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 ${}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Hg}{}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Au}$ 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 μCi 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 jnterstudy difference was 4 ±3 percent. Thus, sufficiently high yield and dose are obtained from the ${}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Hg}{}^{\mathrm{<mtext>195</mtext><mtext>m</mtext>}}\text{Au}$ 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.