MR-Conditional Actuations: A Review

Development of a Low-Profile, Piezoelectric Robot for MR-Guided Abdominal Needle Interventions

PURPOSE

Minimally invasive needle-based interventions are commonly used in cancer diagnosis and treatment, including procedures, such as biopsy, brachytherapy, and microwave ablation. Although MR-guided needle placement offers several distinct advantages, such as high-resolution target visualization and accurate device tracking, one of the primary limitations that affect its widespread adoption is the ergonomic constraints of the closed-bore MRI environment, requiring the patients to be frequently moved in and out to perform the needle-based procedures. This paper introduces a low-profile, body-mounted, MR-guided robot designed to address this limitation by streamlining the operation workflow and enabling accurate needle placement within the MRI scanner.

METHODS

The robot employs piezoelectric linear actuators and stacked Cartesian XY stages to precisely control the position and orientation of a needle guide. A kinematic model and control framework was developed to facilitate accurate targeting. Additionally, clinical workflow for the liver interventions was developed to demonstrate the robot's capability to replicate existing procedures. The proposed system was validated in benchtop environment and 3T MRI scanner to quantify the system performance.

RESULTS

Experimental validations conducted in free space demonstrated a position accuracy of 2.38 ± 0.94 mm and orientation error of 1.40 ± 2.89°. Additional tests to confirm MR-conditionality and MR-guided phantom placements were carried out to assess the system's performance and safety in MRI suite, yielding a position error of 2.01 ± 0.77 mm and an orientation error of 1.57 ± 1.31°.

CONCLUSION

The presented robot shows exceptional compatibility with a wide range of patients and bore sizes while maintaining clinically significant accuracy. Future work will focus on the validations in dynamic liver environments.

An MR-Safe Pneumatic Stepper Motor: Design, Control, and Characterization

Magnetic resonance imaging (MRI) can provide high contrast soft tissue visualization without ionizing radiation, which makes it an attractive imaging modality for interventional procedures. However, the strong magnetic and radio frequency (RF) fields impose significant challenges to the development of robotic systems within the magnetic resonance environment. Consequently, designing MRI-compatible actuators is crucial for advancing MRI-guided robotic systems. This paper reports the design, control, and characterization of a gear-based pneumatic stepper motor. The motor is designed with three actuating piston units and a geared rotor. The three actuating pistons are driven sequentially by compressed air to push the geared rotor and to generate bidirectional stepwise motion. Experiments were conducted to characterize the motor in terms of torque, speed, control, and MRI compatibility. The results demonstrate that the motor can deliver a maximum continuous torque of 1300 mNm at 80 pounds per square inch (PSI) (0.55 MPa) with 9 m air hoses. The closed-loop control evaluation demonstrates the steady-state error of position tracking was 0.81±0.52 deg. The MRI compatibility study indicated negligible image quality degradation. Therefore, the proposed pneumatic stepper motor can effectively serve as an actuator for MRI-guided robotic applications.

Body-Mounted MR-Conditional Robot for Minimally Invasive Liver Intervention

MR-guided microwave ablation (MWA) has proven effective in treating hepatocellular carcinoma (HCC) with small-sized tumors, but the state-of-the-art technique suffers from sub-optimal workflow due to the limited accuracy provided by the manual needle insertions. This paper presents a compact body-mounted MR-conditional robot that can operate in closed-bore MR scanners for accurate needle guidance. The robotic platform consists of two stacked Cartesian XY stages, each with two degrees of freedom, that facilitate needle insertion pose control. The robot is actuated using 3D-printed pneumatic turbines with MR-conditional bevel gear transmission systems. Pneumatic valves and control mechatronics are located inside the MRI control room and are connected to the robot with pneumatic transmission lines and optical fibers. Free-space experiments indicated robot-assisted needle insertion error of 2.6 ± 1.3 mm at an insertion depth of 80 mm. The MR-guided phantom studies were conducted to verify the MR-conditionality and targeting performance of the robot. Future work will focus on the system optimization and validations in animal trials.

Modeling and Control of an MR-Safe Pneumatic Radial Inflow Motor and Encoder (PRIME)

Magnetic resonance (MR) conditional actuators and encoders are the key components for MR-guided robotic systems. In this article, we present the modeling and control of our MR-safe pneumatic radial inflow motor and encoder. A comprehensive model is developed that considers the primary dynamic elements of the system, including: 1) motor dynamics, 2) pneumatic transmission line dynamics, and 3) valve dynamics. After model validation, we present a simplified third order model that facilitates design of a first order sliding mode controller (TO-SMC). Finally, the motor hardware is tested in a 7T MRI. No image distortion or artifacts were observed. We posit the MR-safe motor and dynamic model will lower the entry barriers for researchers interested in MR-guided robots and promote wider adoption of MR-guided robotic systems.

A magnetic resonance conditional robot for lumbar spinal injection: Development and preliminary validation

PURPOSE

This work presents the design and preliminary validation of a Magnetic Resonance (MR) conditional robot for lumbar injection for the treatment of lower back pain.

METHODS

This is a 4-degree-of-freedom (DOF) robot that is 200 × 230 × 130 mm3 in volume and has a mass of 0.8 kg. Its lightweight and compact features allow it to be directly affixed to patient's back, establishing a rigid connection, thus reducing positional errors caused by patient movements during treatment.

RESULTS

To validate the positioning accuracy of the needle by the robot, an electromagnetic (EM) tracking system and a needle with an EM sensor embedded in the tip were used for the free space evaluation with position accuracy of 0.88 ± 0.46 mm and phantom mock insertions using the Loop-X CBCT scanner with target position accuracy of 3.62 ± 0.92 mm.

CONCLUSION

Preliminary experiments demonstrated that the proposed robot showed improvements and benefits in its rotation range, flexible needle adjustment, and sensor protection compared with previous and existing systems, offering broader clinical applications.

Non-Metallic MR-Guided Concentric Tube Robot for Intracerebral Hemorrhage Evacuation

OBJECTIVE

We aim to develop and evaluate an MR-conditional concentric tube robot for intracerebral hemorrhage (ICH) evacuation.

METHODS

We fabricated the concentric tube robot hardware with plastic tubes and customized pneumatic motors. The robot kinematic model was developed using a discretized piece-wise constant curvature (D-PCC) approach to account for variable curvature along the tube shape, and tube mechanics model was used to compensate torsional deflection of the inner tube. The MR-safe pneumatic motors were controlled using a variable gain PID algorithm. The robot hardware was validated in a series of bench-top and MRI experiments, and the robot's evacuation efficacy was tested in MR-guided phantom trials.

RESULTS

The pneumatic motor was able to achieve a rotational accuracy of 0.32°±0.30° with the proposed variable gain PID control algorithm. The kinematic model provided a positional accuracy of the tube tip of 1.39 ± 0.54 mm. The robot was able to evacuate an initial 38.36 mL clot, leaving a residual hematoma of 8.14 mL after 5 minutes, well below the 15 mL guideline suggesting good post-ICH evacuation clinical outcomes.

CONCLUSION

This robotic platform provides an effective method for MR-guided ICH evacuation.

SIGNIFICANCE

ICH evacuation is feasible under MRI guidance using a plastic concentric tube, indicating potential feasibility in future live animal studies.

Robotic Instruments Inside the MRI Bore: Key Concepts and Evolving Paradigms in Imaging-enhanced Cranial Neurosurgery

Intraoperative MRI has been increasingly used to robotically deliver electrodes and catheters into the human brain using a linear trajectory with great clinical success. Current cranial MR guided robotics do not allow for continuous real-time imaging during the procedure because most surgical instruments are not MR-conditional. MRI guided robotic cranial surgery can achieve its full potential if all the traditional advantages of robotics (such as tremor-filtering, precision motion scaling, etc.) can be incorporated with the neurosurgeon physically present in the MRI bore or working remotely through controlled robotic arms. The technological limitations of design optimization, choice of sensing, kinematic modeling, physical constraints, and real-time control had hampered early developments in this emerging field, but continued research and development in these areas over time has granted neurosurgeons far greater confidence in using cranial robotic techniques. This article elucidates the role of MR-guided robotic procedures using clinical devices like NeuroBlate and Clearpoint that have several thousands of cases operated in a "linear cranial trajectory" and planned clinical trials, such as LAANTERN for MR guided robotics in cranial neurosurgery using LITT and MR-guided putaminal delivery of AAV2 GDNF in Parkinson's disease. The next logical improvisation would be a steerable curvilinear trajectory in cranial robotics with added DOFs and distal tip dexterity to the neurosurgical tools. Similarly, the novel concept of robotic actuators that are powered, imaged, and controlled by the MRI itself is discussed in this article, with its potential for seamless cranial neurosurgery.

Review of Robot-Assisted HIFU Therapy

This paper provides an overview of current robot-assisted high-intensity focused ultrasound (HIFU) systems for image-guided therapies. HIFU is a minimally invasive technique that relies on the thermo-mechanical effects of focused ultrasound waves to perform clinical treatments, such as tumor ablation, mild hyperthermia adjuvant to radiation or chemotherapy, vein occlusion, and many others. HIFU is typically performed under ultrasound (USgHIFU) or magnetic resonance imaging guidance (MRgHIFU), which provide intra-operative monitoring of treatment outcomes. Robot-assisted HIFU probe manipulation provides precise HIFU focal control to avoid damage to surrounding sensitive anatomy, such as blood vessels, nerve bundles, or adjacent organs. These clinical and technical benefits have promoted the rapid adoption of robot-assisted HIFU in the past several decades. This paper aims to present the recent developments of robot-assisted HIFU by summarizing the key features and clinical applications of each system. The paper concludes with a comparison and discussion of future perspectives on robot-assisted HIFU.

Open Source MR-Safe Pneumatic Radial Inflow Motor and Encoder (PRIME): Design and Manufacturing Guidelines

Actuators and encoders used in MR-guided robotic interventions are subject to strict requirements to ensure patient safety and MR imaging quality. In this paper, we present an open source computer aided design (CAD) of our MR-safe Pneumatic Radial Inflow Motor and Encoder (PRIME). PRIME is a parametrically designed motor that enables scalability based on torque and speed requirements for a wide range of MR-guided robotic procedures. The design consists of five primary modifiable parameters that define the entire motor geometry. All components of the motor are either 3D printed or available off-the-shelf. Quadrature encoding is achieved using a 3D printed housing and four fiber optic cables. Benchtop experiments were performed to validate the performance of the proposed design. To the best of our knowledge, this is the first open source MR-safe pneumatic motor and encoder in the field. We aim to share the design and manufacturing guidelines to lower the entry barriers for researchers interested in MR-guided robotics.

Design of a 6-DoF Parallel Robotic Platform for MRI Applications

In this work, the design, analysis, and characterization of a parallel robotic motion generation platform with 6-degrees of freedom (DoF) for magnetic resonance imaging (MRI) applications are presented. The motivation for the development of this robot is the need for a robotic platform able to produce accurate 6-DoF motion inside the MRI bore to serve as the ground truth for motion modeling; other applications include manipulation of interventional tools such as biopsy and ablation needles and ultrasound probes for therapy and neuromodulation under MRI guidance. The robot is comprised of six pneumatic cylinder actuators controlled via a robust sliding mode controller. Tracking experiments of the pneumatic actuator indicates that the system is able to achieve an average error of 0.69 ± 0.14 mm and 0.67 ± 0.40 mm for step signal tracking and sinusoidal signal tracking, respectively. To demonstrate the feasibility and potential of using the proposed robot for minimally invasive procedures, a phantom experiment was performed in the benchtop environment, which showed a mean positional error of 1.20 ± 0.43 mm and a mean orientational error of 1.09 ± 0.57°, respectively. Experiments conducted in a 3T whole body human MRI scanner indicate that the robot is MRI compatible and capable of achieving positional error of 1.68 ± 0.31 mm and orientational error of 1.51 ± 0.32° inside the scanner, respectively. This study demonstrates the potential of this device to enable accurate 6-DoF motions in the MRI environment.

Minimally Invasive Intracerebral Hemorrhage Evacuation: A review

Intracerebral hemorrhage is a leading cause of morbidity and mortality worldwide. To date, there is no specific treatment that clearly provides a benefit in functional outcome or mortality. Surgical treatment for hematoma evacuation has not yet shown clear benefit over medical management despite promising preclinical studies. Minimally invasive treatment options for hematoma evacuation are under investigation but remain in early-stage clinical trials. Robotics has the potential to improve treatment. In this paper, we review intracerebral hemorrhage pathology, currently available treatments, and potential robotic approaches to date. We also discuss the future role of robotics in stroke treatment.

Preliminary Evaluation of Hydraulic Needle Delivery System for Magnetic Resonance Imaging-Guided Prostate Biopsy Procedures

In clinical routine, the prostate biopsy procedure is performed with the guidance of transrectal ultrasound (TRUS) imaging to diagnose prostate cancer. However, the TRUS-guided prostate biopsy brings reliability concerns due to the lack of contrast difference between prostate tissue and lesions. In this study, a novel hydraulic needle delivery system that is designed for performing magnetic resonance imaging (MRI)-guided prostate biopsy procedure with transperineal approach is introduced. The feasibility of the overall system was evaluated through in vitro phantom experiments under an MRI guidance. The in vitro experiments performed using a certified prostate phantom (incorporating MRI visible lesions). MRI experiments showed that overall hydraulic biopsy needle delivery system has excellent MRI compatibility (signal to noise ratio (SNR) loss < 3%), provides acceptable targeting accuracy (average 2.05±0.46 mm) and procedure time (average 40 min).