T_1ρ mapping improvement using stretched-type adiabatic locking pulses for assessment of human liver function at 3T

The purpose of this study is to investigate the performance of stretched-type adiabatic spin lock pulses for homogeneous spin locking with a flexible spin lock time (TSL) setting.

T_1ρ values were obtained from 61 patients and five normal volunteers who were categorized using the Child-Pugh classification and scanned using each spin lock pulse type. The pulses used were the block and two kinds of hyperbolic secant (HS); HS8_10, and HS8_5. Visual scoring was categorized using a four point scale (1:Severe, 2:Moderate, 3:Mild and 4:None) to evaluate the homogeneity of the T_1ρ map and the source images obtained by each spin lock pulse. Mean T_1ρ values among the patient groups with different Child-Pugh classification were compared.

The visual assessment scores were 1.98 ± 1.05 for block pulse locking, 3.87 ± 0.39 for HS8_10 pulse locking, and 3.83 ± 0.45 for HS8_5 pulse locking, respectively. The scores between block pulse and HS8_10 were significantly different (p < 0.001), as were those between block pulse and HS8_5 (p < 0.001). The median T_1ρ values of normal liver function, Child-Pugh A, and Child-Pugh B or C were 37.00 ms, 40.77 ms, and 42.20 ms for block pulse, 46.75 ms, 50.78 ms, and 55.60 ms for HS8_10, and 48.80 ms, 55.42 ms, and 57.80 ms for HS8_5, respectively.

The spin locking sequence using stretched-type adiabatic pulses provides homogeneous liver T_1ρ maps with reduced artifact and is necessary for a robust evaluation of liver function using T_1ρ.