Ultra-Low Field MRI Food Inspection System Using HTS-SQUID with Flux Transformer

Saburo TANAKA  Satoshi KAWAGOE  Kazuma DEMACHI  Junichi HATTA  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E101-C   No.8   pp.680-684
Publication Date: 2018/08/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E101.C.680
Type of Manuscript: PAPER
Category: Superconducting Electronics
Keyword: 
high-Tc SQUID,  ultra-low field MRI,  food inspection,  LC resonator,  2D-FFT,  

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Summary: 
We are developing an Ultra-Low Field (ULF) Magnetic Resonance Imaging (MRI) system with a tuned high-Tc (HTS)-rf-SQUID for food inspection. We previously reported that a small hole in a piece of cucumber can be detected. The acquired image was based on filtered back-projection reconstruction using a polarizing permanent magnet. However the resolution of the image was insufficient for food inspection and took a long time to process. The purpose of this study is to improve image quality and shorten processing time. We constructed a specially designed cryostat, which consists of a liquid nitrogen tank for cooling an electromagnetic polarizing coil (135mT) at 77K and a room temperature bore. A Cu pickup coil was installed at the room temperature bore and detected an NMR signal from a sample. The signal was then transferred to an HTS SQUID via an input coil. Following a proper MRI sequence, spatial frequency data at 64×32 points in k-space were obtained. Then, a 2D-FFT (Fast Fourier Transformation) method was applied to reconstruct the 2D-MR images. As a result, we successfully obtained a clear water image of the characters “TUT”, which contains a narrowest width of 0.5mm. The imaging time was also shortened by a factor of 10 when compared to the previous system.