T1-Weighted Image by Ultra-Low Field SQUID-MRI

We are developing an ultra-low field (ULF) magnetic resonance imaging (MRI) system with a high-temperature superconductor superconducting quantum interference device (SQUID) for the purpose of food contaminant inspection. Our previous ULF SQUID-MRI system for food inspection used a resonant circuit to detect a magnetic field, which was tuned at the Larmor frequency. However, when the MR signal frequency decreases, the signal bandwidth becomes narrower. Since the line width of the nuclear magnetic resonance spectrum of food with a short relaxation time becomes broad, it is difficult to measure the MR signal. Therefore, to address this issue, we employed a non-resonant method to widen the bandwidth. In this paper, we describe a ULF SQUID-MRI system using a non-resonant Cu wound flux transformer to image food with a shorter relaxation time. As a result, T
₁
-weighted images of samples containing water and oil could be acquired by varying the polarizing time.