Rapid high-resolution T mapping using a highly accelerated radial steady-state free-precession technique.

Li Z, Bilgin A, Johnson K, Galons J-P, Vedantham S, Martin DR, Altbach MI. 2019. Rapid high-resolution T mapping using a highly accelerated radial steady-state free-precession technique. J Magn Reson Imaging. 49:239–252. doi:10.1002/jmri.26170.

BACKGROUND: T mapping is often used in some clinical protocols. Existing techniques are limited in slice coverage, and/or spatial-temporal resolution, or require long acquisitions. Here we present a multi-slice inversion-recovery (IR) radial steady-state free precession (radSSFP) pulse sequence combined with a principal component (PC) based reconstruction that overcomes these limitations.

PURPOSE: To develop a fast technique for multi-slice high-resolution T mapping.

STUDY TYPE: Technical efficacy study done prospectively.

PHANTOM/SUBJECTS: IR-radSSFP was tested in phantoms, five healthy volunteers, and four patients with abdominal lesions.

FIELD STRENGTH/SEQUENCE: IR-radSSFP was implemented at 3T.

ASSESSMENT: Computer simulations were performed to optimize the flip angle for T estimation; testing was done in phantoms using as reference an IR spin-echo pulse sequence. T mapping with IR-radSSFP was also assessed in vivo (brain and abdomen) and T values were compared with literature. T maps were also compared with a radial IR-FLASH technique.

STATISTICAL TESTS: A two-tailed t-test was used to compare T values in phantoms. A repeatability study was carried out in vivo using Bland-Altman analysis.

RESULTS: Simulations and phantom experiments showed that a flip angle of 20o was optimal for T mapping. When comparing single to multi-slice experiments in phantoms there were no significant differences between the means T values (P = 0.0475). In vivo results show that T maps with spatial resolution as high as 0.69 mm × 0.69 mm × 2.00 mm (brain) and 0.83 mm × 0.83 mm × 3.00 mm (abdomen) can be generated for 84 brain slices in 3 min and 10 abdominal slices in a breath-hold; T values were comparable to those reported in literature. The coefficients of variation from the repeatability study were 1.7% for brain and 2.5-2.7% in the abdomen.

DATA CONCLUSION: A multi-slice IR-radSSFP technique combined with a PC-based reconstruction was demonstrated for higher resolution T mapping. This technique is fast, motion-insensitive and yields repeatable T values comparable to those in literature.

LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:239-252.