Arjen Lindenholz

12 CHAPTER 1 which will most reliably show enhancement, or suffice with a postcontrast T 1 - weighted sequence alone. Improvements in this area are ongoing, and various innovative techniques are being investigated to achieve a reduction in acquisition time while maintaining acceptable image quality ( Chapter 4 ). 20,21 3T versus 7T MRI As discussed, intracranial vessel wall MRI requires a high SNR – translating to a high spatial resolution and high CNR – to obtain clear visualization of the vessel wall. As the SNR increases with increasingmagnetic field strength, the step towards > 3TMRI platforms for intracranial vessel wall MR imaging seems inevitable. Although 7T MRI platforms have been research-only until October 2017, over the last two decades many new techniques and applications have been generated and tested at 7T worldwide, for a wide variety of clinical and radiological purposes ( Chapter 2 ). One main field of interest of the research department of the University Medical Center Utrecht has been neuroimaging, and in 2009 the first intracranial 7T vessel wall MRI sequence was developed, followed by several technical improvements in hardware and field-of-view (FOV) in the subsequent years. Initial results showed high quality of visualization of the intracranial vessel wall and clear assessment of vessel wall abnormalities. 16,22-24 Three subsequent large clinical studies using 7T intracranial vessel wall MR imaging have recently been completed; the Intracranial Vessel wall Imaging (IVI) study, the Posterior Intracranial Vessel wall Imaging (PIVI) study and Diagnosing Cerebral Vasculitis (DIVA) study. They provide detailed assessment of respectively the intracranial vessel wall in healthy adults, patients with anterior or posterior ischemic stroke and TIA, and patients with central nervous system vasculitis. Data of the IVI study has been used in this thesis for clinical correlation ( Chapters 5-7 ). In general, 7T MR imaging has been shown to be superior to 3T MRI in visualizing the intracranial vessel wall, enabling assessment of even very small vessel wall abnormalities that are not visible with lower field strengths. 25,26 An additional advantage of 7T is the relative ease with which CSF suppression is achieved, something that has not been matched at 3T yet. Finally, high SNRs and CNRs of 7T MRI enable more detailed assessment of other neurological pathology like (micro)infarcts and (micro)bleeds, which together with highly detailed vessel wall MR imaging might provide information on the cerebrovascular status of the individual patient. 27,28 However, the question remains whether these advantages have additional clinical value over data acquired at 3T. Nevertheless, for all its advantages, a major drawback of 7T MRI is that these platforms are only sparsely available, which makes widespread implementation of 7TMRI sequences in clinical practice currently impossible. Therefore, it is important that technical advancements and newly acquired insights can be translated back to 3T MR systems (or even lower MR field strength platforms).