MR compatible robotics

Recently I had a chance to attend a labmate, Greg Fisher's defense for the doctoral title in mechanical engineering. He has done an enormous amount of work here in the past couple of years, taking part in many projects, doing work in mechanical design, US signal processing, robot control, 3D display implementation, system verification and many other issues. His major work was to develop an MR compatible robotic system for prostate biopsy and brachitherapy. He designed built and tested two generations of the robots, and the later one is in clinical trials now. A recent publication on the robot is available here (IEEE Xplore). More information on MR compatible surgical robotics can be found in the latest special issue of the IEEE Engineering in Medicine and Biology magazine (Issue: 3, May/June, 2008) .
For further details, here is the synopsis of Greg's work:

by Gregory Fischer

"Magnetic Resonance Imaging (MRI) can provide high-quality 3D visualization of the target anatomy and surrounding tissue, thus granting potential to be a superior medical imaging modality for guiding and monitoring interventions. However, the benefits can not be readily harnessed for interventional procedures due to difficulties that surround the use of Highfield (1.5T or greater) MRI. The inability to use conventional mechatronics and the confined physical space make it extremely challenging to access the patient.
This work describes the development of two apparently very different systems that represent different approaches to the same surgical problem - coupling information and action to perform percutaneous (through the skin) needle placement with MR imaging. The first system addressed takes MR images and projects them along with a surgical plan directly on the interventional site, thus providing in-situ imaging and is know and the MR Image Overlay. With anatomical images and a corresponding plan visible in the appropriate pose, the clinician can use this information to perform the surgical action. The Image Overlay system, with its ability to help guide in-plane needle insertions without the requirement for real-time visualization, is ideally suited for applications where needle insertion in the MRI suite is beneficial. Development of the system for providing optically stable, in-situ images under MRI is presented here.
My primary research effort has focused on a robotic assistant system that overcomes the difficulties inherent to MR-guided procedures, and promises safe and reliable intra-prostatic needle placement inside closed high-field MRI scanners. The robot is a servo pneumatically operated automatic needle guide, and effectively guides needles under real-time MR imaging. MRI compatibility of the robot has been evaluated under 3T field strength using standard prostate imaging sequences and average SNR loss is limited to 5%. Needle alignment accuracy of the robot under servo pneumatic control is better than 0.94mm RMS per axis. The complete system workflow has been evaluated in phantom studies with accurate visualization and targeting. The thesis describes development of the robotic system including requirements, workspace analysis, mechanism design and optimization, and evaluation of MR compatibility. Further, a generally applicable MR compatible robot controller is developed, the pneumatic control system is implemented and evaluated, and the system is deployed in pre-clinical trials."


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