Volumetric real-time MRI for the guidance of cardiac catheterization at 0.55T.
BACKGROUND Interventional cardiovascular MRI (iCMR) uses rapid high-contrast images to guide invasive procedures, such as right-heart catheterization (RHC), an important diagnostic tool for characterizing pulmonary hypertension and heart failure. Current iCMR uses interleaved multi-planar 2D acquisitions (1-3 planes) with balanced steady-state free precession (bSSFP) contrast. A common challenge is tracking devices as they move out of plane and the operational burden of updating views in real-time. We propose a volumetric method that images the heart and great vessels in their entirety, and offers flexible real-time re-slicing, volumetric 3D visualization, and the potential for improved device monitoring. METHODS Volumetric real-time MRI (3DRT) was implemented at 0.55T using a stack-of-spirals bSSFP acquisition paired with a low-latency online spatiotemporally constrained image reconstruction, to achieve 3.5 mm3 isotropic spatial resolution and ~500 ms/volume temporal resolution. Numerical simulations were performed to evaluate tracking capability of gadolinium balloons as a function of device speed, and to verify image quality. Six healthy volunteers were imaged without catheterization to test performance on human subjects. Six naïve pigs were imaged during RHC, with gadolinium-filled polymer balloon wedge end-hole catheters. RESULTS Simulation experiments demonstrated that 3DRT imaging with low-latency spatiotemporally constrained reconstruction can resolve moving catheters at ~2.0cm/s. 3DRT with bSSFP contrast was successfully demonstrated for right-heart catheterization procedures in porcine models, providing adequate blood-myocardium contrast, and balloon-blood contrast to track the catheter tip. 3DRT images provided adequate image quality and resolved respiratory motion in healthy volunteers. Volumes were re-sliced live and re-sliced planes could be flexibly manipulated during the scan in real-time before the next volume was acquired. CONCLUSION Volumetric real-time MRI is feasible for the guidance of invasive procedures such as right-heart catheterization at 0.55T. 3DRT imaging has been demonstrated in model pig experiments with ~500 ms temporal resolution and 3.5 mm3 isotropic spatial resolution, providing improved balloon tracking.