the optical systems and methods described here - in increase contrast and depth of skin penetration to reveal veins that can not be found by manual methods . three main approaches are taken that can be used independently or together to achieve this result : a . providing incident radiation in one or more wavelengths of hemoglobin absorption that is normal or near normal to the surface . using a reflector based system , preferred embodiment , or a lens based system , single or multiple radiation sources can be used , each illuminating the whole scene through the optical systems . the further the amount of deviation of the radiating source from the optical system &# 39 ; s point of focus , the greater the greater the angular spread of the near normal radiation on the surface being illuminated . this reduces both specular from the surface and direct reflection from more reflective objects between the surface and the vein such as adipose tissue . furthermore , the angular dispersion can be controlled by design or manipulated on a frame by frame basis through turning off and on different sources . turning off one or more sources of the extended source also changes the radiation pattern , allowing a radiation angle that has a large specular reflection component to be removed . a method is provided to achieve this goal . b . providing a static pattern of incident ( normal ) radiation which includes areas of full illumination and areas with little or no direct illumination . areas with full illumination and no illumination would be sampled with different criteria and by sampling for contrast changes within each area that would possibly indicate a vein in that area note that areas with no incident radiation would be more sensitive to deeper veins since no skin reflection would obscure fainter veins , and deeper veins would have less scattering above them . this is in complete contrast to the luminetx patents for producing a uniform surface illumination and hence non - obvious . in the no surface illumination case , the light scattered within the tissue serves as the illumination source . such a pattern could be composed of spaced lines of light and dark areas , or a two dimensional pattern of light and dark spaces . the major criteria is that there be only minor aliasing effects between the veins and the sampling illumination pattern . any such effects can be minimized using the technique in c ) below . c . deliberately changing the source location of the incident light . in combination with a ) above , this can be used to remove shadows caused by irregularities in the light source or other optical issues and possibly certain surface blemishes such as wrinkles or hair , which are orientation dependent . in combination with b ) above , moving the pattern allows for additional vein resolution and detection by sampling at different low surface illumination points . in both of these cases , processing to determine the scene differences would be employed . in the case of a ) above , optical imperfections can be readily removed since they always will exist in a known location within the illuminated field and could be removed by changing the chosen source . for instance , should the sources be located to provide a +− 1 . 5 degree shift in incident angle , small enough so that the internal scattering pattern would be essentially unchanged , and , as an example , if the offending defect were 2 ″ away from the surface , the defect would be moved 0 . 1 ″, sufficient for easy removal through software . likewise , any patterns would be shifted by a similar amount , and through proper design , a surface area that was illuminated using one source could be shifted into coincide with a previous dark area from another source . fig1 a , top view reference system , shows a typical apparatus as a reference device in which the illumination subsystem exists . it consists of the following major subsystems : ( 1 ) an electronics subsystem which holds the processing elements , power , and other such components . ( 2 ) a display subsystem which can be a separate lcd , or a direct skin projection subsystem . ( 3 ) a source of optical radiation , as represented by the dashed lines , used to illuminate the reflector ( 4 ) and after reflection illuminates the skin area being imaged . ( 4 ) a reflector shaped to take the incident radiation from ( 3 ) and project it on to the skin such that the radiation hits the skin near a 90 degree angle . the reflector can be a spherical subsection or optics specifically designed to optimize light angle . ( 5 ) the skin surface being scanned for veins , which is underneath the reflector in the area between the dashed lines ( 6 ) a camera with appropriate wavelength filters used to pick up the reflected light from the skin . fig1 b , side view reference system , shows a side view of the illumination subsystem of 1 a with two of the light rays ( 7 ) traced . a secondary mirror , ( 8 ) may be used to make the optics more compact . if a spherical subsection is used for the reflector , its radius can be calculated by a competent optical engineer based upon its size and distance from the light source . the reflector can be manufacture from polished metal , metalized plastic , or be made from transparent plastic such as acrylic with an optically reflective coating ( 9 ). a dichroic reflective coating which reflects near infrared light allows visible light to pass through so an operator an unrestricted view of the skin surface below . note that the reflector is tilted at an angle ( a ) with respect to the surface . this angle is derived from the apparent angle , ( b ) of the source ( 3 ) with respect to the center point of the reflector ( 4 ). the source needs to be outside of the scanned area ( 5 ) or it will show up as a very bright , undesirable artifact in the vein image . angle a ( 10 ) is angle b / 2 ( 9 ). in place of a dichroic filter , a coating ( 9 ) that reflects only polarized light can be used with a source ( 3 ) that is similarly polarized . this has an advantage if visible rather than infrared light is used . candidates for the extended source ( 3 ) are leds or oleds with the desired wavelength and with an emission angle such that the reflector ( 4 ) is fully illuminated , or a laser with the desired wavelength whose beam has been expanded to fully illuminate the reflector ( 4 ). fig2 a , extended led source with beam dispersion shows a cross section of an alternative scheme with multiple individual light sources possibly with a lens ( 11 ) or internal reflector which controls the beam dispersion . fig2 b , top view extended led source example shows an array of leds ( 3 ) whose spacing and number can be designed to provide the desired angular dispersion of the combined beam . fig3 b , side view of extended source with collimation lens shows an alternative to the reflector approach shown in fig1 a and 1b . as in the case of the reflector ( 9 ), each source fully illuminates the optical collimation element , in this case ( 33 ), whose exit radiation is nearly perpendicular to the lens element ( 33 ). however , each off center source provides parallel but not perpendicular rays ( 34 ). this added dispersion diminishes specular reflections . fig3 a , top view collimation plate , and fig3 b , side view collimation plate , shows yet another method of achieving the same objective of producing light normal to the skin surface . fig3 a shows a light source or light source ( s ) which produces a wide , narrow beam ( 7 ) which interacts with a plate ( 14 ) with multiple prisms ( 13 ) along its top . fig3 b shows the prisms in more detail , each with a reflective coating ( 15 ). these prisms are angled to reflect lines of light normal to the surface . depending on the dispersion of the light source , the light could project narrow lines or varying intensity lines on the surface as shown in fig4 a . note that other variations of this same theme can be conceived . fig4 a , spaced line illumination , shows a simple example of a pattern of incident radiation on the surface of the skin composed of illuminated lines ( 16 ) with areas of little or no direct illumination ( 17 ) and are illuminated mainly by internally scattered light . all of the tissue gets some illumination from nearby lighted areas since directly illuminated tissue scatters light into adjacent tissue without direct light . fig4 b , patterned illumination , shows a simple example of patterned illumination where the dark areas ( 17 ) of the skin ( 5 ) are not directly illuminated and the light area ( 16 ) is . note that the indirect illumination comes from not just the local light area , but also from extended light areas around other dark areas which could be a half an inch or more away . fig5 , interaction between illumination and two veins shows an example of the contrast enhancement using this technique . a vein that is close to the surface ( 18 ) or has a large cross section absorption area appears in both the area directly and indirectly illuminated whereas a deeper vein ( 19 ) is not visible under direct illumination but is revealed under indirect illumination of the incident radiation scattered by the tissue . the two criteria for either of these examples to work is that the projected patterns on the camera sensor be imaged by the sensor , at least 3 times the size of camera pixel , and that they be sufficiently smaller than the minimum vein thickness or larger than the maximum vein thickness such that major aliasing effects to not occur . in addition the camera &# 39 ; s sensor must have good dynamic range and a high signal - to - noise ratio . absorbing the light in the areas where it is unwanted . in general this is not the preferred embodiment since optical systems generally suffer from a shortage of radiation . absorbing the light either adds to the power requirement by requiring the source to be brighter or adds to the sensor requirements by requiring a higher signal - to - noise ratio . passing the light through an additional optical system such as a micro lens array or a cylindrical lens array or doing the equivalent using a laser and hologram . again this is not the preferred embodiment unless an array of sources is used as detailed in fig2 a & amp ; b in which case only the specifications of the lens array change . otherwise , this approach , due to the additional component and system complexity is not preferred . when using the spherical reflector approach , add to the design of the mirror used to fold the optical path to include either a stamped pattern to shape the light output or fresnel optical elements to meet the desired patterned radiation specification . fig6 , external object shift with two sources , shows a simple optical system consisting of two illumination sources ( 22 ) ( 24 ) a focusing reflector ( 4 ) and various ray traces . the sources have a smooth radiation angular distribution pattern which serves to illuminate the reflector ( 4 ). the reflector is designed in such a way that with a source centered at its midpoint ( 23 ), the reflected radiation is perpendicular to the surface ( 5 ) it strikes . such a reflector can be constructed from a reflective spherical surface canted , if necessary ( shown in fig1 b ), to compensate for a source off center with respect to the reflector . other reflectors are possible . a spherical surface can be further optimized to remove spherical aberration if desired . with two sources equidistant from the center point , the radiation strikes the surface slightly off perpendicular as shown in the two rays ( 26 ) ( 27 ) corresponding to light sources ( 24 ) and ( 26 ) respectively . if there is a blemish , defect , or pattern on the reflector ( 20 ), its position will be shifted on the surface due to the shift in source ( 24 ) from optical center as shown by rays ( 29 ) to a new apparent surface position ( 28 ). likewise , using the other source ( 22 ), there is a shift in apparent position of the object in the other direction . however , none of the structures under the surface will appear to have moved . using a computing element , a comparison can be made of the two pictures and only stationary objects need be displayed . note that in the case where the optical system is moving with respect to the surface , that translation in position can also be separately compensated for in the computing element , and only the objects under the surface displayed . should a pattern or object be located other than on the reflector such as on surface ( 21 ) the displacement still occurs as shown in ray traces ( 33 ) with the resulting ( in this case magnified ) object positions 31 and 32 . since the position of the radiation source is different any fixed patterns in the optics will move with a change in source , while the radiation hitting the surface will still be essentially normal to the surface . by design , the degree to which the radiation varies from perpendicular can be held to less than +− 5 degrees and with an average of less than +− 2 . 5 degrees , so as not to significantly change the depth of penetration or radiation scattering characteristics . by turning on the one light source at a time synchronously with the start of a new camera frame , the radiation pattern is changed as desired in different frames . as previously stated , this allows further processing to remove undesirable artifacts . it also allows the illumination pattern on the skin to be shifted , so that areas in a previous frame that had direct illumination now receive only scattered illumination from the tissue itself . this has the advantage of providing greater detail and allowing deeper veins to be better revealed . this technique is not the same as a structured light approach that is sometimes used to reveal depth information about objects hidden behind scattered light . this approach provides an increase in contrast . more complex pattern movement can be achieved by using more than two sources . note that this same technique can be used with the illumination design shown in fig2 . rows , blocks , or individual sources can be turned on or off synchronously with the camera frame to optimize contrast . in particular , this can be done dynamically — when a potential vein is recognized , the leds over that vein can be turned off so the vein is illuminated by scattered light alone . a second approach involves moving the optical pattern through mechanical means . this is not the preferred approach due to the design issues and additional complexity .
the illumination apparatus and methods described herein increase the depth of the illumination &# 39 ; s tissue penetration , help minimize surface reflections and back - scatter for a non - contact camera based imaging system thus providing increased tissue - structure contrast and more information about the structures beneath the surface . it does this by using one or more of the following techniques : using optics to provide radiation which hits the surface at or near 90 degrees for better tissue penetration ; using optics and radiation source placement to control the angular distribution of light from surface vertical to minimize surface specular reflection and subsurface reflection ; removing some surface light reflection through patterning the intensity of the light source thus increasing contrast in areas of no or low direct irradiation ; synchronously with respect to camera frames or through user selection , switching on and off light sources which has the effect of 1 ) dynamically changing the overall angular distribution of light thus changing surface level reflectance ; 2 ) revealing and through processing removing unwanted patterning caused by optical defects or contaminants on optical surfaces or surface hair ; 3 ) moving illumination patterns to permit contrast enhancement in all areas of the surface .