Contrast-enhanced supraaortic MRA at 3.0T using parallel acquisition with acceleration factors up to 16

Purpose: Contrast-enhanced 3D MRA (CE-3DMRA) has become a routine application in the assessment of supraaortic steno-occlusive disease. However, acquisition time has to be chosen according to arterial bolus characteristics limiting spatial resolution and/or the number of acquired slices, i.e. the anatomic coverage. Parallel imaging allows for a reduction of acquisition time at the expense of signal-to-noise ratio while spatial resolution is maintained. Supraaortic MRA at 3.0T offers increased signal-to-noise and theoretically holds promise to use higher acceleration factors (i.e. >2) in parallel imaging while maintaining image quality. The purpose of the study was the implementation and evaluation of supraaortic 3D MRA with SENSE at 3.0T using high parallel imaging acceleration factors up to 16.

Methods: CE-3DMRA of the supraaortic arteries with randomly segmented central k-space ordering (CENTRA) and SENSE was performed in 20 patients and 5 volunteers on a clinical whole body 3.0T MR system (Achieva, Philips Medical Systems, Best, NL) using 8-channel and 16-channel neurovascular coils (Philips Medical Systems, Best, NL). CE-3DMRA protocols were created using SENSE factors (SF) ranging from 1 to 16 (SF 1, n=1; SF 2, n=2; SF 4, n=15; SF 9, n=5; SF 16, n=2). An acquired matrix of 512×512 (SF 2, SF 4; coronal), 656×656 (SF 9; sagittal) and 752×768 (SF 16, sagittal) were acquired over a 320 to 350mm FOV with 0.98 and 0.90mm thin slices (0.49 and 0.45mm overcontiguous) yielding an acquired sub-millimetre spatial resolution ranging from (0.63×0.63×0.90) to (0.46×0.46×0.98)mm³ as compared to (0.81×0.81×1.0)mm³ with SF 1 (matrix 432×432). Acquisition time was reduced from 2:09min. (SF 1) to 1:37min., 1:24min., 0:58min., and 1:23min (SF 2, SF 4, SF 9 and SF 16), respectively, while increasing the number of slices substantially from 150 slices (SF 1) up to 365 slices (SF 4, SF 9 and SF 16).

Results: Supraaortic CE-3DMRA with SENSE at 3.0T was successfully performed in 25/25 patients. Despite of shorter acquisition times, the added number of slices (i.e. increased scan volume) (SF 4, 9 and 16) and the higher spatial resolution in supraaortic CE-3DMRA (SF 2, 4, 9 and 16) with high SENSE acceleration allowed for visualization of head and neck arteries that were not covered by the standard protocol with SF 1. Furthermore, the added scan volume simplifies planning of the sequence and potentially helps to cover distal portions of the vertebral arteries (V3– V4 segments) as well as peripheral segments of the intracranial arteries.

Conclusion: Supraaortic CE-3DMRA with SENSE acceleration factors up to 16 is clinically feasible at 3.0T and a very useful technique to provide additional anatomic information and higher spatial resolution while reducing acquisition time. Compared to standard imaging (SF 1), it simplifies the positioning of the scan volume, which therefore makes it even more beneficial for clinical application.