Myovation

Under deep isoflurane-inhalation anesthesia, each intact heart was rapidly removed from the chest and flushed with warmed isotonic saline. Once the heart was rinsed, it was weighed and instantaneously placed in 60cc of 10% buffered formalin (Sigma-Aldrich Corp., St. Louis, MO, USA) to induce tissue fixation at a contraction state. All hearts of this study were approximately in the same state of contraction as confirmed by measurements of the mean ventricular wall thickness (Omann et al., 2019 (link)). The whole-body weight before excision was also recorded. The period between harvest and imaging was approximately 1 week, following the advice on cardiac specimen preparation by Giannakidis et al. (2016a (link)). Before euthanasia, and as part of a separate study (Hernandez et al., 2013 (link)), the living rats were imaged using a small animal PET/CT scanner (Inveon dedicated PET docked with CT in the multi-modality platform; Siemens Medical Solutions) and the ¹⁸F-FDHROL radiotracer to evaluate the left-ventricular ejection fraction (EF). EF was measured using the clinical cardiac software Myovation designed for the Xeleris workstation (GE Healthcare).

From ¹⁵O-water, LV volumes and LVEF were calculated from V_B and FP images using blood-pool gated SPECT (BPGS), a program based on Myovation (GE Healthcare) and QBS (Cedars Sinai). Gated transaxial V_B and FP images were imported into the application on a Xeleris workstation for automatic segmentation and quantification. QBS provides three different methods for calculation of LV volumes and LVEF: surface- (s), count- (c) and volume-based (v) methods. The results from all three methods were used for comparison.
From MRI, LV volumes and LVEF were calculated using ViewForum (Philips). The endocardial contour was manually traced in end-diastole and in end-systole. The most basal slices had to show at least 50% visible myocardial circumference to be included. The LV outflow tract was included in the endocardial contour using the aortic valve as the lateral border. The papillary muscles and trabeculae were included in the blood volume. Stroke volume (SV) was calculated as EDV-ESV and LVEF as SV/EDV expressed as a percentage. All ¹⁵O-water-based LV volumes and LVEF calculations were performed by a medical physicist (JN), and for assessment of inter-operator repeatability, calculations were also performed by an experienced nuclear medicine physician (TK).

The noncorrected and motion-corrected images were reconstructed by applying an iterative dedicated reconstruction algorithm with maximum-likelihood expectation maximization (Myovation, Xeleris 3.1, GE Healthcare). The use of dedicated software (Make SA and Fil3DBatch, Xeleris 3.1, GE healthcare) allowed to reconstruct both the noncorrected and motion-corrected images using the exact same alignment and masking, excluding possible reproducibility errors.16 (link)
Each image was automatically normalized to the maximum peak activity and the 17-segmental uptake values were presented as the percentage of the maximum myocardial regional uptake. Total perfusion deficit (TPD) was automatically calculated for all scans (Quantitative Perfusion SPECT (QPS) 2009, Sedar Senai). TPD is defined as the percentage of segments below the predefined uniform average deviation threshold, as explained in detail by Berman et al.20 (link) Scans were displayed in the traditional short, vertical long, and horizontal long axes and reviewed using a color scale.