High resolution MRI of the intracranial vessel wall provides important insights in the assessment of intracranial vascular disease. 3D fast spin echo sequences with a variable flip angle echo train (SPACE, Siemens Healthcare, or equivalent) is a leading candidate for vessel wall imaging because it has high resolution and an intrinsic black blood effect. It has been successfully used at both 3T¹ and 7T² with 0.5mm to 0.8mm isotropic resolution. However, a direct comparison between the abilities of clinical 3T scanners and research 7T scanners is lacking. The long echo train of SPACE may be associated with a wide point spread function (PSF) that causes spatial blurring that degrades the nominal imaging resolution, but it has not been fully investigated. In this study, we aim: 1) to investigate the effect of refocusing flip angle train design on image quality at 3T and 7T; and 2) to compare the ability of 3T and 7T in intracranial vessel wall imaging in a small group of patients. Theoretical Simulations: Different echo train length (ETL, 40-60) and flip angle train design (maximal flip angle αmax fixed around 140°, minimal flip angle αmin from 23° to 47°) were simulated in a custom-designed software (Figure 1). 3T-ETL40 was the scanner default design, and 3T-ETL60 and 7T-ETL40 were custom designs. Signal evolution curves and PSFs were simulated. Full width at half maximum (FWHM) of the PSFs was calculated and the relative SNR was estimated by averaging the first 5 echoes, and the value of 3T-ETL40 was set to 1 as a reference. Patient studies: 11 patients with intracranial artery disease (5 atherosclerotic plaques and 6 aneurysms) were imaged on Siemens 3T Skyra and 7T scanners using SPACE both pre and post Gd contrast injection at a single scan visit. Scanning protocols are shown on Table 1. Wall to lumen contrast ratio (CRwall/lumen), contrast enhancement ratio (ER) and the sharpness ³ of the vessel wall were quantified and compared between field strengths. An experienced radiologist evaluated the image quality on a 0-5 scale.Both 3T and 7T achieved good image quality with high resolution (nominal 0.5mm isotropic) and whole brain coverage within ~10 minutes scan time. Simulation (Figure 1) shows 3T and 7T have similar SNR (3T-ETL40: 1; 3T-ETL60: 0.95; 7T: 0.98), but 7T has a much narrower PSF (FWHM: 7T: 1.5; 3T-ETL40: 2.6; 3T-ETL60: 2.8). Patient studies (Table 2 & Figure 2-4) show that the CRwall-lumen at 3T and 7T (3.11±0.74 vs. 3.43±1.61, p=0.45) and the ER measurements (1.58±0.41 vs. 1.56±0.35, p=0.83, Pearson’s r =0.69) are comparable. The 7T images are 43% sharper (sharpness: 2.69±0.50 vs. 1.88±0.53 mm^-1, p<0.001) with higher image quality ( score: 3.5±1.1 vs. 2.4±1.1, p=0.002) compared to 3T.To our knowledge, this is the first study that systematically compares the abilities of 3T and 7T scanners for the imaging of the intracranial vessel wall. The comparison was performed using both theoretical simulations and in vivo patients studies. Flip angle train design and ETL can significantly influence the SNR and sharpness of the images. Previous high resolution studies ^{1 2} used very long ETLs (58-116), which can possibly lead to different levels of blurring of the vessel wall. We found that while a lower flip angle train design and short ETL significantly reduced image blurring, it also decreased the SNR. At 3T, high flip angle was used to maintain sufficient SNR, which agree with previous studies¹. Low flip angle design at 3T results in significantly low SNR (image not shown). At 7T, the inherent high signal allows the use of a low flip angle design that maintains both sufficient SNR and good image sharpness. This study focused on T1 weighted SPACE development and optimization because it is useful for identifying intra-plaque haemorrhage and contrast enhancement and is time efficient. We found both 3T and 7T could be used to characterize contrast enhancement, which is often linked to neurological symptoms ⁴. In one patient with basilar artery plaque (Figure 4), it was possible with the improved image quality at 7T to visualize a thick fibrous cap and a large lipid core, which were not shown at 3T. With continued development, 7T has the potential to more fully characterize intracranial plaque composition in vivo.3D T1-weighted high resolution SPACE can be used for whole brain intracranial vessel wall evaluation at both 3T and 7T. 7T provides significantly better image quality and improves the confidence of diagnosis. These techniques have great promise for risk stratification of patients with intracranial vascular disease.