Toward Noninvasive Magnetic Resonance-Based Target Delineation for Ventricular Tachycardia Stereotactic Radiation Therapy: Development of a 3-Dimensional Wideband Late Gadolinium-Enhanced Magnetic Resonance Imaging Technique.

PURPOSE: Cardiac stereotactic body radiation therapy (SBRT) offers a noninvasive alternative to conventional radiofrequency 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 computed tomography and implanted cardioverter-defibrillator (ICD)-related magnetic resonance imaging (MRI) artifacts. We developed and evaluated a 3-dimensional (3D) wideband (WB) late gadolinium-enhanced (LGE) MRI protocol for artifact suppression, geometric accuracy, and scar delineation in SBRT planning.

METHODS AND MATERIALS: The 3D WB LGE sequence employs a 6 kHz WB hyperbolic-secant inversion pulse to suppress ICD-induced hyperintense artifacts, followed by a 3D gradient-echo readout. Both electrocardiogram and respiratory navigator gating were employed to manage cardiac and respiratory motion, respectively. Protocol optimization was performed on phantoms and 4 healthy volunteers with ICDs positioned near the chest. Geometric distortion was measured using MagPhan and American College of Radiology phantoms. Clinical feasibility was tested in a 73-year-old patient undergoing cardiac SBRT. The 3D LGE MRI was registered with the planning computed tomography and compared with electroanatomic mapping using the American Heart Association 17-segment model.

RESULTS: Phantom analysis showed minimal sequence-related distortion, well within clinical tolerance. ICD-induced distortion was negligible when the device was placed 10 cm from the target. The WB inversion pulse successfully suppressed ICD-related hyperintense artifacts in phantoms and healthy volunteers compared with conventional narrowband LGE MRI. In the VT patient, 3D WB LGE MRI enabled volumetric scar delineation, with good correlation between gadolinium enhancement and electroanatomic mapping-defined targets. Acquisition time for the 3D WB LGE MRI was optimized to approximately 5 minutes.

CONCLUSIONS: 3D WB LGE MRI is feasible for cardiac SBRT simulation, achieving reliable suppression of ICD artifacts and minimal distortion while providing good noninvasive visualization of the scar. Its integration into clinical workflows may improve VT target delineation accuracy in patients with implanted devices.