Institute of Biomaterials and Biomedical Engineering, University of Toronto, Rosebrugh Building, 164 College Street, Room 407, Toronto, ON, M5S3G9, Canada.
Division of Neurosurgery, The Hospital for Sick Children, 555 University Avenue, Room 1504, Toronto, ON, M5G1X8, Canada.
Med Biol Eng Comput. 2018 Jan;56(1):61-70. doi: 10.1007/s11517-017-1665-3. Epub 2017 Jul 3.
Ultrasonic motors (USMs) are common actuators that can be safely used in the magnetic resonance imaging (MRI) environment. However, lack of MRI compatibility results in issues such as image distortion. This fact led researchers to shift focus from USMs to pneumatic and hydraulic actuators in development of surgical robots. The aim is to quantify and compensate the geometric distortion of MR images as generated by the presence of USMs. An ultrasonic motor was positioned in three orientations with respect to the bore axis. The induced distortions were compared across four image sequences. To reduce the distortions, three artifact reduction methods were employed. Geometric distortion is the only artifact in image slices farther from the motor. The various motor orientations lead to different distortions, with the lowest distortion for the z orientation. The maximum measured distortion of ten pixels occurred. This maximal distortion is equal to a 1-cm displacement of the displayed points relative to their actual locations and it is beyond the acceptable level for medical display standards. Bandwidth reduction reduced the distortion, with a 50% reduction for a doubled bandwidth. In conclusion, USMs can be preferred alternative because accurate targeting of pathologies can occur in free distorted images.
超声电机（USM）是一种常见的执行器，可在磁共振成像（MRI）环境中安全使用。然而，缺乏 MRI 兼容性会导致图像失真等问题。这一事实促使研究人员将重点从 USM 转移到气动和液压执行器上，以开发手术机器人。目的是量化和补偿由 USM 产生的 MR 图像的几何失真。将超声电机置于三个相对于孔轴的方位。在四个图像序列中比较了感应到的失真。为了减少失真，采用了三种消除伪影的方法。图像切片中只有几何失真，远离电机。各种电机方位会导致不同的失真，z 方向的失真最小。测量到的最大失真为十个像素。这种最大失真相当于显示点相对于其实际位置的 1 厘米位移，超出了医学显示标准的可接受水平。带宽减少会降低失真，带宽增加一倍时会降低 50%。总之，USM 可以作为替代方案，因为可以在自由失真的图像中对病变进行精确的靶向治疗。
