A Cylindrical, Inner Volume Selecting 2D-T2-Prep Improves GRAPPA-Accelerated Image Quality in MRA of the Right Coronary Artery

Abstract

BackgroundTwo-dimensional (2D) spatially selective radiofrequency (RF) pulses may be used to excite restricted volumes. By incorporating a "pencil beam" 2D pulse into a T2-Prep, one may create a "2D-T2-Prep" that combines T2-weighting with an intrinsic outer volume suppression. This may particularly benefit parallel imaging techniques, where artefacts typically originate from residual foldover signal. By suppressing foldover signal with a 2D-T2-Prep, image quality may therefore improve. We present numerical simulations, phantom and in vivo validations to address this hypothesis.MethodsA 2D-T2-Prep and a conventional T2-Prep were used with GRAPPA-accelerated MRI (R = 1.6). The techniques were first compared in numerical phantoms, where per pixel maps of SNR (SNRmulti), noise, and g-factor were predicted for idealized sequences. Physical phantoms, with compartments doped to mimic blood, myocardium, fat, and coronary vasculature, were scanned with both T2-Preparation techniques to determine the actual SNRmulti and vessel sharpness. For in vivo experiments, the right coronary artery (RCA) was imaged in 10 healthy adults, using accelerations of R = 1,3, and 6, and vessel sharpness was measured for each.ResultsIn both simulations and phantom experiments, the 2D-T2-Prep improved SNR relative to the conventional T2-Prep, by an amount that depended on both the acceleration factor and the degree of outer volume suppression. For in vivo images of the RCA, vessel sharpness improved most at higher acceleration factors, demonstrating that the 2D-T2-Prep especially benefits accelerated coronary MRA.ConclusionSuppressing outer volume signal with a 2D-T2-Prep improves image quality particularly well in GRAPPA-accelerated acquisitions in simulations, phantoms, and volunteers, demonstrating that it should be considered when performing accelerated coronary MRA.

Combined T2‐preparation and multidimensional outer volume suppression for coronary artery imaging with 3D cones trajectories

“…A contributing factor for superior coronary image quality with the proposed sequence could be attributed to superior stopband suppression and fat suppression, as demonstrated by the Bloch simulation and phantom results. Superior stopband suppression improves coronary image quality by reducing aliasing and improving parallel imaging performance to reduce g‐factor . Superior fat suppression improves coronary image quality by reducing off‐resonance blurring from fat onto the coronary arteries.…”

“…Superior stopband suppression improves coronary image quality by reducing aliasing and improving parallel imaging performance to reduce g-factor. 11,12 Superior fat suppression improves coronary image quality by reducing off-resonance blurring from fat onto the coronary arteries. As a tradeoff, in the presence of B 0 and B 1 inhomogeneities, suppressing one spatial dimension at a time results in diminished suppression in the dimension first suppressed.…”

“…Furthermore, OVS may improve motion correction by suppressing unwanted anatomy . Suppressing signal outside the ROI also improves the dynamic range and parallel imaging performance …”

“…9 Suppressing signal outside the ROI also improves the dynamic range 10 and parallel imaging performance. 11,12 OVS methods largely fall into two paradigms. The first paradigm uses multiple 1D slab saturation pulses to suppress signal outside the ROI.…”

Improved respiratory self‐navigation for 3D radial acquisitions through the use of a pencil‐beam 2D‐T2‐prep for free‐breathing, whole‐heart coronary MRA

“…Although this technique has been reported for navigator‐based coronary imaging , it has not yet been tested with whole‐heart self‐navigated 3D radial MRA. Because whole‐heart MRA is frequently T 2 ‐prepared, replacing a conventional T 2 ‐Prep with this 2D‐T 2 ‐Prep should add no additional time requirements.…”