Abstract
The IQ-SPECT system equipped with a multifocal (SMARTZOOM) collimator using an ordered subset conjugate gradient minimization (OSCGM) algorithm reduces the acquisition time of myocardial perfusion imaging (MPI) compared to conventional gamma cameras equipped with low-energy high-resolution (LEHR) collimators. We compared IQ-SPECT with a conventional single-photon emission computed tomography (SPECT) system for estimating the left ventricular ejection fraction (LVEF) in small-heart patients. Methods: The study group consisted of 98 consecutive patients who underwent a 1-day stress-rest MPI study with a 99mTc-labeled agent for preoperative risk assessment. Data were reconstructed using a filtered back projection (FBP) method for conventional SPECT, and an OSCGM algorithm for IQ-SPECT. End-systolic volume (ESV), end-diastolic volume (EDV), and LVEF were evaluated using quantitative software for gated perfusion SPECT (QGS) and cardioREPO (cREPO). We compared the LVEF of gated myocardial perfusion SPECT to echocardiographic measurements (Echo). Results: The EDV, ESV, and LVEF calculated by conventional SPECT, IQ-SPECT, and Echo showed good to excellent correlation using both QGS and cREPO. While LVEF calculated using QGS significantly differed between conventional SPECT (65.4 ± 13.8%) and IQ-SPECT (68.4 ± 15.2%; P = 0.0002), no significant difference was observed between IQ-SPECT (69.5 ± 11.0%) and conventional SPECT (69.5 ± 10.6%) for LVEF calculated using cREPO. In small-heart patients (ESV < 20 mL), a significant difference was observed between the LVEF calculated using the QGS of conventional SPECT (75.0 ± 9.6) and IQ-SPECT (79.5 ± 8.3) (P = 0.0005). No significant difference was observed between the LVEF calculated using the cREPO of conventional SPECT (72.3 ± 9.0%) and IQ-SPECT (74.3 ± 8.3%). Conclusion: The difference in calculated LVEF between IQ-SPECT and conventional SPECT was less with cREPO than with QGS in small-heart patients.