Arjen Lindenholz

88 CHAPTER 4 An expert neuroradiologist (JH with > 15 year of experience), specialized in intracranial vessel wall imaging, assessed both pre- and postcontrast vessel wall images in multiple planes for image quality, which includes the visibility of the arterial vessel wall, the suppression of blood and CSF and the existence of artifacts (slow-flow, motion and free induction decay (FID) artifacts). The images of the 10 subjects who received contrast agent injection were also assessed for the presence of vessel wall lesions, including location and configuration (eccentric or concentric) and contrast-enhancement using methods previously described. 24,26 All scans were blinded and randomly ordered before assessment. When a lesion was found in only one of the variants, the location was re-examined in the other variant to check if the lesion could be identified retrospectively. Furthermore, the vessel wall images were cross-correlated with the TOF-MRA images for a correct interpretation of the specific arteries, the potential vessel wall lesions and the lumen of the artery. Included vessels were the anterior cerebral arteries (A1 and A2 segments), distal intracranial internal carotid arteries (clinoid or C5 and cavernous or C4 segments), middle cerebral arteries (M1, M2 and M3 segments), posterior cerebral arteries (P1 and P2 segment), the distal intracranial basilar artery, and distal intracranial vertebral arteries. Statistical analysis All statistical comparisons were conducted using IBM SPSS statistics (version 21, IBM Corp., Armonk, NY, USA). Pairwise comparisons were performed between the clinically relevant SNRs and CNRs of the reference variant and the 6 other variants using generalized estimation equations to account for repeated measures on the same subjects. A Friedman test was performed for differences in SNR and CNR between both precontrast and postcontrast images of variant 3 and 7. A post hoc analysis with the Wilcoxon signed-rank tests was conducted with a Bonferroni correction applied to correct for multiple comparisons. A p-value < 0.008 was considered significant. Results All 15 subjects underwent the MRI examination successfully. The quality of all images was sufficient to be used for analysis. Image assessment was not hampered by motion artifacts in any of the scanned subjects. Comparison of all seven scan variants Typical images of the 7 vessel wall scan variants are shown in Figure 2 (axial plane), Figure 3 (sagittal plane) and Supplemental Figure 1 (coronal plane). The images show clear differences among the variants in contrast and visibility of the vessel