Direct quantitative in vivo comparison of calcified atherosclerotic plaque on vascular MRI and CT by multimodality image registration

Purpose: To investigate direct volumetric in vivo correspondence of calcified atherosclerotic plaque lesions in MRI and CT images of the thoracic aorta by multimodality image registration and fusion. Materials and Methods: Twelve CT (11 noncontrast and one contrast) and MRI (TruFISP, contrast T1-weighted volumetric interpolated breath-hold examination (VIBE)) data sets were coregistered by approximate segmentation of the aorta and subsequent automatic coregistration by maximization of mutual information (MI). We quantitatively assessed 22 coregistered calcified plaque lesions on CT and MRI. Results: The three-dimensional registration consistency and accuracy were 1.74 +/- 1.3 mm, and 2.42 +/- 1.65 mm, respectively. The ratio of CT/MRI calcified plaque volume decreased asymptotically with MRI Volume, and correlated with average CT lesion density (r = 0.72) for small lesions (less than 25 mm(3)). The average calcified plaque volume, circumferential extent, and maximal radial width by MRI were significantly smaller compared to CT (35%. 68%, and 53%, respectively; P < 0.05). Conclusion: Software coregistration allowed precise, direct, and voxel-based comparison of calcified atherosclerotic plaque lesions imaged by MRI and CT. In comparison with coregistered MRI, overestimation of calcified plaque in aortic CT due to "blooming" Correlates with the average lesion density for small plaques, and is greater for small plaques.