4D-Flow MRI enables the visualization of blood flow and quantification of hemodynamic parameters for characterizations of cardiovascular diseases (CVD). However, the analysis and interpretation of 4D-Flow data alone is often challenging. For example, vessel segmentation is required for quantification and the frequently used PC angiogram can become unreliable in cases of slow or irregular flow patterns (1). Contrast-enhanced MR angiogram offers improves vessel segmentation but is not co-registered to the 4D-flow data. Further, new interpretation of flow features may be enhanced by the incorporation of alternative contrasts, such as arterial wall enhancement (2, 3) superimposed on 4D flow data. The purpose of this work is to develop an imaging visualization paradigm that harnesses the synergistic information of a multi-contrast vascular exam. Paramount to this technique is collection of high-resolution 3D vascular scans and accurate registration before the joint visualization, which may be challenging in cases of dissimilar contrast. To evaluate the registration accuracy of dissimilar MRI images, a set of T1 weighted black blood (BB) and 4D-Flow intracranial scans were performed twice on four healthy volunteers as shown in Figure 1. First, BB and 4D-Flow scans were acquired back to back with the subject instructed to remain as still as possible (BB₁ and Flow₁). Subsequently, subjects were asked to rotate their head (~5-10°) and the scans were repeated (BB₂ and Flow₂). Imaging was performed on a 3T scanner (MR750, GE Healthcare, WI, USA) with a 32channel head coil (Nova Medical, MA, USA). Sagittal BB images were collected utilizing a DANTE (4) prepared spin echo sequence with 0.75x0.8x0.8mm³ resolution. 4D-Flow was collected with an axial 3D radially undersampled sequence(5) with 0.7mm isotropic spatial resolution. 3D rigid image registration was performed with open-source software (Advanced Normalization Tools) using a mutual information metric. First, BB₁ and BB₂ were registered to their counterpart Flow₁ and Flow₂. Next, images before and after the head rotation were registered using dissimilar images (e.g. BB₁-Flow₂ and Flow₁-BB₂). Within the inherent registration error due to interpolation and noise, the registration between Flow₁ and Flow₂ should be equivalent to the registration involving two dissimilar registrations (e.g. Flow₁-BB₁-Flow₂). Quality of the registration between rotations was assessed via correlation of PC angiograms (Flow₁ and Flow₂), as the correlation is not a suitable measure for registration quality between dissimilar image series such as BB and 4D-Flow. Registration was incorporated into a multi-contrast vascular workup, including 4D-Flow, CE-MRA, and black blood images in a patient scan. After preprocessing, images were visualized jointly in a commercial flow visualization package (EnSight, CEI, Apex, USA) before and after registration of a subject with an intracranial aneurysm. Due to the extended exam time (~40min), interscan motion was expected. All images were registered to the 4D-Flow scan. BB and 4D-Flow magnitude images demonstrated excellent registration between the pre- and post-rotation data sets, as shown in Figure 2. The correlation between the pre- and post-rotation angiograms (averaged over all four volunteers) increased from 0.167±0.081 before the registration to 0.810±0.117 after the registration, similar to correlation using the direct registration of the two 4D-Flow images: 0.874±0.058. (Imperfect ρ<1 is partially due to non-rigid motion of superficial temporal arteries). When the dissimilar registration was applied to the aneurysm patient, the overlay of the bright vessels from the 4D flow scan matches with the black “lumens” of the dark vessels in the BB images (Fig. 3, right), instead of tissues (Fig. 3, left). Joint visualization of the brain aneurysm with the 4D flow MRI and BB sequence shows that blood flow is accurately displayed within the vessels of BB only after the dissimilar registration between 4D flow MRI and BB sequence.Satisfactory registration between the pre- and post-rotation data sets, as visualized in Fig. 2 and quantified by increased correlations above, indicates that dissimilar registration using BB and 4D-Flow images can identify and match anatomical similarities between the two seemingly different images (Fig. 1). As shown with the aneurysm patient (Fig. 3 and 4), joint visualization of 4D-Flow MRI and other diagnostic images in everyday clinical settings must be preceded by dissimilar registrations between them, as done in this study. This analysis platform may be useful in studies investigating the complex relationships between hemodynamic conditions and vascular remodeling in cases of aneurysms, atherosclerosis, and arterial venous malformations.