Gold- 195m, a new generator-produced short-lived radionuclide for sequential assessment of ventricular performance by first pass radionuclide angiocardiography.

The feasibility of performing rapid sequential first pass radionuclide angiocardiography using a new short-lived radiotracer, gold-195m (195mAu) half-life 30.5 seconds) was evaluated. This radionuclide emits a 262 keV gamma ray and is the daughter of mercury-195 (195mHg) (half-life 41.6 hours). The prototype tabletop 195mHg/195mAu generator produced 20 to 25 mCi of 195mAu in 2 ml of eluate (yield of 40 percent). The breakthrough of 195mHg in the eluate was 0.02 percent of the amount of 195mHg in the generator. The eluate contained 20 microCi of 195mHg per study, resulting in an estimated human radiation dose of 0.007 rad/study to the whole body and 0.34 rad/study to the kidney. Four dogs each had 15 to 20 sequential first pass studies performed with 195mHg at 3 to 10 minute intervals using a computerized multicrystal gamma camera. During the left ventricular phase, 160,000 to 190,000 counts/s were acquired. The end-diastolic left ventricular region of interest contained 3,000 to 6,000 counts (background- and decay-corrected). Multiple reproducible values for left ventricular ejection fraction were obtained during stable conditions. The mean (+/- standard deviation) interstudy variability was 4 +/- 2 percent. During infusion of isoproterenol, rapid increase of left ventricular ejection fraction was demonstrated. Excellent agreement was observed between studies performed with technetium-99m diethylenetriaminepentaacetic acid (99mTc-DTPA) and 195mAu. The mean interstudy difference was 4 +/- 3 percent. Thus, sufficiently high yield and dose are obtained from the 195mHg/195mAu generator for reliable high count rate first pass determination of left ventricular ejection fraction. This new short-lived radiotracer makes possible rapid sequential assessments of ventricular function at greatly reduced patient exposure to radiation.