Volumetric multicomponent T1ρ relaxation mapping of the human liver under free breathing at 3T

Abstract

Purpose: To develop a 3D sequence for T_1ρ relaxation mapping using radial volumetric encoding (3D-T_1ρ -RAVE) and to evaluate the multi relaxation components in the liver of healthy controls and chronic liver disease (CLD) patients.

Methods: Fat saturation and T_1ρ preparation modules were followed by a train of gradient-echo acquisitions and T₁ restoration delay. The series of T_1ρ -weighted images were fitted using mono-exponential, bi-exponential, and stretched-exponential models. The repeatability and reproducibility of the proposed technique were evaluated on National Institute of Standards and Technology phantom by calculating the coefficient of variation between test-retest scans on the same scanner and between two different 3T scanners, respectively. Mann-Whitney U-test was performed to assess differences in T_1ρ components among patients (n = 3) and a control group (n = 10).

Results: The phantom study showed an error of 8.9% and 11.5% in mono T₂ relaxation time measurement relative to the reference on 2 different scanners. The coefficient of variation for test-retest scans performed on the same scanner was 5.7% and 2.4% for scans performed on 2 scanners. The comparison between healthy controls and CLD patients showed a significant difference (P < .05) in mono relaxation time (P = .002), stretched-exponential relaxation parameter (P = .04). The Akaike information criteria C criterion showed 2.53 ± 0.9% (2.3 ± 0.3% for CLD) of the voxels are bi-exponential while in 65.3 ± 5.8% (81.2 ± 0.06% for CLD) of the liver voxels, the stretched-exponential model was preferred.

Conclusion: The 3D-T_1ρ -RAVE sequence allows volumetric, multicomponent T_1ρ assessment of the liver during free breathing and can distinguish between healthy volunteers and CLD patients.

Keywords: RAVE; T1ρ relaxation; bi-exponential fitting; stretched-exponential model.

Figure 1.

3D-T_1ρ-RAVE (a) Pulse sequence timing diagram: Fat suppression module was followed by a self-compensated paired T_1ρ preparation module, and a series of excitations to acquire one spoke for all the slices in a centric manner. A delay was applied before repeating the modules for next spoke to reduce the T1 contamination. (b) K-space radial golden angle stack of stars trajectory.

Figure 2.

(a) NIST Phantom (b) representative MR scans of T₂ spheres and the T₂ mono exponential map of the selected spheres. (c) Ground truth T₂ vs. Estimated T₂ from 3D-T_1ρ-RAVE sequence on two different scanners (d) repeatability (Prisma vs. Prisma) and reproducibility (Prisma vs. Skyra) test-retest experiment results.

Figure 3.

The representative T_1ρ-weighted scans acquired from the same slice from a healthy volunteer at different t_sl.

Figure 4.

The representative T_1ρ relaxation maps in (a) a CLD patient and (b) a healthy volunteer. The AIC comparison maps show the preferred model for each voxel based on the AIC_C criterion. A decrease in T_1ρ,bs, T_1ρ,se, and α_se can be observed in CLD patients.

Figure 5.

Boxplots comparison of T_1ρ relaxation components for (a) ten healthy controls and three CLD patients. (b) Four age-matched healthy controls and three CLD patients. A red line shows the median of each group. The scatter circles show the values for each subject. The p-values of comparison between the two groups are shown on the top of each plot. The parameters with significant difference (p<0.05) are marked with an asterisk (*).

Figure 6.

Histogram comparison of (a) mono, (b, c) stretched, and (d-f) biexponential T_1ρ relaxation components between healthy controls and CLD patients.