Arjen Lindenholz

84 CHAPTER 4 Materials and Methods Participants Fifteen subjects were included in this study. In 5 subjects (4 male; mean age 37 years, range 28–54 years) all 7 scan variants were performed (precontrast-only). Additionally, precontrast and postcontrast comparisons were performed in 10 other subjects (9 male; mean age 53 years, range 24–68 years). Approval for this study was obtained from the Institutional Review Board of University Medical Center Utrecht. The 10 volunteers who received contrast agent were part of the PIVI-study and IVI-study (Posterior Intracranial Vessel wall Imaging and Intracranial Vessel wall Imaging; NTR5688 and NTR2119, respectively, www.trialregister.nl ). All subjects gave written informed consent. Imaging protocol We used a 3T MRI-system (Achieva, Philips Healthcare, Best, The Netherlands) with an 8-channel phased-array sensitivity encoding (SENSE) head coil. All vessel wall sequences consisted of a 3D fast turbo spin-echo (TSE) sequence and a number of acquisitions (NSA) of 1. Starting from our earlier described vessel wall sequence (variant 3 in Table 1 ), 23 six different variants were created, of which one is previously described (variant 2). 19 In the scan protocol of the precontrast-only acquisitions, the sequence acquisition order was equal in each subject (consecutively variant 2, 5, 3, 4, 7, 1 and 6; Table 1 ). Variant 3 was used as reference sequence for the 6 different precontrast-only acquisitions. Various trade-offs were created among contrast (repetition time (TR), Anti-Driven Equilibrium), spatial resolution (voxel- size, elliptical k -space shutter), SNR (oversample factor in phase-encoding direction, SENSitivity Encoding (SENSE) reduction factor, readout bandwidth, overcontiguous (overlapping) slices, TSE-train flip-angle refocusing control), and scan duration ( Table 1 ). All vessel wall scans were repeated with the radiofrequency and gradient turned off for sampling noise images from the receiver coil elements, including image reconstruction effects such as elliptical k -space shutter and parallel (SENSE) reconstruction sensitivities. The noise images were accelerated by leaving out the delay after each TSE train to the next (turned off) excitation. The total scan session took 65 minutes and included the preparation phase, TOF-MRA (acquired voxel size 0.4 x 0.7 x 1.0 mm 3 , reconstructed voxel size 0.36 x 0.36 x 0.5 mm 3 , acquisition time 5 minutes 12 seconds) and the 7 vessel wall scan variants, including their corresponding noise images. For the vessel wall sequences, the field-of-view (FOV) was planned in a transverse / oblique orientation, which covered all large cerebral arteries of the circle of Willis.