Viable myocardium identified by reinjection thallium-201 imaging: comparison with regional wall motion and metabolic activity on FDG-PET.

Reinjection thallium-201 scans were performed in 68 patients with coronary artery disease after the routine stress-delayed scans for more accurate identification of new fill-in. Following the stress and 3 hour delayed thallium-201 SPECT scans, 40 MBq (1.1 mCi) was injected at rest, and 10 min later, the reinjection SPECT scan was obtained. To determine whether the reinjection method can aid in identifying ischemic but viable myocardium, the thallium-201 findings were compared with regional wall motion on radionuclide ventriculography in 61 patients and with metabolic activity on positron emission tomography (PET) using F-18 fluorodeoxyglucose (FDG) in 18 patients. The reinjection scan identified new fill-in which had not been shown on the stress-delayed scans in 6 of the 22 patients (27%) or in 29 of the 105 segments (28%). Regional wall motion was preserved more in the segments that exhibited new fill-in after reinjection (wall motion score = 1.64 +/- 1.29) than in those without new fill-in (score = 2.72 +/- 1.04) (p < 0.01). In the comparative study with FDG-PET, persistent FDG uptake was observed in all segments with new fill-in (20/20 segments: 100%); whereas, it was seen in only 7 of the 28 segments (25%) without new fill-in after reinjection (p < 0.05). We concluded that the segments having new fill-in after reinjection may represent ischemic but viable myocardium. Thus, the reinjection thallium-201 scan should be performed to identify ischemic myocardium which occasionally cannot be detected by the routine stress-delayed thallium-201 scans.