A noninvasive medical-imaging system produces false-color images that show regions of ischemia (reduced oxygenated blood flow) in organs and tissues. The system operates in real time, providing immediate guidance for surgery or other treatment. For example, the system can be used to identify tissues that should be removed in treating burns or in other surgical procedures.
The detection of ischemia involves the determination of the relative oxyhemoglobin and deoxyhemoglobin contents of blood in the affected organ or tissue. Heretofore, this has been done in nonimaging fashion by use of in-place monitors, such as pulse oximetry, which is not organ specific. The present noninvasive, real-time system is a multispectral imaging system that utilizes the spectral signatures of oxy- and deoxyhemoglobin.
The system (see figure) includes three charge-coupled-device (CCD) video cameras aimed at the same spot with the help of beam splitters. The light entering each camera passes through a narrow-band-pass filter at a unique wavelength. One possibility for wavelengths of the three filters is 541, 577, and 558 nm. These wavelengths were chosen because oxyhemoglobin has absorption peaks at 541 and 577 nm, while deoxyhemoglobin has an absorption peak at 558 nm. Another choice could include one of the one of the isobestic points. Thus, as oxyhemoglobin is converted to deoxyhemoglobin, the 541-nm and 577-nm absorption peaks become depressed and the 558-nm absorption peak appears. Another choice may be 558 (deoxy peak), 569, and 586 (isobestic points).
The images acquired simultaneously at the three wavelengths can be processed and combined in such a way as to enhance the spectral contrast between deoxyhemoglobin and oxyhemoglobin. For this purpose, the video outputs of the three cameras are fed to a digital signal processor (DSP), which produces a false-color (red/green/blue) image of the organ or tissue that shows blood oxygen content. The DSP uses an algorithm derived from clinical data. This false-color image is displayed on a video monitor.
This work was done by Gregory H. Bearman, Thomas G. Chrien, and Michael L. Eastwood of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the category.