Daniel Sodickson MD, PhD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: To evaluate the feasibility of order-of-magnitude accelerations of MR image acquisition using parallel MRI with a 32-element RF coil array. Methods and Materials: In order to explore the performance limits of parallel MRI with large numbers of RF coils, a prototype 32-receiver system was constructed. For this prototype, multiple sets of MR system electronics (GE Medical Systems, Milwaukee, WI) were integrated into a single 1.5T MR scanner. All receivers were frequency- and trigger-locked to each other. Pulse sequences were adapted to accommodate this synchronization mechanism. A tailored 32-element coil array was constructed for use with this system. The array has a total of 32 loop elements on two separated clamshells, each with 16 elements in a regular 2D grid. Simulations were used in the design process to characterize baseline signal-to-noise ratio (SNR) for unaccelerated scans, and reconstruction-related noise amplification (or g-factor) for accelerated scans, as a function of individual coil size and spacing. Abdominal and thoracic image volumes were acquired in adult subjects using 3D gradient echo and 3D spin echo imaging sequences. Unaccelerated reference images were compared with images obtained using a reduced set of phase encoding steps along two perpendicular phase-encoding directions. Data at various levels of acceleration were reconstructed using a conditioned SENSE algorithm, either with a separately acquired coil sensitivity reference or using calibration data placed within the accelerated acquisition itself. Results: Acceleration factors as high as 24 (6-fold acceleration in one phase encoding direction and 4-fold in the other) were achieved with minimal reconstruction artifact. Low g-factors were obtained, and the observed scaling of SNR with acceleration matched theoretical expectations, with an approximately 4-fold reduction in SNR at 12-fold acceleration, and an approximately 10-fold reduction at 24-fold acceleration. Also in accordance with theory, multidimensional accelerations yielded improved SNR compared with equivalent accelerations along any single direction. Conclusion: Order-of-magnitude accelerations are possible using many-element arrays. Although the SNR cost at very high accelerations may be prohibitive for signal-starved applications, such highly accelerated acquisitions hold particular promise for areas such as contrast-enhanced angiography, in which dynamic volumetric imaging is required in the context of high contrast-to-noise ratio.     (D.K.S. has a patent license agreement with GE Medical Systems and Siemens Medical Solutions. C.J.H., Y.Z., R.O.G., G.K. are employees of General Electric.) Questions about this event email: dsodicks@bidmc.harvard.edu

Sodickson MD, PhD, D, Highly Accelerated Parallel MRI on an MR Scanner with 32 Receiver Channels.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3106948.html