Towards personalized injected patient doses for cardiac perfusion SPECT imaging: A retrospective study

Reduction of the injected radionuclide dose in myocardial perfusion imaging (MPI) has become a major effort among clinicians and researchers alike. The aim of this study was to retrospectively determine the relationship between injected radioactivity and total projection counts in the heart region of clinically acquired Tc-99m sestamibi patients in an effort to formulate a strategy to better calculate individual and personalized doses prior to injection using easily measured metrics From a pool of 601 patients (304 female) 101 patients that undergone exercise stress testing and were read as having a normal perfusion distribution or small perfusion defects were included for the initial investigation. For all patients, injected activity at the time of the stress myocardial perfusion imaging (MPI) were determined. All patient BMI's were calculated and circumference measurements of the chest, abdomen and hips obtained. For all patients, list mode acquisitions were available and attenuation maps were derived from cone-beam CT acquisitions (BrightView SPECT/CT scintillation camera, Philips, Cleveland, OH). Total projection counts in the heart region were determined using a fixed region-of-interest (ROI) and counts per injected activity plotted against either BMI or chest circumference. Correlations were calculated. Using this information, 25 patients' list mode data were resampled randomly to create acquisition with only a fraction of the counts in the original study such that the heart region counts in all of the patients were equal to ~750K. Correlations with BMI were again determined using the reduced radioactive dose. The proposed method reduced the radioactive dose by between 29% and 66% while maintaining image fidelity. Therefore, we established an initial strategy to calculate an individual and personalized injected dose for every patient prior to showing up at the MPI clinic using the correlation between BMI and count level in the heart region.