Signal analysis and liver tumor discrimination by using a high-T_c SQUID-based low-field NMR system in hospital

In this paper, a high-T_c SQUID-based nuclear magnetic resonance (NMR) spectrometer was set up in National Taiwan University Hospital to discriminate liver tumor. In order to overcome the surrounding noise, a four-layer Al shielded box and a cylindrical magnetic shield were employed to avoid the electromagnetic noise in the coils part and the SQUID part, respectively. For NMR measurement, the larmor frequency is varying with time due to the variation of static field in hospital. Therefore, the time-domain frequency adjusted average method guided by a fluxgate was used to correct the frequency variation and average the NMR signal in the time domain. For tumor discrimination, the T₁ relaxation times of normal tissue and tumor tissue were demonstrated. Our high-T_c SQUID-based low-field MRI system shows the feasibility for biomedical application in a clinic environment.