Impact of Wiener filter in determining the left ventricular volume and ejection fraction using thallium-201 gated...

Patient morphology, as well as the acquisition and reconstruction parameters, may influence the evaluation of the left ventricular volume (LVV) and left ventricular ejection fraction (LVEF) using gated single-photon emission computed tomography (SPECT). The purpose of this study was to examine the influence of gender and reconstruction filter on the measurement of LVV and LVEF using 201Tl gated SPECT. Using a static torso phantom, a female shape was created by the addition of two saline solution-filled balloons fixed on the anterior rib cage. The following parameters were similar for all acquisitions: 90 degrees dual-head gamma camera; 32 projections; 64x64 matrix (pixel size=6.77x6.77 mm); two 20% energy windows centred at 70 and 167 keV. The following acquisition times were tested: 1.25, 10, 20, 30 and 40 s per projection, leading to a total of 10 successive acquisitions. The effect of over-sampling was tested by 2.5 post-acquisition zooming. All SPECT images were successively reconstructed using filtered back-projection with Butterworth and Wiener filters. The effect of gender and reconstruction filter was also studied in 30 patients (15 males and 15 females) with a low likelihood of coronary artery disease. LVVs were calculated using QGS software. By multivariate analysis, the following factors influenced the accuracy of phantom measurement using QGS software: zooming (F=49, P<0.0001), phantom shape (F=61, P<0.0001) and filter type (F=240, P<0.0001). LVV was underestimated in the female shape phantom, even when using the Wiener filter. In patients, LVV and LVEF measurements were independently influenced by gender (P<0.0001) and filter (P<0.0001), but not by zooming. In conclusion, it was demonstrated that LVV was significantly decreased in the female shape phantom, suggesting a significant impact of breast interposition. This underestimation was minimized by use of the Wiener filter. In patients, the impact of the Wiener filter on the assessment of LVVs and LVEF was powerful, but independent of gender, and failed to correct the underestimation of LVVs and the overestimation of LVEF in females.