Abstract
BackgroundImproved motion-sensitized driven-equilibrium (iMSDE) preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T2 decay, eddy current effects and B1+ inhomogeneity. In this study, we investigate the signal to noise ratio (SNR) and blood suppression performance of iMSDE using composite RF pulses and sinusoidal gradients. Optimized first moment (m1) values for iMSDE prepared T1- and T2- weighted (T1- and T2-w) imaging are presented.MethodsTwelve healthy volunteers and six patients with carotid artery disease underwent iMSDE and double inversion recovery (DIR) prepared T1- and T2-w fast spin echo (FSE) MRI of the carotid arteries. Modified iMSDE module using composite RF pulses and sinusoidal gradients were evaluated with a range of m1. SNR of adjacent muscle, vessel wall and the lumen were reported. The optimized iMSDE module was also tested in a 3D variable flip angle FSE (CUBE) acquisition.ResultsThe SNR of muscle was highest using sinusoidal gradients, and the relative improvement over the trapezoidal gradient increased with higher m1 (p<0.001). Optimal SNR was observed using an iMSDE preparation scheme containing two 180° composite pulses and standard 90° and -90° pulses (p=0.151). iMSDE produced better blood suppression relative to DIR preparations even with a small m1 of 487 mT*ms2/m (p<0.001). In T1-w iMSDE, there was a SNR decrease and an increased T2 weighting with increasing m1. In T2-w iMSDE, by matching the effective echo time (TE), the SNR was equivalent when m1 was <= 1518 mT*ms2/m, however, higher m1 values (2278 – 3108 mT*ms2/m) reduced the SNR. In the patient study, iMSDE improved blood suppression but reduced vessel wall CNR efficiency in both T1-w and T2-w imaging. iMSDE also effectively suppressed residual flow artifacts in the CUBE acquisition.ConclusionsiMSDE preparation achieved better blood suppression than DIR preparation with reduced vessel wall CNR efficiency in T1-w and T2-w images. The optimized m1s are 487 mT*ms2/m for T1-w imaging and 1518 mT*ms2/m for T2-w imaging. Composite 180° refocusing pulses and sinusoidal gradients improve SNR performance. iMSDE further improves the inherent blood suppression of CUBE.
Highlights
Improved motion-sensitized driven-equilibrium preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T2 decay, eddy current effects and B1+ inhomogeneity
T2 decay during TiMSDE was responsible for the majority of the signal decrease. Improved motion-sensitized driven-equilibrium (iMSDE) using sinusoidal gradients demonstrated a better signal to noise ratio (SNR) performance compared to iMSDE using trapezoidal gradients with equivalent m1s, with this trend becoming more significant with increasing m1
In this study we demonstrated that a small m1 (487 mT*ms2/m) can achieve better blood suppression, albeit with reduced SNR in T1-w and T2-w fast spin echo (FSE) compared with conventional double inversion recovery (DIR) preparation
Summary
Improved motion-sensitized driven-equilibrium (iMSDE) preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T2 decay, eddy current effects and B1+ inhomogeneity. Double inversionrecovery (DIR) methods [4] have become the de facto standard for blood suppressed vessel wall imaging. This method is sensitive to the rate of flow replenishment which leads to plaque-mimicking artefacts in the presence of slow and turbulent flow that often occurs around the carotid bifurcation [3]. Motion-sensitized driven-equilibrium (MSDE) preparation has been proposed as an alternative blood suppression technique [5,6]. Since iMSDE requires a shorter preparation time relative to DIR preparation, it is more time efficient
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