A general-purpose MR-compatible robotic system: implementation and image guidance for performing minimally invasive interventions

Challenges regarding MR compatibility of an MRgFUS robotic system

Numerous challenges are faced when employing Magnetic Resonance guided Focused Ultrasound (MRgFUS) hardware in the Magnetic Resonance Imaging (MRI) setting. The current study aimed to provide insights on this topic through a series of experiments performed in the framework of evaluating the MRI compatibility of an MRgFUS robotic device. All experiments were performed in a 1.5 T MRI scanner. The main metric for MRI compatibility assessment was the signal to noise ratio (SNR). Measurements were carried out in a tissue mimicking phantom and freshly excised pork tissue under various activation states of the system. In the effort to minimize magnetic interference and image distortion, various set-up parameters were examined. Significant SNR degradation and image distortion occurred when the FUS transducer was activated mainly owing to FUS-induced target and coil vibrations and was getting worse as the output power was increased. Proper design and stable positioning of the imaged phantom play a critical role in reducing these vibrations. Moreover, isolation of the phantom from the imaging coil was proven essential for avoiding FUS-induced vibrations from being transferred to the coil during sonication and resulted in a more than 3-fold increase in SNR. The use of a multi-channel coil increased the SNR by up to 50 % compared to a single-channel coil. Placement of the electronics outside the coil detection area increased the SNR by about 65 %. A similar SNR improvement was observed when the encoders' counting pulses were deactivated. Overall, this study raises awareness about major challenges regarding operation of an MRgFUS system in the MRI environment and proposes simple measures that could mitigate the impact of noise sources so that the monitoring value of MR imaging in FUS applications is not compromised.

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.

Pressure based MRI-compatible muscle fascicle length and joint angle estimation

BACKGROUND

Functional magnetic resonance imaging (fMRI) provides critical information about the neurophysiology of the central nervous systems (CNS), posing clinical significance for the understanding of neuropathologies and advancement of rehabilitation. Typical fMRI study designs include subjects performing designed motor tasks within specific time frames, in which fMRI data are then analyzed by assuming that observed functional brain activations correspond to the designed tasks. Therefore, developing MRI-compatible sensors that enable real-time monitoring of subjects' task performances would allow for highly accurate fMRI studies. While several MRI-compatible sensors have been developed, none have demonstrated the ability to measure individual muscle fascicle length during fMRI, which could help uncover the complexities of the peripheral and central nervous systems. Furthermore, previous MRI-compatible sensors have been focused on biologically intact populations, limiting accessibility to populations such as those who have undergone amputation.

METHODS

We propose a lightweight, low-cost, skin impedance-insensitive pressure-based muscular motion sensor (pMMS) that provides reliable estimates of muscle fascicle length and joint angle. The muscular motions are captured through measured pressure changes in an air pocket wrapped around the muscle of interest, corresponding to its muscular motion. The muscle fascicle length and joint angle are then estimated from the measured pressure changes based on the proposed muscle-skin-sensor interaction dynamics. Furthermore, we explore an integration method of multiple pMMS systems to expand the sensor capacity of estimating muscle fascicle length and joint angle. Ultrasound imaging paired with joint encoder measurements are utilized to assess pMMS estimation accuracy of muscle fascicle length in the tibialis anterior (TA) and ankle joint angle, respectively, of five biologically intact subjects.

RESULTS

We found that a single pMMS sufficiently provides robust and accurate estimations of TA muscle fascicle length and ankle joint angle during dorsiflexion at various speeds and amplitudes. Further, differential pressure readings from two pMMSs, in which each pMMS were proximally and distally placed, were able to mitigate errors due to perturbations, expanding pMMS capacity for muscle fascicle length and ankle joint angle estimation during the full range of plantar flexion and dorsiflexion.

CONCLUSIONS

Our results from this study demonstrate the feasibility of the pMMS system to further be incorporated in fMRI settings for real-time monitoring of subjects' task performances, allowing sophisticated fMRI study designs.

Review of Robotic Needle Guide Systems for Percutaneous Intervention

Numerous research groups in the past have designed and developed robotic needle guide systems that improve the targeting accuracy and precision by either providing a physical guidance for manual insertion or enabling a complete automated intervention. Here we review systems that have been reported in the last 11 years and limited to straight line needle interventions. Most systems fall under the category of image guided systems as they either use magnetic resonance image, computed tomography, ultrasound or a combination of these modalities for real time image feedback of the intervention path being followed. Actuation and control technology along with materials used for construction are the main aspects that differentiate these systems from each other and have been reviewed here. Image compatibility test details and results are also reviewed as they are used to ensure proper functioning of these systems under the respective imaging environments. We have also reviewed needle guide systems which either don't use any image feedback or have not reported any but provide physical guidance. Throughout this paper, we provide a comprehensive review of the technological aspects and trends in the field of robotic, straight line, needle guide intervention systems.

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.

Phenomenological universalities: a novel tool for the analysis of dynamic contrast enhancement in magnetic resonance imaging

Dynamic contrast enhancement in magnetic resonance imaging (DCE-MRI) is a promising tool for the clinical diagnosis of tumors, whose implementation may be improved through the use of suitable hemodynamic models. If one prefers to avoid assumptions about the tumor physiology, empirical fitting functions may be adopted. For this purpose, in this paper we discuss the exploitation of a recently proposed phenomenological universalities (PUN) formalism. In fact, we show that a novel PUN class may be used to describe the time-signal intensity curves in both healthy and tumoral tissues, discriminating between the two cases and thus potentially providing a convenient diagnostic tool. The proposed approach is applied to analysis of the DCE-MRI data relative to a study group composed of ten patients with spine tumors.

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 Needle Manipulator Concept Based on Elastically Averaged Dielectric Elastomer Actuators for Prostate Cancer Treatment: An Accuracy and MR-Compatibility Evaluation in Phantoms

A parallel manipulator concept using bistable polymer actuators has been developed to perform prostate cancer biopsy, and deliver therapy within the bore of a magnetic resonance imaging (MRI) scanner. The dielectric elastomer actuators (DEAs) used in this manipulator concept are promising for MRI-compatible robotics because they do not interfere with the high magnetic fields of MRI while having good mechanical performance and being low cost. In the past, these actuators have been plagued by robustness problems when used in a continuous manner. Recent studies show that reliability significantly improves when DEAs are used in a bistable manner, as proposed here. This paper investigates the potential of the proposed manipulator concept by evaluating the positioning accuracy and MRI compatibility of a laboratory prototype, developed for clinically relevant design criteria. An analytical model of the manipulator kinematics is presented. Analytical and experimental results validate that the proposed technology can provide an accurate needle placement required to perform prostate cancer treatments. The prototype’s MRI compatibility is validated in a 3 T clinical MRI scanner. The parallel manipulator concept using bistable polymer actuators is shown to be a viable approach to perform MRI-guided needle insertions for prostate cancer biopsy and therapy.