Ordered subset expectation maximization and wide beam reconstruction “half-time” gated myocardial perfusion SPECT functional imaging: A comparison to “full-time” filtered backprojection
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Objectives: Compared to filtered back projection (FBP), OSEM with resolution recovery (OSEM-RR) and wide beam reconstruction (WBR)(UltraSPECT Ltd.), which resolve resolution and suppress noise simultaneously during reconstruction, have been shown to maintain/improve myocardial perfusion SPECT quality, even with low count density half-time acquisitions. We postulated that their characteristics would be advantageous for gated SPECT, where each frame is only 1/8th the count density of the summed perfusion images.
Methods: An 9 mCi rest/32 mCi (333/1184 MBq) stress Tc99m sestamibi protocol was used. 15-min FBP, and additional 7-min OSEM-RR and WBR post-stress 8-frame/cardiac cycle SPECT scans were acquired with 90°-angled dual-headed detectors equipped with high resolution collimators in 156 patients. In 82 patients (48F, 34M) (123–252 lbs) with perfusion defects gated image quality was graded visually: 1 (poor)-5 (excellent) Regional LV wall motion (WM) was scored: 0 (normal)- 4 (dyskinesis) in a total of 50 vascular territories with defects. Using Myometrix® software (GE Healthcare), post-stress EDV, ESV, and EF were calculated for each method. Additionally, for purposes of comparison, the FBP gated tomograms were processed with other commercially available packages, Emory Toolbox® and Cedars QGS®.
Results: Despite half-time acquisitions, compared to FBP, image quality increased marginally with OSEM-RR (P=.09) but very significantly with WBR (P=1.9×10−21). The WM score was greater only for WBR (P=4.8×10−8). Although quantitative parameters correlated well with those determined by FBP (all EF r’s>0.85; all volume r’s>0.93), EFs were significantly lower (P=.0001 for OSEM-RR, 3.4×10−14 for WBR), primarily due to a decrease in EDV with OSEM-RR (P=7.3×10−13) and an increase in ESV with WBR (P=9.2×10−5). However, inter-method differences in these parameters were of similar magnitude to differences encountered among the commercially available software methods.
Conclusions: Half-time OSEM-RR and particularly WBR improve gated SPECT diagnostic quality compared to full-time FBP due to increased resolution and reduced noise. However, these attributes, which affect endocardial edge detection, result in a systematic offset in EDV, ESV, and EF.
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