Toward Non-Invasive MR-Based Target Delineation for Ventricular Tachycardia Stereotactic Radiotherapy: Development of a 3D Wideband LGE MRI Technique.

Abstract

Cardiac stereotactic body radiotherapy (SBRT) offers a noninvasive alternative to the conventional radiofrequency (RF) catheter ablation for treating refractory ventricular tachycardia (VT) in patients who are poor candidates for ablation procedures. However, accurate target delineation remains challenging due to limited scar visualization on CT and implanted cardioverter-defibrillator (ICD)-related MRI artifacts. We developed and evaluated a 3D wideband (WB) late gadolinium-enhanced (LGE) MRI protocol for artifact suppression, geometric accuracy, and scar delineation in SBRT planning. The 3D WB LGE sequence employs a 6-kHz wideband hyperbolic secant inversion pulse to suppress ICD-induced hyperintense artifacts followed by a 3D gradient-echo readout. Both electrocardiogram (ECG) and respiratory navigator gating were employed to manage the cardiac and respiratory motion, respectively. Protocol optimization was performed in phantoms and four healthy volunteers with ICDs positioned near the chest. Geometric distortion was measured using MagPhan and American College of Radiology (ACR) phantoms. Clinical feasibility was tested in a 73-year-old patient undergoing cardiac SBRT. The 3D LGE MRI was registered with the planning CT and compared with electroanatomic mapping (EAM) using the AHA 17-segment model. Phantom analysis showed minimal sequence-related distortion, well within the clinical tolerance. ICD-induced distortion was negligible when the device was placed 10 cm away from the target. The WB inversion pulse successfully suppressed ICD-related hyperintense artifacts in phantoms and healthy volunteers compared to conventional narrowband (NB) LGE MRI. In the VT patient, 3D WB LGE MRI enabled volumetric scar delineation with good correlation between gadolinium enhancement and EAM-defined targets. Acquisition time for the 3D WB LGE MRI was optimized to be approximately 5 minutes. 3D WB LGE MRI is feasible for cardiac SBRT simulation, achieving reliable ICD artifact suppression and minimal distortion while providing good scar visualization non-invasively. Its integration into clinical workflows may improve VT target delineation accuracy in patients with implanted devices.