Quantitation of left-to-right shunting with Iridium-191m radionuclide angiocardiography

The purpose of this study was to determine whether iridium-191m (Ir-191m) radionuclide angiocardiography (RAC) could be used for the detection and quantitation of left-to-right shunting. In 36 patients' pulmonary-to-systemic flow ratios (Qp:Qs) were calculated using Ir-191m RAC and oximetry at cardiac catheterization. Patients were aged from 4 mos. to 31 yrs. (average 6.5 yrs.). One additional patient was 58 yrs. old. The referral diagnoses included VSD (29 pts.), ASD (3 pts.), PDA (1 pt.) and post-surgery (3 pts.). Ir-191m (tl/2=4.96 sec.) was obtained from an Os-191-)> Ir-191m radionuclide generator. Doses of Ir-191m ranged from 10-100 mCi and were injected as a 1-2 ml bolus in an external jugular vein or into a catheter placed in the inferior vena cava. RAC's were recorded on a computerized gamma camera at 2 frames/sec. This study concludes: Ir-191m RAC allows reliable detection and quantitation of left-to-right shunts. Advantages of Ir-191m include; extremely low radiation exposure to the patient, high photon flux and ability to repeat studies within a short period of time