The use of iridium-191m for pulmonary blood flow imaging

A preliminary evaluation of the potential utilization of osmium-191/iridium-191m for pulmonary blood flow imaging was performed. This evaluation was part of a more general study concerning the use of 191mIr for first-pass radionuclide angiocardiography (FPRNA). In eight selected patients with suspected pulmonary disease, we generated, from the data collected during FPRNA, an image representing blood flow distribution to the lungs. A software program was developed in order to differentiate the lungs from the heart, to define the wash-in lung phase and finally to construct an image representing pulmonary blood flow distribution. We compared that image with a standard lung perfusion image using technetium-99m macroaggregated albumin (MAA) and plain chest X-ray and computerized tomography (CT). The obtained 191mIr perfusion images showed a spatial activity distribution similar to that seen on 99mTc-MAA lung perfusion scans, and in most cases the same perfusion defects. Disease revealed by plain chest X-ray and CT was nicely correlated with perfusion defects seen on the 191mIr images. The combined information of lung perfusion and dynamic cardiac parameters obtained by FPRNA (right and left ventricular ejection fractions) added another relevant dimension to the clinical picture of patients with pulmonary embolism, chronic obstructive lung disease, lung tumour or suspected congestive heart failure. We conclude that 191mIr may become a practical tool for achieving the conceptually promising approach of combined lung-heart real-time imaging.