New hardware, new software, different results: The estimation of left ventricular volumes and ejection fractions with ga
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Department of Diagnostic Radiology & Nuclear Medicine, University of Maryland School of Medicine, Baltimore, MD
Received Nov 2, 2018; accepted Nov 2, 2018 doi:10.1007/s12350-018-01523-9
See related article, https://doi.org/10.10 07/s12350-018-1457-7. It is important to evaluate results from new cardiac imaging technologies in a clinical setting and, when needed, to compare them with those from existing methods. In this issue of the Journal of Nuclear Cardiology, Leva et al.1 compare the left ventricular ejection fraction (LVEF), end-diastolic volume (EDV) and endsystolic volume (ESV) derived from a novel myocardial perfusion imaging strategy (IQ-SPECT) with results from a conventional myocardial perfusion imaging strategy employing a low-energy, high-resolution (LEHR) parallel hole collimator and filtered backprojection (FBP) image reconstruction. This novel approach, termed IQ-SPECT by the vendor (Siemens Healthineers, Erlangen, Germany),2 has three major hardware and software components. A variable focus collimator3 (trade name Smartzoom) has holes that are angled to increase sensitivity in the cardiac region. The orbit of the gamma camera is adjusted to keep the heart in the high-sensitivity part of the field of view of the collimator. Iterative image reconstruction with resolution recovery, i.e., depth-dependent collimator response modeling, is then performed4 (trade name Flash3D). For both IQ-SPECT and conventional acquisition and image reconstruction the Quantitative Gated SPECT (QGS; Cedars-Sinai) software package5 was used to process the reconstructed gated cardiac perfusion images. The LV Reprint requests: Mark F. Smith, PhD, Department of Diagnostic Radiology [email protected] J Nucl Cardiol 1071-3581/$34.00 Copyright Ó 2018 American Society of Nuclear Cardiology.
chamber volumes were determined throughout the cardiac cycle, and the LVEF was computed from the EDV and ESV. The paper analyzed results from stress myocardial perfusion imaging (MPI) studies performed with Tc99m tetrofosmin. Patients were imaged with long-duration IQ-SPECT acquisition (Method A), short-duration IQ-SPECT acquisition (Method B) and standard clinical acquisition with a parallel hole collimator (Method C). The principal findings were that LVEF values with IQSPECT are biased upward by 3 to 4% with respect to parallel hole collimator acquisition and that the 95% limits of agreement ranged between - 11 and ? 17%. The latter finding is of greater consequence in the clinical environment. A COMPARISON OF THE METHODS: FACTORS THAT MAY EXPLAIN THE DIFFERENT RESULTS When the results of two methods for estimating the same quantities are compared, but there are multiple differences in methodology, it can be very difficult to determine the relative influence of the individual factors contributing to the differences in the results. With a look toward the acquisition and image reconstruction parameters in Table 2 in1, one can make an effort to try to understand the possible influence of various factors on EDV, ESV and LVEF. The authors have dis
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