fig1 shows an x - ray machine suitable for obtaining stereographic x - ray negatives of the breast . like any other x - ray machine , this machine includes an x - ray tube 1 emitting x - rays along a main axis 2 towards a breast 3 to be x - rayed , which breast is supported on a support tray 4 . the tray 4 is fixed to a frame 5 of the machine . after passing through the breast 3 , the x - rays produce an image on a photosensitive plate 6 placed in a cassette 7 . the cassette is held in place relative to the x - ray tube 1 . a stereographic breast x - ray machine is also capable of making an image at different locations , on the same plate 6 , e . g . on the left 8 or on the right 9 depending on whether the x - ray tube 1 is in a first orientation 10 or a second orientation 11 relative to the breast 3 . these different orientations are made possible by carrying the tube 1 on a boom which rotates about a center of rotation . the images of the breast 3 are then projected respectively at locations 12 and 13 on the plate 6 . on the basis of the two images 12 and 13 which are thus preferably to be found side by side on a single negative , and which correspond to a known difference of angle of incidence 14 , it is possible to point to matching characteristic regions , respectively 15 and 16 , in each of these images and to use a computer to determine the position in three dimensions ( e . g . above the breast - supporting tray 4 ) of a portion of the breast 3 whose shadows correspond to said matching regions . under these conditions , it is possible to use a needle - carrying tray 17 including a biopsy needle 18 driven by a motor 19 to insert the needle into the breast 3 at the particular location from which tissue is to be taken for the purpose of analysis . fig2 shows a light box implementing the invention . the special feature of the light box of the invention is that it includes a graphics screen 20 which , in the preferred embodiment , comprises a transparent slab 21 placed over a plane grid 22 of light - emitting diodes ( leds ). the graphics screen 20 is controlled by a microprocessor 23 so that all of the leds in the grid 22 emit light . when the screen 20 is a plasma screen or a cathode ray screen , then the microprocessor generates a video signal such that all of the points on the screen are illuminated prior to any index marks being put into place . a control box 24 is coupled to the microprocessor and has a set of knobs such as 25 to 28 for enabling one of the available index marks , e . g . i 25 , to be selected . once selected , the index marks i 25 to i 28 can be moved over the surface of the screen 20 by means of a set of potentiometers 29 and 30 for controlling x and y displacements . the control box 24 is shown here merely by way of example . in particular , it may comprise control means which are more ergonomic , for example a mouse or a trackball . when the control box 24 is manipulated , instructions are sent to the microprocessor which cause it to display an index mark . as it does this , the microprocessor naturally stores in its memory the addresses of the positions of the index marks in terms of x and y offsets relative to a reference mark 31 on the screen . thereafter , given the pitch of the image points ( pixels ) on the graphics screen , it is easy to compute the co - ordinates of the positions of these index marks . the accuracy of the device of the invention depends only on the linearity of the pixel pitch . the resolution with which the index marks can be put into place depends only on the pixel pitch of the graphics screen itself . for a given graphics screen , these two parameters are fixed by construction . given the production technology for graphics screen masks , these positions are thus very accurate and easily reproducible from one screen to another . in one example , using 10 cm × 20 cm screens , suitable for stereotaxy in mammography , it is easy to find screens having a pixel pitch of about 0 . 25 mm to 0 . 3 mm . this is sufficiently accurate . it can immediately be seen that a device made in this way cannot go out of adjustment . its accuracy is obtained by construction and not by ( frequently repeated ) adjustments of a mechanical linkage . in addition , there is no wear , and thus very little maintenance , thereby ensuring that the apparatus is very reliable . finally , the falling prices of electronic components make it possible to anticipate production costs which are considerably lower than present costs . however using a graphics screen together with a microprocessor also provides much greater operator comfort . in particular , a character generator 34 can be used for distinguishing various types of associated pairs of corresponding index marks . for example , index marks i 25 and i 26 may be represented by small crosses , whereas index marks i 27 and i 28 may be represented by small crosses within respective circles . it can immediately be seen that by selecting a different type of character in this way , the index marks can be associated in as many pairs as desired , and also that by using a microprocessor associated with a graphics screen , it is possible to displace the index marks without worrying about possible mechanical linkage overlaps . the characters displayed as index marks may also be distinguished from each other by brightness : e . g . by being brighter than the background . they may also be distinguished by color , if the graphics screen is a color screen . an index mark may therefore correspond to a single pixel or to a plurality of pixels on the screen . similarly , by reserving a region 32 at the periphery of the screen 20 , the character generator can be used to write messages such as &# 34 ; confirm pointing &# 34 ;, thereby informing the operator who is manipulating the control box 24 how to perform the next expected operation . in addition , the light box of the invention makes all sorts of improvements possible . for example , the positioning of the film 6 on the surface of the slab 21 can be replaced by injecting a digital representation of the image of the film 6 . transforming an x - ray image into a digital image is common practice . the digital image can then be stored via the microprocessor 23 in an image memory 33 . the image memory 33 is read by the microprocessor 23 and is displayed on the graphics screen 20 simultaneously with its display of the index marks i 25 to i 28 . as mentioned above , it is known how to perform the processing required for computing the co - ordinates of a lesion . the microprocessor 23 may be capable of running a program 35 for performing this processing . when processing is completed , it can deliver data representative of the position in three dimensions of the point specified by combined examination of the two stereographic images together . this information may be displayed on a display monitor 36 . this information may also be used for controlling the motor 19 for displacing the biopsy needle 18 . in order to make this chain more effective , the film 6 contained in the cassette 7 may be replaced by an x - ray image intensifier screen . the video signal delivered by this intensifier screen can be processed and transformed into a digital image which can be displayed directly on the graphics screen 20 . the operator who performs the stereographic examination can then manipulate the control box 24 to inform the microprocessor 3 of the corresponding positions of the points to be treated . the microprocessor 23 then runs the program 35 and can control the motor 19 , almost in real time . this can accelerate therapy which a patient always finds arduous .
a light box for x - rays is made by using a graphics screen coupled to a microprocessor , with the screen being used with inverse brightness . under these conditions , the graphics screen emits light at nearly all points , other than special locations whose positions can be controlled by means of a control box . an x - ray negative to be examined is placed over the graphics screen . the control box is used to move the non - illuminated regions of the screen to point to special locations in the negative . the light box is particularly applicable t studying stereographic negatives for mammography . it makes it possible to determine more quickly and more accurately the locations of lesions in breasts under examination .