Evaluation of Scanning Condition and Early Organ Accumulation with Large Field of View Gamma Camera in ²⁰¹Tl Myocardial Scan

Abstract

Recently many articles according to usefulness of ²⁰¹Tl myocardial scan have appeared after early investigation by Lebowitz, Bradley-Moore and others. The authors had opportunity to evaluate ²⁰¹Tl as myocardial scanning agent and studied its scanning condition and early organ accumulation up to 10 minutes after intravenous injection with large field of view gamma camera (Toshiba GCA-401) in order to obtain basic information for ²⁰¹Tl myocardial scan.
The study with liver slice phantom showed best results in 80 keV photopeak with 20% window width in low energy collimator. Normal myocardium (NM) and lung activity decreased rapidly to reach plateau within 3 minutes after injection. Activity in NM and liver changed little after 5 minutes postinjection, but infareted myocardium (MI) and lung activity still continued to decrease. In each case MI always showed low activity compared to normal area of the myocardium, and mean MI/NM ratio distributed from 0.74 to 0.80 up to 10 minutes postinjection. Blood disappearance of ²⁰¹Tl was two exponential: 2.5 minutes (rapid phase) and 54.7 minutes (slow phase) . Effective half life of ²⁰¹Tl in the whole body measured by linear scan was 2.22±0.46 days, and whole body radiation dose was thought to be about 160 mrads/mCi.
²⁰¹Tl myocardial scan taken from 5 minutes after injection delineated MI as a cleararea of decreased activity. Kidney showed highest activity, and NM showed same as and/or slightly greater than liver and spleen activity. Mediastinal activity always showed lowest activity, resulting good contrast myocardial scan. From these results, time to begin myocardial scan could be as early as 5 minutes after injection.