Feasibility of quantifying intramyocardial blood volume using SPECT/CT

Objectives SPECT/CT quantification of intramyocardial blood volume (IMBV) using Tc99m labeled red blood cell (RBC) can provide invaluable information on myocardial microcirculatory function and microvascular disease. However, the RBC tracer concentration within the blood pool is much higher than the adjacent myocardium, causing substantial “spill-in” activity due to partial volume effect (PVE), scatter, and respiratory/cardiac motion, resulting in substantial overestimation of IMBV. We developed methods to correct for PVE, scatter, and motion, and evaluated the IMBV responses to various vasodilators using simulation and large animal studies.

Methods Respiratory motion was corrected by extracting listmode data from the end-expiration phases, which was further rebinned into dual gated data to correct for cardiac motion. CT angiography was used to define the myocardium to facilitate region-based voxel-wise partial volume correction (PVC). To suppress the noise amplification introduced by PVC while preserving quantification, an anatomical-based non-local means filter (ANLM) was applied. Triple energy window (TEW) method was used to correct for scatter. We studied the IMBV changes as a response to various vasodilators in a dog study to investigate the IMBV sensitivity to the change of microcirculation function. All data were acquired using a dedicated cardiac SPECT/CT system (GE Discovery NM/CT 570c).

Results Corrections of PVC, respiratory and cardiac motion, and scatter effectively reduced the activity contamination from blood pool to myocardium. In simulation study, PVC with ANML filter reduced image noise while preserving accurate quantification of both blood pool and myocardium. In animal study, the IMBV increased by 22.5%, 9.7%, and 15.4% with adenosine, nitroglycerin, and dobutamine, respectively.

Conclusions With quantitative correction methods, it is feasible to accurately quantify IMBV using Tc99m-RBC SPECT/CT. The SPECT-derived IMBV is sensitive to the intervention of microcirculation function.