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Evaluation of the B0 Field Uniformity On a Compact 3T MR Scanner with High Performance Gradients
Y Shu1*, S Tao1 , M Xu2 , E Laskaris2 , T Foo2 , P Weavers1 , J Trzasko1 , J Huston1 , M Bernstein1 , (1) Mayo Clinic, Rochester, MN, (2) GE Global Research, Niskayuna, NY
Presentations
MO-L-GePD-I-2 (Monday, July 31, 2017) 1:15 PM - 1:45 PM Room: Imaging ePoster Lounge
Purpose: Recently, a novel, high-performance, compact 3T MR scanner has been developed. It is equipped with a conduction-cooled magnet that uses only 12-liter liquid helium. The compact design enables substantial weight saving and size reduction. The scanner has a 37cm bore size, and the diameter-spherical-volume(DSV) provided by the gradients permits up to a 26cm FOV. The scanner is currently under clinical evaluation at our institution, and the B0 field was shimmed to 1.68 peak-peak ppm at 26cm DSV through passive shimming upon installation (before gradient shimming). The uniformity of the magnetic field is an important specification in performance evaluation as it is directly related to image quality. This work demonstrates on-site evaluation of the B0 field uniformity of this system using the ACR recommended test procedures.
Methods: A spherical liquid phantom with 26-cm diameter was placed in the scanner bore center and scanned using a non-selective FIDCSI spectroscopy sequence. The same phantom was then scanned using a 3D B0 mapping sequence based on the phase difference method. With IRB-approved protocol, a volunteer was scanned using an 8-channel head coil and a clinically T2-weighted fast spin echo sequence to examine the fat saturation uniformity.
Results: The FWHM measured with spectroscopy is 52Hz, corresponding to a global inhomogeneity of 0.4 ppm. The spectral width at 10% of the full maximum is 146 Hz(1.14 ppm). The field mapping result shows that the measured field deviation for the whole 22cm spherical VOI are +66 Hz and -44 Hz(0.86 ppm). Axial T2 brain images show excellent, uniform suppression for the adipose tissue around the scalp, which corroborates the other uniformity measurements.
Conclusion: We demonstrate on-site evaluation of the B0 field uniformity of the compact 3T system based on the ACR recommended test procedures. The uniformity of this system reaches the designed specification for clinical imaging.
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