Program Information
Head-Only Asymmetric Gradient System Evaluation: ACR Image Quality and Acoustic Noise
P Weavers1*, Y Shu1 , S Tao1 , S Lee2 J Piel2 , J-B Mathieu3 , T Foo2 , M Bernstein1 , (1) Mayo Clinic, Rochester, Minnesota, (2) GE Global Research, Niskayuna, NY, (3) GE Healthcare, Florence, SC
Presentations
TU-G-CAMPUS-I-14 (Tuesday, July 14, 2015) 5:30 PM - 6:00 PM Room: Exhibit Hall
Purpose: A high-performance head-only magnetic resonance imaging gradient system with an acquisition volume of 26 cm employing an asymmetric design for the transverse coils has been developed. It is able to reach a magnitude of 85 mT/m at a slew rate of 700 T/m/s, but operated at 80 mT/m and 500 T/m/s for this test. A challenge resulting from this asymmetric design is that the gradient nonlinearly exhibits both odd- and even-ordered terms, and as the full imaging field of view is often used, the nonlinearity is pronounced. The purpose of this work is to show the system can produce clinically useful images after an on-site gradient nonlinearity calibration and correction, and show that acoustic noise levels fall within non-significant risk (NSR) limits for standard clinical pulse sequences.
Methods: The head-only gradient system was inserted into a standard 3T wide-bore scanner without acoustic damping. The ACR phantom was scanned in an 8-channel receive-only head coil and the standard American College of Radiology (ACR) MRI quality control (QC) test was performed. Acoustic noise levels were measured for several standard pulse sequences.
Results: Images acquired with the head-only gradient system passed all ACR MR image quality tests; Both even and odd-order gradient distortion correction terms were required for the asymmetric gradients to pass. Acoustic noise measurements were within FDA NSR guidelines of 99 dBA (with assumed 20 dBA hearing protection) A-weighted and 140 dB for peak for all but one sequence. Note the gradient system was installed without any shroud or acoustic batting. We expect final system integration to greatly reduce noise experienced by the patient.
Conclusion: A high-performance head-only asymmetric gradient system operating at 80 mT/m and 500 T/m/s conforms to FDA acoustic noise limits in all but one case, and passes all the ACR MR image quality control tests.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by the NIH grant 5R01EB010065
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