A Wireless Radio Frequency Triggered Acquisition Device (WRAD) for Self-Synchronised Measurements of the Rate of Change of the MRI Gradient Vector Field for Motion Tracking.
A Wireless Radio Frequency Triggered Acquisition Device (WRAD) for Self-Synchronised Measurements of the Rate of Change of the MRI Gradient Vector Field for Motion Tracking.
复制标题
一种无线射频触发采集设备 (WRAD)，用于自同步测量 MRI 梯度矢量场的变化率以进行运动跟踪。
DOI：
10.1109/tmi.2019.2891774
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发表时间：
2019
影响因子：
10.6
通讯作者：
vanderKouwe,Andre
中科院分区：
文献类型：
--
作者：
vanNiekerk,Adam;Meintjes,Ernesta;vanderKouwe,Andre
在本文中，我们提出了一种设备，能够无线同步到MRI脉冲序列时间帧的亚微秒精度。这通过使用小谐振电路检测母脉冲序列中的射频脉冲来实现。该设备采用了一个3轴拾波线圈，采用传统的印刷电路板（PCB）制造技术，以测量梯度波形相对于时间的变化率。利用麦克斯韦方程，假设旋度和发散的变化率可以忽略不计，提出了一个预期的梯度导数（回转）矢量场的模型。3轴Halleeffect磁力计允许在设备坐标系中测量静磁场的方向。通过将磁力计测量与拾取线圈电压和回转矢量场模型相结合，可以使用持续的脉冲序列分别在0.1度和0.1 mm的精度内确定取向和位置。梯度脉冲被设计为正弦的，使得能够检测拾取线圈数字化电路的时间帧与梯度放大器之间的相移。信号处理由设备上的低功耗微控制器执行，结果使用低延迟2.4 GHz无线电链路传输到扫描仪孔外。该器械识别出与梯度放大器的脉宽调制频率相关的非预期40 kHz振荡，主要在静磁场方向上。所提出的无线射频触发采集设备使用户能够以最小的硬件设置来探测扫描仪梯度回转矢量场，并显示出对前瞻性运动校正未来发展的承诺。
In this paper, we present a device that is capable of wireless synchronization to the MRI pulse sequence time frame with sub-microsecond precision. This is achieved by detecting radio frequency pulses in the parent pulse sequence using a small resonant circuit. The device incorporates a 3-axis pickup coil, constructed using conventional printed circuit board (PCB) manufacturing techniques, to measure the rate of change of the gradient waveforms with respect to time. Using Maxwell’s equations, assuming negligible rates of change of curl and divergence, a model of the expected gradient derivative (slew) vector field is presented. A 3-axisHalleffect magnetometer allows for the measurement of the direction of the static magnetic field in the device co-ordinate frame. By combining the magnetometer measurement with the pickup coil voltages and slew vector field model, the orientation and position can be determined to within a precision of 0.1 degrees and 0.1 mm, respectively, using a pulse series lasting. The gradient pulses are designed to be sinusoidal, enabling the detection of a phase shift between the time frame of the pickup coil digitization circuit and the gradient amplifiers. The signal processing is performed by a low power micro-controller on the device and the results are transmitted out of the scanner bore using a low latency 2.4 GHz radio link. The device identified an unexpected 40 kHz oscillation relating to the pulse width modulation frequency of the gradient amplifiers that is predominantly in the direction of the static magnetic field. The proposed wireless radio frequency triggered acquisition device enables users to probe the scanner gradient slew vector field with minimal hardware set-up and shows promise for the future developments in the prospective motion correction.