Silent MRA analysis

Two neuroradiologists (C.W. and Z.Z., with 12 and 15 years of experience, respectively), blinded to the results of DSA and clinical data, independently reviewed all the conventional MR images and silent MRA images in a randomized order.

Measurements of the nidus were performed on the conventional MRI in three dimensions. The largest diameter among the three dimensions was recorded as the BAVM size. Location was classified as being in an eloquent or non-eloquent area.

A region of interest (ROI) analysis was performed on the silent MRA source images on GE AW 4.7 Workstation. We used a circular shape for all ROIs. For draining veins (DV), the closest area to the nidus was first determined on MIP images. The ROI was put on the site on silent MRA source images and did not overlap with adjacent vessels (Fig. ​(Fig.1).1). To calculate the rSI, the cavernous ICA ipsilateral to the nidus was selected as the denominator for the rSI reference, which can easily be identified and measured on axial source images (refer to Fig. ​Fig.1).1). For replication purposes, we performed similar analyses using the raw value of the SI of draining veins (see supplementary materials). Each ROI was set to be no larger than the target vessels, and the ROI size changed according to the vessel of interest. The ROI should exactly match the diameter of the vessel of interest. Each SI value was measured as the mean of 2 ROIs. Ratios of SI (rSI) were calculated as SI-DV / SI-ICA. The maximum ratio of SI (rSImax) was defined as the highest rSI of all draining veins in each patient. If the draining vein demonstrated on DSA cannot be visualized on silent MRA, the rSI was recorded as zero.

a ROI setting on Silent MRA. b ROIs were set on the cavernous ICA ipsilateral to the nidus (red circle) and (c-d) the proximal segment of drainage veins (green and blue circle) on axial source images. The ratio of signal intensity of each draining vein was calculated.

For each patient, the assessment included (1) rSI of each draining vein; (2) rSImax of all the draining veins; and (3) the diameter of the draining vein with rSImax.

Subsequent statistical analysis was based on the rSI values measured by the first neuroradiologist (C.W.). On DSA, the venous drainage patterns (venous ectasia, deep venous drainage, and single venous drainage) of the draining vein with rSImax were recorded.