Arjen Lindenholz

56 CHAPTER 3 Patient preparation Proper patient preparation plays an important role in the acquisition of high-quality intracranial vessel wall images. The patient (or legal representative) needs to be informed about the MRI examination and the MR imaging staff needs to assess if any possible contraindications for MR imaging (claustrophobia, contraindicatedmetal objects in or on the body, pregnancy) or for gadolinium-containing contrast agents (known allergic reaction to gadolinium-containing contrast agent, severely impaired renal function) exist. Also, because of the relatively long acquisition time of vessel wall MRI sequences, imaging staff needs to assess whether the patient is clinically able to undergo the examination: it may be challenging to lay still for a long period of time, especially for neurologically impaired patients. Prior to scanning, a peripheral intravenous catheter is placed in the antecubital vein for contrast administration. 42,43,53 Our complete vessel wall MRI protocol ( Table 1 and Table 2 ) takes approximately 23 and 48 minutes for the 3T and 7T protocol, respectively. The vessel wall MRI sequence has an acquisition time of 8 minutes 3 seconds for the 3T and 10 minutes 40 seconds for the 7T protocol. Vessel wall MRI sequences are susceptible to motion artifacts because of the relatively long acquisition duration, and visibility of the vessel wall decreases rapidly when patients move their head during acquisition. We therefore use foam cushions positioned around the patient’s head to aid in limiting movement artifacts. Pre-assessment case preparation – What do we need to know? Clinical information For a complete assessment of intracranial vessel wall images several clinical aspects are important to know. In general, when requesting vessel wall MRI, the actual clinical status of the patient (neurological status, ability to lie still for a prolonged period of time) should be reported in order to assess the a priori chance of acquiring images of sufficient diagnostic quality. Next, a specific clinical question is important for defining a patient-tailored vessel wall MRI protocol. For instance, if the clinician is suspicious of disease in the anterior cerebral vasculature, the (small) FOV of the 3T sequence needs to be placed in a more transverse orientation in line with the arteries of the anterior circulation part of the circle of Willis. When the area of interest lies predominantly in the posterior circulation, a more transverse oblique angulation can be used to include a longer trajectory of the basilar and vertebral arteries. On the other hand, when there is suspicion of a dissection or intraplaque hemorrhage, a precontrast vessel wall MRI sequence can be added to a postcontrast-only protocol. Further, previous (MRI) examinations showing arterial disease (e.g., stenoses) on conventional sequences need to be taken into account for both FOV planning and evaluation of progression.