In-bore setup and software for 3T MRI-guided transperineal prostate biopsy

Kinematic and mechanical modelling of a novel 4-DOF robotic needle guide for MRI-guided prostate intervention

Traditionally ultrasound-guided biopsy has been used to diagnose prostate cancer despite of its poor soft tissue contrast and frequent false negative results. Magnetic Resonance Imaging (MRI) has the advantage of excellent soft tissue contrast for guiding and monitoring prostate biopsy. However, its working area and access in the confined MRI bore space limit the use of interventional guide devices including robotic systems. To provide robotic precision, greater access, and compact design, we designed a novel robotic mechanism that can provide four degrees of freedom (DOF) manipulation in a compact form comparable to size of manual templates. To develop the mechanism, we established a mathematical model of inverse and forward kinematics and prototyped a proof-of-concept needle guide for MRI guided prostate biopsy. The mechanism was materialized using four discs that house small passive spherical joints that can be moved by rotating the discs consisting of grooved profile. With an initial needle insertion angle range of ±15°, we identified mathematical and kinematic parameters for the mechanism design and fabricated the first prototype that has dimension of 40 × 110 × 180 mm3. The prototype demonstrated that the unique robotic manipulation can physically be delivered and could provide precise needle guidance including angulated needle insertion with higher structural rigidity.

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.

Preliminary Study of a Modular MR-Compatible Robot for Image-Guided Insertion of Multiple Needles

Percutaneous needle-based interventions such as transperineal prostate brachytherapy require the accurate placement of multiple needles to treat cancerous lesions within the target organ. To guide needle placement, magnetic resonance imaging (MRI) offers excellent visualization of the target lesion without the need for ionizing radiation. To date, multi-needle insertion relies on a grid template, which limits the ability to steer individual needles. This work describes an MR-compatible robot designed for the sequential insertion of multiple non-parallel needles under MR guidance. The 6-DOF system is designed with an articulated arm to extend the reach of the robot. This strategy presents a novel approach enabling the robot to maneuver around existing needles while minimizing the footprint of the robot. Forward kinematics as well as optimization-based inverse kinematics are presented. The impact of the robot on image quality was tested for four sequences (T1w-TSE, T2w-TSE, THRIVE and EPI) on a 3T Philips Achieva system. Quantification of the signal-to-noise ratio showed a 46% signal loss in a gelatin phantom when the system was powered on but no further adverse effects when the robot was moving. Joint level testing showed a maximum error of 2.10 ± 0.72°s for revolute joints and 0.31 ± 0.60 mm for prismatic joints. The theoretical workspace spans the proposed clinical target surface of 10 x 10 cm. Lastly, the feasibility of multi-needle insertion was demonstrated with four needles inserted under real-time MR-guidance with no visible loss in image quality.

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.

In-Bore MRI-guided Prostate Biopsies in Patients with Prior Positive Transrectal US-guided Biopsy Results: Pathologic Outcomes and Predictors of Missed Cancers

Purpose

To evaluate the role of confirmatory in-bore MRI-guided biopsy in patients with low- or intermediate-risk disease diagnosed at prior transrectal US-guided biopsy and to evaluate the rate and predictors for missed cancers.

Materials and Methods

A retrospective evaluation of 50 consecutive men who had previously undergone transrectal US-guided biopsy with positive results and who underwent subsequent in-bore MRI-guided biopsy at our university hospital (average time interval, 11 months) between 2012 and 2016 was performed. Ten men were excluded because of a history of treatment after transrectal US-guided biopsy. A total of 40 men (mean age, 63 years; range, 47-84 years) were included in this study. Multiparametric 3-T MRI (T2-weighted, diffusion-weighted, and dynamic contrast material-enhanced) and transrectal in-bore MRI-guided biopsy were performed. Cancer detection, disease-grade changes, and cancers missed at in-bore MRI-guided biopsy were evaluated. Descriptive statistics were used to report different rates. The Fisher exact test was used for categoric variables. The Mann-Whitney U test and independent Student t test were used for nonparametric and parametric data, respectively. The McNemar test was used for paired data.

Results

The overall cancer detection rate when using in-bore MRI-guided biopsy was 65% (26 of 40). In-bore MRI-guided biopsy detected 14 previously undiscovered cancerous lesions (clinically significant cancers [CSCs], 57.1% [eight of 14]). An overall disease upgrade by in-bore MRI-guided biopsy occurred in 40% (16 of 40) of cases (61.5% [16 of 26] of cases with positive results from in-bore MRI-guided biopsy). One case was downgraded from a Gleason score (GS) of 3 + 4 = 7 to a GS of 3 + 3 = 6. Out of 71 sextant biopsies with positive results detected by transrectal US-guided biopsy (from all 40 patients), 80% (57 of 71) were visible on MR images (in-bore MRI-guided biopsy results were positive in 52.6% [30 of 57]), and 20% (14 of 71) had no image correlates on MR images. In-bore MRI-guided biopsy upgraded 60% (18 of 30) and downgraded 3.3% (one of 30) of detected lesions. The false-negative rate was 35% (14.2% [two of 14] of patients had CSCs; GS ≥ 7), was higher in prostate volumes of greater than 40 mL, and was lower in the anterior gland location (P = .04 and .01, respectively).

Conclusion

Performing confirmatory in-bore MRI-guided biopsy following positive transrectal US-guided biopsy resulted in a high disease-upgrade incidence with subsequently improved disease-risk stratification, particularly when considering patients for active surveillance or focal therapy. Supplemental material is available for this article. © RSNA, 2020See also the commentary by Weiss and Solomon in this issue.

Development of a Device-to-Image Registration Free Needle Guide for Magnetic Resonance Imaging-Guided Targeted Prostate Biopsy

Significant research has been done in the past decade for the development of magnetic resonance imaging (MRI) guided needle guide (NG) systems for prostate intervention. Most of these systems have been restricted to application in the lab environment with lack of progress toward clinical application. Bulky and complex designs can be attributed to this practice. These systems also demand complex technical setup and usage procedures, which require extra technical personnel during the intervention in addition to specialized training for physicians. Moreover, “device-to-image” registration, essential for accurate and precise targeting, further complicates the overall process while increasing total time for intervention. In order to address these limitations, a simplified, MRI-guided, transperineal prostate biopsy NG system was designed and developed for rapid adoption into the clinical environment. The system consists of a NG device and a software toolkit. It does not require any special intraprocedural technical expertise or dedicated training. Also, to simplify and shorten total procedure time, the device uses the unique concept of “fixed coordinate device” eliminating the need for any device-to-image registration making it clinically friendly. To verify the NG design along with the registration free feature, image quality tests and agar phantom-based targeting experiments were performed under the guidance of 3T MRI scanner. The imaging tests resulted in a distortion of less than 1% in presence of the device and an average change of 1.3% in signal-to-noise ratio. For targeting experiments, maximum in-plane error distance of 3.8 mm with a mean of 2.2 mm and standard deviation of 0.8 mm was observed. The results show that an MRI-compatible simplified intervention device without the need of device-to-image registration is technically feasible.

Open Source Platform for Transperineal In-Bore MRI-Guided Targeted Prostate Biopsy

OBJECTIVE

Accurate biopsy sampling of the suspected lesions is critical for the diagnosis and clinical management of prostate cancer. Transperineal in-bore MRI-guided prostate biopsy (tpMRgBx) is a targeted biopsy technique that was shown to be safe, efficient, and accurate. Our goal was to develop an open source software platform to support evaluation, refinement, and translation of this biopsy approach.

METHODS

We developed SliceTracker, a 3D Slicer extension to support tpMRgBx. We followed modular design of the implementation to enable customization of the interface and interchange of image segmentation and registration components to assess their effect on the processing time, precision, and accuracy of the biopsy needle placement. The platform and supporting documentation were developed to enable the use of software by an operator with minimal technical training to facilitate translation. Retrospective evaluation studied registration accuracy, effect of the prostate segmentation approach, and re-identification time of biopsy targets. Prospective evaluation focused on the total procedure time and biopsy targeting error (BTE).

RESULTS

Evaluation utilized data from 73 retrospective and ten prospective tpMRgBx cases. Mean landmark registration error for retrospective evaluation was 1.88 ± 2.63 mm, and was not sensitive to the approach used for prostate gland segmentation. Prospectively, we observed target re-identification time of 4.60 ± 2.40 min and BTE of 2.40 ± 0.98 mm.

CONCLUSION

SliceTracker is modular and extensible open source platform for supporting image processing aspects of the tpMRgBx procedure. It has been successfully utilized to support clinical research procedures at our site.

Enabling In-Bore MRI-Guided Biopsies With Force Feedback

Limited physical access to target organs of patients inside an MRI scanner is a major obstruction to real-time MRI-guided interventions. Traditional teleoperation technologies are incompatible with the MRI environment and although several solutions have been explored, a versatile system that provides high-fidelity haptic feedback and access deep inside the bore remains a challenge. We present a passive and nearly frictionless MRI-compatible hydraulic teleoperator designed for in-bore liver biopsies. We describe the design components, characterize the system transparency, and evaluate the performance with a user study in a laboratory and a clinical setting. The results demonstrate % difference between input and output forces during realistic manipulation. A user study with participants conducting mock needle biopsy tasks indicates that a remote operator performs equally well when using the device as when holding a biopsy needle directly in hand. Additionally, MRI compatibility tests show no reduction in signal-to-noise ratio in the presence of the device.

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.

System Integration and Preliminary Clinical Evaluation of a Robotic System for MRI-Guided Transperineal Prostate Biopsy

This paper presents the development, preclinical evaluation, and preliminary clinical study of a robotic system for targeted transperineal prostate biopsy under direct interventional magnetic resonance imaging (MRI) guidance. The clinically integrated robotic system is developed based on a modular design approach, comprised of surgical navigation application, robot control software, MRI robot controller hardware, and robotic needle placement manipulator. The system provides enabling technologies for MRI-guided procedures. It can be easily transported and setup for supporting the clinical workflow of interventional procedures, and the system is readily extensible and reconfigurable to other clinical applications. Preclinical evaluation of the system is performed with phantom studies in a 3 Tesla MRI scanner, rehearsing the proposed clinical workflow, and demonstrating an in-plane targeting error of 1.5mm. The robotic system has been approved by the institutional review board (IRB) for clinical trials. A preliminary clinical study is conducted with the patient consent, demonstrating the targeting errors at two biopsy target sites to be 4.0mm and 3.7mm, which is sufficient to target a clinically significant tumor foci. First-in-human trials to evaluate the system's effectiveness and accuracy for MR image-guide prostate biopsy are underway.

Template for MR Visualization and Needle Targeting

To improve the targeting accuracy and reduce procedure time in magnetic resonance imaging (MRI)-guided procedures, a 3D-printed flexible template was developed. The template was printed using flexible photopolymer resin FLFLGR02 in Form 2 printer^® (Formlabs, Inc., Somerville, MA). The flexible material gives the template a unique advantage by allowing it to make close contact with human skin and provide accurate insertion with the help of the newly developed OncoNav software. At the back of the template, there is a grid comprised of circular containers filled with contrast agent. At the front of the template, the guide holes between the containers provide space and angular flexibility for needle insertion. MRI scans are initially used to identify tumor position as well as the template location. The OncoNav software then pre-selects a best guide hole for targeting a specific lesion and suggests insertion depth for the physician A phantom study of 13 insertions in a CT scanner was carried out for assessing needle placement accuracy. The mean total distance error between planned and actual insertion is 2.7 mm, the maximum error was 4.78 mm and standard deviation was 1.1 mm. The accuracy of the OncoNav-assisted and template-guided needle targeting is comparable to the robot-assisted procedure. The proposed template is a low-cost, quickly-deployable and disposable medical device. The presented technology will be further evaluated in prostate cancer patients to quantify its accuracy in needle biopsy.

Evaluation of robot-assisted MRI-guided prostate biopsy: needle path analysis during clinical trials

While the interaction between a needle and the surrounding tissue is known to cause a significant targeting error in prostate biopsy leading to false-negative results, few studies have demonstrated how it impacts in the actual procedure. We performed a pilot study on robot-assisted MRI-guided prostate biopsy with an emphasis on the in-depth analysis of the needle-tissue interaction in vivo. The data were acquired during in-bore transperineal prostate biopsies in patients using a 4 degrees-of-freedom (DoF) MRI-compatible robot. The anatomical structures in the pelvic area and the needle path were reconstructed from MR images, and quantitatively analyzed. We analyzed each structure individually and also proposed a mathematical model to investigate the influence of those structures in the targeting error using the mixed-model regression. The median targeting error in 188 insertions (27 patients) was 6.3 mm. Both the individual anatomical structure analysis and the mixed-model analysis showed that the deviation resulted from the contact between the needle and the skin as the main source of error. On contrary, needle bending inside the tissue (expressed as needle curvature) did not vary among insertions with targeting errors above and below the average. The analysis indicated that insertions crossing the bulbospongiosus presented a targeting error lower than the average. The mixed-model analysis demonstrated that the distance between the needle guide and the patient skin, the deviation at the entry point, and the path length inside the pelvic diaphragm had a statistically significant contribution to the targeting error (p  <  0.05). Our results indicate that the errors associated with the elastic contact between the needle and the skin were more prominent than the needle bending along the insertion. Our findings will help to improve the preoperative planning of transperineal prostate biopsies.

Beyond transrectal ultrasound-guided prostate biopsies: available techniques and approaches

OBJECTIVES

Recent advances have led to the use of magnetic resonance imaging (MRI) alone or with fusion to transrectal ultrasound (TRUS) images for guiding biopsy of the prostate. Our group sought to develop consensus recommendations regarding MRI-guided prostate biopsy based on currently available literature and expert opinion.

METHODS

The published literature on the subject of MRI-guided prostate biopsy was reviewed using standard search terms and synthesized and analyzed by four different subgroups from among the authors. The literature was grouped into four categories-MRI-guided biopsy platforms, robotic MRI-TRUS fusion biopsy, template mapping biopsy and transrectal MRI-TRUS fusion biopsy. Consensus recommendations were developed using the Oxford Center for Evidence Based Medicine criteria.

RESULTS

There is limited high level evidence available on the subject of MRI-guided prostate biopsy. MRI guidance with or without TRUS fusion can lead to fewer unnecessary biopsies, help identify high-risk (Gleason ≥ 3 + 4) cancers that might have been missed on standard TRUS biopsy and identify cancers in the anterior prostate. There is no apparent significant difference between MRI biopsy platforms. Template mapping biopsy is perhaps the most accurate method of assessing volume and grade of tumor but is accompanied by higher incidence of side effects compared to TRUS biopsy.

CONCLUSIONS

Magnetic resonance imaging-guided biopsies are feasible and better than traditional ultrasound-guided biopsies for detecting high-risk prostate cancer and anterior lesions. Judicious use of MRI-guided biopsy could enhance diagnosis of clinically significant prostate cancer while limiting diagnosis of insignificant cancer.

In-bore MRI-guided biopsy: can it optimize the need for periodic biopsies in prostate cancer patients undergoing active surveillance? A pilot test-retest reliability study

OBJECTIVE

To evaluate the test-retest reliability of repeated in-bore MRI-guided prostate biopsy (MRGB).

METHODS

19 lesions in 7 patients who had consecutive MRGBs were retrospectively analysed. Five patients had 2 consecutive MRGBs and two patients had 3 consecutive MRGBs. Both multiparametric MRI and MRGBs were performed using a 3T MRI scanner. Pathology results were categorized into benign, suspicious and malignant. Consistency between first and subsequent biopsy results were analysed as well as the negative predictive value (NPV) for prostate cancer.

RESULTS

15 lesions (≈79%) had matching second biopsy and 4 (21%) had non-matching second biopsy. Lesions with both Prostate Imaging - Reporting and Data System(PIRADS) categories 1 and 4 were all benign and had matching pathology results. Lesions with non-matching results had PIRADS categories 2, 3 and 5. NPV for prostate cancer in first biopsy was 87.5%. Overall agreement was 78.9% and overall disagreement was 21.1%.κ = 0.55 denoting moderate agreement (p = 0.002). 10/19 lesions had a third biopsy session. 9/10 (90%) had matching pathology results across the three biopsy sessions and all matching lesions were benign.

CONCLUSION

In-bore MRI-guided prostate biopsy may have a better reliability for repeat biopsies compared to TRUS biopsy. Final conclusion awaits a prospective analysis on a larger cohort of patients. Advances in knowledge: This pilot study showed that repeated prostate in-bore MRI-guided prostate biopsy may have better reliability compared to TRUS biopsy with a suggested high NPV.

Robotics in MRI-Guided Interventions

Robots have been found to be a useful tool in magnetic resonance imaging (MRI)-guided intervention. The utility of robots in MRI-guided therapy ranges from aid for precision targeting to high-dexterity surgical tools to improve or even enable new MRI-guided therapy options. The objective of this article is to review the technical aspects of robotics in MRI-guided interventions, highlight the role of MRI robots in prostate interventions, and finally discuss the future contribution of emerging robotics technology useful in MRI-guided intervention.

The MIRIAM Robot: A Novel Robotic System for MR-Guided Needle Insertion in the Prostate

Early prostate cancer detection and treatment are of major importance to reduce mortality rate. magnetic resonance (MR) imaging provides images of the prostate where an early stage lesion can be visualized. The use of robotic systems for MR-guided interventions in the prostate allows us to improve the clinical outcomes of procedures such as biopsy and brachytherapy. This work presents a novel MR-conditional robot for prostate interventions. The minimally invasive robotics in an magnetic resonance imaging environment (MIRIAM) robot has 9 degrees-of-freedom (DoF) used to steer and fire a biopsy needle. The needle guide is positioned against the perineum by a 5 DoF parallel robot driven by piezoelectric motors. A 4 DoF needle driver inserts, rotates and fires the needle during the procedure. Piezoelectric motors are used to insert and rotate the needle, while pneumatic actuation is used to fire the needle. The MR-conditional design of the robot and the needle insertion controller are presented. MR compatibility tests using T2 imaging protocol are performed showing a SNR reduction of 25% when the robot is operational within the MR scanner. Experiments inserting a biopsy needle toward a physical target resulted in an average targeting error of 1.84[Formula: see text]mm. Our study presents a novel MR-conditional robot and demonstrated the ability to perform MR-guided needle-based interventions in soft-tissue phantoms. Moreover, the image distortion analysis indicates that no visible image deterioration is induced by the robot.

The Current State of MR Imaging-targeted Biopsy Techniques for Detection of Prostate Cancer

Systematic transrectal ultrasonography (US)-guided biopsy is the standard approach for histopathologic diagnosis of prostate cancer. However, this technique has multiple limitations because of its inability to accurately visualize and target prostate lesions. Multiparametric magnetic resonance (MR) imaging of the prostate is more reliably able to localize significant prostate cancer. Targeted prostate biopsy by using MR imaging may thus help to reduce false-negative results and improve risk assessment. Several commercial devices are now available for targeted prostate biopsy, including in-gantry MR imaging-targeted biopsy and real-time transrectal US-MR imaging fusion biopsy systems. This article reviews the current status of MR imaging-targeted biopsy platforms, including technical considerations, as well as advantages and challenges of each technique. ^© RSNA, 2017.

MR Safe Robot, FDA Clearance, Safety and Feasibility Prostate Biopsy Clinical Trial

Compatibility of mechatronic devices with the MR environment has been a very challenging engineering task. After over a decade of developments, we report the successful translation to clinical trials of our MR Safe robot technology. MrBot is a 6-degree-of-freedom, pneumatically actuated robot for transperineal prostate percutaneous access, built exclusively of electrically nonconductive and nonmagnetic materials. Its extensive pre-clinical tests have been previously reported. Here, we present the latest technology developments, an overview of the regulatory protocols, and technically related results of the clinical trial. The FDA has approved the MrBot for the biopsy trial, which was successfully performed in 5 patients. With no trajectory corrections, and no unsuccessful attempts to target a site, the robot achieved an MRI based needle targeting accuracy of 2.55 mm. To the best of our knowledge, this is the first robot approved by the FDA for the MR environment. The results confirm that it is possible to perform safe and accurate robotic manipulation in the MRI scanner, and the development of MR Safe robots is no longer a daunting technical challenge.

Trends in targeted prostate brachytherapy: from multiparametric MRI to nanomolecular radiosensitizers

The treatment of localized prostate cancer is expected to become a significant problem in the next decade as an increasingly aging population becomes prone to developing the disease. Recent research into the biological nature of prostate cancer has shown that large localized doses of radiation to the cancer offer excellent long-term disease control. Brachytherapy, a form of localized radiation therapy, has been shown to be one of the most effective methods for delivering high radiation doses to the cancer; however, recent evidence suggests that increasing the localized radiation dose without bound may cause unacceptable increases in long-term side effects. This review focuses on methods that have been proposed, or are already in clinical use, to safely escalate the dose of radiation within the prostate. The advent of multiparametric magnetic resonance imaging (mpMRI) to better identify and localize intraprostatic tumors, and nanomolecular radiosensitizers such as gold nanoparticles (GNPs), may be used synergistically to increase doses to cancerous tissue without the requisite hazard of increased side effects.

Segmented diffusion-weighted imaging of the prostate: Application to transperineal in-bore 3T MR image-guided targeted biopsy

OBJECTIVE

This study aims to evaluate the applicability of using single-shot and multi-shot segmented diffusion-weighted imaging (DWI) techniques to support biopsy target localization in a cohort of targeted MRI-guided prostate biopsy patients.

MATERIALS AND METHODS

Single-shot echo-planar diffusion-weighted imaging (SS-DWI) and multi-shot segmented (MS-DWI) were performed intra-procedurally on a 3Tesla system in a total of 35 men, who underwent in-bore prostate biopsy inside the scanner bore. Comparisons between SS-DWI and MS-DWI were performed with (in 16 men) and without (in 19 men) parallel coil acceleration (iPAT) for SS-DWI. Overall image quality and artifacts were scored by a radiologist and scores were compared with the Wilcoxon-Mann-Whitney rank test. Correlation between the presence of air and image quality scores was evaluated with Spearman statistics. To quantify distortion, the anteroposterior prostate dimension was measured in SS and MS b=0 diffusion- and T2-weighted images. Signal-to-noise ratio was estimated in a phantom experiment. Agreement and accuracy of targeting based on retrospective localization of restricted diffusion areas in DWI was evaluated with respect to the targets identified using multi-parametric MRI (mpMRI).

RESULTS

Compared to SS-DWI without iPAT, the average image quality score in MS-DWI improved from 2.0 to 3.3 (p<0.005) and the artifact score improved from 2.3 to 1.4 (p<0.005). When iPAT was used in SS-DWI, the average image quality score in MS-DWI improved from 2.6 to 3.3 (p<0.05) and the artifact score improved from 2.1 to 1.4 (p<0.01). Image quality (ρ=-0.74, p<0.0005) and artifact scores (ρ=0.77, p<0.0005) both showed strong correlation with the presence of air in the rectum for the SS-DWI sequence without iPAT. These correlations remained significant when iPAT was enabled (ρ=-0.52, p<0.05 and ρ=0.64, p<0.01). For the comparison MS-DWI vs SS-DWI without iPAT, median differences between diffusion- and T2-weighted image gland measurements were 1.1(0.03-10.4)mm and 4.4(0.5-22.7)mm, respectively. In the SS-DWI-iPAT cohort, median gland dimension differences were 2.7(0.4-5.9)mm and 4.2(0.7-8.9)mm, respectively. Out of the total of 89 targets identified in mpMRI, 20 had corresponding restricted diffusion areas in SS-DWI and 28 in MS-DWI. No statistically significant difference was observed between the distances for the targets in the target-concordant SS- and MS-DWI restricted diffusion areas (5.5mm in SS-DWI vs 4.5mm in MS-DWI, p>0.05).

CONCLUSIONS

MS-DWI applied to prostate imaging leads to a significant reduction of image distortion in comparison with SS-DWI. There is no sufficient evidence however to suggest that intra-procedural DWI can serve as a replacement for tracking of the targets identified in mpMRI for the purposes of targeted MRI-guided prostate biopsy.

A Review of Imaging Methods for Prostate Cancer Detection

Imaging is playing an increasingly important role in the detection of prostate cancer (PCa). This review summarizes the key imaging modalities-multiparametric ultrasound (US), multiparametric magnetic resonance imaging (MRI), MRI-US fusion imaging, and positron emission tomography (PET) imaging-used in the diagnosis and localization of PCa. Emphasis is laid on the biological and functional characteristics of tumors that rationalize the use of a specific imaging technique. Changes to anatomical architecture of tissue can be detected by anatomical grayscale US and T2-weighted MRI. Tumors are known to progress through angiogenesis-a fact exploited by Doppler and contrast-enhanced US and dynamic contrast-enhanced MRI. The increased cellular density of tumors is targeted by elastography and diffusion-weighted MRI. PET imaging employs several different radionuclides to target the metabolic and cellular activities during tumor growth. Results from studies using these various imaging techniques are discussed and compared.

Piezoelectrically Actuated Robotic System for MRI-Guided Prostate Percutaneous Therapy

This paper presents a fully-actuated robotic system for percutaneous prostate therapy under continuously acquired live magnetic resonance imaging (MRI) guidance. The system is composed of modular hardware and software to support the surgical workflow of intra-operative MRI-guided surgical procedures. We present the development of a 6-degree-of-freedom (DOF) needle placement robot for transperineal prostate interventions. The robot consists of a 3-DOF needle driver module and a 3-DOF Cartesian motion module. The needle driver provides needle cannula translation and rotation (2-DOF) and stylet translation (1-DOF). A custom robot controller consisting of multiple piezoelectric motor drivers provides precision closed-loop control of piezoelectric motors and enables simultaneous robot motion and MR imaging. The developed modular robot control interface software performs image-based registration, kinematics calculation, and exchanges robot commands and coordinates between the navigation software and the robot controller with a new implementation of the open network communication protocol OpenIGTLink. Comprehensive compatibility of the robot is evaluated inside a 3-Tesla MRI scanner using standard imaging sequences and the signal-to-noise ratio (SNR) loss is limited to 15%. The image deterioration due to the present and motion of robot demonstrates unobservable image interference. Twenty-five targeted needle placements inside gelatin phantoms utilizing an 18-gauge ceramic needle demonstrated 0.87 mm root mean square (RMS) error in 3D Euclidean distance based on MRI volume segmentation of the image-guided robotic needle placement procedure.

3T MR-guided in-bore transperineal prostate biopsy: A comparison of robotic and manual needle-guidance templates

PURPOSE

To demonstrate the utility of a robotic needle-guidance template device as compared to a manual template for in-bore 3T transperineal magnetic resonance imaging (MRI)-guided prostate biopsy.

MATERIALS AND METHODS

This two-arm mixed retrospective-prospective study included 99 cases of targeted transperineal prostate biopsies. The biopsy needles were aimed at suspicious foci noted on multiparametric 3T MRI using manual template (historical control) as compared with a robotic template. The following data were obtained: the accuracy of average and closest needle placement to the focus, histologic yield, percentage of cancer volume in positive core samples, complication rate, and time to complete the procedure.

RESULTS

In all, 56 cases were performed using the manual template and 43 cases were performed using the robotic template. The mean accuracy of the best needle placement attempt was higher in the robotic group (2.39 mm) than the manual group (3.71 mm, P < 0.027). The mean core procedure time was shorter in the robotic (90.82 min) than the manual group (100.63 min, P < 0.030). Percentage of cancer volume in positive core samples was higher in the robotic group (P < 0.001). Cancer yields and complication rates were not statistically different between the two subgroups (P = 0.557 and P = 0.172, respectively).

CONCLUSION

The robotic needle-guidance template helps accurate placement of biopsy needles in MRI-guided core biopsy of prostate cancer.

Transperineal in-bore 3-T MR imaging-guided prostate biopsy: a prospective clinical observational study

PURPOSE

To determine the detection rate, clinical relevance, Gleason grade, and location of prostate cancer ( PCa prostate cancer ) diagnosed with and the safety of an in-bore transperineal 3-T magnetic resonance (MR) imaging-guided prostate biopsy in a clinically heterogeneous patient population.

MATERIALS AND METHODS

This prospective retrospectively analyzed study was HIPAA compliant and institutional review board approved, and informed consent was obtained. Eighty-seven men (mean age, 66.2 years ± 6.9) underwent multiparametric endorectal prostate MR imaging at 3 T and transperineal MR imaging-guided biopsy. Three subgroups of patients with at least one lesion suspicious for cancer were included: men with no prior PCa prostate cancer diagnosis, men with PCa prostate cancer who were undergoing active surveillance, and men with treated PCa prostate cancer and suspected recurrence. Exclusion criteria were prior prostatectomy and/or contraindication to 3-T MR imaging. The transperineal MR imaging-guided biopsy was performed in a 70-cm wide-bore 3-T device. Overall patient biopsy outcomes, cancer detection rates, Gleason grade, and location for each subgroup were evaluated and statistically compared by using χ(2) and one-way analysis of variance followed by Tukey honestly significant difference post hoc comparisons.

RESULTS

Ninety biopsy procedures were performed with no serious adverse events, with a mean of 3.7 targets sampled per gland. Cancer was detected in 51 (56.7%) men: 48.1% (25 of 52) with no prior PCa prostate cancer , 61.5% (eight of 13) under active surveillance, and 72.0% (18 of 25) in whom recurrence was suspected. Gleason pattern 4 or higher was diagnosed in 78.1% (25 of 32) in the no prior PCa prostate cancer and active surveillance groups. Gleason scores were not assigned in the suspected recurrence group. MR targets located in the anterior prostate had the highest cancer yield (40 of 64, 62.5%) compared with those for the other parts of the prostate (P < .001).

CONCLUSION

In-bore 3-T transperineal MR imaging-guided biopsy, with a mean of 3.7 targets per gland, allowed detection of many clinically relevant cancers, many of which were located anteriorly.

Multimodal imaging for improved diagnosis and treatment of cancers

The authors review methods for image-guided diagnosis and therapy that increase precision in the detection, characterization, and localization of many forms of cancer to achieve optimal target definition and complete resection or ablation. A new model of translational, clinical, image-guided therapy research is presented, and the Advanced Multimodality Image-Guided Operating (AMIGO) suite is described. AMIGO was conceived and designed to allow for the full integration of imaging in cancer diagnosis and treatment. Examples are drawn from over 500 procedures performed on brain, neck, spine, thorax (breast, lung), and pelvis (prostate and gynecologic) areas and are used to describe how they address some of the many challenges of treating brain, prostate, and lung tumors. Cancer 2015;121:817-827. © 2014 American Cancer Society.

Multi-slice-to-volume registration for MRI-guided transperineal prostate biopsy

PURPOSE

Prostate needle biopsy is a commonly performed procedure since it is the most definitive form of cancer diagnosis. Magnetic resonance imaging (MRI) allows target-specific biopsies to be performed. However, needle placements are often inaccurate due to intra-operative prostate motion and the lack of motion compensation techniques. This paper detects and determines the extent of tissue displacement during an MRI-guided biopsy so that the needle insertion plan can be adjusted accordingly.

METHODS

A multi-slice-to-volume registration algorithm was developed to align the pre-operative planning image volume with three intra-operative orthogonal image slices of the prostate acquired immediately before needle insertion. The algorithm consists of an initial rigid transformation followed by a deformable step.

RESULTS

A total of 14 image sets from 10 patients were studied. Based on prostate contour alignment, the registrations were accurate to within 2 mm.

CONCLUSION

This algorithm can be used to increase the needle targeting accuracy by alerting the clinician if the biopsy target has moved significantly prior to needle insertion. The proposed method demonstrated feasibility of intra-operative target localization and motion compensation for MRI-guided prostate biopsy.

Application of tolerance limits to the characterization of image registration performance

Deformable image registration is used increasingly in image-guided interventions and other applications. However, validation and characterization of registration performance remain areas that require further study. We propose an analysis methodology for deriving tolerance limits on the initial conditions for deformable registration that reliably lead to a successful registration. This approach results in a concise summary of the probability of registration failure, while accounting for the variability in the test data. The (β, γ) tolerance limit can be interpreted as a value of the input parameter that leads to successful registration outcome in at least 100β% of cases with the 100γ% confidence. The utility of the methodology is illustrated by summarizing the performance of a deformable registration algorithm evaluated in three different experimental setups of increasing complexity. Our examples are based on clinical data collected during MRI-guided prostate biopsy registered using publicly available deformable registration tool. The results indicate that the proposed methodology can be used to generate concise graphical summaries of the experiments, as well as a probabilistic estimate of the registration outcome for a future sample. Its use may facilitate improved objective assessment, comparison and retrospective stress-testing of deformable.

Configurable automatic detection and registration of fiducial frames for device-to-image registration in MRI-guided prostate interventions

We propose a novel automatic fiducial frame detection and registration method for device-to-image registration in MRI-guided prostate interventions. The proposed method does not require any manual selection of markers, and can be applied to a variety of fiducial frames, which consist of multiple cylindrical MR-visible markers placed in different orientations. The key idea is that automatic extraction of linear features using a line filter is more robust than that of bright spots by thresholding; by applying a line set registration algorithm to the detected markers, the frame can be registered to the MRI. The method was capable of registering the fiducial frame to the MRI with an accuracy of 1.00 +/- 0.73 mm and 1.41 +/- 1.06 degrees in a phantom study, and was sufficiently robust to detect the fiducial frame in 98% of images acquired in clinical cases despite the existence of anatomical structures in the field of view.

Errors in device localization in MRI using Z-frames

The use of a passive MRI-visible tracking frame is a common method of localizing devices in MRI space for MRI-guided procedures. One of the most common tracking frame designs found in the literature is the z-frame, as it allows six degree-of-freedom pose estimation using only a single image slice. Despite the popularity of this design, it is susceptible to errors in pose estimation due to various image distortion mechanisms in MRI. In this paper, the absolute error in using a z-frame to localize a tool in MRI is quantified over various positions of the z-frame relative to the MRI isocenter, and for various levels of static magnetic field inhomogeneity. It was found that the error increases rapidly with distance from the isocenter in both the horizontal and vertical directions, but the error is much less sensitive to position when multiple contiguous slices are used with slice-select gradient nonlinearity correction enabled, as opposed to the more common approach of only using a single image slice. In addition, the error is found to increase rapidly with an increasing level of static field inhomogeneity, even with the z-frame placed within 10 cm of the isocenter.

Prostate cancer detection and diagnosis: the role of MR and its comparison with other diagnostic modalities--a radiologist's perspective

It is now universally recognized that many prostate cancers are over-diagnosed and over-treated. The European Randomized Study of Screening for Prostate Cancer from 2009 evidenced that, to save one man from death from prostate cancer, over 1400 men need to be screened, and 48 need to undergo treatment. The detection of prostate cancer is traditionally based on digital rectal examination (DRE) and the measurement of serum prostate-specific antigen (PSA), followed by ultrasound-guided biopsy. The primary role of imaging for the detection and diagnosis of prostate cancer has been transrectal ultrasound (TRUS) guidance during biopsy. Traditionally, MRI has been used primarily for the staging of disease in men with biopsy-proven cancer. It has a well-established role in the detection of T3 disease, planning of radiation therapy, especially three-dimensional conformal or intensity-modulated external beam radiation therapy, and planning and guiding of interstitial seed implant or brachytherapy. New advances have now established that prostate MRI can accurately characterize focal lesions within the gland, an ability that has led to new opportunities for improved cancer detection and guidance for biopsy. Two new approaches to prostate biopsy are under investigation. Both use pre-biopsy MRI to define potential targets for sampling, and the biopsy is performed either with direct real-time MR guidance (in-bore) or MR fusion/registration with TRUS images (out-of-bore). In-bore and out-of-bore MRI-guided prostate biopsies have the advantage of using the MR target definition for the accurate localization and sampling of targets or suspicious lesions. The out-of-bore method uses combined MRI/TRUS with fusion software that provides target localization and increases the sampling accuracy of TRUS-guided biopsies by integrating prostate MRI information with TRUS. Newer parameters for each imaging modality, such as sonoelastography or shear wave elastography, contrast-enhanced ultrasound and MRI elastography, show promise to further enrich datasets.

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.

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.