Quantifying absolute MBF in dynamic SPECT
It is accepted within the cardiology community that measurements pertaining to absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) provide additional information about a patient’s heart condition than general perfusion. Researchers are still perfecting a standard procedure for obtaining these measurements, but they seem to be getting close in the case of dynamic SPECT, according to a study published Sept. 4 in the Journal of Nuclear Medicine.
R. Glenn Wells, PhD, from the department of cardiology at the University of Ottawa, and colleagues conducted this preclinical study of the measurement of absolute MBF in dynamic SPECT. The researchers calculated MBF using a multipinhole-dedicated cardiac SPECT camera in a large animal model at rest and at stress using Tl-201, Tc-99m tetrofosmin and Tc-99m sestamibi, all readily available tracers, to evaluate the feasibility of their quantitative protocol.
“Recent development of dedicated cardiac SPECT cameras with better sensitivity and temporal resolution make dynamic SPECT imaging more practical,” wrote the authors.
A total of 19 models were included in this prospective study. Dose for Tc-99m tracers was 370/1,100 MBq with a one-hour delay between rest and stress induced with dipyridamole. For Tl-201 the dose was 37/110 MBq. Models were injected with microspheres and imaged with dynamic SPECT for 11 minutes. The researchers subtracted remaining resting activity from stress data and reconstructed images with energy window-based scatter correction and CT attenuation correction. A kinetic analysis was performed using specialized software and a 1-tissue-compartment model to call out an uptake-rate constant as a function of microsphere MBF.
Results of the study showed accurate values compared to previous studies and strong correlations to microsphere MBF (0.75–0.90). The correlation with MFR had a slightly larger range of correlation (0.57 and 0.94). Absolute MBF with stationary dedicated cardiac SPECT was attainable with available perfusion imaging agents.
“The approach used is readily translated to human studies and could provide incremental diagnostic and prognostic information over relative perfusion alone but will require further validation before it can be clinically implemented,” the researchers concluded.