Visualization and temporal/spatial characterization of cardiac radiofrequency ablation lesions using magnetic resonance imaging

Background-The purpose of this study was to describe a system and method fo r creating, visualizing, and monitoring cardiac radiofrequency ablation (RF A) therapy during magnetic resonance imaging (MRI). Methods and Results-RFA was performed in the right ventricular apex of 6 he althy mongrel dogs with a custom 7F nonmagnetic ablation catheter (4-mm ele ctrode) in a newly developed real-time interactive cardiac MRI system. Cath eters were positioned to intracardiac targets by use of an MRI fluoroscopy sequence, and ablated tissue was imaged with T2-weighted fast spin-echo and contrast-enhanced T1-weighted gradient-echo sequences. Lesion size by MRI was determined and compared with measurements at gross and histopathologica l examination. Ablated areas of myocardium appeared as hyperintense regions directly adjacent to the catheter tip and could be detected 2 minutes afte r RF delivery. Lesions reached maximum size approximate to 5 minutes after ablation, whereas lesion signal intensity increased linearly with time but then reached a plateau at 12.2+/-2.1 minutes. Lesion size by MR correlated well with actual postmortem lesion size and histological necrosis area (55. 4+/-7.2 versus 49.7+/-5.9 mm(2), r=0.958, P<0.05). Conclusions-RFA can be performed in vivo in a new real-time interactive car diac MRT system. The spatial and temporal extent of cardiac lesions can be visualized and monitored by T2- and T1-weighted imaging, and MRI lesion siz e agrees well with actual postmortem lesion size. MRI-guided RFA may be a u seful approach to help facilitate anatomic lesion placement and to provide insight into the biophysical effects of new ablation techniques and technol ogies.