Intracranial large artery atheroma is a major cause of stroke worldwide, however the optimal treatment has not been established ¹. With the development of high resolution black blood MRI techniques, intracranial vessel wall characteristics have been increasingly studied as possible markers of neurological symptoms ². However, the natural history of intracranial atherosclerotic plaque is still poorly understood. Previous longitudinal studies using angiography or trans-cranial ultrasound failed to evaluate pathological changes of the vessel wall ³. This study aims: 1) to evaluate the feasibility of MRI for monitoring intracranial plaque progression in patients with recent stroke or TIA, and 2) to preliminary investigate the possible risk factors correlated with plaque progression and recurrence of ischemic events.Study population: 63 patients (49 male, mean age 66) with recent stroke or TIA who were identified with intracranial artery stenosis were recruited in the MIPP study. 76 stenotic intracranial arteries were identified including 65 middle cerebral arteries (MCAs) and 11 basilar arteries (BAs). Patients first underwent baseline MRI imaging, and then were followed with repeated MRI at least once (follow up time 3 months to 3 years). Recurrence of neurological symptoms during the follow up period was recorded. All patients were under best medical therapy. MRI acquisition: For each visit, patients underwent multi-contrast high resolution MRI of the plaque and clinical brain MRI. Plaque imaging included black blood sequences: pre- and post-Gd contrast T1-weighted fast spin echo (FSE), T2 and proton-density (PD) weighted FSE. An in-plane resolution of 0.4mm and a slice thickness of 2mm were used. Brain imaging included T1/T2-weighted FSE, FLAIR and DWI. Image analysis: Lumen and outer wall boundaries were manually segmented on T2-weighted images by a radiologist and the plaque area and volume were quantified. Contrast enhancement on T1-weighted MRI was graded by three categories: 0: no enhancement; 1: possible enhancement; 2: obvious enhancement. Statistics: T-tests were used to compare the group differences. We documented patient clinical characteristics and performed multivariable logistic regression analysis to investigate their correlation with plaque progression. In this initial report, we analysed data from 22 patients (18 male, age 56±13, stenosis 70.2±22.9%) with follow up scan at ~6 months. 26 plaques were identified (22 MCAs, 4 BAs). Two patients had recurrent TIAs; however, no additional infarcts were identified on DWI in all patients. Overall there was no significant plaque volume change (annual progression rate: 0.8±21.0%), however with a big SD and range (-45.9% to 40.1%). Representative images of patients with plaque progression (Figure 1), regression (Figure 2) and no change (Figure 3) are shown. At baseline, 4 plaques showed no enhancement, 8 plaque showed possible enhancement, and 10 plaques showed strong enhancement. At follow up, 5 plaques showed a category decrease in contrast enhancement, while 17 plaques were un-changed. Regression analysis showed that there was no significant correlation between clinical factors, contrast enchantment status, stenosis values or baseline volume with progression rate (p>0.05). However, patients with hypertension tended to progress faster compared with patients without hypertension with a borderline significance (p=0.057) (Table 1), and there was a moderate inverse relationship between baseline HDL levels and plaque progression (Pearson’s r = -0.34, p=0.08, Figure 4).To our best knowledge, this is the first study that reports the natural history of the intracranial artery wall. We showed that high resolution MRI is feasible for monitoring intracranial plaque progression even during a relatively short period of time. Plaque volume and contrast enhancement changes were evident, indicating an active progress of the intracranial plaque development. Therefore, vessel wall MRI has the potential to evaluate treatment response in a short period of time, rather than waiting for patient long-term outcome data. The current initial report is limited by a small sample size and short follow up time, thus the statistics did not reach significance. Plaque volume was used in this study as the only end point given that only two patients had recurrent TIAs. In a previous reproducibility study ⁴, we have proved that plaque volume was more sensitive to detect changes compared with plaque area. High resolution vessel wall MRI is feasible to monitor intracranial plaque progression and pathological changes in a short period of time. These techniques can be potentially used to better understand the natural history of intracranial plaque, evaluate treatment response, and investigate risk factors associated with future ischemic events.