Ultra-high resolution imaging of the human brain using acquisition-weighted imaging at 9.4T

One of the main goals of ultra-high field MRI is to increase the spatial resolution reached in structural and functional images. Here, the possibility to obtain in vivo images of the human brain with voxel volumes below 0.02mm(3) is shown at 9.4T. To optimize SNR and suppress ringing artifacts, an acquisition-weighted 3D gradient-echo sequence is used, which acquires more averages in the center than in the outer regions of k-space. The weighting function is adjusted to avoid losses in spatial resolution and scan duration compared to a conventional experiment with an equal number of scans and otherwise identical parameters. Spatial resolution and SNR of the weighted sequence are compared to conventionally acquired images by means of phantom and in vivo measurements, and show improved image quality with unchanged spatial resolution and an SNR increase of up to 36% in phantoms and 20%±5% in vivo. Ultra-high resolution images with a voxel volume of 0.014mm(3) (0.13×0.13×0.8mm(3)) from the human brain have sufficient SNR and show fine intracortical detail, demonstrating the potential of the technique. The combination of acquisition-weighted imaging and highly sensitive array coils at ultra-high fields thus makes it possible to obtain images with ultra-high spatial resolutions within acceptable scan times.