Minimizing patient-specific tracer dose in myocardial perfusion imaging using CZT SPECT

Abstract

Myocardial perfusion imaging (MPI) with SPECT is widely adopted in clinical practice but is associated with a relatively high radiation dose. The aim of this study was to determine the minimum product of tracer dose and scan time that will maintain diagnostic value for cadmium zinc telluride (CZT) SPECT MPI. Methods: Twenty-four patients underwent clinically indicated stress MPI using CZT SPECT and a body weight-dependent (3 MBq/kg) 99m Tc-tetrofosmin tracer dose. Data were acquired for 8 min in list mode. Next, images were reconstructed using 2-, 4-, 6-, and 8-min time frames. Differences between the 8-min reference scan and the shorter scans were determined in segmental uptake values (using the 17-segment cardiac model), ejection fraction, and end-diastolic volume. A 5% difference in segmental uptake was considered to significantly influence the diagnostic value. Next, the quality of the 4-, 6-, and 8-min scans was scored on a 4-point scale by consensus by 3 experienced nuclear medicine physicians. The physicians did not know the scan time or patient information. Results: Differences in segmental uptake values, ejection fraction, and end-diastolic volume were greater for shorter scans than for the 8-min reference scan. On average, the diagnostic value was influenced in 7.7 segments per patient using the 2-min scans, in comparison to 2.0 and 0.8 segments per patient using the 4-and 6-min scans, respectively. In addition, the 4-min scans led to a significantly reduced image quality compared with the 8-min scans (P < 0.05). This was not the case for the 6-min scan. Conclusion: Six minutes was the shortest acquisition time in stress MPI using CZT SPECT that did not affect the diagnostic value for a tracer dose of 3 MBq/kg. Hence, the patient-specific product of tracer dose and scan time can be reduced to a minimum of 18 MBq min/kg, which may lower the effective radiation dose for patients to values below 1 mSv.