Initial clinical validation of respiratory motion-corrected myocardial viability PET and simultaneous coronary MR angiography

Introduction: Cardiac PET-MR has shown promising results for the comprehensive assessment of coronary artery disease [1]. A recently proposed framework for simultaneous motion corrected PET/MR imaging allows the visualisation of myocardial metabolic integrity by 18F-FDG PET and coronary lumen integrity by Coronary Magnetic Resonance Angiography (CMRA) in a single efficient examination [2]. Here we present an initial clinical validation of this method in a cohort of patients with known cardiovascular disease.

Methods: The proposed method consists in an ECG-triggered free-breathing sequence simultaneously acquired with list-mode cardiac PET data. Respiratory motion is estimated from MR images and used to correct the MR data while simultaneously providing non-rigid motion fields for MR-based PET respiratory motion correction for both the emission data and attenuation maps. Fourteen patients (66.1±9.5 years) with chronic total occlusion (CTO) of at least one coronary artery were scanned on a Biograph mMR scanner (Siemens Healthcare). Clinical PET-MR imaging included a 40 to 50 min insulin-clamped 18F-FDG list-mode PET acquisition, the proposed PET-CMRA framework [2], and a 2D-PSIR Late Gadolinium Enhancement (LGE) acquisition. CMRA and PET data were reconstructed with the proposed motion correction scheme (MC) [2] and without motion correction (NMC). PET image reconstruction was performed offline using reconstruct-transform-average [3] motion correction in Siemens e7 Tools (OSEM, 3 iterations, 21 subsets, PSF modelling, 2.03x2.08x2.08mm voxel size, 127x344x344 matrix size). RESULTS: Average acquisition time for the proposed PET-CMRA acquisition was 11.2±2.4 minutes. Two patients were excluded as there was no overlap between the PET and the MR acquisition, and one patient for was not being able to receive Gadolinium-based contrast agent. MR images were reformatted to simultaneously visualize the left and right coronary arteries. MC MR images showed sufficient quality for depicting the proximal coronary anatomy (Fig1a), which was in agreement with X-ray angiography (not shown). For PET images, motion correction improved visualisation of small structures as well as delineation of myocardial defects (Fig1b). The degree of transmurality of viability defects was better depicted in MC PET images and an improved agreement with the LGE was observed. Integral tracer in the LV myocardium as quantified with a volumetric analysis, increased significantly especially in inferior and lateral regions after motion correction, indicating improved signal recovery of myocardial tracer uptake.

Conclusions: We have presented the clinical validation of a novel respiratory motion-corrected cardiac PET-MR framework for simultaneous visualization of coronary anatomy and myocardial integrity in patients with coronary artery disease. Motion corrected 18F-FDG PET images were in good agreement with LGE-MRI and show a more accurate depiction of both transmural and non-transmural viability defects. REFERENCES: [1] Rischpler C et al. Hybrid PET/MR imaging of the heart: potential, initial experiences, and future prospects. J Nucl Med 2013;54:402-415.[2] Munoz C et al. Motion-corrected simultaneous cardiac positron emission tomography and coronary MR angiography with high acquisition efficiency. Magn Reson Med 2017. doi: 10.1002/mrm.26690[3] Picard Y et al. Motion correction of PET images using multiple acquisition frames. IEEE Trans Med Imaging 1997;16:137-144.

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