Abstract
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Objectives: To determine the feasibility of evaluating murine left ventricular function with ultrahigh spatial and temporal resolution 99mTc RBC ECG gated blood pool (GBP) SPECT.
Methods: Normal C57BL/6 control mice (NL; n=6) and C57BL/6 mice with myocardial infarction induced through left anterior coronary artery ligation (n=6) were studied with GBP SPECT imaging and M-mode echocardiography. After 8 weeks of recovery, echocardiography was performed and left ventricular fractional shortening (FS) used to categorize mice into mild (MI-Mild; FS> 45%; n=3) or severe dysfunction (MI-Severe; FS<45%; n=3). In vivo RBC radiolabeling was performed with 12mCi of 99mTc pertechnetate. SPECT acquisition parameters included: 3-detector gamma camera with 1.0 mm tungsten pinhole collimators, 2 degrees/projection over 360 degree circular rotation, 45-60 heartbeats/projection with 8 time-bin frames/ECG cycle. Iterative reconstruction (4 subsets, 5 iterations) resulted in voxel size of 0.125 μl/voxel. SPECT LV end-systolic and end-diastolic volumes were defined by phase analysis and a semi-automated threshold method. Higher temporal resolution of 16 time frames/ECG cycle was obtained using similar acquisition times and processing parameters except for list-mode data acquisition (n=3).
Results: GBP SPECT demonstrated high contrast images of ventricular blood pool and high spatial resolution with clear delineation of ventricular boundaries. The mean LV blood pool: lung background ratio was > 10:1 with a mean of 18.1+6.8 (range=10.3-29.4; n=12) for all mice. ECG GBP SPECT of NL mice demonstrated normal wall motion and LVEF of 63.8%+8.3%. All MI-Mild mice displayed normal wall motion with no significant difference in mean LVEF (72.0%+8.8%; p=0.25) compared to NL. All MI-Severe mice showed focal apical wall motion abnormalities, and significantly lower mean LVEF (27.2%+13.1%; p=0.02) compared to NL. Apical wall motion abnormalities were seen on parametric phase imaging in all MI-severe mice. List-mode reconstruction demonstrated excellent image quality with clear visualization of cardiac blood pool and LV wall motion using 16 time frames/ECG cycle. High LV:lung background contrast was similarly > 10:1.
Conclusions: Ultrahigh spatial and temporal resolution ECG gated blood pool SPECT is feasible. This technique is a promising new modality to detect and quantify ventricular dysfunction in murine models of heart failure.
- Society of Nuclear Medicine, Inc.