Abstract:BackgroundSafe robot-assisted intervention using magnetic resonance imaging (MRI) guidance requires the precise control of assistive devices, and most currently available tools are rarely MRI-compatible. To obtain high precision, it is necessary to characterize and develop existing MRI-safe actuators for use in a high magnetic field (≥3 T). Although an ultrasonic motor (USM) is considered to be an MRI-safe actuator, and can be used in the vicinity of a high field scanner, its presence interferes with MR images… Show more
“…To deal with the MRI compatibility, in addition to hydraulic 56,57 or pneumatic 27,58–60 actuators, other types such as ultrasonic or piezoelectric motors, which have been the favorite so far due to their non-magnetic core, short response time and small size 61,62 , could have been utilized. However, no commercially available piezo motors are available for the 14.1 T MRI scanner and it has been recently shown that piezo motors could induce geometric distortions in MR images even at a lower magnetic field strength 63,64 . Also, different MRI sequences could have effects on the behavior of ultrasonic motors 65 .…”
Optical fiber-mediated optogenetic activation and neuronal Ca
2+
recording in combination with fMRI provide a multi-modal fMRI platform. Here, we developed an MRI-guided robotic arm (MgRA) as a flexible positioning system with high precision to real-time assist optical fiber brain intervention for multi-modal animal fMRI. Besides the ex vivo precision evaluation, we present the highly reliable brain activity patterns in the projected basal forebrain regions upon MgRA-driven optogenetic stimulation in the lateral hypothalamus. Also, we show the step-wise optical fiber targeting thalamic nuclei and map the region-specific functional connectivity with whole-brain fMRI accompanied by simultaneous calcium recordings to specify its circuit-specificity. The MgRA also guides the real-time microinjection to specific deep brain nuclei, which is demonstrated by an Mn-enhanced MRI method. The MgRA represents a clear advantage over the standard stereotaxic-based fiber implantation and opens a broad avenue to investigate the circuit-specific functional brain mapping with the multi-modal fMRI platform.
“…To deal with the MRI compatibility, in addition to hydraulic 56,57 or pneumatic 27,58–60 actuators, other types such as ultrasonic or piezoelectric motors, which have been the favorite so far due to their non-magnetic core, short response time and small size 61,62 , could have been utilized. However, no commercially available piezo motors are available for the 14.1 T MRI scanner and it has been recently shown that piezo motors could induce geometric distortions in MR images even at a lower magnetic field strength 63,64 . Also, different MRI sequences could have effects on the behavior of ultrasonic motors 65 .…”
Optical fiber-mediated optogenetic activation and neuronal Ca
2+
recording in combination with fMRI provide a multi-modal fMRI platform. Here, we developed an MRI-guided robotic arm (MgRA) as a flexible positioning system with high precision to real-time assist optical fiber brain intervention for multi-modal animal fMRI. Besides the ex vivo precision evaluation, we present the highly reliable brain activity patterns in the projected basal forebrain regions upon MgRA-driven optogenetic stimulation in the lateral hypothalamus. Also, we show the step-wise optical fiber targeting thalamic nuclei and map the region-specific functional connectivity with whole-brain fMRI accompanied by simultaneous calcium recordings to specify its circuit-specificity. The MgRA also guides the real-time microinjection to specific deep brain nuclei, which is demonstrated by an Mn-enhanced MRI method. The MgRA represents a clear advantage over the standard stereotaxic-based fiber implantation and opens a broad avenue to investigate the circuit-specific functional brain mapping with the multi-modal fMRI platform.
“…We further analyzed the effects of motor orientations in Refs. [18], [19].Fig. 3Eight consecutive slices of the phantom in the presence of the motor scanned with a T2W sequence to indicate the types of generated image artifacts.…”
Background
The safe performance of magnetic resonance imaging (MRI)-guided robot-assisted interventions requires full control and high precision of assistive devices. Because many currently available tools are not MRI-compatible, the characterization of existing tools and development of new ones are necessary. The purpose of this research is to identify and minimize the image artifacts generated by a USM in MR images.
Methods
The behavior of an ultrasonic motor (USM), the most common MRI-safe actuator, in a high-field scanner was investigated. The motor was located in three orientations with respect to the bore axis with the power on or off. The induced image artifacts were compared across four sequences. Three artifact reduction methods (employing ultrashort sequences, slice thickness reductions, and bandwidth increments) were tested.
Results
Signal voids, pileups, and geometric distortions were observed when the motor was off. The artifact size was minimal when the motor shaft was aligned with the bore axis. In addition to the above artifacts, zipper and motion artifacts were noted when the motor was running, and these artifacts increased with increasing motor speed. Increasing the bandwidth slightly reduced the artifacts. However, decreasing the slice thickness from 5 mm to 3 mm and from 5 mm to 1 mm reduced artifact size from 30% to 40% and from 60% to 75%, respectively.
Conclusion
The image artifacts were due to the non-homogenous nature of the static and gradient fields caused by the motor structure. The operating motor interferes with the RF field, causing zipper and motion artifacts.
Abstract:The risk of accidental dislodgement of robot-operated surgical mechanisms can lead to morbidity or mortality. The force and torque applied by a 3.0-tesla scanner on an ultrasonic motor are not fully known. The force and torque may displace the motor, which is not fully magnetic resonance imaging (MRI)-compatible but can be safely used in MR environments. A suspension apparatus was designed to measure the angles of deflection and rotation applied to the motor by MR magnetic fields. Three orientations and two power states of the motor were assessed inside the MR bore. The displacement force and torque were measured at eight locations with respect to the bore. The displacement force on the motor from 10 cm outside the magnet bore to 20 cm inside the bore ranged from 3 to 7 gF. The experimental measurements are in agreement with the theoretical values. Running the motor altered the force by 1 gF. The force does not significantly change when the MRI scanner is on. Considerable displacement force is applied to the motor, and no deflection torque is observed. Quantified values can be used to solve dynamic equations for robotic mechanisms intended for MRI-guided operations.
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