Involvement of the visual pathway is not a risk factor of visual field deficits in patients with occipital arteriovenous malformations: an fMRI study

Imaging acquisition

A 3 T Siemens Tim Trio magnetic resonance imaging (MRI) scanner with a 12-channel head coil was used for scanning protocol. T1-weighted structural imaging, blood oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI), time of flight magnetic resonance angiography (TOF-MRA), and DTI were collected for each patient. All imaging and image processing were performed by two technical assistants at the Medical Imaging Center, the 306th Hospital of PLA. All data analyzing procedures were done by two physicians at our institution.

T1-weighted three-dimensional magnetization-prepared rapid acquisition gradient echo sequence was measured with a echo time (TE) of 2.98 ms, a repetition time (TR) of 2300 ms, a matrix size of 256?×?256, a field of view of 250?×?250 mm, a slice thickness of 1 mm, and a slab size of 17.6 cm.

For BOLD-fMRI, maps of neural activity within the visual cortex were generated in each patient. Visual task given was “black white checkerboard”. A “block” design was used in which there were 80 dynamics and every 10 dynamics of activity was alternated with 10 dynamics of rest, beginning with rest. The total time of the task was 240 s. The fMRI sequence was a fast-field echo single-shot echo planar imaging technique with an echo planar imaging factor of 79, a TR of 3000 ms, a TE of 30 ms, and a flip angle of 90. Contiguous slices, 6 mm thick, were taken, and 30 slices were obtained. The field of view was 210?×?210 mm, with a matrix size of 64 mm, resulting in an in-plane resolution of 3.3 mm. Voxel size was 3.3?×?3.3?×?4.0 mm. For each slice, 80 dynamic time points were collected, providing a total imaging time of 4 min and 8 s, 30.1 s for each run.

Time of flight MRA (TOF-MRA) was obtained by the following parameters: TR, 22 ms; TE, 3.86 ms; matrix size, 384?×?256; field of view, 220?×?180 mm; bandwidth, 178 Hz per pixel; voxel size, 0.8?×?0.6?×?1.0 mm; flip angle; 18. 30 slices were obtained, and the total imaging time was 3 min and 29 s.

For DTI, we applied a single-shot spin-echo diffusion-weighted echo planar imaging sequence (TE, 93 ms; TR, 6100 ms; matrix size, 128?×?128; field of view, 230?×?230 mm; bandwidth, 1396 Hz per pixel; voxel size, 1.8?×?1.8?×?3 mm and diffusion-encoding gradients in 12 directions using b values of 0 and 1000 s/mm²). We used 45 slices with no intersection gap. The slice thickness was 3 mm, and each slice was angulated by 40° anteriorly to cover the optic chiasm, the occipital lobe, the corpus callosum, and the upper two thirds of the temporal lobe. The time needed for image acquisition was 6 min and 38 s.