Arjen Lindenholz

184 CHAPTER 8 Over the last two decades vessel wall MRI has seen many technical improvements and an associated increase in clinical applicability. While initially only the large extracranial arteries could be visualized, nowadays several sequences are available for imaging the intracranial arteries as well, facilitated by technical advances as well as higher achievable signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and spatial resolution at increasing magnetic field strengths (3T and 7T). As a result, the submillimeter thin intracranial vessel wall can now be visualized and scrutinized for abnormalities, and new imaging features for a variety of vascular pathologies have become available. Nevertheless, intracranial vessel wall MRI has not been systematically applied in the clinical setting yet, mainly because of the difficulty in obtaining histopathological validation of the true nature of the detected MR findings and the lack of studies addressing the clinical value of intracranial vessel wall lesions in patient management. The first part of this thesis addressed the technical aspects and challenges of intracranial vessel wall MRI in relation to magnetic field strength and acquisition time. An overview of the advantages and challenges of using 7T MRI in vascular neurological diseases including ischemic stroke was given in Chapter 2 . The differences, similarities andgeneral challengesof specifically intracranial vessel wall MRI at 3T and 7T were discussed in Chapter 3 . Whereas 3T as imaging platform of the intracranial vessel wall is more practical from a clinical standpoint, can achieve high-resolution images of the vessel wall, and can aid in differentiating between vascular pathologies, 7T MRI has the advantage of clearer delineation of the vessel wall due to superior CFS suppression, and generally visualizes more lesions. In Chapter 3 we also attempted to aid the radiologist in assessing intracranial vessel wall MR images, i.e., what to look for (and what to look out for), how to interpret abnormalities and which pathology to diagnose. Chapter 4 addressed the long acquisition times of most intracranial vessel wall MRI sequences, caused by the time-demanding sequence parameters. By adapting spatial resolution, SNR, CNR or a combination of these factors, various intracranial vessel wall sequences were tested for image quality. The results demonstrated that acquisition time could be reduced by 30% compared with the current clinically used sequence while maintaining both qualitative and quantitative satisfactory image quality. The second part of this thesis attempted to further elucidate the nature of vessel wall lesions (in an indirect way) and, consequently, the role intracranial vessel wall MRI could play in clinical decision-making. In Chapter 5 , we showed that in a group of patients with ischemic stroke or TIA, several cardiovascular risk factors – including increasing age, diabetes mellitus and hypertension – were associated with a higher number of intracranial vessel wall lesions. In the same population, Chapter 6 demonstrated that a higher number of vessel wall lesions was associated with the presence of cerebral parenchymal damage, including presence of infarcts often