Jeffrey Lee Creasy MD, Presenter: Nothing to Disclose

Edward B. Welch PhD, Abstract Co-Author: Employee, Koninklijke Philips Electronics NV

Robin Avison RT, Abstract Co-Author: Nothing to Disclose

Adam W. Anderson, Abstract Co-Author: Nothing to Disclose

John C. Gore PhD, Abstract Co-Author: Nothing to Disclose

Malcolm Avison PhD, Abstract Co-Author: Nothing to Disclose

To optimize a clinical protocol for imaging of CNS pathologies at 7T.

Studies were performed on a Philips Achieva 7T MRI scanner with volume transmit and 16-channel SENSE receive head-coil. The performance of a range of sequences, including 3D T1W turbo field echo (TFE), multi-slice gradient and spin echo (GRASE), and 3D susceptibility weighted fast field echo (FFE), were assessed in healthy young adults. Sequences were iteratively modified to achieve improved spatial resolution, tissue contrast and SNR, or decreased imaging time.

Initial results confirm the need for careful consideration of the impact of static and radiofrequency field inhomogeneities on image contrast and uniformity when using standard sequences. These factors, together with the increase in T1, decrease in T1 dispersion, and decreased T2 and T2*, require significant modifications to standard imaging parameters to achieve high quality images. Further modifications are required to maintain SAR within acceptable limits. Despite these constraints, 7T neuroimaging demonstrated excellent contrast and increased sensitivity, permitting greater SENSE acceleration without significant image degradation when compared with 3T, allowing either reduced imaging times, or increased spatial resolution for the same imaging time. A current standard protocol consists of: Axial 3D T1W TFE (scan time 03:07) and Axial 3D TFE (scan time 05:00) with voxel sizes 0.5x0.5x2.5 mm; Isotropic 3D T1W TFE (voxel size = 1.0 x 1.0 x 1.0 mm, scan time 07:14); Sagittal 3D TFE (0.33 x 0.33 x 4.0 mm, scan time 02:37); Multi-slice T2W GRASE (voxel size = 0.5 x 0.5 x 2.0 mm, scan time 06:48); and an SWI sequence (voxel size = 1.0 x 1.0 x 1.0 mm, scan time 04:32). The total scan time including set up and pre-scanning is less than 40 minutes.

While 7T imaging presents some challenges, a standard set of imaging sequences can be optimized to provide high quality images with excellent contrast and greater spatial resolution than at lower fields in reasonable times.

As with human systems at 3T and 1.5T, imaging at 7T will require continual refinement of pulse sequences to account for field-dependent effects and to maximize clinical utility.

Creasy, J, Welch, E, Avison, R, Anderson, A, Gore, J, Avison, M, Anatomic Imaging of Human Brain at 7T.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5009483.html