Tc-99m MAA total-body imaging to detect intrapulmonary right-to-left shunts and to evaluate the therapeutic effect in pulmonary arteriovenous shunts.
The appearance of radiotracer in the systemic circulation to document the visualization of the brain, kidneys, and spleen after intravenous administration of Tc-99m MAA indicates right-to-left shunts because MAA particles (20-60 microns) are supposedly trapped in the pulmonary bed (less than 15 microns). Six hypoxemia patients (1 male, 5 females; age range, 12-52 years) with intrapulmonary right-to-left shunts were evaluated by Tc-99m MAA dynamic perfusion imaging and total-body scans. Tc-99m MAA total-body imaging of the six patients with intrapulmonary right-to-left shunts (3 patients with chronic liver disease/cirrhosis of the liver and 3 patients with pulmonary arteriovenous fistulae) revealed significant radiotracer uptake in extrapulmonary organs such as the brain, kidneys, and spleen; a shunt ratio, estimated by a semiquantitative method, ranged from 17.8% to 52%. All dynamic pulmonary perfusion scans showed a normal sequence of cardiopulmonary flow without intracardiac shunts. Three patients with pulmonary arteriovenous fistulae underwent a second Tc-99m MAA total-body imaging after embolization therapy (2 patients) or lobectomy (1 patient). The result in lobectomized patients were negative for uptake in extrapulmonary organs; the two patients who underwent embolization therapy demonstrated only mild improvement. As a consequence of these findings, the authors conclude that Tc-99m MAA total-body imaging can be used for the diagnosis of intrapulmonary right-to-left shunts, as well as for the evaluation of postshunt therapy.