Marc Rea

The case for MR-compatible robotics: a review of the state of the art

The numerous imaging capabilities of magnetic resonance imaging (MRI) coupled with its lack of ionizing radiation has made it a desirable modality for real‐time guidance of interventional procedures. The combination of these abilities with the advantages granted by robotic systems to perform accurate and precise positioning of tools has driven the recent development of MR‐compatible interventional and assistive devices.

The feasibility of MR-Image guided prostate biopsy using piezoceramic motors inside or near to the magnet isocentre

The excellent soft tissue contrast of Magnetic Resonance Imaging (MRI) has encouraged the development of MRI compatible systems capable of combining the advantages of robotic manipulators with high quality anatomical images. Continuing this development, a new five DOF prostate biopsy manipulator has been designed for use inside a closed 1.5T MRI scanner. Space constraints in the bore and the current trend to restrict field strength exposure for operators indicate that a master-slave configuration is ideal for controlling the robotic system from outside the bore. This system has been designed to work with piezoceramic motors and optical encoders placed inside or near the field of view of the scanner, using real time image guidance for targeting biopsies to specific lesions in the prostate. MRI tests have been performed to prove the feasibility of this concept and a one DOF proof-of-concept test rig implementing closed loop position control has been tested and is presented here. A first prototype of the slave manipulator has been designed and manufactured incorporating this new technology.

A Modular Approach to MRI-Compatible Robotics

The objective of the research described in this article is to create individual MR-compatible modules consisting of 1-DoF stages complete with actuators and position encoders for implementation of the closed-loop position control. These modules can connect together to form multi-DoF assemblies that can be located inside the scanner bore near to the patient anatomy that requires the intervention. This avoids the problems associated with remote actuation and transmission mechanisms, considerably reducing the size of the manipulator. As most robots consist of kinematic chains of 1-DoF stages, these modules would be suitable for a wide range of interventions, and their design can be optimized for the procedure for which they are applied to.

System for 3-D Real-Time Tracking of MRI-Compatible Devices by Image Processing

Real-time processing of MRIs is reported as a method of 3D tracking of mechanical devices within the field of view using passive microcoil fiducials. The specific implementation described makes use of two scan planes for full 3D tracking of a 5-DOF manipulator arm used for prostate biopsy under image guidance. Real-time tracking was observed with a maximum update rate of 0.42 frames per second for a maximum probe velocity of 10 mm/s. The localization of fiducials had a mean error of 0.36 (plusmn0.17) mm (p < 0.02), leading to a mean error in the needle tip position of 2.6 (plusmn0.3) mm (p < 0.05).

Robotic System for Transrectal Biopsy of the Prostate: Real-Time Guidance Under MRI

In this paper, to harness the possibility of real-time guidance of MRI, a robotic system has been developed to perform transrectal prostate biopsy inside a 1.5-T closed bore scanner. A specially developed MR pulse sequence is capable of tracking the needle location in real time while dynamically updating the scan planes to always include the needle and target.

Haptic Needle Unit for MR-Guided Biopsy and Its Control

MRI provides high-resolution anatomical images and is ideal for certain image-guided interventions. Due to the physical separation between the patient region of interest and the workspace accessible by the clinician, direct force feedback from the target anatomy is missing during the interventions. This paper demonstrates the use of a master-slave haptic device for magnetic resonance-guided biopsy, using a novel haptic control scheme based upon a neural network speed model. Results have shown the feasibility of the proposed hardware design and control scheme.

Magnetic resonance imaging using linear magneto-inductive waveguides

Magneto-inductive waveguides are arrays of magnetically coupled, lumped element resonators, which support slow waves at radio frequency. Their use in internal magnetic resonance imaging (MRI), where they may provide an intrinsically safe method of signal detection and transmission, is described. A catheter-based receiver formed from a thin-film printed circuit mounted on a tubular scaffold using heat-shrink tubing is demonstrated, and its electrical response and imaging sensitivity are explained in terms of the excitation and propagation of magneto-inductive waves. The theoretical predictions are confirmed using the results of electrical measurement and 1H MRI at 1.5 T, and imaging is achieved over a total length greater than 1.5 m using a single receiver.

Needle-Guiding Robot for Laser Ablation of Liver Tumors Under MRI Guidance

This paper presents the design, control, and experimental evaluation of a needle-guiding robot intended for use in laser ablation (LA) of liver tumors under guidance by magnetic resonance imaging (MRI). The robot provides alignment of a needle guide inside the MRI scanner bore and employs manual needle insertion. In order to minimize MR-image deterioration, the robot is actuated using plastic pneumatic cylinders and long pipes connecting to control valves located outside the MRI scanner room. A new time-delay control scheme was employed to achieve high position accuracy without requiring pressure or force measurements in the MRI scanner. The control scheme was compared with experiments to a previously developed sliding mode controller. A marker localization method based on the convolution theorem of Fourier transform was employed to register the robot in the MRI scanner coordinate system and to verify the position of the needle guide before the manual needle insertion. Experiments in a closed-bore MRI scanner showed a variation in SNR below 5%. A phantom study indicates that the targeting error in robot-assisted needle insertions is below 5 mm and suggest a potential time saving of 30 min compared to the manual MRI-guided LA procedure.

Magneto-Inductive Catheter Receiver for Magnetic Resonance Imaging

A catheter-based RF receiver for internal magnetic resonance imaging is demonstrated. The device consists of a double-sided thin-film circuit, wrapped around a hollow catheter and sealed in place with heat-shrink tubing. Signals are detected using a resonant LC circuit at the catheter tip and transmitted along the catheter using an array of coupled LC circuits arranged as a magneto-inductive waveguide, a form of low frequency metamaterial. Coupling to a conventional RF system is accomplished using a demountable inductive transducer. Protection against external B 1 and E fields is obtained by using figure-of-eight elements with an electrical length shorter than that of an immersed dipole. The system is primarily designed for biliary imaging, can pass the biopsy channel of a side-opening duodenoscope, and is guidewire-compatible, potentially allowing clinicians to implement MR image guided procedures without changing their standard practice. Decoupling against B 1 and E fields is verified, and in vitro 1H magnetic resonance imaging with submillimeter resolution is demonstrated at 1.5 T using phantoms.

A haptic unit designed for magnetic-resonance-guided biopsy.

Abstract The magnetic fields present in the magnetic resonance (MR) environment impose severe constraints on any mechatronic device present in its midst, requiring alternative actuators, sensors, and materials to those conventionally used in traditional system engineering. In addition the spatial constraints of closed-bore scanners require a physical separation between the radiologist and the imaged region of the patient. This configuration produces a loss of the sense of touch from the target anatomy for the clinician, which often provides useful information. To recover the force feedback from the tissue, an MR-compatible haptic unit, designed to be integrated with a five-degrees-of-freedom mechatronic system for MR-guided prostate biopsy, has been developed which incorporates position control and force feedback to the operator. The haptic unit is designed to be located inside the scanner isocentre with the master console in the control room. MR compatibility of the device has been demonstrated, showing a negligible degradation of the signal-to-noise ratio and virtually no geometric distortion. By combining information from the position encoder and force sensor, tissue stiffness measurement along the needle trajectory is demonstrated in a lamb liver to aid diagnosis of suspected cancerous tissue.