Abdominal simultaneous 3D water T1 and T2 mapping using a free-breathing Cartesian acquisition with spiral profile ordering.

Abstract

Purpose: To develop a method for abdominal simultaneous 3D water $T_1$ ( $w{T}_1$ ) and $T_2$ ( $w{T}_2$ ) mapping with isotropic resolution using a free-breathing Cartesian acquisition with spiral profile ordering (CASPR) at 3 T.

Methods: The proposed data acquisition combines a Look-Locker scheme with the modified BIR-4 adiabatic preparation pulse for simultaneous $w{T}_1$ and $w{T}_2$ mapping. CASPR is employed for efficient and flexible k-space sampling at isotropic resolution during free breathing. The imaging pipeline includes subspace reconstruction, water-fat separation, and $B_0$ -specific dictionary matching. The proposed method was validated in a water-fat relaxometry phantom using spin echo-based reference techniques and was compared with MOLLI $T_1$ and GRASE $T_2$ mapping in 10 volunteers. The method's flexibility was assessed at isotropic resolutions of 2.5, 3, and 3.5 mm, with corresponding scan times of 7:19, 5:23, and 3:52 min. Additionally, the method was applied to 9 oncological patients with abdominal pathologies.

Results: Phantom experiments demonstrated good agreement between the proposed method and spin echo-based reference techniques across a wide range of $w{T}_1$ and $w{T}_2$ values. The volunteer study assessed in vivo quantification performance and demonstrated the flexibility of the proposed method at different spatial resolutions. The 3 mm method was successively performed in patients with abdominal pathologies, whereby lesions with diameters below 1 cm could be assessed.

Conclusion: The proposed Look-Locker-based method using CASPR enables efficient, flexible, and simultaneous $w{T}_1$ and $w{T}_2$ mapping at isotropic resolution in a fixed scan time during free breathing.