Imaging small pulmonary ischemic lesions after radioactive carbon monoxide inhalation

A new method is described for imaging small ischemic regions in the lung immediately after a single breath of radioactive carbon monoxide (11CO). A tungsten-collimated scintillation camera is used to visualize the 0.51-MeV annihilation photons due to the 11C. In normal dogs the entire field is cleared of 11CO within 10 sec. However, in dogs with experimentally occluded 2-mm-diam segmental arteries, the ischemic but well-ventilated segment appears as a region of persistent high radioactivity, due most likely to temporary entrapment of 11CO-labeled red blood cells in the ischemic region. This technique also provides a simple noninvasive means for instantly labeling the systemic circulation without left heart catheterization.