Rapid high-resolution T1 mapping using a highly accelerated radial steady-state free-precession technique

Abstract

Background: T₁ 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 T₁ 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 T₁ estimation; testing was done in phantoms using as reference an IR spin-echo pulse sequence. T₁ mapping with IR-radSSFP was also assessed in vivo (brain and abdomen) and T₁ values were compared with literature. T₁ maps were also compared with a radial IR-FLASH technique.

Statistical tests: A two-tailed t-test was used to compare T₁ 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 20˚ was optimal for T₁ mapping. When comparing single to multi-slice experiments in phantoms there were no significant differences between the means T₁ values (P = 0.0475). In vivo results show that T₁ 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; T₁ 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 T₁ mapping. This technique is fast, motion-insensitive and yields repeatable T₁ values comparable to those in literature.

Level of evidence: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:239-252.

Keywords: T1; T1 mapping; compressed sensing; model-based; radial MRI.