, , , , , , *

(1.Department of Radiology, Beijing Friendship Hospital, Capital Medical University,Beijing 100050, China; 2.College of Information Engineering,China Jiliang University, Hangzhou 310018, China)

Stability tests and action limits setting for central frequency and transmitter gain of MRI scanners

YINHongxia1,YANGPingping2,LIUYawen2,ZHONGZhaohui1,ZHUJianming2,YANGZhenghan1,WANGZhenchang1*

(1.DepartmentofRadiology,BeijingFriendshipHospital,CapitalMedicalUniversity,Beijing100050,China; 2.CollegeofInformationEngineering,ChinaJiliangUniversity,Hangzhou310018,China)

Objective To test the central frequency (CF) and transmitter gain(TG) of MRI scanners, and set up their action limits. Methods Three different MRI devices (GE 3.0T HD, GE 1.5T HDi and GE 3.0T 750W) were tested by scanning American College of Radiology (ACR) phantom with the axial T1WI series. In the pre-scanning of T1WI series for the ACR phantom, the CF and TG were recorded. It was tested for eight times when MRI scanners were in good condition. The action limits of CF and TG were calculated based on mean values and standard deviations. Results The mean values of CF for three devices were (127 725 772.38±39.68)Hz, (63 875 740.13±34.15)Hz, and (127 771 958.38±12.19)Hz, respectively. Their action limits were ≤119.04 Hz, ≤68.30 Hz, and ≤36.57 Hz, respectively. The mean values of TG for three devices were (125.25±1.28)dB, (101.75±1.98)dB, and (113.25±0.89)dB, respectively. Their action limits were (125.25±2.56)dB, (101.75±3.96)dB, and (113.25±1.78)dB, respectively. Conclusion The CF and TG for three MRI scanners are all consistent with the action limits in this study. The CF and TG action limits will provide criterions for the clinical quality control.

Central frequency; Transmitter gain; Quality control; Action limits

自1980年第一台全身MRI设备投入临床应用以来，MRI技术在医学影像中占有越来越重要的地位。在临床应用中，为获得高质量的医学图像，必须有相应的临床质量控制流程，以保证MRI设备在最佳状态运行。因此，MRI设备质量控制成为放射科的重要工作之一[1-4]。美国医学物理学会(American Association of Physicists in Medicine, AAPM)和美国放射学会(American College of Radiology, ACR)等机构对MRI设备临床质量控制提出了一系列标准化流程和技术规范，其中中心频率和发射增益是临床质量控制的重要检测指标[5-8]。本文对本院3台MRI设备的中心频率和发射增益进行稳定性检测，并建立其处置界限，为临床质量控制提供检测标准。

1 材料与方法

1.1设备与材料 MRI设备1为GE 3.0T HD(2006年装机)，MRI设备2为GE 1.5T HDi(2012年装机)，MRI设备3为GE 3.0T 750W(2016年装机)；正交鸟笼头线圈；ACR模体(型号J12731，制造商J.M.SPECIALTY PARTS，SAN DIEGO, CA)，直径190 mm，高148 mm，内部填充10 mmol/L的氯化镍溶液和75 mmol/L的氯化钠溶液。

1.2方法与参数 将ACR模体正确摆放于正交鸟笼头线圈内，行三维定位扫描。后扫描轴位T1WI序列，扫描层数为11层，第1层和第11层的扫描线分别对应于矢状定位图像中心层面的2个45°楔形夹角处(图1)，定位中心层面出现45°楔形夹角提示轴位定位精准，如中心层上下只出现一半楔形图，提示模体放置不正，应重新摆位。扫描参数：SE序列，TR 500 ms，TE 20 ms，NEX 1，层厚5 mm，层间距5 mm，FOV 25 cm×25 cm，矩阵256×256。

预扫描阶段，中心频率和发射增益会在扫描界面直接显示；序列扫描结束后，可在图像浏览界面打开Series Textpage进行回溯查看，记录中心频率和发射增益。

1.3建立处置界限 在3台MRI设备运行状态良好情况下，对每台设备的中心频率和发射增益连续检测8次，计算均值和标准差。……