Impact of zooming and filtering on gated myocardial perfusion SPECT in patients with small hearts

摘要

Objectives: Underestimation of end-diastolic volume (EDV), end-systolic volume(ESV) and overestimation of left ventricular ejection fraction(LVEF) in patients with small hearts is a reported problem of the gated SPECT. The aim of this study was to evaluate the influence of zooming and filtering on left ventricular function parameters measurements in patients with small hearts. Methods: Thirty patients with small hearts (ESV≤25 ml using acquisition zoom of 1.45 and cut-off frequency 0.35 cycle/cm) were collected for the study. All patients underwent rest Tc-99m Sestamibi gated myocardial perfusion SPECT using acquisition zooms of 1.45 and 1.78 consecutively. After reconstruction by filtered back-projection(Butterworth, 0.35, 0.40, 0.45, 0.50 and 0.55 cycles/cm cut-off, order 5), LVEF, EDV and ESV were computed using quantitative gated SPECT (QGS) program. Results: Good correlation was noticed between two methods of acquisition. EDV and ESV using acquisition zoom of 1.78 were significantly higher than EDV and ESV by zoom of 1.45 respectively. However, LVEF using zoom of 1.45 was overestimated compared with LVEF by zoom of 1.78. By increasing the cut-off frequency of the Butterworth filter from a smooth 0.35 to a sharper 0.55cycles/cm, larger volumes and a significant decrease in LVEF were obtained by QGS. Mean difference of LVEF between two methods of acquisition (zooms of 1.78 and 1.45) were significantly different between different filtering (P<0.001). As the cut-off frequency of the filter was increased, change in the LV volumes and LVEF is decreased. Difference in LVEF between two acquisition zooms was decreased by sharper cut-off frequencies. Thus effect of zooming on measurement of LVEF in higher cut-off frequencies is decreased. On the other hand, effect of cut-off frequency in LVEF value is decreased in higher zoom as compared to the lower zoom. Conclusion: Filtering and zooming greatly influenced EDV, ESV and LVEF measurements. Increasing in zooming or filter cut-off frequency results higher LV volumes but lower LVEF. A higher zooming and/or a sharper filter might be suggested for quantitative gated SPECT in patients with a small heart.