How much shorter is better? Investigating image acquisition time reduction on left ventricular phase analysis for cardiac dyssynchrony

Abstract

Myocardial perfusion imaging is a widespread technique with proven added value for CAD diagnosis, prognostication, and therapeutic monitoring. In the last decade, there have been many improvements in gammacamera hardware, software reconstructions algorithms including resolution recovery methods, and cardiac evaluation software. This has led to shortening of the acquisition time as compared to previous guidelines, going from 30 seconds down to 15 seconds per projection (the so-called ‘‘half-time’’ acquisition). Gating the acquisition with ECG has the ability to measure cardiac wall motion and thickening and left ventricular systolic and diastolic volumes, as well as ejection fraction (EF). The shortening of the acquisition time brings advantages in terms of images degradation due to patient movement, upwards heart creep in poststress period, patients throughput, as well as in patients comfort at the expense of perfusion defects detectability due to increase in image noise. A developing application of gated-SPECT MPI has been the investigation of left ventricular dyssynchrony using the phase analysis technique. This method delivers unique information about the intrinsic contractile ventricular properties, which can help deciding on which to refer patients to resynchronization therapy, as well as adding prognostication. There has not been any investigation published on examining the effect of SPECT acquisition time reduction on phase analysis. This is exactly the aim of the work by Kortelainen and co-authors published in this issue. The authors investigated the relation of left ventricular functional parameters and phase histogram to acquisition time reduction in a population of 24 patients referred for stress/rest gated-SPECT MPI. Among these patients, 20 (83%) had at least some slight perfusion abnormalities at rest and 9 (37.5%) patients had previous cardiac infarct or heart failure. Methodologically, the authors used listmode acquisitions and recording of the ECG to mimic shorter acquisition times (80%, 60%, 50%, 40%, 30%, 20%) than the initial 30 seconds per projection (100%). In a nutshell, the authors found that reducing acquisition time from 30 seconds down to 15 seconds had no clinically significant effect in left ventricular EF (Figure 1), wall motion, or wall thickening. When decreasing acquisition time further, statistically lower values were noted in end diastolic volume (EDV) and stroke volume (SV). Interestingly, end systolic volume (ESV) and EF were not affected (Figure 1). In contrary, contrast-to-noise ratio (CNR) already presented significant differences when acquisition time was reduced down to 60% (18 seconds per projection), with differences at half-time acquisition reaching -15% and -11% for systolic and diastolic CNR, respectively. Moreover, it was the same with phase analysis, where already statistically significant differences were encountered when the acquisition duration was only decreased to 80% (phase histogram bandwidth, BW), or 60% (phase histogram standard deviation, StDev and entropy, ENT), with already large errors at half-time acquisition See related article, pp. 643–651