Development of a Pneumatic Robot for MRI-guided Transperineal Prostate Biopsy and Brachytherapy: New Approaches

MRI Distortion Correction and Robot-to-MRI Scanner Registration for an MRI-Guided Robotic System

Magnetic resonance imaging (MRI) guided robotic procedures require safe robotic instrument navigation and precise target localization. This depends on reliable tracking of the instrument from MR images, which requires accurate registration of the robot to the scanner. A novel differential image based robot-to-MRI scanner registration approach is proposed that utilizes a set of active fiducial coils, where background subtraction method is employed for coil detection. In order to use the presented preoperative registration approach jointly with the real-time high speed MRI image acquisition and reconstruction methods in real-time interventional procedures, the effects of the geometric MRI distortion in robot to scanner registration is analyzed using a custom distortion mapping algorithm. The proposed approach is validated by a set of target coils placed within the workspace, employing multi-planar capabilities of the scanner. Registration and validation errors are respectively 2.05 mm and 2.63 mm after the distortion correction showing an improvement of respectively 1.08 mm and 0.14 mm compared to the results without distortion correction.

Differential Image Based Robot to MRI Scanner Registration with Active Fiducial Markers for an MRI-Guided Robotic Catheter System

In magnetic resonance imaging (MRI) guided robotic catheter ablation procedures, reliable tracking of the catheter within the MRI scanner is needed to safely navigate the catheter. This requires accurate registration of the catheter to the scanner. This paper presents a differential, multi-slice image-based registration approach utilizing active fiducial coils. The proposed method would be used to preoperatively register the MRI image space with the physical catheter space. In the proposed scheme, the registration is performed with the help of a registration frame, which has a set of embedded electromagnetic coils designed to actively create MRI image artifacts. These coils are detected in the MRI scanner's coordinate system by background subtraction. The detected coil locations in each slice are weighted by the artifact size and then registered to known ground truth coil locations in the catheter's coordinate system via least-squares fitting. The proposed approach is validated by using a set of target coils placed withing the workspace, employing multi-planar capabilities of the MRI scanner. The average registration and validation errors are respectively computed as 1.97 mm and 2.49 mm. The multi-slice approach is also compared to the single-slice method and shown to improve registration and validation by respectively 0.45 mm and 0.66 mm.

A study on observed ultrasonic motor-induced magnetic resonance imaging (MRI) artifacts

Background

The safe performance of magnetic resonance imaging (MRI)-guided robot-assisted interventions requires full control and high precision of assistive devices. Because many currently available tools are not MRI-compatible, the characterization of existing tools and development of new ones are necessary. The purpose of this research is to identify and minimize the image artifacts generated by a USM in MR images.

Methods

The behavior of an ultrasonic motor (USM), the most common MRI-safe actuator, in a high-field scanner was investigated. The motor was located in three orientations with respect to the bore axis with the power on or off. The induced image artifacts were compared across four sequences. Three artifact reduction methods (employing ultrashort sequences, slice thickness reductions, and bandwidth increments) were tested.

Results

Signal voids, pileups, and geometric distortions were observed when the motor was off. The artifact size was minimal when the motor shaft was aligned with the bore axis. In addition to the above artifacts, zipper and motion artifacts were noted when the motor was running, and these artifacts increased with increasing motor speed. Increasing the bandwidth slightly reduced the artifacts. However, decreasing the slice thickness from 5 mm to 3 mm and from 5 mm to 1 mm reduced artifact size from 30% to 40% and from 60% to 75%, respectively.

Conclusion

The image artifacts were due to the non-homogenous nature of the static and gradient fields caused by the motor structure. The operating motor interferes with the RF field, causing zipper and motion artifacts.

MRI Robots for Needle-Based Interventions: Systems and Technology

Magnetic resonance imaging (MRI) provides high-quality soft-tissue images of anatomical structures and radiation free imaging. The research community has focused on establishing new workflows, developing new technology, and creating robotic devices to change an MRI room from a solely diagnostic room to an interventional suite, where diagnosis and intervention can both be done in the same room. Closed bore MRI scanners provide limited access for interventional procedures using intraoperative imaging. MRI robots could improve access and procedure accuracy. Different research groups have focused on different technology aspects and anatomical structures. This paper presents the results of a systematic search of MRI robots for needle-based interventions. We report the most recent advances in the field, present relevant technologies, and discuss possible future advances. This survey shows that robotic-assisted MRI-guided prostate biopsy has received the most interest from the research community to date. Multiple successful clinical experiments have been reported in recent years that show great promise. However, in general the field of MRI robotic systems is still in the early stage. The continued development of these systems, along with partnerships with commercial vendors to bring this technology to market, is encouraged to create new and improved treatment opportunities for future patients.

MRI-Guided Robotically Assisted Focal Laser Ablation of the Prostate Using Canine Cadavers

OBJECTIVE

a magnetic resonance imaging (MRI)-conditional needle guidance robot is developed to enhance MRI-guided focal laser ablation (FLA) therapy in patients with focal prostate cancer.

METHODS

inspired by the workflow of the manual FLA therapy, we developed an MRI-conditional robot with two degrees of freedom to provide the guidance for laser ablation catheter. This robot is powered by pneumatic turbine motors and encoded with the custom-designed optical encoder. The needle could be inserted manually through the designed robotic system, which keeps the patients inside MRI bore throughout the procedure. The robot hardware is integrated with the custom ablation planning and monitoring software (OncoNav) to provide an iterative treatment plan to cover the whole ablation zone. Virtual tumors were selected in three canine cadavers as targets to validate the performance of the proposed hardware and software system.

RESULTS

phantom studies show that the average targeting error is less than 2 mm and the workflow of the entire procedure lasts for 100 minutes. Canine cadaver experiment results show that all the targets were successfully ablated in no more than three administrations.

SIGNIFICANCE

MRI-guided prostate FLA is feasible using the proposed hardware and software system, indicating potential utility in future human trials.

Signal-to-noise ratio evaluation of magnetic resonance images in the presence of an ultrasonic motor

Background

Safe robot-assisted intervention using magnetic resonance imaging (MRI) guidance requires the precise control of assistive devices, and most currently available tools are rarely MRI-compatible. To obtain high precision, it is necessary to characterize and develop existing MRI-safe actuators for use in a high magnetic field (≥3 T). Although an ultrasonic motor (USM) is considered to be an MRI-safe actuator, and can be used in the vicinity of a high field scanner, its presence interferes with MR images. Although an MR image provides valuable information regarding the pathology of a patient’s body, noise, generally of a granular type, decreases the quality of the image and jeopardizes the true evaluation of any existing pathological issues. An eddy current induced in the conductor material of the motor structure can be a source of noise when the motor is close to the isocenter of the image. We aimed to assess the effects of a USM on the signal-to-noise ratio (SNR) of MR images in a 3-T scanner. The SNR was compared for four image sequences in transverse directions for three orientations of the motor (x, y, and z) when the motor was in the “off” state. The SNR was evaluated to assess three artifact reduction methods used to minimize the motor-induced artifacts.

Results

The SNR had a range of 5–10 dB for slices close to the motor in the x and y orientations, and increased to 15–20 dB for slices far from the motor. Averaging the SNR for slices in all cases gave an SNR loss of about 10 dB. The maximum SNR was measured in the z orientation. In this case, the SNR loss was almost the same as that of other motor orientations, approximately 10 dB, but with a higher range, approximately 20–40 dB.

Conclusions

The selection of certain scanning parameters is necessary for reducing motor-generated artifacts. These parameters include slice selection and bandwidth. In developing any MRI-compatible assisted device actuated by a USM, this study recommends the use of an approximately 3-mm slice thickness with minimum bandwidth to achieve optimized SNR values when a USM is operating close to (within approximately 40 mm) the region being imaged. The SNR can be further enhanced by increasing the number of signal averages, but this is achieved only at the cost of increased scan duration.

Robotic system with multiplex power transmission for MRI-guided percutaneous interventions

In minimally invasive prostate percutaneous interventions, Magnetic Resonance Imaging (MRI) compatible robotic assistive systems developed over the years tend to have multiple degrees of freedom (DOF) to accomplish complex surgical tasks. This paper presents a novel design of an MRI-compatible transmission that allows one driving motor to control a multiplexed DOF robot system. The transmission could reduce the number of motors in the system, while maintaining the functionality of the system, by controlling each motion sequentially rather than simultaneously. A series of preliminary experiments as well as a targeting accuracy test are conducted to evaluate the accuracy of the system.

Prostate biopsies assisted by comanipulated probe-holder: first in man

PURPOSE

A comanipulator for assisting endorectal prostate biopsies is evaluated through a first-in-man clinical trial. This lightweight system, based on conventional robotic components, possesses six degrees of freedom. It uses three electric motors and three brakes. It features a free mode, where its low friction and inertia allow for natural manipulation of the probe and a locked mode, exhibiting both a very low stiffness and a high steady-state precision.

METHODS

Clinical trials focusing on the free mode and the locked mode of the robot are presented. The objective was to evaluate the practical usability and performance of the robot during clinical procedures. A research protocol for a prospective randomized clinical trial has been designed. Its specific goal was to compare the accuracy of biopsies performed with and without the assistance of the comanipulator.

RESULTS

The accuracy is compared between biopsies performed with and without the assistance of the comanipulator, across the 10 first patients included in the trial. Results show a statistically significant increase in the precision.

Reduced dose to urethra and rectum with the use of variable needle spacing in prostate brachytherapy: a potential role for robotic technology

Purpose

Several robotic delivery systems for prostate brachytherapy are under development or in pre-clinical testing. One of the features of robotic brachytherapy is the ability to vary spacing of needles at non-fixed intervals. This feature may play an important role in prostate brachytherapy, which is traditionally template-based with fixed needle spacing of 0.5 cm. We sought to quantify potential reductions in the dose to urethra and rectum by utilizing variable needle spacing, as compared to fixed needle spacing.

Material and methods

Transrectal ultrasound images from 10 patients were used by 3 experienced planners to create 120 treatment plans. Each planner created 4 plan variations per patient with respect to needle positions: ¹²⁵I fixed spacing, ¹²⁵I variable spacing, ¹⁰³Pd fixed spacing, and ¹⁰³Pd variable spacing. The primary planning objective was to achieve a prostate V₁₀₀ of 100% while minimizing dose to urethra and rectum.

Results

All plans met the objective of achieving prostate V₁₀₀ of 100%. Combined results for all plans show statistically significant improvements in all assessed dosimetric variables for urethra (U_max, U_mean, D₃₀, D₅) and rectum (R_max, R_mean, R_V100) when using variable spacing. The dose reductions for mean and maximum urethra dose using variable spacing had p values of 0.011 and 0.024 with ¹⁰³Pd, and 0.007 and 0.029 with ¹²⁵I plans. Similarly dose reductions for mean and maximum rectal dose using variable spacing had p values of 0.007 and 0.052 with ¹⁰³Pd, and 0.012 and 0.037 with ¹²⁵I plans.

Conclusions

The variable needle spacing achievable by the use of robotics in prostate brachytherapy allows for reductions in both urethral and rectal planned doses while maintaining prostate dose coverage. Such dosimetric advantages have the potential in translating to significant clinical benefits with the use of robotic brachytherapy.

In-bore prostate transperineal interventions with an MRI-guided parallel manipulator: system development and preliminary evaluation

BACKGROUND

Robot-assisted minimally-invasive surgery is well recognized as a feasible solution for diagnosis and treatment of prostate cancer in humans.

METHODS

This paper discusses the kinematics of a parallel 4 Degrees-of-Freedom (DOF) surgical manipulator designed for minimally invasive in-bore prostate percutaneous interventions through the patient's perineum. The proposed manipulator takes advantage of four sliders actuated by MRI-compatible piezoelectric motors and incremental rotary encoders. Errors, mostly originating from the design and manufacturing process, need to be identified and reduced before the robot is deployed in clinical trials.

RESULTS

The manipulator has undergone several experiments to evaluate the repeatability and accuracy (about 1 mm in air (in x or y direction) at the needle's reference point) of needle placement, which is an essential concern in percutaneous prostate interventions.

CONCLUSION

The acquired results endorse the sustainability, precision and reliability of the manipulator. Copyright © 2015 John Wiley & Sons, Ltd.

A new hybrid actuation scheme with artificial pneumatic muscles and a magnetic particle brake for safe human–robot collaboration

Interest in the field of human-centered robotics continues to grow, particularly in utilizing pneumatic artificial muscles (PAMs) for close human–robot collaborations. Addressing the limited control performance of PAMs, we proposed a hybrid actuation scheme that combines PAMs (macro) and a low-inertia DC motor (mini). While the scheme has shown significantly improved control performance and robot safety, a small DC motor has difficulties in handling the large stored energies of the PAMs, particularly for large changes in initial load due to PAM failure. In order to further improve robot safety, we develop a new hybrid actuation scheme with PAMs (macro) and a particle brake (mini). This design allows for a higher torque-to-weight ratio and inherently stable energy dissipation. Addressing optimal mini actuation selection between a motor and a brake, and a control strategy for PAMs and a brake, we conducted comparative studies of hybrid actuations with (1) a DC motor and (2) a brake for concept validation. Experimental comparisons show that the hybrid actuation with PAMs and a brake provides higher energy efficiency for control bandwidths under 2 Hz, and more effective reduction of large impact forces due to the brake’s high torque capacity and passive energy dissipation.

Teleoperation System with Hybrid Pneumatic-Piezoelectric Actuation for MRI-Guided Needle Insertion with Haptic Feedback

This paper presents a surgical master-slave tele-operation system for percutaneous interventional procedures under continuous magnetic resonance imaging (MRI) guidance. This system consists of a piezoelectrically actuated slave robot for needle placement with integrated fiber optic force sensor utilizing Fabry-Perot interferometry (FPI) sensing principle. The sensor flexure is optimized and embedded to the slave robot for measuring needle insertion force. A novel, compact opto-mechanical FPI sensor interface is integrated into an MRI robot control system. By leveraging the complementary features of pneumatic and piezoelectric actuation, a pneumatically actuated haptic master robot is also developed to render force associated with needle placement interventions to the clinician. An aluminum load cell is implemented and calibrated to close the impedance control loop of the master robot. A force-position control algorithm is developed to control the hybrid actuated system. Teleoperated needle insertion is demonstrated under live MR imaging, where the slave robot resides in the scanner bore and the user manipulates the master beside the patient outside the bore. Force and position tracking results of the master-slave robot are demonstrated to validate the tracking performance of the integrated system. It has a position tracking error of 0.318mm and sine wave force tracking error of 2.227N.

Accuracy study of a robotic system for MRI-guided prostate needle placement

BACKGROUND

Accurate needle placement is the first concern in percutaneous MRI-guided prostate interventions. In this phantom study, different sources contributing to the overall needle placement error of a MRI-guided robot for prostate biopsy have been identified, quantified and minimized to the possible extent.

METHODS

The overall needle placement error of the system was evaluated in a prostate phantom. This error was broken into two parts: the error associated with the robotic system (called 'before-insertion error') and the error associated with needle-tissue interaction (called 'due-to-insertion error'). Before-insertion error was measured directly in a soft phantom and different sources contributing into this part were identified and quantified. A calibration methodology was developed to minimize the 4-DOF manipulator's error. The due-to-insertion error was indirectly approximated by comparing the overall error and the before-insertion error. The effect of sterilization on the manipulator's accuracy and repeatability was also studied.

RESULTS

The average overall system error in the phantom study was 2.5 mm (STD = 1.1 mm). The average robotic system error in the Super Soft plastic phantom was 1.3 mm (STD = 0.7 mm). Assuming orthogonal error components, the needle-tissue interaction error was found to be approximately 2.13 mm, thus making a larger contribution to the overall error. The average susceptibility artifact shift was 0.2 mm. The manipulator's targeting accuracy was 0.71 mm (STD = 0.21 mm) after robot calibration. The robot's repeatability was 0.13 mm. Sterilization had no noticeable influence on the robot's accuracy and repeatability.

CONCLUSIONS

The experimental methodology presented in this paper may help researchers to identify, quantify and minimize different sources contributing into the overall needle placement error of an MRI-guided robotic system for prostate needle placement. In the robotic system analysed here, the overall error of the studied system remained within the acceptable range.

Towards Clinically Optimized MRI-guided Surgical Manipulator for Minimally Invasive Prostate Percutaneous Interventions: Constructive Design

This paper undertakes the modular design and development of a minimally invasive surgical manipulator for MRI-guided transperineal prostate interventions. Severe constraints for the MRI-compatibility to hold the minimum artifact on the image quality and dimensions restraint of the bore scanner shadow the design procedure. Regarding the constructive design, the manipulator kinematics has been optimized and the effective analytical needle workspace is developed and followed by proposing the workflow for the manual needle insertion. A study of the finite element analysis is established and utilized to improve the mechanism weaknesses under some inevitable external forces to ensure the minimum structure deformation. The procedure for attaching a sterile plastic drape on the robot manipulator is discussed. The introduced robotic manipulator herein is aimed for the clinically prostate biopsy and brachytherapy applications.

A Fully Actuated Robotic Assistant for MRI-Guided Prostate Biopsy and Brachytherapy

Intra-operative medical imaging enables incorporation of human experience and intelligence in a controlled, closed-loop fashion. Magnetic resonance imaging (MRI) is an ideal modality for surgical guidance of diagnostic and therapeutic procedures, with its ability to perform high resolution, real-time, high soft tissue contrast imaging without ionizing radiation. However, for most current image-guided approaches only static pre-operative images are accessible for guidance, which are unable to provide updated information during a surgical procedure. The high magnetic field, electrical interference, and limited access of closed-bore MRI render great challenges to developing robotic systems that can perform inside a diagnostic high-field MRI while obtaining interactively updated MR images. To overcome these limitations, we are developing a piezoelectrically actuated robotic assistant for actuated percutaneous prostate interventions under real-time MRI guidance. Utilizing a modular design, the system enables coherent and straight forward workflow for various percutaneous interventions, including prostate biopsy sampling and brachytherapy seed placement, using various needle driver configurations. The unified workflow compromises: 1) system hardware and software initialization, 2) fiducial frame registration, 3) target selection and motion planning, 4) moving to the target and performing the intervention (e.g. taking a biopsy sample) under live imaging, and 5) visualization and verification. Phantom experiments of prostate biopsy and brachytherapy were executed under MRI-guidance to evaluate the feasibility of the workflow. The robot successfully performed fully actuated biopsy sampling and delivery of simulated brachytherapy seeds under live MR imaging, as well as precise delivery of a prostate brachytherapy seed distribution with an RMS accuracy of 0.98mm.

Development and preliminary evaluation of a motorized needle guide template for MRI-guided targeted prostate biopsy

To overcome the problems of limited needle insertion accuracy and human error in the use of a conventional needle guide template in magnetic resonance imaging (MRI)-guided prostate intervention, we developed a motorized MRI-compatible needle guide template that resembles a transrectal ultrasound-guided prostate template. The motorized template allows automated, gapless needle guidance in a 3T MRI scanner with minimal changes in the current clinical procedure. To evaluate the impact of the motorized template on MRI, signal-to-noise ratio and distortion were measured under various system configurations. A maximum of 44% signal-to-noise ratio decrease was found when the ultrasonic motors were running, and a maximum of 0.4% image distortion was observed due to the presence of the motorized template. To measure needle insertion accuracy, we performed four sets of five random target needle insertions mimicking four biopsy procedures, which resulted in an average in-plane targeting error of 0.94 mm with a standard deviation of 0.34 mm. The evaluation studies indicated that the presence and operation of the motorized template in the MRI bore create insignificant image degradation, and provide submillimeter targeting accuracy. The automated needle guide that is directly controlled by navigation software eliminates human error so that the safety of the procedure can be improved.

Design of a Teleoperated Needle Steering System for MRI-guided Prostate Interventions

Accurate needle placement plays a key role in success of prostate biopsy and brachytherapy. During percutaneous interventions, the prostate gland rotates and deforms which may cause significant target displacement. In these cases straight needle trajectory is not sufficient for precise targeting. Although needle spinning and fast insertion may be helpful, they do not entirely resolve the issue. We propose robot-assisted bevel-tip needle steering under MRI guidance as a potential solution to compensate for the target displacement. MRI is chosen for its superior soft tissue contrast in prostate imaging. Due to the confined workspace of the MRI scanner and the requirement for the clinician to be present inside the MRI room during the procedure, we designed a MRI-compatible 2-DOF haptic device to command the needle steering slave robot which operates inside the scanner. The needle steering slave robot was designed to be integrated with a previously developed pneumatically actuated transperineal robot for MRI-guided prostate needle placement. We describe design challenges and present the conceptual design of the master and slave robots and the associated controller.

Development and Evaluation of an Actuated MRI-Compatible Robotic System for MRI-Guided Prostate Intervention

This paper reports the design, development, and magnetic resonance imaging (MRI) compatibility evaluation of an actuated transrectal prostate robot for MRI-guided needle intervention in the prostate. The robot performs actuated needle MRI-guidance with the goals of providing (i) MRI compatibility, (ii) MRI-guided needle placement with accuracy sufficient for targeting clinically significant prostate cancer foci, (iii) reducing interventional procedure times (thus increasing patient comfort and reducing opportunity for needle targeting error due to patient motion), (iv) enabling real-time MRI monitoring of interventional procedures, and (v) reducing the opportunities for error that arise in manually actuated needle placement. The design of the robot, employing piezo-ceramic-motor actuated needle guide positioning and manual needle insertion, is reported. Results of a MRI compatibility study show no reduction of MRI signal-to-noise-ratio (SNR) with the motors disabled. Enabling the motors reduces the SNR by 80% without RF shielding, but SNR is only reduced by 40% to 60% with RF shielding. The addition of radio-frequency shielding is shown to significantly reduce image SNR degradation caused by the presence of the robotic device. An accuracy study of MRI-guided biopsy needle placements in a prostate phantom is reported. The study shows an average in-plane targeting error of 2.4 mm with a maximum error of 3.7 mm. These data indicate the system's needle targeting accuracy is similar to that obtained with a previously reported manually actuated system, and is sufficient to reliably sample clinically significant prostate cancer foci under MRI-guidance.

Reconfigurable MRI-guided robotic surgical manipulator: prostate brachytherapy and neurosurgery applications

This paper describes a modular design approach for robotic surgical manipulator under magnetic resonance imaging (MRI) guidance. The proposed manipulator provides 2 degree of freedom (DOF) Cartesian motion and 2-DOF pitch and yaw motion. Primarily built up with dielectric materials, it utilizes parallel mechanism and is compact in size to fit into the limited space of close-bore MRI scanner. It is ideal for needle based surgical procedures which usually require positioning and orientation control for accurate imaging plane alignment. Specifically, this mechanism is easily reconfigurable to over constrained manipulator structure which provides 2-DOF Cartesian motion by simple structure modification. This modular manipulator integrated with different end-effector modules is investigated for prostate brachytherapy and neurosurgery applications as preliminary evaluation.

Preclinical evaluation of an MRI-compatible pneumatic robot for angulated needle placement in transperineal prostate interventions

PURPOSE

To evaluate the targeting accuracy of a small profile MRI-compatible pneumatic robot for needle placement that can angulate a needle insertion path into a large accessible target volume.

METHODS

We extended our MRI-compatible pneumatic robot for needle placement to utilize its four degrees-of-freedom (4-DOF) mechanism with two parallel triangular structures and support transperineal prostate biopsies in a closed-bore magnetic resonance imaging (MRI) scanner. The robot is designed to guide a needle toward a lesion so that a radiologist can manually insert it in the bore. The robot is integrated with navigation software that allows an operator to plan angulated needle insertion by selecting a target and an entry point. The targeting error was evaluated while the angle between the needle insertion path and the static magnetic field was between -5.7° and 5.7° horizontally and between -5.7° and 4.3° vertically in the MRI scanner after sterilizing and draping the device.

RESULTS

The robot positioned the needle for angulated insertion as specified on the navigation software with overall targeting error of 0.8 ± 0.5mm along the horizontal axis and 0.8 ± 0.8mm along the vertical axis. The two-dimensional root-mean-square targeting error on the axial slices as containing the targets was 1.4mm.

CONCLUSIONS

Our preclinical evaluation demonstrated that the MRI-compatible pneumatic robot for needle placement with the capability to angulate the needle insertion path provides targeting accuracy feasible for clinical MRI-guided prostate interventions. The clinical feasibility has to be established in a clinical study.

Focal laser ablation of prostate cancer: definition, needs, and future

Current challenges and innovations in prostate cancer management concern the development of focal therapies that allow the treatment of only the cancer areas sparing the rest of the gland to minimize the potential morbidity. Among these techniques, focal laser ablation (FLA) appears as a potential candidate to reach the goal of focusing energy delivery on the identified targets. The aim of this study is to perform an up-to-date review of this new therapeutic modality. Relevant literature was identified using MEDLINE database with no language restrictions (entries: focal therapy, laser interstitial thermotherapy, prostate cancer, FLA) and by cross-referencing from previously identified studies. Precision, real-time monitoring, MRI compatibility, and low cost of integrated system are principal advantages of FLA. Feasibility and safety of this technique have been reported in phase I assays. FLA might eventually prove to be a middle ground between active surveillance and radical treatment. In conclusion, FLA may have found a role in the management of prostate cancer. However, further trials are required to demonstrate the oncologic effectiveness in the long term.

Biopsy needle artifact localization in MRI-guided robotic transrectal prostate intervention

Recently a number of robotic intervention systems for magnetic resonance image (MRI)-guided needle placement in the prostate have been reported. In MRI-guided needle interventions, after a needle is inserted, the needle position is often confirmed with a volumetric MRI scan. Commonly used titanium needles are not directly visible in an MRI, but they generate a susceptibility artifact in the immediate neighborhood of the needle. This paper reports the results of a quantitative study of the relationship between the true position of titanium biopsy needle and the corresponding needle artifact position in MRI, thereby providing a better understanding of the influence of needle artifact on targeting errors. The titanium needle tip artifact extended 9 mm beyond the actual needle tip location with tendency to bend toward the scanner's B (0) magnetic field direction, and axially displaced 0.38 and 0.32 mm (mean) in scanner's frequency and phase encoding direction, respectively.

Robotic system for MRI-guided prostate biopsy: feasibility of teleoperated needle insertion and ex vivo phantom study

PURPOSE

Magnetic Resonance Imaging (MRI) combined with robotic assistance has the potential to improve on clinical outcomes of biopsy and local treatment of prostate cancer.

METHODS

We report the workspace optimization and phantom evaluation of a five Degree of Freedom (DOF) parallel pneumatically actuated modular robot for MRI-guided prostate biopsy. To shorten procedure time and consequently increase patient comfort and system accuracy, a prototype of a MRI-compatible master-slave needle driver module using piezo motors was also added to the base robot.

RESULTS

Variable size workspace was achieved using appropriate link length, compared with the previous design. The 5-DOF targeting accuracy demonstrated an average error of 2.5 mm (STD = 1.37 mm) in a realistic phantom inside a 3T magnet with a bevel-tip 18G needle. The average position tracking error of the master-slave needle driver was always below 0.1 mm.

CONCLUSION

Phantom experiments showed sufficient accuracy for manual prostate biopsy. Also, the implementation of teleoperated needle insertion was feasible and accurate. These two together suggest the feasibility of accurate fully actuated needle placement into prostate while keeping the clinician supervision over the task.

An MRI-compatible robotic system with hybrid tracking for MRI-guided prostate intervention

This paper reports the development, evaluation, and first clinical trials of the access to the prostate tissue (APT) II system-a scanner independent system for magnetic resonance imaging (MRI)-guided transrectal prostate interventions. The system utilizes novel manipulator mechanics employing a steerable needle channel and a novel six degree-of-freedom hybrid tracking method, comprising passive fiducial tracking for initial registration and subsequent incremental motion measurements. Targeting accuracy of the system in prostate phantom experiments and two clinical human-subject procedures is shown to compare favorably with existing systems using passive and active tracking methods. The portable design of the APT II system, using only standard MRI image sequences and minimal custom scanner interfacing, allows the system to be easily used on different MRI scanners.

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.

A Study of Needle Image Artifact Localization in Confirmation Imaging of MRI-guided Robotic Prostate Biopsy

Recently several systems for magnetic resonance image (MRI) guided needle placement in the prostate have been reported. In comparison to conventional ultrasound-guided needle placement in the prostate, these MRI-guided systems promise improved targeting accuracy for prostate intervention procedures including biopsy, fiducial marker insertion, injection and focal therapy. In MRI-guided needle interventions, after a needle is inserted, the needle position is often confirmed with a volumetric MRI scan. Commonly used titanium needles are not directly visible in an MR image, but they generate a susceptibility artifact in the immediate neighborhood of the needle. This paper reports the results of a quantitative study of the relation between the true position of titanium biopsy needle and the corresponding needle artifact position in MR images. The titanium needle artifact was found to be displaced 0.38 mm and 0.32 mm shift in scanner's frequency and phase encoding direction, respectively. The artifact at the tip of the titanium needle was observed to bend toward the scanner's B(0) magnetic field direction.

High-field MRI-compatible needle placement robot for prostate interventions

This paper presents the design of a magnetic resonance imaging (MRI) compatible needle placement system actuated by piezoelectric actuators for prostate brachytherapy and biopsy. An MRI-compatible modular 3 degree-of-freedom (DOF) needle driver module coupled with a 3-DOF x-y-z stage is proposed as a slave robot to precisely deliver radioactive brachytherapy seeds under interactive MRI guidance. The needle driver module provides for needle cannula rotation, needle insertion and cannula retraction to enable the brachytherapy procedure with the preloaded needles. The device mimics the manual physician gesture by two point grasping (hub and base) and provides direct force measurement of needle insertion force by fiber optic force sensors. The fabricated prototype is presented and an experiment with phantom trials in 3T MRI is analyzed to demonstrate the system compatibility.

Preliminary Evaluation of a MRI-compatible Modular Robotic System for MRI-guided Prostate Interventions

Magnetic Resonance Imaging (MRI) guided robotic interventions have been introduced in order to advance prostate cancer detection and treatment. To overcome problems of such robotic interventions, we have been developing a pneumatically actuated MRI-compatible modular robotic system for MRI-guided transperineal prostate intervention and its interventional procedure. For system evaluation, a series of experiments have been conducted and this paper reports a needle insertion experiment using prostate phantom and patient mockup trials. The needle insertion experiment resulted in noticeable consistent error in one direction, which we will investigate further. Nonetheless, patient mockup experiences suggest that the modular robotic system and its interventional procedure are well integrated and implemented in clinical environment.