7T susceptibility sensitive T2*-weighted imaging, which allows for an unprecedented resolution (pixel size: 0.23×0.23mm2) and contrast of even rather small vascular structures, clearly delineates the intimate relation between lesions and veins in MS. In our two RRMS patients, we were able to demonstrate a total of 80 MS lesions, 58 and 22 lesions independently, and all lesions showed a strict perivascular distribution, following the form, orientation, and course of the vessels, this feature being best noted in small lesions (). The diameter of veins associated with lesions ranged from 0.3mm–0.7mm.
7T high resolution axial T2*-weighted images in Patient 1
In Patient 1 on initial 7T scans, we found that 34 of 58 total lesions were small (less than 15mm2 in area), and of these, 23 and 11 were associated with well-defined and ill-defined central veins, respectively. In the 24 remaining large lesions, 11 of these had well-defined central veins and 13 obscured including 3 T1 black holes. Several small lesions showed subtle abnormal signal intensities strictly at the perivascular spaces, with well-defined central veins, as well as small lesions with relatively obscured veins, and large lesions with well-defined and ill-defined vessels (). In , white matter tracts, such as those of the optic radiations, being well depicted on 7T, allowed us to accurately visualize MS lesions along a venous distribution but not aligned with the course of the fiber tracts (). Compared to normal control (), there was marked increase in iron deposition in the basal ganglia and thalamic areas in this patient (). In addition, a lesion embedded within the cortical sulcus was found on 7T but not on 3T images (). On 3T T2*-weighted image (), the perivenous relationship of lesions is poorly detected as compared to 7T MRI with the similar sequence acquisitions.
T2*-weighted images at the level of the basal ganglia on 7T MRI in Normal Control (A) and Patient 1 (B) as well as on 3T MRI in Patient 1 (C)
On follow-up imaging at 7T in Patient 1 nine months later, we noted the same number of total lesions, and furthermore, found that of the 34 small lesions counted, 5 had increased whereas 3 had decreased in size, with the 26 remaining lesions demonstrating no change (). On 3T with Gd-enhanced scans, we did not note any contrast enhancement corresponding to lesions observed on 7T (). In addition, venous vasculature associated with lesions was not visualized on either gradient-echo or T2-weighted imaging on 3T.
High resolution axial T2*-weighted images in Patient 1 at baseline (A) and follow up over nine months (B) on 7T as well as enhanced T1-weighted image (C) on 3T
In Patient 2, we noted 16 small and 6 large lesions. Of these small lesions, 13 had well-defined veins in their centers, and 3 had indistinct veins, as noted in . All except one of the large lesions were associated with indistinct central veins.
7T high resolution axial T2*-weighted images in Patient 2