Beware the pitfalls of beauty: High-quality myocardial images with resolution recovery

Effects of Acquisition Matrix Size on the Accuracy and Repeatability of Parameters of Left Ventricular Function

Background: The voxel size in ECG-gated myocardial SPECT (GSPECT) is a compromise between geometric resolution and count statistics with varying values and is rather inconsistent in different centers. We investigated the influence of typical acquisition matrix sizes for GSPECT on the reproducibility and accuracy of left ventricular function parameters using a dynamic heart phantom. Methods: Ten paired acquisitions, each pair with slightly different phantom positions, were obtained using identical imaging parameters except acquisition matrix: 128 × 128 matrix (3.3 mm voxel) and 64 × 64 matrix (6.6 mm voxel). In the next step, 128 × 128 data sets were compressed to an additional set of 64 × 64 matrix images. Results: Nominal value of left ventricular ejection fraction (LVEF) of the phantom was 67%. Both acquisition matrices led to significant overestimation of the LVEF. Overestimation was more pronounced in 64 × 64 than in 128 × 128 studies (79.8 ± 2.5% vs. 73.6 ± 1.4%, p<0.05). Calculated volumes were closer to the nominal values with 128 × 128 than with 64 × 64 studies. Variance showed a trend to be higher with 64 × 64 matrix, but the effect did not reach the level of statistical significance. Conclusions: LVEF overestimation and volume underestimation can be reduced by using finer matrix size without any negative effect on the reproducibility.