Spatially selective implementation of the adiabatic T₂prep sequence for magnetic resonance angiography of the coronary arteries

Abstract

In coronary magnetic resonance angiography, a magnetization-preparation scheme for T2-weighting (T2Prep) is widely used to enhance contrast between the coronary blood-pool and the myocardium. This pre-pulse is commonly applied without spatial selection to minimize flow sensitivity, but the non-selective implementation results in a reduced magnetization of the in-flowing blood and a related penalty in signal-to-noise-ratio (SNR). It is hypothesized that a spatially-selective T2Prep would leave the magnetization of blood outside the T2Prep volume unaffected, and thereby lower the SNR penalty. To test this hypothesis, a spatially-selective T2Prep was implemented where the user could freely adjust angulation and position of the T2Prep slab to avoid covering the ventricular blood-pool and saturating the in-flowing spins. A time gap of 150ms was further added between the T2Prep and other pre-pulses to allow for in-flow of a larger volume of unsaturated spins. Consistent with numerical simulation, the spatially-selective T2Prep increased in vivo human coronary artery SNR (42.3±2.9 vs. 31.4±2.2, n=22, p<0.0001) and contrast-to-noise-ratio (18.6±1.5 vs. 13.9±1.2, p=0.009) as compared to those of the non-selective T2Prep. Additionally, a segmental analysis demonstrated that the spatially-selective T2Prep was most beneficial in proximal and mid segments where the in-flowing blood volume was largest compared to the distal segments.

Slice‐selective adiabatic magnetization T2‐preparation (SAMPA) for efficient T2‐weighted imaging at ultrahigh field strengths

“…To our knowledge, this is the first fully adiabatic slice‐selective T 2 ‐prep proposed. In a previous work, a twice‐refocused T 2 ‐prep was modified to achieve slice selection using the tip–down and tip–up pulses ; however, the presence of conventional 90° pulses reduces the B 1 robustness of such T 2 ‐prep. Slice‐selective B 1 ‐insensitive pulses (STABLE) derived from BIR4 designs have also been proposed to achieve adiabatic excitation at high field .…”

Single-breath-hold whole-heart coronary MRA in healthy volunteers at 3.0-T MRI

“…Therefore, a large value of T2prep could improve image quality. Sahar et al reported that T2 prep technic increased image quality compared to non T2 prep technic (Soleimanifard et al 2013 ). Mueller et al state that dual-source RF transmission with RF shimming results in an optimized SAR distribution, thereby reducing local SAR peaks (Mueller et al 2012 ).…”

Repositioning precision of coronary arteries measured on X-ray angiography and its implications for coronary MR angiography

“…Future improvements of the T 2 ‐post pulse sequence may include the implementation of a slice‐selective T 2 preparation module. Soleimanifard et al demonstrated that the slice‐selective T 2 ‐prep with a time interval of 150 ms between T 2 ‐prep and the acquisition can improve the SNR and CNR of coronary artery images in diastole. This concept can theoretically also be applied to systolic imaging with the T 2 ‐post technique.…”

“…The simulated sequence parameters were the same as for the sequence protocol mentioned below. Tissue parameters were used as follows: arterial blood T 1 /T 2 = 1650/230ms ; myocardium T 1 /T 2 = 1470/43 ms . While a segmented k ‐space gradient echo imaging sequence with multiple RF excitations per cardiac cycle was simulated, the signal from the first RF excitation was used for further analysis.…”