Development and validation of a patient-tailored dose regime in myocardial perfusion imaging using conventional SPECT

BACKGROUND: The decreasing image quality in heavier patients can be compensated by administration of a patient-specific dose in myocardial perfusion imaging (MPI) using a cadmium zinc telluride-based SPECT camera. Our aim was to determine if the same can be achieved when using a conventional SPECT camera. METHODS: 148 patients underwent SPECT stress MPI using a fixed Tc-99m tetrofosmin tracer dose. Measured photon counts were normalized to administered tracer dose and scan time and were correlated with body weight, body mass index, and mass per length to find the best predicting parameter. From these data, a protocol to provide constant image quality was derived, and subsequently validated in 125 new patients. RESULTS: Body weight was found to be the best predicting parameter for image quality and was used to derive a new dose formula; A(admin) (MBq) = 223·body weight (kg)(0.65)/T(scan) (min). The measured photon counts decreased in heavier patients when using a fixed dose (P < .01) but this was no longer observed after applying a body-weight-dependent protocol (P = .20). CONCLUSIONS: Application of a patient-specific protocol resulted in an image quality less depending on patient’s weight. The results are most likely independent of the type of SPECT camera used, and, hence, adoption of patient-specific dose and scan time protocols is recommended.