Regional variations in myocardial tissue oxygenation mapped by near-infrared spectroscopic imaging

Near-infrared fibre-optic single point spectroscopy has been widely exploited to provide information regarding blood volume and oxygenation in vivo, but it does not provide any information on regional differences in perfusion. We have combined the chemical sensitivity of spectroscopy with the spatial sensitivity of imaging to generate maps of regional cardiac oxygenation. Spectroscopic images were acquired for isolated, arrested, blood-perfused porcine hearts (n=4) over the wavelength range 650 and 1050 nm. Spectroscopic images were acquired during normal perfusion, regional ischemia (occlusion of left anterior descending artery) global ischemia, and reperfusion. Hemoglobin (Hb) and myoglobin (Mb) content and oxygenation were determined by reconstructing the tissue spectra measured at each pixel as weighted sums of water, oxy- and deoxy-Hb (and -Mb) absorptivity spectra. The spectroscopic images acquired during regional ischemia clearly revealed increased deoxy-(Hb+Mb) levels and decreased oxy-(Hb+Mb) levels in the ischaemic regions relative to the normally-perfused regions. Global ischemia produced a dramatic decrease in oxy-(Hb+Mb) levels and a moderate increase in deoxy-(Hb+Mb). These images confirm that blood oxygenation can be mapped in cardiac tissue by near-infrared spectroscopic imaging.