T1ρ magnetic resonance fingerprinting

Abstract

T_1ρ relaxation imaging is a quantitative imaging technique that has been used to assess cartilage integrity, liver fibrosis, tumors, cardiac infarction, and Alzheimer's disease. T₁ , T₂ , and T_1ρ relaxation time constants have each demonstrated different degrees of sensitivity to several markers of fibrosis and inflammation, allowing for a potential multi-parametric approach to tissue quantification. Traditional magnetic resonance fingerprinting (MRF) has been shown to provide quick, quantitative mapping of T₁ and T₂ relaxation time constants. In this study, T_1ρ relaxation is added to the MRF framework using spin lock preparations. An MRF sequence involving an RF-spoiled sequence with T_R , flip angle, T_1ρ , and T₂ preparation variation is described. The sequence is then calibrated against conventional T₁ , T₂ , and T_1ρ relaxation mapping techniques in agar phantoms and the abdomens of four healthy volunteers. Strong intraclass correlation coefficients (ICC > 0.9) were found between conventional and MRF sequences in phantoms and also in healthy volunteers (ICC > 0.8). The highest ICC correlation values were seen in T₁ , followed by T_1ρ and then T₂ . In this study, T_1ρ relaxation has been incorporated into the MRF framework by using spin lock preparations, while still fitting for T₁ and T₂ relaxation time constants. The acquisition of these parameters within a single breath hold in the abdomen alleviates the issues of movement between breath holds in conventional techniques.

Keywords: body; quantitation; relaxometry; sampling strategies.

Figure 1:

(A) Under-sampled spiral used for acquisition in the proposed sequence. (B) Spin Lock Preparation (SLP) used for T₁ρ contrast. (C) T₂ MLEV preparation used for T₂ contrast.

Figure 2:

(A) Flip Angle (FA) variations for the proposed sequence. The blue region is primarily for T₁ contrast, the red region is mainly for T₁ρ contrast, and the green region is mainly for T₂ contrast. (B) TR variation, (C) SLP placement and TSL times, and (D) T₂ preparation placement and preparation time for the proposed sequence.

Figure 3:

Phantom T₁, T₂, and T₁ρ relaxation maps for conventional methods (VFA T₁, TSE T₂, T₁ρ) and the proposed MRF sequence.

Figure 4:

(Left) Plots of the mean T₁, T₂, and T₁ρ relaxation times in phantoms for conventional (VFA T₁, TSE T₂, T₁ρ) and MRF methods. The dashed red line indicates a theoretical 1:1 relationship, while the black line is a linear fit of the data (with fitting equation, Spearman’s rho value, and p-value shown in upper left). (Right) Plots of the difference the conventional and MRF mean values for the T₁, T₂, and T₁ρ relaxation times, along with the mean difference and the confidence interval of the difference (indicated by the dashed lines). The coefficient of variation is shown in the upper right.

Figure 5:

Comparison of in vivo T₁, T₂, and T₁ρ relaxation maps for conventional (VFA T₁, TSE T₂, T₁ρ) and MRF sequences for one of the healthy volunteers

Figure 6:

Plots of the mean T₁, T₂, and T₁ρ relaxation times in healthy volunteers for conventional (VFA T₁, TSE T₂, T₁ρ) and MRF methods. The dashed red line indicates a 1:1 relationship, while the black line is a linear fit of the data. The dashed red line indicates a theoretical 1:1 relationship, while the black line is a linear fit of the data (with fitting equation, R value, and p-value shown in upper left). (Right) Plots of the difference the conventional and MRF mean values for the T₁, T₂, and T₁ρ relaxation times, along with the mean difference and the confidence interval of the difference (indicated by the dashed lines). The coefficient of variation is shown in the upper right.