Abdominal T2-Weighted Imaging and T2 Mapping Using a Variable Flip Angle Radial Turbo Spin-Echo Technique.

Area of Science:

• Radiology and Medical Imaging
• Biomedical Engineering
• Magnetic Resonance Imaging (MRI)

Background:

• Current T2 mapping techniques in abdominal imaging suffer from limitations including low resolution, restricted slice coverage, motion sensitivity, and prolonged acquisition times.
• There is a need for advanced MRI sequences that can provide high-quality T2 mapping efficiently within a single breath-hold.

Purpose of the Study:

• To develop and evaluate a radial turbo spin-echo technique with refocusing variable flip angles (RADTSE-VFA) for enhanced spatiotemporal T2 mapping.
• To assess the performance of RADTSE-VFA against its constant flip angle counterpart (RADTSE-CFA) in terms of image quality, T2 accuracy, and specific absorption rate (SAR).
• To determine the efficacy of RADTSE-VFA for efficient slice coverage during breath-hold abdominal MRI.

Main Methods:

• A prospective technical efficacy study was conducted using agarose phantoms and 12 human patients.
• The RADTSE-VFA sequence was developed using a constrained objective function to optimize refocusing flip angles.
• Phantom and in vivo data were analyzed to compare RADTSE-VFA and RADTSE-CFA regarding relative contrast, T2 estimation accuracy, SAR, and focal liver lesion classification.

Main Results:

• Phantom studies showed no significant differences in relative contrast or T2 accuracy between RADTSE-VFA and RADTSE-CFA, but RADTSE-CFA exhibited T2 overestimation with added noise.
• In vivo imaging revealed comparable spleen-to-liver and kidney-to-liver relative contrast between the two techniques.
• Mean T2 values for spleen and kidney medulla were similar, but liver T2 was significantly higher with RADTSE-CFA, consistent with phantom findings. RADTSE-VFA demonstrated significantly lower SAR, enabling 1.5 times greater slice coverage.

Conclusions:

• RADTSE-VFA provides noise-robust T2 estimation and comparable image contrast to RADTSE-CFA.
• The variable flip angle approach in RADTSE-VFA minimizes SAR, enhancing slice efficiency for breath-hold abdominal imaging.
• RADTSE-VFA represents a promising advancement for high-quality, efficient T2 mapping in abdominal MRI.