Weavers Paul T, Shu Yunhong, Tao Shengzhen, Huston John, Lee Seung-Kyun, Graziani Dominic, Mathieu Jean-Baptiste, Trzasko Joshua D, Foo Thomas K-F, Bernstein Matt A
Mayo Clinic, Rochester, Minnesota 55905.
GE Global Research, Niskayuna, NY 12309, USA and CNIR, Department of Biomedical Engineering, Sungkyunkwan University, Suwon 440-746, South Korea.
Med Phys. 2016 Mar;43(3):1259-64. doi: 10.1118/1.4941362.
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.
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.
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.
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.
已研发出一种紧凑型3特斯拉磁共振成像（MRI）系统。其特点是患者孔径为37厘米，可使用商用接收线圈。其设计允许同时实现85毫特斯拉每米（mT/m）的持续梯度幅度和700特斯拉每米每秒（T/m/s）的 slew 率。梯度系统的尺寸使得在几乎没有或没有周围神经刺激的情况下能够实现这些同时的性能目标，但也引发了对几何畸变的担忧，因为大部分成像将在系统最大26厘米视野附近进行。此外，快速切换能力引发了对声学噪声的担忧。这项工作根据美国放射学会（ACR）的MRI图像质量协议以及美国食品药品监督管理局（FDA）对MR的非显著风险（NSR）声学噪声限制对该系统进行了评估。通过这两项测试对于临床接受至关重要。
在这项工作中，梯度系统分别以80 mT/m的最大幅度和500 T/m/s的 slew 率运行。几何畸变校正通过使用基准体模和位置跟踪软件迭代确定高达十阶的球谐系数来完成，在ACR测试中使用七阶校正。使用几种标准临床脉冲序列测量声学噪声。
该系统通过了所有ACR图像质量测试。当梯度线圈插入全身MRI系统时测量的声学噪声符合FDA的NSR限制。
紧凑型系统同时允许高梯度幅度和高 slew 率。通过将球谐校正扩展到更高阶，减轻了对几何畸变的担忧。声学噪声在FDA限制范围内。
