Wide beam reconstruction “quarter-time” gated myocardial perfusion SPECT functional imaging: a comparison to “full-time” ordered subset expectation maximum

Previously we reported that compared to iterative reconstruction with ordered subset expectation maximum (OSEM), wide beam reconstruction (WBR), which incorporates resolution recovery and controls noise during reconstruction without applying a post-processing filter, allows half-time SPECT acquisition with preserved diagnostic quality. We now postulate that with further Poisson noise treatment, quarter-time acquisition is possible.

The half-time WBR algorithm was optimized for quarter-time acquisition based upon anthropomorphic cardiac phantom data and a pilot group of 48 patients (pts). Then using the modified algorithm, 209 pts (91 men, 118 women, mean chest circumference = 40 in) were imaged at rest (R) and stress (S) (9/32 mCi ^99mTc-sestamibi) full-time with OSEM, and again quarter-time with the modified WBR algorithm. The 180°, 64-stop, full-time single-day rest (R) (25 second-per-stop, sps) and 8-frame per cardiac cycle post-stress (S) (20 sps) gated SPECT, and then quarter-time R (6 sps) and post-S (4 sps) gated SPECT were acquired. Blinded observers graded scan quality (1 = poor to 5 = excellent) based on myocardial uniformity, endocardial/epicardial edge definition, and background noise. Perfusion defects were scored using a 17-segment model. Using three commercially available software methods, end-diastolic volume (EDV), end-systolic volume (ESV), and left ventricular ejection fraction (LVEF) were calculated.

For the 209 prospective pts, mean image quality for R full-time OSEM and quarter-time WBR were similar (3.5 ± 0.9 vs 3.6 ± 0.7, p NS). For S, quarter-time WBR quality was superior to full-time OSEM (4.3 ± 0.7 vs 3.9 ± 0.7) (P = 1.78 × 10⁻¹⁷). In 35 pts with chest circumferences >44 inches a longer, 10 sps WBR acquisition improved resting image quality. Of 48 pts with abnormal scans (SSSs > 2 by OSEM) mean summed stress scores, summed rest scores, and summed difference scores were not significantly different with quarter-time WBR vs full-time OSEM (11.2 vs 10.9), (9.1 vs 9.0), (2.0 vs 1.9) (P NS). For the three software methods, there was a good correlation of LVEF, EDV, and ESV determined by WBR vs OSEM (all r > 0.92). ESVs were generally higher with WBR, primarily due to better delineation of the valve plane at end-systole, whereas EDVs were similar. Thus, EFs were significantly lower with WBR.

For perfusion SPECT quarter-time WBR affords image quality, defect characterization, and functional assessment equivalent to full-time OSEM.