Comparison of Filled-in Myocardial Segments After Early and Late Reinjection of Thallium-201

Influence of the Timing of Reinjection on Fill-in

Abstract

Thallium-201 (²⁰¹Tl) late reinjection after stress-redistribution imaging improves the detection of viable myocardium. Recently, early reinjection of ²⁰¹Tl immediately after stress imaging was proposed as a new method for distinguishing ischemic myocardium, hibernating myocardium, and myocardial scar. However, there are no data on the influence of the timing of reinjection on "fill-in." This study was designed to assess whether the reinjection time influences "fill-in" in chronic coronary artery disease. Thirty-three patients with chronic coronary artery disease were studied. All patients underwent exercise ²⁰¹Tl tomography. Immediately after stress imaging, 37 MBq of thallium was reinjected earlier than usual and early reinjection delayed image (ERDI) was acquired 3 h later. With the same protocol, all patients also underwent a second study involving late reinjection of ²⁰¹Tl within 1 week. An additional 37 MBq of thallium was reinjected 3 h after stress imaging, and late reinjection delayed image (LRDI) was obtained 10 min later. All images were analyzed qualitatively using a 4-point grading uptake score. Of the 72 hypoperfused segments on stress images, 66 segments showed fill-in and 6 showed persistent defects on ERDI, and of the same 72 segments 55 segments displayed fill-in and the remaining 17 showed persistent defects on LRDI (p<0.05). The delta uptake score (the uptake score of the delayed image minus that of stress image) in early reinjection was 1.60±0.80, which was significantly higher than that in late reinjection (1.24 ±0.94, p<0.01). A small dose of thallium reinjected immediately after stress imaging with delayed images obtained 3 h later is convenient and might provide another technique for determining myocardial viability. (Jpn Circ J 1998; 62: 178 - 182)