Objective: Cardiac single-photon emission computed tomography (SPECT) imaging using Cadmium-zinc-telluride (CZT) camera has the potential to become shorter scan time and reduce patient's radiation exposure. We prospectively compared the myocardial counts and image quality at low dose protocol with those at standard dose protocol. Methods: The study group comprised 100 consecutive patients who underwent 1-day stress/rest 99mTc tetrofosmin SPECT. Standard dose (296/740MBq) protocol was performed in 50 patients with a 5-min scan time for stress, a 3-min for at rest. And low dose (185/370MBq) protocol was performed in 50 patients with a 10-min for stress, a 6-min for at rest. Myocardial image quality score was graded on a 4-point scale (1=poor, 2=adequate, 3=good, 4=excellent) and myocardial counts was assessed in both of protocol. Results: Myocardial image quality score with low dose scans were similar to those with standard dose (3.8 ± 0.4 vs 3.9 ± 0.3; for stress, 3.8 ± 0.4 vs 3.9 ± 0.3; for rest, respectively). Myocardial counts were similar between low dose scan and standard dose scan in both of stress (11,312,451.3 ± 2,045,607.6 vs 11,928,572.7 ± 2,635,742.7) and rest (16,490,955.6 ± 2,164,093.1 vs 16,382,476.3 ± 3,808,452.0). Conclusion: These results suggested that low dose scan with longer scan time obtain higher myocardial counts and enable to reduce patient's radiation exposure without loss of image quality.

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