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Blood flow measurement from first pass time/activity curves: influence of bolus spreading

Organ blood flow as a fraction of cardiac output can be measured from the first pass time/activity curves recorded over the organ and over ‘arterial’ regions of interst (ROIs). The right lung, left ventricle and aorta can all be used as the arterial ROI, and separate estimates of blood flow corresponding to each ROI can be derived, Organ blood flow based on the lung ROI was significantly less than that based on the left ventricle in adults, with a mean ratio of 0.94 (S.D.) 0.14; p < 0.001), but not in children (1.02 (0.13); p > 0.1). Blood flow based on the aorta was greater than that based on the left ventricle in adults and children with respective ratios of 1.05 (0.18; p < 0.01) and 1.08 (0.16; p > 0.05). Because of its clearer definition and relatively later point of recirculation, the lung curve should give the most reliable estimate of blood flow. However, because some bolus spreading occurs between the pulmonary vein and organ (e.g. kidney), organ blood flow based on the lung ROI should be multiplied by 1.06.