Magnetization Transfer Knee Imaging at 0.05 Tesla with Extremely Low SAR

Motivation: The intrinsic low specific absorption rate (SAR) at ultra-low-field (ULF) enables the application of versatile RF pulses for magnetization transfer (MT) knee imaging. Goal(s): To explore MT knee imaging for articular cartilage evaluation at 0.05 Tesla. Approach: GRE sequences, without and with sinc-modulated RF pulse train (SPT) modules as MT preparation, were utilized for knee imaging. Results: Articular cartilage exhibits strong MT effects, with MT ratios exceeding 30% for different subjects. Both inter-examination test and multiple subject results demonstrate the robustness of ULF MT knee imaging. Moreover, the MT preparation SAR is estimated to be extremely low as 3.1mW/kg. Impact: MT knee imaging is demonstrated at 0.05 Tesla for the first time. Strong MT effects have been observed in articular cartilage with an extremely low SAR of 3.1mW/kg, rendering the potential of ULF MT knee imaging for articular cartilage evaluation.