A Prototype Manipulator for Magnetic Resonance-Guided Interventions Inside Standard Cylindrical Magnetic Resonance Imaging Scanners

A Platform Integrating Acquisition, Reconstruction, Visualization, and Manipulator Control Modules for MRI-Guided Interventions

This work presents a platform that integrates a customized MRI data acquisition scheme with reconstruction and three-dimensional (3D) visualization modules along with a module for controlling an MRI-compatible robotic device to facilitate the performance of robot-assisted, MRI-guided interventional procedures. Using dynamically-acquired MRI data, the computational framework of the platform generates and updates a 3D model representing the area of the procedure (AoP). To image structures of interest in the AoP that do not reside inside the same or parallel slices, the MRI acquisition scheme was modified to collect a multi-slice set of intraoblique to each other slices; which are termed composing slices. Moreover, this approach interleaves the collection of the composing slices so the same k-space segments of all slices are collected during similar time instances. This time matching of the k-space segments results in spatial matching of the imaged objects in the individual composing slices. The composing slices were used to generate and update the 3D model of the AoP. The MRI acquisition scheme was evaluated with computer simulations and experimental studies. Computer simulations demonstrated that k-space segmentation and time-matched interleaved acquisition of these segments provide spatial matching of the structures imaged with composing slices. Experimental studies used the platform to image the maneuvering of an MRI-compatible manipulator that carried tubing filled with MRI contrast agent. In vivo experimental studies to image the abdomen and contrast enhanced heart on free-breathing subjects without cardiac triggering demonstrated spatial matching of imaged anatomies in the composing planes. The described interventional MRI framework could assist in performing real-time MRI-guided interventions.

MRI-guided robotic arm drives optogenetic fMRI with concurrent Ca2+ recording

Optical fiber-mediated optogenetic activation and neuronal Ca2+ 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.

Design of a Magnetic Resonance-Safe Haptic Wrist Manipulator for Movement Disorder Diagnostics

Tremor, characterized by involuntary and rhythmical movements, is the most common movement disorder. Tremor can have peripheral and central oscillatory components which properly assessed may improve diagnostics. A magnetic resonance (MR)-safe haptic wrist manipulator enables simultaneous measurement of proprioceptive reflexes (peripheral components) and brain activations (central components) through functional magnetic resonance imaging (fMRI). The presented design for an MR-safe haptic wrist manipulator has electrohydraulic closed-circuit actuation, optical position and force sensing, and consists of exclusively nonconductive and magnetically compatible materials inside the MR-environment (Zone IV). The MR-safe hydraulic actuator, a custom-made plastic vane motor, is connected to the magnetic parts and electronics located in the shielded control room (Zone III) via hydraulic hoses and optical fibers. Deliberate internal leakage provides backdriveability, damping, and circumvents friction. The manipulator is completely MR-safe and therefore operates safely in any MR-environment while ensuring fMRI imaging quality. Undesired external leakage in the actuator prevented the use of prepressure, limiting the control bandwidth. The compact end effector design fits in the MR-scanner, is easily setup, and can be clamped to the MR-scanner bed. This enables use of the manipulator with the subject at the optimal fMRI location and allows it to be setup quickly, saving costly MR-scanner time. The actuation and sensor solutions performed well inside the MR-environment and did not deteriorate image quality, which allows for various motor control experiments. Enabling prepressure by carrying out the recommendations on fabrication and sealing should improve the bandwidth and fulfill the requirements for proprioceptive reflex identification.

Manipulator-driven selection of semi-active MR-visible markers

BACKGROUND

A method for the identification of semi-active fiducial magnetic resonance (MR) markers is presented based on selectively optically tuning and detuning them.

METHODS

Four inductively coupled solenoid coils with photoresistors were connected to light sources. A microcontroller timed the optical tuning/detuning of coils and image collection. The markers were tested on an MR manipulator linking the microcontroller to the manipulator control to visibly select the marker subset according to the actuated joint.

RESULTS

In closed-loop control, the average and maximum were 0.76° ± 0.41° and 1.18° errors for a rotational joint, and 0.87 mm ± 0.26 mm and 1.13 mm for the prismatic joint.

CONCLUSIONS

This technique is suitable for MR-compatible actuated devices that use semi-active MR-compatible markers.

Robotic-assisted real-time MRI-guided TAVR: from system deployment to in vivo experiment in swine model

PURPOSE

Real-time magnetic resonance imaging (rtMRI) guidance provides significant advantages during transcatheter aortic valve replacement (TAVR) as it provides superior real-time visualization and accurate device delivery tracking. However, performing a TAVR within an MRI scanner remains difficult due to a constrained procedural environment. To address these concerns, a magnetic resonance (MR)-compatible robotic system to assist in TAVR deployments was developed. This study evaluates the technical design and interface considerations of an MR-compatible robotic-assisted TAVR system with the purpose of demonstrating that such a system can be developed and executed safely and precisely in a preclinical model.

METHODS

An MR-compatible robotic surgical assistant system was built for TAVR deployment. This system integrates a 5-degrees of freedom (DoF) robotic arm with a 3-DoF robotic valve delivery module. A user interface system was designed for procedural planning and real-time intraoperative manipulation of the robot. The robotic device was constructed of plastic materials, pneumatic actuators, and fiber-optical encoders.

RESULTS

The mechanical profile and MR compatibility of the robotic system were evaluated. The system-level error based on a phantom model was 1.14 ± 0.33 mm. A self-expanding prosthesis was successfully deployed in eight Yorkshire swine under rtMRI guidance. Post-deployment imaging and necropsy confirmed placement of the stent within 3 mm of the aortic valve annulus.

CONCLUSIONS

These phantom and in vivo studies demonstrate the feasibility and advantages of robotic-assisted TAVR under rtMRI guidance. This robotic system increases the precision of valve deployments, diminishes environmental constraints, and improves the overall success of TAVR.

Development of an MRI-Compatible, Compact, Rotary-Linear Piezoworm Actuator

A piezoelectric actuator was developed to operate safely deep inside the magnetic resonance imaging (MRI) machine bore. It is based on novel design that produces linear and rotary motion simultaneously increasing the accuracy of medical needle insertion procedures. The actuation method is based on the piezoworm principle, minimizing the actuator size, maximizing output force, and permitting micrometer scale insertion accuracy. Beryllium copper with high stiffness and strength was used in constructing the actuator to minimize image distortion and to achieve the targeted performance. Performance tests were performed by controlling the frequency input and observing the effect on speed, force and torque. The device achieved a linear speed of 5.4 mm/s and a rotary speed of 10.5 rpm.

An MRI-powered and controlled actuator technology for tetherless robotic interventions

This paper presents a novel actuation technology for robotically assisted MRI-guided interventional procedures. In the proposed approach, the MRI scanner is used to deliver power, estimate actuator state and perform closed-loop control. The actuators themselves are compact, inexpensive and wireless. Using needle driving as an example application, actuation principles and force production capabilities are examined. Actuator stability and performance are analyzed for the two cases of state estimation at the input versus the output of the actuator transmission. Closed-loop needle position control is achieved by interleaving imaging pulse sequences to estimate needle position (transmission output estimation) and propulsion pulse sequences to drive the actuator. A prototype needle driving robot is used to validate the proposed approach in a clinical MRI scanner.

MRI-powered Actuators for Robotic Interventions

This paper presents a novel actuation technology for robotically assisted MRI-guided interventional procedures. Compact and wireless, the actuators are both powered and controlled by the MRI scanner. The design concept and performance limits are described and derived analytically. Simulation and experiments in a clinical MR scanner are used to validate the analysis and to demonstrate the capability of the approach for needle biopsies. The concepts of actuator locking mechanisms and multi-axis control are also introduced.

Stereotaxy: breaking the limits of current radiofrequency ablation techniques

Radiofrequency ablation (RFA) allows for local curative tumor treatment by inducing coagulation necrosis with high-frequency alternating current. However, the tumor size is the major limiting factor due to a mismatch of the tumor volume and the induced necrotic zone. RFA probes have to be optimally distributed in and around the tumor in order to produce overlapping ablation zones. Due to different guidance and ablation strategies the result is strongly operator dependent and there is a lack of reliability. These challenges can be managed by 3D-planning using a frameless stereotactic navigation system, allowing for the simultaneous display of multiple trajectories. The spatial information gained from 3D imaging is available in coordinates and thus forms an accurate input for performing the intervention. Stereotaxy enables highly accurate probe positioning. Stereotactic radiofrequency ablation (SRFA) may substantially improve the safety and efficacy in clinical practice, especially in the treatment of large and irregularly shaped tumors. The proposed methods may also be used for similar percutaneous local tumor treatments.

MRI-guided robotics at the U of Houston: evolving methodologies for interventions and surgeries

Currently, we witness the rapid evolution of minimally invasive surgeries (MIS) and image guided interventions (IGI) for offering improved patient management and cost effectiveness. It is well recognized that sustaining and expand this paradigm shift would require new computational methodology that integrates sensing with multimodal imaging, actively controlled robotic manipulators, the patient and the operator. Such approach would include (1) assessing in real-time tissue deformation secondary to the procedure and physiologic motion, (2) monitoring the tool(s) in 3D, and (3) on-the-fly update information about the pathophysiology of the targeted tissue. With those capabilities, real time image guidance may facilitate a paradigm shift and methodological leap from "keyhole" visualization (i.e. endoscopy or laparoscopy) to one that uses a volumetric and informational rich perception of the Area of Operation (AoO). This capability may eventually enable a wider range and level of complexity IGI and MIS.

An MRI-compatible system for focused ultrasound experiments in small animal models

The development of novel MRI-guided therapeutic ultrasound methods including potentiated drug delivery and targeted thermal ablation requires extensive testing in small animals such as rats and mice due to the widespread use of these species as models of disease. An MRI-compatible, computer-controlled three-axis positioning system was constructed to deliver focused ultrasound exposures precisely to a target anatomy in small animals for high-throughput preclinical drug delivery studies. Each axis was constructed from custom-made nonmagnetic linear ball stages driven by piezoelectric actuators and optical encoders. A range of motion of 5 x 5 x 2.5 cm3 was achieved, and initial bench top characterization demonstrated the ability to deliver ultrasound to the brain with a spatial accuracy of 0.3 mm. Operation of the positioning system within the bore of a clinical 3 T MR imager was feasible, and simultaneous motion and MR imaging did not result in any mutual interference. The system was evaluated in its ability to deliver precise sonications within the mouse brain, linear scanned exposures in a rat brain for blood barrier disruption, and circular scans for controlled heating under MR temperature feedback. Initial results suggest that this is a robust and precise apparatus for use in the investigation of novel ultrasound-based therapeutic strategies in small animal preclinical models.

Advancements in magnetic resonance-guided robotic interventions in the prostate

Magnetic resonance imaging (MRI) provides more detailed anatomical images of the prostate compared with the transrectal ultrasound imaging. Therefore, for the purpose of intervention in the prostate gland, diagnostic or therapeutic, MRI guidance offers a possibility of more precise targeting that may be crucial to the success of prostate interventions. However, access within the scanner is limited for manual instrument handling and the MR environment is most demanding among all imaging equipment with respect to the instrumentation used. A solution to this problem is the use of MR-compatible robots purposely designed to operate in the space and environmental restrictions inside the MR scanner allowing real-time interventions. Building an MRI-compatible robot is a very challenging engineering task because, in addition to the material restrictions that MRI instruments have, the robot requires actuators and sensors that limit the type of energies that can be used. Several important design problems have to be overcome before a successful MR-compatible robot application can be built. A number of MR-compatible robots, ranging from a simple manipulator to a fully automated system, have been developed, proposing ingenious solutions to the design challenge. Several systems have been already tested clinically for prostate biopsy and brachytherapy. As technology matures, precise image guidance for prostate interventions performed or assisted by specialized MR-compatible robotic devices may provide a uniquely accurate solution for guiding the intervention directly based on MR findings and feedback. Such an instrument would become a valuable clinical tool for biopsies directly targeting imaged tumor foci and delivering tumor-centered focal therapy.

A magnetic-resonance-compatible limb-positioning device to facilitate magic angle experiments in vivo

Owing to their highly ordered structure, tendons and cartilage appear with low signal intensity when imaged using magnetic resonance imaging (MRI) scanners. A significant increase in signal can be observed when these structures are oriented at 55 degrees (termed the magic angle) with respect to the static field B0. There is a clear clinical importance in exploiting this effect as part of the diagnosis of injury. Experimental studies of this phenomenon have been made harder by the practical difficulties associated with tissue positioning and orientation in the confined environment of closed-bore scanners. An MRI-compatible mechatronic system has been developed, which is capable of positioning a number of limbs to a desired orientation inside the scanner, to be used as a diagnostic and research tool. It is actuated with a novel pneumatic motor consisting of a heavily geared-down air turbine, presenting high torques and good accuracy. The system is shown to be magnetic resonance compatible and the results of preliminary trials using the device to image the Achilles tendon of human volunteers at different orientations are presented. An increase of four fold to thirteen fold in signal intensity can be observed at the magic angle.

Transperineal prostate intervention: robot for fully automated MR imaging--system description and proof of principle in a canine model

The study was approved by the animal care and use committee. The purpose of the study was to prospectively establish proof of principle in vivo in canines for a magnetic resonance (MR) imaging-compatible robotic system designed for image-guided prostatic needle intervention. The entire robot is built with nonmagnetic and dielectric materials and in its current configuration is designed to perform fully automated brachytherapy seed placement within a closed MR imager. With a 3.0-T imager, in four dogs the median error for MR imaging-guided needle positioning and seed positioning was 2.02 mm (range, 0.86-3.18 mm) and 2.50 mm (range, 1.45-10.54 mm), respectively. The robotic system is capable of accurate MR imaging-guided prostatic needle intervention within a standard MR imager in vivo in a canine model.

The Interconnection of MRI Scanner and MR-Compatible Robotic Device: Synergistic Graphical User Interface to Form a Mechatronic System

MRI scanner and magnetic resonance (MR)-compatible robotic devices are mechatronic systems. Without an interconnecting component, these two devices cannot be operated synergetically for medical interventions. In this paper, the design and properties of a graphical user interface (GUI) that accomplishes the task is presented. The GUI interconnects the two devices to obtain a larger mechatronic system by providing command and control of the robotic device based on the visual information obtained from the MRI scanner. Ideally, the GUI should also control imaging parameters of the MRI scanner. Its main goal is to facilitate image-guided interventions by acting as the synergistic component between the physician, the robotic device, the scanner, and the patient.

Fast and efficient radiological interventions via a graphical user interface commanded magnetic resonance compatible robotic device

The graphical user interface for an MR compatible robotic device has the capability of displaying oblique MR slices in 2D and a 3D virtual environment along with the representation of the robotic arm in order to swiftly complete the intervention. Using the advantages of the MR modality the device saves time and effort, is safer for the medical staff and is more comfortable for the patient.

Magnetic resonance-compatible robotic and mechatronics systems for image-guided interventions and rehabilitation: a review study

The continuous technological progress of magnetic resonance imaging (MRI), as well as its widespread clinical use as a highly sensitive tool in diagnostics and advanced brain research, has brought a high demand for the development of magnetic resonance (MR)-compatible robotic/mechatronic systems. Revolutionary robots guided by real-time three-dimensional (3-D)-MRI allow reliable and precise minimally invasive interventions with relatively short recovery times. Dedicated robotic interfaces used in conjunction with fMRI allow neuroscientists to investigate the brain mechanisms of manipulation and motor learning, as well as to improve rehabilitation therapies. This paper gives an overview of the motivation, advantages, technical challenges, and existing prototypes for MR-compatible robotic/mechatronic devices.

Automatic brachytherapy seed placement under MRI guidance

The paper presents a robotic method of performing low dose rate prostate brachytherapy under magnetic resonance imaging (MRI) guidance. The design and operation of a fully automated MR compatible seed injector is presented. This is used with the MrBot robot for transperineal percutaneous prostate access. A new image-registration marker and algorithms are also presented. The system is integrated and tested with a 3T MRI scanner. Tests compare three different registration methods, assess the precision of performing automated seed deployment, and use the seeds to assess the accuracy of needle targeting under image guidance. Under the ideal conditions of the in vitro experiments, results show outstanding image-guided needle and seed placement accuracy.

Robotic prostate surgery

The increasing popularity of robot-assisted radical prostatectomy has put the field of robotics in the spotlight. However, the relationship between medical robotics and the field of urology is older than most urologists know and it will most likely have a bright future beyond any contemporary application. The objective of this review is to provide an insight into the fundamentals of medical robotics and to highlight the history, the present and the future of urological robotic systems with an emphasis on robotic prostate interventions.

Magnetic resonance imaging compatible robotic system for fully automated brachytherapy seed placement

OBJECTIVES

To introduce the development of the first magnetic resonance imaging (MRI)-compatible robotic system capable of automated brachytherapy seed placement.

METHODS

An MRI-compatible robotic system was conceptualized and manufactured. The entire robot was built of nonmagnetic and dielectric materials. The key technology of the system is a unique pneumatic motor that was specifically developed for this application. Various preclinical experiments were performed to test the robot for precision and imager compatibility.

RESULTS

The robot was fully operational within all closed-bore MRI scanners. Compatibility tests in scanners of up to 7 Tesla field intensity showed no interference of the robot with the imager. Precision tests in tissue mockups yielded a mean seed placement error of 0.72 +/- 0.36 mm.

CONCLUSIONS

The robotic system is fully MRI compatible. The new technology allows for automated and highly accurate operation within MRI scanners and does not deteriorate the MRI quality. We believe that this robot may become a useful instrument for image-guided prostate interventions.

Performance of interventions with manipulator-driven real-time MR guidance: implementation and initial in vitro tests

The purpose of this work was to implement and assess the performance of interventions inside a cylindrical magnetic resonance imaging (MRI) scanner with an MR-compatible manipulator system and manipulator-driven real-time MR guidance. The interventional system is based on a seven degree-of-freedom MR-compatible manipulator, which offers man-in-the-loop control either with a graphical user interface or with a master/slave device. The position and the orientation of the interventional tool are sent to an MR scanner for a manipulator-driven dynamic update of the imaging plane to track, visualize and guide the motion of an end-effector. Studies on phantoms were performed with a cylindrical 1.5-T scanner using an operator-managed triggered gradient-recalled echo (GRE) or a computer-managed dynamic True Fast Imaging with Steady Precession (TrueFISP). Targets were acquired with an accuracy of 3.2 mm and with an in-plane path orientation of 2.5 degrees relative to the prescribed one. Path planning, including negotiation of obstacles and needle bending, was successfully performed. The signal-to-noise ratio (SNR) of TrueFISP was 25.3+/-2.1 when the manipulator was idle and was 18.6+/-2.4 during its operation. The SNR of triggered GRE (acquired only when the manipulator was idle) was 61.3+/-1.8. In conclusion, this study shows the feasibility of performing manually directed interventions inside cylindrical MR scanners with real-time MRI.

A MR compatible mechatronic system to facilitate magic angle experiments in vivo

When imaging tendons and cartilage in a MRI scanner, an increase in signal intensity is observed when they are oriented at 55 degrees with respect to Bo (the "magic angle"). There is a clear clinical importance for considering this effect as part of the diagnosis of orthopaedic and other injury. Experimental studies of this phenomenon have been made harder by practical difficulties of tissue positioning and orientation in the confined environment of cylindrical scanners. An MRI compatible mechatronic system has been developed to position a variety of limbs inside the field of view of the scanner, to be used as a diagnostic and research tool. It is actuated with a novel pneumatic motor comprised of a heavily geared down air turbine, and is controlled in a closed loop using standard optical encoders. MR compatibility is demonstrated as well as the results of preliminary trials used to image the Achilles tendon of human volunteers at different orientations. A 4 to 13 fold increase in signal at the tendon is observed at the magic angle.