Abstract:
An apparatus and method for insuring the proper alignment of a detected vein pattern and a projected vein pattern are disclosed. The apparatus enhances the visual appearance of veins so that an error that can lead to improper patient care or injury can be avoided.

Description:
This application claims priority on U.S. Provisional Application Ser. No. 60/937,618 filed Jun. 28, 2007 the disclosures of which are incorporated herein by reference. 
    
    
     SUMMARY OF THE INVENTION 
     An apparatus and method for insuring the proper alignment of a detected vein pattern and a projected vein pattern in a apparatus that enhances the visual appearance of veins so that an error that can lead to improper patient care or injury can be avoided. 
     BACKGROUND OF THE INVENTION 
     It is known in the art to use an apparatus to enhance the visual appearance of the veins and arteries in a patient to facilitate insertion of needles into those veins and arteries as well as other medical practices that require the identification of vein and artery locations. Such a system is described in U.S. Pat. Nos. 5,969,754 and 6,556,858 incorporated herein by reference as well as publication entitled “The Clinical Evaluation of Vein Contrast Enhancement”. Luminetx is currently marketing such a device under the name “Veinviewer Imaging System” and information related thereto is available on their website, which is incorporated herein by reference. 
     The Luminetx Vein Contrast Enhancer (hereinafter referred to as LVCE) utilizes a light source for flooding the region to be enhanced with near infrared light generated by an array of LEDs. A CCD imager is then used to capture an image of the infrared light reflected off the patient. The resulting captured image is then digitally enhanced and then projected by a visible light projector onto the patient in a position that must be closely aligned with position of the captured image. The practitioner uses this projected image to determine the position in which to insert a needle. Should the image be misaligned, the patient can be injured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an embodiment of a vein contrast enhancer. 
         FIG. 2  is a representation of a patient&#39;s arm. 
         FIG. 3  shows an embodiment of a laser contrast enhancer 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIG. 1 , a typical embodiment of a vein contrast enhancer (VCE)  100  contains a camera  101  which is used to capture an image of a patient&#39;s body  105 , a processing system (not shown) that enhances the image captured by the camera to highlight the positions of veins, and a projector  102  that shows an image of the enhanced vein pattern back onto the patient&#39;s body  105 . Since the camera and projector are physically separate devices they reach the patient&#39;s body from different source points along different paths  103 ,  104 . In some embodiments, the paths are made coaxial within the body of the VCE, however at some point the paths are separate since the devices (camera and projector) are physically separate devices. Since the purpose of a VCE is to allow the practitioner to insert a needle into the highlighted vein, it is critically important that the projected image and the actual vein location be aligned. Typically this alignment is done as a separate step in the use of the VCE. A card with a known pattern is placed with the viewing/projecting field of the VCE. This card has a florescent material applied to it so that when it is struck by green light, it emits infrared light that can be seen by the camera. This image is used to align the VCE. 
     This invention describes methods for achieving this alignment without requiring the operator to take a separate step. 
     Referring to  FIG. 2 , a representation of the patient&#39;s arm  201  is shown along with several veins. A bounding box is shown around a single vein  200 . In  FIG. 3 , a schematic representation of the bounded area of the single vein is shown  305 . Typically, the enhancement image will light up the area around the vein and will be dark on the vein. When properly aligned, the bright part of the image  300  will have edges that properly align with the edges of the vein  303 ,  304 . As previously described, the VCE will typically have an alignment mode wherein a known pattern, typically presented on an alignment card, will be placed in front of the VCE and an alignment will be performed. This alignment can either be automatically performed by the VCE or manually performed by the operator. The weakness of this kind of implementation is that it relies on the expectation that the alignment will be maintained over time. If the alignment should shift, patient injury can occur. 
     In a typical VCE, an infrared light source and a camera that is sensitive only to infrared light is used to detect the vein position. Furthermore, the projected image is often green in color to insure that the light from the projector is ignored since the camera is sensitive only to light near the infrared region. This selectivity can be implemented either with filters or with selectively sensitive camera elements. 
     Referring back to  FIG. 3 , in a typical LCE, the camera, by design, is blind to the projected light. In our invention, the camera is by design, able to selectively see the projected light. In a preferred embodiment, a multi-color capable projector is used. As usual, green is used to fill the area outside of the vein  300 . That green projection goes to the edges of the vein position  303 ,  304  and the vein area itself is left dark. A camera that is sensitive to red and infrared light is used in this embodiment. In addition to the green fill, red lines are drawn at the edges of the veins  303 ,  304 . Since the camera can see these red lines, the image enhancement software can look to see if the red lines are at the proper position and if needed automatic alignment can be performed. An alternative embodiment would be to paint a red line  306  down the middle of the vein position. An alternative embodiment would be to paint some pattern of red light over a desired portion of the vein. 
     Typically the cameras used in an LCE are monochrome and unable to discriminate between light of different wavelengths. Depending on the sensitivity of the camera and the brightness of the projector compared to the infrared flood lighting provided by the LCE, various techniques can be used to aid the camera in the detection of the red lines. One method is to simply look for the brightening caused by the addition of the red lines to the reflected infrared light. A second method is to periodically turn off the infrared lighting such that only ambient infrared and the projected red are seen by the camera. This can make it easier for the system to detect the red lines. 
     Although we&#39;ve described the invention using red and green lights, various combinations of colors can be used. Red and infrared light are known in the art to be useful for vein detection. Any combinations of colors of shorter wavelengths can be used for projection and alignment images as long as the camera selected is properly selected or filtered to achieve the desired discrimination between wavelengths. Furthermore, while discrimination between projection, detection and alignment signals in the preferred embodiment has been described using different wavelengths to separate the signals, in an embodiment with less freedom of projected color, time division can be used where the projected image is shown most of the time and the alignment image is shown interspersed on a lower duty cycle basis. Properly implemented, the alignment image will be quite visible to the VCE&#39;s camera, but invisible to the operator of the VCE. 
     Projectors in VCEs can be either monochrome (e.g., projecting green only) or multicolor (e.g., projecting RGB). The advantage of a monochrome implementation is that since an array of single color LEDs can be used in place of white bulbs and a color wheel typically found in a multicolor projector the system can be of lower cost, generate less heat and have higher reliability. In such an embodiment, the time division scheme describe above would be appropriate. In this monochrome configuration, an alternative embodiment would be to add a smaller array of a second color of LEDs (i.e., red). This alignment array can be smaller than the projection array in that it doesn&#39;t need to be visible to the operator, just to the camera. The projection LEDs and the alignment LEDs could then be time multiplexed as previously described.