Trevor Andrews PhD, Presenter: Employee, Koninklijke Philips Electronics NV

George Ernest Gentchos MD, Abstract Co-Author: Nothing to Disclose

Marc Kouwenhoven PhD, Abstract Co-Author: Researcher, Koninklijke Philips Electronics NV

Melanie S Kotys DSC, Abstract Co-Author: Researcher, Koninklijke Philips Electronics NV

Jay Gonyea, Abstract Co-Author: Nothing to Disclose

Christopher G. Filippi MD, Abstract Co-Author: Nothing to Disclose

Alisa Kathleen Johnson MD, Abstract Co-Author: Nothing to Disclose

B1-shimming significantly improved image quality and reduced shading artifact for 3T black blood MRI in all cases.

Standing wave artifacts produce patient-dependent focal signal loss in some cardiac MR sequences limiting clinical acceptance of 3T cardiac MR imaging. Shading artifacts may simulate or mask cardiac pathology. This is typically caused by RF transmit (B1) inhomogeneity. In this study, we assess the efficacy of B1-shimming for reducing or eliminating shading artifacts in cardiac black blood imaging on a clinical 3T MR system.

9 healthy volunteers were imaged on a Philips 3.0T Achieva Multitransmit MR scanner (Best, Netherlands) with two RF transmitters for automated B1 shimming. For each subject a single-breathhold, 2D B1 shimming calibration was performed with saturated dual-angle method. Patient-specific RF transmitter settings were calculated on the console for later B1-shimmed scans. A breath-held, single-phase, 4-chamber view black blood TSE acquisition was obtained without B1-shimming: TR 2 beats, TE 10ms, slice 8mm, FOV 320 x 320mm, 3 slices, gap 5mm, TSE factor 23, acq. Resolution 1.4 x 1.75mm, SENSE=1, trigger delay mid-diastole. A noise image with identical receiver settings was acquired for later SNR and CNR calculations. These images were reacquired with B1-shimming. To assess image quality ROIs were drawn within the unshimmed slice with the most shading artifact in the darkest region of the septum and the blood pool. A chest radiologist assessed image quality using a 5-point scale (1=non-diagnostic; 5= no standing wave artifact).

Unshimmed images for all subjects had at least some shading artifact noted by the radiologist, usually at the septum near the apex or adjacent to the sternum and RV wall. For all radiologist-assessments the B1-shimmed images were scored no less than 4. The image quality score improved significantly from 3.00±0.71 to 4.78±0.44 [p=0.005, Friedman rank test] using B1-shimming. For the unshimmed image SNR in the septum ROI varied between subjects from 52 to 249. SNR in the septum ROI increased in every case with B1-shimming between 30% and 199%. Septum-to-blood-pool CNR also improved between 55% and 349%.

Andrews, T, Gentchos, G, Kouwenhoven, M, Kotys, M, Gonyea, J, Filippi, C, Johnson, A, Reduction in Shading Artifacts at 3.0T Black Blood TSE Cardiac MR Imaging Using B1 Shimming.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9015637.html