title: Technical Note: Compact three-tesla magnetic resonance imager with high-performance gradients passes ACR image quality and acoustic noise tests.
abstract: OBJECTIVE
  A compact, three-tesla magnetic resonance imaging (MRI) system has been developed. It features a 37 cm patient aperture, allowing the use of commercial receiver coils. Its design allows simultaneously for gradient amplitudes of 85 millitesla per meter (mT/m) sustained and 700 tesla per meter per second (T/m/s) slew rates. The size of the gradient system allows for these simultaneous performance targets to be achieved with little or no peripheral nerve stimulation, but also raises a concern about the geometric distortion as much of the imaging will be done near the system's maximum 26 cm field-of-view. Additionally, the fast switching capability raises acoustic noise concerns. This work evaluates the system for both the American College of Radiology's (ACR) MRI image quality protocol and the Food and Drug Administration's (FDA) nonsignificant risk (NSR) acoustic noise limits for MR. Passing these two tests is critical for clinical acceptance.
  
  
  METHODS
  In this work, the gradient system was operated at the maximum amplitude and slew rate of 80 mT/m and 500 T/m/s, respectively. The geometric distortion correction was accomplished by iteratively determining up to the tenth order spherical harmonic coefficients using a fiducial phantom and position-tracking software, with seventh order correction utilized in the ACR test. Acoustic noise was measured with several standard clinical pulse sequences.
  
  
  RESULTS
  The system passes all the ACR image quality tests. The acoustic noise as measured when the gradient coil was inserted into a whole-body MRI system conforms to the FDA NSR limits.
  
  
  CONCLUSIONS
  The compact system simultaneously allows for high gradient amplitude and high slew rate. Geometric distortion concerns have been mitigated by extending the spherical harmonic correction to higher orders. Acoustic noise is within the FDA limits.
authors.affiliation: Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Weavers
authors.affiliation: Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Yunhong
authors.initials: Y
authors.lastname: Shu
authors.affiliation: Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Shengzhen
authors.initials: S
authors.lastname: Tao
authors.affiliation: Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: John
authors.initials: J
authors.lastname: Huston
authors.affiliation: GE Global Research, Niskayuna, NY 12309, USA and CNIR, Department of Biomedical Engineering, Sungkyunkwan University, Suwon 440-746, South Korea.
authors.forename: Seung-Kyun
authors.initials: SK
authors.lastname: Lee
authors.affiliation: GE Global Research, Niskayuna, New York 12309.
authors.forename: Dominic
authors.initials: D
authors.lastname: Graziani
authors.affiliation: GE Healthcare, Florence, South Carolina 29501.
authors.forename: Jean-Baptiste
authors.initials: JB
authors.lastname: Mathieu
authors.affiliation: Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Trzasko
authors.affiliation: GE Global Research, Niskayuna, New York 12309.
authors.forename: Thomas K-F
authors.initials: TK
authors.lastname: Foo
authors.affiliation: Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Matt A
authors.initials: MA
authors.lastname: Bernstein
mesh_terms: D000162:Acoustics; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D011786:Quality Control; D011871:Radiology; D012306:Risk; D059629:Signal-To-Noise Ratio; D012955:Societies, Medical