A high temperature superconducting imaging coil for low-field MRI

Abstract

In low field MRI (<0.5T), the signal-to-noise ratio (SNR) is predominantly degraded by thermal noise due to the electrical resistance of the imaging coil. This means using an imaging coil made of materials with a low intrinsic resistivity such as high temperature superconductors (HTS) should improve the SNR significantly when compared to an equivalent copper coil. The aim of this study was to perform a quantitative analysis on the performance of a cryogenically-cooled HTS coil in low field MRI. A 70 mm circular spiral HTS resonator was fabricated by using YBa2Cu3O7 (YBCO) onto a sapphire substrate. The HTS coil was placed inside a cryogenic Dewar flask made of G10 materials to allow cooling using liquid nitrogen. A copper coil with the same layout was also fabricated to provide reference data for SNR comparisons. From the quality factor (Q) measurement results, the cryogenically-cooled HTS coil was estimated to give SNR gains of 4.0 and 1.9 when compared to the copper coil at room temperature (292 K) and at the same cryogenic temperature (81.5 K) respectively. The phantom imaging results showed good agreement with these estimations in which SNR gains of 3.7 and 1.8 were recorded for the same comparisons. Similar SNR gains of 3.2 and 1.8 were also measured from invivo hand imaging results, confirming the advantage of HTS coils over equivalent copper coils in low field MRI. Meanwhile, the SNR gain of the HTS coil against the room temperature copper coil dropped to 1.8 when the coil-to-sample separation in the latter setup was minimized to around 1 mm. © 2010 Wiley Periodicals, Inc.