Dose reduction in half-time myocardial perfusion SPECT-CT with multifocal collimation

Background. Recent technological advances in myocardial perfusion imaging may warrant the use of lower injected activity. We evaluated whether quantitative measures of stress myocardial perfusion defects using Tc-99m sestamibi and low-energy high-resolution (LEHR) collimators are equivalent to lower dose SPECT-CT with cardiac multifocal collimators and software (IQ.SPECT). Methods. 93 patients underwent one-day rest-stress gated SPECT-CT. Following conventional rest imaging, 925-1100 MBq (25-30 mCi) of Tc-99m sestamibi was injected during stress testing. Stress SPECT-CT images were acquired two ways: with LEHR (13 minutes) and IQ +/- SPECT (7 minutes). Low-dose IQ +/- SPECT stress was simulated by subsampling the full-dose data to half-, quarter-, and eighth-count levels. Abnormalities were quantified using the total perfusion deficit (TPD) score and dose-specific databases. Results. The mean +/- SD of the differences between LEHR and IQ SPECT TPD scores were -1.01 +/- 5.36%, -0.10 +/- 5.81%, 1.78 +/- 4.81%, and 1.75 +/- 6.05% at full, half, quarter, and eighth doses, respectively. Differences were statistically significant for quarter and eighth doses. Correlation between LEHR and IQSPECT was excellent at all doses (R = 0.93). Bland-Altman plots demonstrated minimal bias. Conclusions. With IQ.SPECT, quantitative stress SPECT-CT imaging is possible with half of the standard injected activity in half the time.