Robust cardiac T 1 ρ $$ {\mathrm{T}}_{1_{\boldsymbol{\rho}}} $$ mapping at 3T using adiabatic spin-lock preparations

Abstract

Purpose: The aim of this study is to develop and optimize an adiabatic $T_{1\rho }$ ( $T_{1\rho ,\text{adiab}}$ ) mapping method for robust quantification of spin-lock (SL) relaxation in the myocardium at 3T.

Methods: Adiabatic SL (aSL) preparations were optimized for resilience against $B_0$ and $B_1^{+}$ inhomogeneities using Bloch simulations. Optimized $B_0$ -aSL, Bal-aSL and $B_1$ -aSL modules, each compensating for different inhomogeneities, were first validated in phantom and human calf. Myocardial $T_{1\rho }$ mapping was performed using a single breath-hold cardiac-triggered bSSFP-based sequence. Then, optimized $T_{1\rho ,\text{adiab}}$ preparations were compared to each other and to conventional SL-prepared $T_{1\rho }$ maps (RefSL) in phantoms to assess repeatability, and in 13 healthy subjects to investigate image quality, precision, reproducibility and intersubject variability. Finally, aSL and RefSL sequences were tested on six patients with known or suspected cardiovascular disease and compared with LGE, $T_1$ , and ECV mapping.

Results: The highest $T_{1\rho ,\text{adiab}}$ preparation efficiency was obtained in simulations for modules comprising 2 HS pulses of 30 ms each. In vivo $T_{1\rho ,\text{adiab}}$ maps yielded significantly higher quality than RefSL maps. Average myocardial $T_{1\rho ,\text{adiab}}$ values were 183.28 $\pm$ 25.53 ms, compared with 38.21 $\pm$ 14.37 ms RefSL-prepared $T_{1\rho }$ . $T_{1\rho ,\text{adiab}}$ maps showed a significant improvement in precision (avg. 14.47 $\pm$ 3.71% aSL, 37.61 $\pm$ 19.42% RefSL, p < 0.01) and reproducibility (avg. 4.64 $\pm$ 2.18% aSL, 47.39 $\pm$ 12.06% RefSL, p < 0.0001), with decreased inter-subject variability (avg. 8.76 $\pm$ 3.65% aSL, 51.90 $\pm$ 15.27% RefSL, p < 0.0001). Among aSL preparations, $B_0$ -aSL achieved the better inter-subject variability. In patients, $B_1$ -aSL preparations showed the best artifact resilience among the adiabatic preparations. $T_{1\rho ,\text{adiab}}$ times show focal alteration colocalized with areas of hyper-enhancement in the LGE images.

Conclusion: Adiabatic preparations enable robust in vivo quantification of myocardial SL relaxation times at 3T.

Keywords: B 0 $$ {\mathrm{B}}_0 $$ / B 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneities; T1ρ mapping; adiabatic RF; myocardium; spin-lock relaxation.