Publications [#268967] of G. Allan Johnson

Papers Published

1. Miller, JR; Hurlston, SE; Ma, QY; Face, DW; Kountz, DJ; MacFall, JR; Hedlund, LW; Johnson, GA, Performance of a high-temperature superconducting probe for in vivo microscopy at 2.0 T., Magn Reson Med, vol. 41 no. 1 (January, 1999), pp. 72-79, ISSN 0740-3194 [10025613], [doi]
   (last updated on 2024/04/19)

   Abstract:
   The use of a high-temperature superconducting probe for in vivo magnetic resonance microscopy at 2 T is described. To evaluate the performance of the probe, a series of SNR comparisons are carried out. The SNR increased by a factor of 3.7 compared with an equivalent copper coil. Quantitative measures of the SNR gain are in good agreement with theoretical predictions. A number of issues that are unique to the application of HTS coils are examined, including the difficulty in obtaining homogenous excitation without degrading the SNR of the probe. The use of the HTS probe in transmit-receive mode is simple to implement but results in nonuniform excitation. The effect of using the probe in this mode of operation on the T1 and T2 contrast is investigated. Methods for improving homogeneity are explored, such as employing a transmit volume coil. It is found that the cost of using an external transmit coil is an increased probe noise temperature and a reduced SNR by approximately 30%. Other important aspects of the probe are considered, including the effect of temperature on probe stability. Three-dimensional in vivo imaging sets are acquired to assess the stability of the probe for long scans. High-resolution images of the rat brain demonstrate the utility of the probe for microscopy applications.

   Keywords:
   Animals • Artifacts • Brain • Female • Heat* • Image Processing, Computer-Assisted • Magnetic Resonance Imaging • Microscopy • Models, Theoretical • Rats • Rats, Inbred F344 • Thermal Conductivity • anatomy & histology • methods* • physiology*