To compare the left ventricular (LV) ejection fraction (EF), end-diastolic volume (EDV), and end-systolic volume (ESV) from electrocardiogram-gated computed tomography (CT) to gated single-photon emission computed tomography (SPECT). Methods Fifty-seven patients underwent electrocardiogram-gated multidetector CT and SPECT examinations within a 3-month period, without interim cardiac events. The LV EF, EDV, and ESV were compared. Results There was an excellent correlation between LV EF obtained from CT (60.25% ± 12.93%) and SPECT (61.90% ± 14.93%) (r = 0.81), with no significant difference (P = 0.17). Computed tomography-derived EDV and ESV correlated well with SPECT (r = 0.88 and 0.94, respectively). The EDV from SPECT (132.21 ± 67.10 mL) was significantly lower than that from CT (147.53 ± 55.03 mL; P = 0.0007); there was a trend for ESV from SPECT (58.39 ± 61.20 mL) to be lower than that from CT (63.79 ± 53.58 mL; P = 0.055). The EF, EDV, and ESV correlation of SPECT with the 64-row multidetector CT was better (r = 0.87, 0.89, and 0.96, respectively) than that with the 16-row CT (r = 0.36, 0.66, and 0.49, respectively). Conclusions There is a good correlation between LV EF, EDV, and ESV from gated SPECT and CT (particularly the 64-row CT). The LV volumes are lower on SPECT than on CT.
Background: Circulatory support with an implantable LVAD has been shown to normalize perfusion pressure, reduce left ventricular (LV) wall stress, and improve LV structure and myocyte function, in some cases enabling LVAD explant. Improvement in myocardial blood flow (MBF) as a consequence of improved hemodynamics may contribute to the subsequent beneficial changes observed in myocyte structure and function following long-term LVAD implant. Methods: Positron emission tomography (PET) with [13N]ammonia imaging was performed in 5 patients with cardiomyopathy (all male, median age 57, 2 ischemic, 3 idiopathic) at the time of evaluation for LVAD implant (HeartMate® LVAD; Thermo Cardiosystems, Inc) and subsequently at 4–6 weeks following implant. In three of the patients, pre and postoperative hemodynamic and exercise testing were available. Results: Following LVAD implant, there was a significant improvement in hemodynamics and peak exercise oxygen consumption (mean improvements in cardiac index 3.5 vs. 1.8 1/min/m2, pulmonary capillary wedge pressure 9 vs. 25 mm Hg, maximum exercise oxygen consumption 17 vs. 13 ml/kg/min, p<.05 for each). In 3 of 5 patients, MBF increased an average of 101%. 2 patients demonstrated no change in MBF. Conclusions: Despite restoration of normal hemodynamics with significant LV unloading, these data suggest that alterations in MBF are variable and may be related to coronary autoregulation and myocardial oxygen demand. These data have implications for potential LV recovery following long-term LVAD support.
650 Objectives: Identification of myocardial inflammation with FDG PET is increasingly used for diagnosis and management of cardiac involvement in sarcoidosis. Because consistent quantitative thresholds are lacking, interpretation of images can vary markedly from site to site. Incomplete metabolic preparation leading to incomplete suppression of physiologic uptake of FDG by cardiomyocytes is also common and difficult to recognize. The University of Michigan protocol [1] consistently suppresses myocardial uptake to levels that are equal to or below blood pool, which is not quantified by existing cardiac metabolic volume (CMV) and activity (CMA) metrics [2]. In this work, we retrospectively analyzed inflammatory FDG PET scans to establish quantitative thresholds for identifying positive studies and performed outcome-based validation.
Methods: 316 inflammatory FDG scans performed at the University of Michigan between June 2015 and June 2018 were processed and reviewed in Corridor4DM (INVIA Medical Imaging Solutions, Ann Arbor, MI, USA). 15 studies were excluded for non-diagnostic preparation (high standardized uptake values (SUV) and low coefficient of variation) confirmed via further review of images, laboratory results, and patient history. Contours were transferred from perfusion studies to inflammatory datasets and polar maps were automatically sampled from the contours. Two myocardial sampling methods were investigated: 1) sampling the max SUV of the corresponding myocardial segment (MAX), and 2) sampling SUV at the midwall of the corresponding segment (MIDWALL). Presence of abnormal FDG uptake in the left ventricle (LV) assessed by the reading physicians was used as reference to validate the quantification calculated by the software. LV metabolic volume (LVMV) and activity (LVMA) were computed analogously to CMV and CMA, using a threshold of 1.5 × mean blood pool SUV. However, they were focused only on the LV, unlike the CMV and CMA which quantify both left and right ventricles. The ratio of maximum tissue SUV to mean blood pool SUV was used to create receiver operating characteristic (ROC) curves for both sampling methods. Cox survival analysis was performed on patients with ejection fraction (EF) ≥ 50% (N=172) for the composite of major adverse cardiac events (ventricular tachycardia, ventricular fibrillation, heart failure hospitalization, ventricular assist device, heart transplant, and death), adjusting for summed rest score (SRS).
Results: MIDWALL sampling resulted in greater area under the ROC curve than MAX sampling (0.89 vs. 0.84, p=0.002). Importantly, LVMA > 0 (marked with X on Figure 1) corresponds to a threshold of 1.5 × mean blood pool SUV, illustrating poor sensitivity. Using a threshold of 1 × mean blood pool SUV with MIDWALL sampling, positive FDG quantification was a significant predictor of MACE (HR=2.65 [95% CI 1.07-6.56], p=0.03). Using the LVMA/CMA published threshold of 1.5 × mean blood pool SUV was not significant (HR=0.61 [95% CI 0.07-5.27], p=0.65).
Conclusions: Quantification of LV myocardial FDG activity above blood pool SUV is a reliable quantitative method for diagnosis of myocardial inflammation and is associated with worse prognosis.
References:
[1] Larson, S.R., Pieper, J.A., Hulten, E.A. et al. Characterization of a highly effective preparation for suppression of myocardial glucose utilization. J. Nucl. Cardiol. (2019) doi:10.1007/s12350-019-01786-w
[2] Ahmadian, A., Brogan, A., Berman, J. et al. Quantitative interpretation of FDG PET/CT with myocardial perfusion imaging increases diagnostic information in the evaluation of cardiac sarcoidosis. J. Nucl. Cardiol.21, 925-939 (2014) doi:10.1007/s12350-014-9901-9
