Assessment of primary mitral regurgitation and lung water content using 15O-water positron emission tomography

Abstract

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Swedish Heart-Lung Foundation, Stockholm, Sweden. Introduction Severe primary mitral valve regurgitation (MR) is associated with significant hemodynamic changes in the cardio-pulmonary system, eventually resulting in lung congestion. The gold standard for assessing the regurgitation volume and fraction (RegVol; RegFraction), and severity of MR is cardiac magnetic resonance (CMR). The PET-tracer 15O-water is considered the gold standard for non-invasive quantitation of myocardial blood flow, but techniques for performing other functional assessments are evolving: using first-pass imaging total LV stroke volume (SV) can be measured with ECG-gating, and cardiac output (CO), forward SV (FSV) and pulmonary transit time (PTT) can be measured with indicator dilution techniques. Purpose The purpose of this study was to evaluate the method for calculating RegVol and RegFraction with 15O-water PET compared to CMR, and to assess the correlation to PWV. Methods N=19 patients with asymptomatic or mildly symptomatic severe MR were imaged on the same day with CMR and 15O-water PET. The PET-examinations were conducted on a digital PET/CT scanner (Discovery MI, GE Healthcare). The scans were performed in resting state and a 4-lead ECG was connected during the procedure. 400 MBq 15O-water was injected as an automated intravenous bolus simultaneous to starting a 4 min PET-emission in list mode. The list mode data was reconstructed into a 4 min dynamic series, and 16 ECG-gated images using the first 50 s of the scan only. The reconstructions were analysed using a semi-automatic software developed in-house. We calculated RegVol=total SV- FSV, RegFraction=RegVol/total SV *100 and PWV=CO*PTT. PWV was indexed against body surface area. Bland-Altman and linear regression analyses were performed and P < 0.05 was considered statistically significant. Results PET-based RegVol and RegFraction correlated significantly with CMR (r=0.94 and 0.89, both p<0.001). Bland-Altman plots showed a systematic underestimation for RegVol and RegFraction calculated by PET compared to CMR, but no proportional bias was present. PET and CMR- based RegFraction correlated significantly with PWV (r=0.70 and 0.78, both p<0.001). Conclusions 15O-water PET can be used to measure the severity of primary mitral regurgitation and the backward impact of regurgitation on lung water accumulation.