Slice-selective implementation of an adiabatic T2Prep sequence increases coronary artery conspicuity at 3T
Journal of Cardiovascular Magnetic Resonance volume 14, Article number: O52 (2012)
In non-contrast coronary MRA, the non-selective T2Prep1-2 has been widely used for contrast enhancement between the coronary blood-pool and the myocardium3-5. This non-selective pre-pulse affects the magnetization both inside and outside the field-of-view, resulting in a reduced steady-state magnetization of the inflowing blood, and consequently a penalty in SNR. We hypothesize that a slice-selective T2Prep would leave the magnetization of blood outside the imaged volume unaffected, and thereby minimize SNR penalty for inflowing blood. The purpose of this work was to implement a slice-selective T2Prep coronary MRA sequence and to assess the SNR gain quantitatively.
bloch equations were simulated to test the above hypothesis and to estimate the expected SNR gain.
the selective T2Prep was implemented by replacing the non-selective 90° RF pulses with slice-selective versions plus flow-compensating gradients, and an additional time gap between the T2Prep and other pre-pulses to allow for inflow of a larger volume of spins with equilibrium magnetization (Figure1). The T2Prep volume was graphically selected along the arterial axis and orthogonal to the imaged volume without covering the ventricles (Figure 1c) to avoid saturation of the inflow spins in the ascending aorta.
volume-targeted 3D free-breathing navigator-gated and corrected coronary MRA5 were acquired on a Philips Achieva 3T a) without T2Prep, b) with the conventional T2Prep, and c) with the proposed slice-selective T2Prep (Tgap=150ms) in 10 healthy volunteers. Repeated measures of blood SNR, vessel-neighborhood CNR, and vessel sharpness were statistically compared using ANOVA with Tukey post hoc test.
Consistent with the hypothesis, numerical simulations suggest that the slice-selective T2Prep leads to an SNR increase in the blood-pool (Figure 1A) when compared to its non-selective counterpart. Figure 1C shows an in vivo result obtained with the slice-selective T2Prep localized along the dark bar (arrows). When compared to the non-selective T2Prep, vessel sharpness improved significantly using the proposed implementation (54.1±2.4% vs. 48.5±2.4%, p<0.05, Figure 2A). While both T2Prep variants led to an SNR penalty when compared to no T2Prep as previously reported3, the slice-selective T2Prep still led to a significantly improved SNR compared to conventional T2Prep (39.9±3.2 vs. 27.7±2.5, p<0.02, Figure 2B). A similar finding was observed in CNR measurements (16.1±1.6 vs. 11.8±1.5, p<0.05, Figure 2C).
A slice-selective adiabatic T2Prep leads to improved coronary artery conspicuity when compared to its conventional non-selective counterpart.
This work was supported in part by the NIH/NHLBI research grants.
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Soleimanifard, S., Schär, M., Prince, J.L. et al. Slice-selective implementation of an adiabatic T2Prep sequence increases coronary artery conspicuity at 3T. J Cardiovasc Magn Reson 14 (Suppl 1), O52 (2012). https://doi.org/10.1186/1532-429X-14-S1-O52