Abstract

Radiation dose to patients from imaging modalities is measured or calculated to assess the risk of the procedure and compare it with the benefits. Periodic review of image acquisition methods and the radiation dose used are an essential part of optimization in medical imaging. The aim of this study was to estimate patient radiation dose from SPECT myocardial perfusion imaging (MPI) using CT images for attenuation correction. 

Methods: SPECT and CT image acquisition parameters such as administered activity (AA), CT dose index (CTDIvol), and dose-length product for 415 patients who had undergone SPECT MPI using CT attenuation correction were reviewed. Effective dose (ED) for the SPECT part, the CT part and the total ED for the procedure were calculated. AA, CTDIvol, and ED values were compared between the 2 sexes and between body mass indexes (BMIs), imaging scanner models, and imaging centers. Statistical analyses were performed using t tests and 1-way ANOVA at P < 0.05 level of significance. 

Results: The range of AAs used for MPI was found to be 1,206-1,964 MBq per patient regardless of sex. The resulting mean ED of 8.8 mSv for men was significantly lower (P = 0.002) than the 10.4 mSv for women for SPECT. The range of CTDIvol was 1.12-3.97 mGy, resulting in an mean ED of 0.8 mSv for men, significantly lower (P < 0.001) than the 1.1 mSv for women for CT. The average combined EDs for male and female patients were 9.6 and 11.5 mSv, respectively. A positive correlation was found between AA and patient BMI (r = 0.48; P < 0.001), indicating patient size-related AAs. However, CTDIvol was found to depend only on the scanner model, regardless of BMI. 

Conclusion: The ED from SPECT/CT MPI studies was around 11 mSv, with 10 mSv being from the SPECT part of the study. The extra risk to the patients from CT imaging for attenuation correction is small compared with the benefit incurred from accurate diagnosis.

Keywords: CT dose index; SPECT/CT; administered activity; effective dose; myocardial perfusion imaging.