1 Toward Magnetic Resonance-Guided Electroanatomical Voltage Mapping for Catheter Ablation of Scar-Related Ventricular Tachycardia: A Comparison of Registration Methods QIAN TAO, Ph.D., ∗ JULIEN MILLES, Ph.D., ∗ CARINE VAN HULS VAN TAXIS, M.D.,† HILDO J. LAMB, M.D., Ph.D., ∗ JOHAN H.C. REIBER, Ph.D., ∗ KATJA ZEPPENFELD, M.D., Ph.D.,† and ROB J. VAN DER GEEST, Ph.D. ∗ From the ∗ Division of Image Processing, Department of Radiology; and †Department of Cardiology Leiden University Medical Center, Leiden, The Netherlands Toward MR-Guided Electroanatomical Voltage Mapping for Catheter Ablation. Introduction: Integration of preprocedural delayed enhanced magnetic resonance imaging (DE-MRI) with electroanatomical voltage mapping (EAVM) may provide additional high-resolution substrate information for catheter ablation of scar-related ventricular tachycardias (VT). Accurate and fast image integration of DE-MRI with EAVM is desirable for MR-guided ablation. Methods and Results: Twenty-six VT patients with large transmural scar underwent catheter ablation and preprocedural DE-MRI. With different registration models and EAVM input, 3 image integration methods were evaluated and compared to the commercial registration module CartoMerge. The performance was evaluated both in terms of distance measure that describes surface matching, and correlation measure that describes actual scar correspondence. Compared to CartoMerge, the method that uses the translation-and- rotation model and high-density EAVM input resulted in a registration error of 4.32±0.69 mm as compared to 4.84 ± 1.07 (P <0.05); the method that uses the translation model and high-density EAVM input resulted in a registration error of 4.60 ± 0.65 mm (P = NS); and the method that uses the translation model and a single anatomical landmark input resulted in a registration error of 6.58 ± 1.63 mm (P < 0.05). No significant difference in scar correlation was observed between all 3 methods and CartoMerge (P = NS). Conclusions: During VT ablation procedures, accurate integration of EAVM and DE-MRI can be achieved using a translation registration model and a single anatomical landmark. This model allows for image integration in minimal mapping time and is likely to reduce fluoroscopy time and increase procedure efficacy. (J Cardiovasc Electrophysiol, Vol. pp. 1-7) catheter ablation, CartoMerge, electroanatomical voltage mapping, image integration, late gadolinium enhance- ment, ventricular tachycardia Introduction Substrate-based catheter ablation of ventricular tachycar- dia (VT) in post-infarct patients relies on accurate delineation of myocardial scar using electroanatomical voltage mapping (EAVM). 1,2 The high-density voltage mapping performed during this procedure is time consuming and associated with significant radiation exposure for both patients and opera- tors. 3,4 Delayed contrast-enhanced magnetic resonance imaging (DE-MRI) is a noninvasive and nonionizing imaging modal- ity that allows high-resolution 3-dimensional (3D) character- ization of myocardial scar. 5-8 Integration of 3D scar informa- tion from preprocedural DE-MRI with EAVM offers relevant high-density information on scar geometry and tissue char- acteristics, potentially facilitating subsequent mapping and ablation. 9-12 Image integration can also reduce the proce- dure and fluoroscopy time, provided that the integration can be performed after short mapping time. No disclosures. Address for correspondence: Qian Tao, E-mail: q.tao@lumc.nl Received 16 March 2011; Revised manuscript received 10 June 2011; Accepted for publication 14 June 2011. doi: 10.1111/j.1540-8167.2011.02167.x The alignment of 2 dataset originating from different sources is referred to as registration. 13-15 In clinical prac- tice, the commercial software CartoMerge (Biosense Web- ster, Inc., Diamond Bar, CA, USA) is often used to perform image integration during the catheter ablation procedure. The software accomplishes the registration by optimizing both point-to-surface distance and landmark alignment, 16,17 usu- ally performed after dense EAVM mapping. Although CartoMerge is a widely used image integration tool in the catheter laboratory, there are 2 concerns in its usage in the MR-guided VT ablation procedure. Firstly, the mapping needed for the registration algorithm may prolong the procedure time and negate the benefit of introducing pre- procedural MRI. Secondly, its registration criteria are not substrate related and thus do not enforce optimal correspon- dence between local areas (e.g., scar border or isthmus) in the registered datasets, especially in view of the rotational symmetry of the LV surface. 18 From the clinical point of view, scar area correspondence in DE-MRI and EAVM data is of essential importance, as it is directly linked to ablation target areas. In this respect, we define the accuracy of registration in terms of both surface matching and area correspondence. While surface match- ing can be directly estimated by point-to-surface distance, the measurement of scar correspondence is not as straight- forward. As it has been demonstrated that the degree of scar transmurality inversely correlates with bipolar voltage in both