Free-Breathing Magnetization Transfer Imaging of the Lung at 0.55 T Using bSTAR

Area of Science:

• Medical Imaging
• Pulmonary Medicine
• Biomarker Development

Background:

• Magnetization transfer (MT) imaging is a valuable MRI technique for assessing tissue microstructure.
• Developing clinically applicable MT imaging for the lung at low magnetic field strengths (0.55 Tesla) presents technical challenges.

Purpose of the Study:

• To establish a clinically feasible method for lung MT imaging at 0.55 Tesla.
• To evaluate the performance of different MT imaging sequences for lung applications.

Main Methods:

• Exploration of three MT imaging techniques at 0.55 Tesla: self-gated 3D half-radial dual-echo balanced steady-state free precession (bSTAR), 2D multi-slice gradient echo (GRE), and self-gated 3D half-radial ultra-short TE (UTE).
• MT contrast was achieved through RF pulse prolongation (bSTAR) or off-resonance irradiation (UTE, GRE).
• Compressed sensing was used for offline reconstruction of self-gated scans.

Main Results:

• Successful MT imaging in healthy volunteers with comparable average MT ratio (MTR) values across sequences (28.8-30.7 pu).
• The bSTAR sequence demonstrated superior resolution compared to UTE and GRE.
• bSTAR MTR imaging showed high reproducibility in volunteers and differentiated MTR values in patients with pulmonary diseases.

Conclusions:

• MT-sensitized bSTAR enables in vivo, high-resolution, free-breathing MTR imaging of the entire lung within clinically acceptable scan times at 0.55 Tesla.
• The technique exhibits high reproducibility.
• Initial findings suggest MT imaging at 0.55 Tesla could serve as a noninvasive biomarker for pulmonary disease investigation and differentiation.