The radiolabeled microsphere technique in gut blood flow measurement--current practice.

Measurement of blood flow to the gut has become an integral part of the physiologic study of the gastrointestinal tract. While many methods have been utilized in measuring tissue blood flow, the one most often practiced today is dependent on injection of radioactively labeled microspheres. The theoretical basis of the microsphere technique is analogous to that of the indicator-dilution method. A bolus of microspheres suspended in a suitable vehicle is injected into the left atrium or left ventricle where they mix uniformly with the oxygenated blood. They are then distributed via aortic blood flow to the capillary beds within each organ in proportion to the volume of microsphere-containing blood. Technical aspects of tissue processing, gamma energy detection, and gamma spectrum analysis are reviewed. Sources of experimental error and techniques for their reduction are also discussed.