Rapid multicontrast brain imaging on a 0.35T MR-linac

Area of Science:

• Medical Physics
• Radiology
• Oncology

Background:

• Magnetic resonance-guided radiation therapy (MRgRT) offers real-time tumor monitoring but quantitative imaging at low fields (0.35T) is limited.
• Accurate quantitative imaging is crucial for precise treatment delivery and monitoring in MRgRT.

Purpose of the Study:

• To benchmark quantitative T1, R2*, and Proton Density (PD) mapping at 0.35T using a novel acquisition method, STAGE (Strategically Acquired Gradient Echo).
• To evaluate the feasibility of STAGE for longitudinal functional imaging in brain tumor patients undergoing MRgRT.

Main Methods:

• STAGE, a novel dual triple-echo gradient echo sequence, was optimized for a 0.35T MR-linac.
• Quantitative mapping (T1, R2*, PD) was benchmarked in an ISMRM/NIST phantom against traditional methods (VFA, IR).
• Longitudinal data from brain tumor patients were acquired to assess STAGE's clinical feasibility.

Main Results:

• STAGE demonstrated good agreement with reference quantitative MR values in the phantom, with low relative error (RE) and coefficient of variability (CV).
• The optimized STAGE sequence achieved whole-brain coverage with 1x1x3 mm^3 resolution in 10 minutes.
• Pilot patient data showed STAGE-derived R2* and T1 maps were sensitive to tumor changes, comparable to 3T MRI.

Conclusions:

• Quantitative T1, R2*, and PD mapping using STAGE are feasible and accurate at 0.35T MR-linac.
• STAGE provides quantitative imaging comparable to traditional methods in significantly less time.
• Initial results suggest STAGE can detect longitudinal changes in brain tumors, potentially aiding recurrence identification and adaptive radiotherapy.