a lateral position sensor and a vertical position sensor . these signals after amplification and filtering are acquired by a analog to digital converter of a digital i / o board 40 . this board 40 may also be on a board with a circuit which provides a digital to analog channel to drive the lateral motion actuator . the vertical scanning actuator is driven from a signal derived from a conventional signal generator 42 . the a to d , d to a and digital i / o board 40 is controlled and data is acquired via software in a personal computer 44 , such as a macintosh quadra 950 . conventional software packages may be used for image analysis and for driving a display 46 , which is shown by way of example as a 1472 by 1088 pixel display . referring to fig3 there is shown the confocal imaging head 32 contacted against the skin 48 of a subject specimen using a mineral oil as an optical index matching fluid , which is an optical contact liquid 21 ( fig1 ) for reducing undesired reflections of light from the surface of the skin . the force against the skin 48 will be limited to that required to press the skin against the contact window 20 of the head 32 . a laser beam 50 which may be relatively low power ( e . g ., 6 . 3 milliwatts of optical power ) is focused into the dermis of the specimen . the laser is operated at a wavelength capable of penetrating into the skin of the specimen , thus the skin may be considered transparent to the laser wavelength ( or in other words , the skin is permeable to electromagnetic radiation of specified frequencies ). the depth of focal point or spot 52 is varied from the surface of the stratum corneum to a few millimeters below the surface of stratum corneum . the nominal beam spot size may be , for example , 2 . 5 micrometers , full width half maximum . the laser spot is scanned laterally across the skin , for example at a rate of 3 to 10 hz . different laser wavelengths may be selectively used for different resolution . inasmuch as the energy delivered is proportional to the illuminating flux focused divided by the diameter of the spot , the scan length and the scan rate or frequency , the amount of incident flux is sufficiently low that damage to the specimen is avoided . the light scattered by the tissue is collected and the lights coherent component is re - imaged onto the pinhole aperture 54 of assembly 30 , as shown in fig1 and 1a . the pinhole 54 transmits the coherent light from the focal region of the incident beam 53 to the detector 55 ( of assembly 30 ) where it converts the light into an electrical signal . as the lens 18 scans laterally , the electrical signal is acquired by the computer and stored . each scan represents a one dimensional trace of the reflectivity and scattering cross section of the dermis at a given level below the surface of the skin 48 . a series of scans are made with the focal point positioned at progressively lower depths thereby providing a vertical cross section image of the skin which may be similar to a b - scan ultrasound image . as stated earlier , these scans may also be horizontal to provide a horizontal cross - section , or at an angle to provide an angular cross - section of the skin . from the foregoing description it will be apparent that there has been provided an embodiment of a confocal imaging system for dermatological pathology applications . variations and modifications of the herein described system and other applications for the invention will undoubtedly suggest themselves to those skilled in the art . accordingly , the foregoing description should be taken as illustrative and not in a limiting sense .
a handheld confocal imaging system for in vivo observation of dermal and subdermal tissue allows diagnosis of conditions substantially beneath the surface of the skin . a confocal head has optics which scan the tissue so as to provide images of vertical sections of the tissue . both two and three dimensional imaging may be provided for diagnosis and location of basal cell carcinomas and melanomas , and so as to enable visualization of tumor borders prior to excision .