MR-Guided Biopsy of the Prostate: An Overview of Techniques and a Systematic Review

Interventional device tracking under MRI via alternating current controlled inhomogeneities

PURPOSE

To introduce alternating current-controlled, conductive ink-printed marker that could be implemented with both custom and commercial interventional devices for device tracking under MRI using gradient echo, balanced SSFP, and turbo spin-echo sequences.

METHODS

Tracking markers were designed as solenoid coils and printed on heat shrink tubes using conductive ink. These markers were then placed on three MR-compatible test samples that are typically challenging to visualize during MRI scans. MRI visibility of markers was tested by applying alternating and direct current to the markers, and the effects of applied current parameters (amplitude, frequency) on marker artifacts were tested for three sequences (gradient echo, turbo spin echo, and balanced SSFP) in a gel phantom, using 0.55T and 1.5T MRI scanners. Furthermore, an MR-compatible current supply circuit was designed, and the performance of the current-controlled markers was tested in one postmortem animal experiment using the current supply circuit.

RESULTS

Direction and parameters of the applied current were determined to provide the highest conspicuity for all three sequences. Marker artifact size was controlled by adjusting the current amplitude, successfully. Visibility of a custom-designed, 20-gauge nitinol needle was increased in both in vitro and postmortem animal experiments using the current supply circuit.

CONCLUSION

Current-controlled conductive ink-printed markers can be placed on custom or commercial MR-compatible interventional tools and can provide an easy and effective solution to device tracking under MRI for three sequences by adjusting the applied current parameters with respect to pulse sequence parameters using the current supply circuit.

3.0-T MR-guided transgluteal in-bore-targeted prostate biopsy under local anesthesia in patients without rectal access: a single-institute experience and review of literature

PURPOSE

To describe the technique and evaluate the performance of MRI-guided transgluteal in-bore-targeted biopsy of the prostate gland under local anesthesia in patients without rectal access.

METHODS

Ten men (mean age, 69 (range 57-86) years) without rectal access underwent 13 MRI-guided transgluteal in-bore-targeted biopsy of the prostate gland under local anesthesia. All patients underwent mp-MRI at our institute prior to biopsy. Three patients had prior US-guided transperineal biopsy which was unsuccessful in one, negative in one, and yielded GG1 (GS6) PCa in one. Procedure time, complications, histopathology result, and subsequent management were recorded.

RESULTS

Median interval between rectal surgery and presentation with elevated PSA was 12.5 years (interquartile range (IQR) 25-75, 8-36.5 years). Mean PSA was 11.9 (range, 4.8 -59.0) ng/ml and PSA density was 0.49 (0.05 -3.2) ng/ml/ml. Distribution of PI-RADS v2.0/2.1 scores of the targeted lesions were PI-RADS 5-3; PI-RADS 4-6; and PI-RADS 3-1. Mean lesion size was 1.5 cm (range, 1.0-3.6 cm). Median interval between MRI and biopsy was 5.5 months (IQR 25-75, 1.5-9 months). Mean procedure time was 47.4 min (range, 29-80 min) and the number of cores varied between 3 and 5. Of the 13 biopsies, 4 yielded clinically significant prostate cancer (csPca), with a Gleason score ≥ 7, 1 yielded insignificant prostate cancer (Gleason score = 6), 7 yielded benign prostatic tissue, and one was technically unsuccessful. 3/13 biopsies were repeat biopsies which detected csPCa in 2 out of the 3 patients. None of the patients had biopsy-related complication. Biopsy result changed management to radiation therapy with ADT in 2 patients with the rest on active surveillance.

CONCLUSION

MRI-guided transgluteal in-bore-targeted biopsy of the prostate gland under local anesthesia is feasible in patients without rectal access.

Image-guided Raman spectroscopy navigation system to improve transperineal prostate cancer detection. Part 1: Raman spectroscopy fiber-optics system and in situ tissue characterization

SIGNIFICANCE

The diagnosis of prostate cancer (PCa) and focal treatment by brachytherapy are limited by the lack of precise intraoperative information to target tumors during biopsy collection and radiation seed placement. Image-guidance techniques could improve the safety and diagnostic yield of biopsy collection as well as increase the efficacy of radiotherapy.

AIM

To estimate the accuracy of PCa detection using in situ Raman spectroscopy (RS) in a pilot in-human clinical study and assess biochemical differences between in vivo and ex vivo measurements.

APPROACH

A new miniature RS fiber-optics system equipped with an electromagnetic (EM) tracker was guided by trans-rectal ultrasound-guided imaging, fused with preoperative magnetic resonance imaging to acquire 49 spectra in situ (in vivo) from 18 PCa patients. In addition, 179 spectra were acquired ex vivo in fresh prostate samples from 14 patients who underwent radical prostatectomy. Two machine-learning models were trained to discriminate cancer from normal prostate tissue from both in situ and ex vivo datasets.

RESULTS

A support vector machine (SVM) model was trained on the in situ dataset and its performance was evaluated using leave-one-patient-out cross validation from 28 normal prostate measurements and 21 in-tumor measurements. The model performed at 86% sensitivity and 72% specificity. Similarly, an SVM model was trained with the ex vivo dataset from 152 normal prostate measurements and 27 tumor measurements showing reduced cancer detection performance mostly attributable to spatial registration inaccuracies between probe measurements and histology assessment. A qualitative comparison between in situ and ex vivo measurements demonstrated a one-to-one correspondence and similar ratios between the main Raman bands (e.g., amide I-II bands, phenylalanine).

CONCLUSIONS

PCa detection can be achieved using RS and machine learning models for image-guidance applications using in situ measurements during prostate biopsy procedures.

Cost-Effectiveness of Multiparametric Magnetic Resonance Imaging and Targeted Biopsy Versus Systematic Transrectal Ultrasound-Guided Biopsy for Prostate Cancer Diagnosis: A Systematic Review

OBJECTIVES

This study aimed to systematically review the cost-effectiveness studies of multiparametric magnetic resonance imaging (mpMRI)-guided biopsy (MRGB) compared with systematic transrectal ultrasonography (TRUS)-guided biopsy for diagnosing prostate cancer (PCa).

METHODS

PubMed, Web of Science core collection, Embase and Scopus, and reference lists of the included studies were searched with no date and language restrictions through January 2020 for full economic evaluation studies (cost-effectiveness, cost-utility analysis, cost-benefit analysis) that assessed mpMRI and MRGB compared with systematic TRUS-guided biopsy or other sequential biopsy strategies in men undergoing initial prostate biopsy or men with previous negative prostate biopsy, with clinical suspicion of PCa based on abnormal prostate-specific antigen or digital rectal examination increase or both. Data were tabulated and analyzed using narrative synthesis. The reporting quality of included studies was assessed using the Consolidated Health Economic Evaluation Reporting Standards checklist. This systematic review was performed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement.

RESULTS

Finally, 9 studies were included. All studies were conducted in high-income countries. All studies found that mpMRI and MRGB was cost-effective in the initial and before repeat biopsy in men with previous negative biopsy. The cognitive-targeted TRUS-guided biopsy was cost-effective in the initial biopsy (dominant or cost-effective at willingness-to-pay threshold of the countries); it was not evaluated for repeat biopsy in men. The direct in-bore magnetic resonance imaging (MRI)-guided biopsy was cost-effective for the initial biopsy (€323 per quality-adjusted life-year gained). The superiority of one of the targeted biopsy approaches (fusion, cognitive, or in-bore) over other approaches has not yet been established.

CONCLUSIONS

This study showed that pre-TRUS-guided biopsy MRI is more cost-effective than TRUS-guided biopsy alone. Furthermore, the use of MRI-ultrasound fusion targeted biopsy in the diagnosis of PCa in the initial biopsy and repeat biopsy and cognitive-targeted TRUS-guided biopsy in the initial biopsy is cost-effective.

Optimizing biopsy strategy for prostate cancer: Bayesian framework of network meta-analysis and hierarchical summary receiver operating characteristic model for diagnostic accuracy

Overdiagnosis and overtreatment are well known problems in prostate cancer (PCa). The transrectal ultrasound (TRUS) Guided biopsy (GB) as a current gold standard investigation has a low positive detection rate resulting in unnecessary biopsies. The choice of optimal biopsy strategy needs to be defined. Therefore, we undertook a Bayesian network meta analysis (NMA) and Bayesian prediction in the hierarchical summary receiver operating characteristic (HSROC) model to present a method for optimizing biopsy strategy in PCa. Twenty eight relevant studies were retrieved through online databases of EMBASE, MEDLINE, and CENTRAL up to February 2020. Markov chain Monte Carlo simulation and Surface Under the Cumulative RAnking curve were used to calculate the rank probability using odds ratio with 95% credible interval. HSROC model was used to formulate the predicted true sensitivity and specificity of each biopsy strategy. Six different PCa biopsy strategies including transrectal ultrasound GB (TRUS GB), fusion GB (FUS GB), fusion + transrectal ultrasound GB (FUS + TRUS GB), magnetic resonance imaging GB (MRI GB), transperineal ultrasound GB (TPUS GB), and contrast enhanced ultrasound GB were analyzed in this study with a total of 7584 patients. These strategies were analyzed on five outcomes including detection rate of overall PCa, clinically significant PCa, insignificant PCa, complication rate, and HSROC. The rank probability showed that the overall PCa detection rate was higher in FUS + TRUS GB, MRI GB, and FUS GB. In terms of clinically significant PCa detection, FUS + TRUS GB and FUS GB had a relatively higher clinically significant PCa detection rate, whereas TRUS GB had a relatively lower rate for clinically significant PCa detection rate. MRI GB (91% and 81%) and FUS GB (82% and 83%) had the highest predicted true sensitivity and specificity, respectively, whereas TRUS GB (62% and 83%) had a lower predicted true sensitivity and specificity. MRI GB, FUS GB, and FUS + TRUS GB were associated with lower complication rate, whereas TPUS GB and TRUS GB were more associated with higher complication rate. This NMA and HSROC model highlight the important finding that FUS + TRUS GB, FUS GB, and MRI GB were superior compared with other strategies to avoid the overdiagnosis and overtreatment of PCa. FUS GB, MRI GB, and FUS + TRUS GB had lower complication rates. These results may assist in shared decision making between patients, carers, and their surgeons.

Feasibility and Initial Results: Fluciclovine Positron Emission Tomography/Ultrasound Fusion Targeted Biopsy of Recurrent Prostate Cancer

PURPOSE

We assessed the feasibility and cancer detection rate of fluciclovine (¹⁸F) positron emission tomography-ultrasound fusion targeted biopsy vs standard template biopsy in the same patient with biochemical failure after nonsurgical therapy for prostate cancer.

MATERIALS AND METHODS

A total of 21 patients with a mean ± SD prostate specific antigen of 7.4 ± 6.8 ng/ml and biochemical failure after nonoperative prostate cancer treatment underwent fluciclovine (¹⁸F) positron emission tomography-computerized tomography (mean 364.1 ± 37.7 MBq) and planning transrectal prostate ultrasound with 3-dimensional image reconstruction. Focal prostatic activity on positron emission tomography was delineated and co-registered with planning ultrasound. During the subsequent biopsy session computer generated 12-core template biopsies were performed and then fluciclovine defined targets were revealed and biopsied. Histological analysis of template and targeted cores were completed.

RESULTS

Template biopsy was positive for malignancy in 6 of 21 patients (28.6%), including 10 of 124 regions and 11 of 246 cores, vs targeted biopsy in 10 of 21 (47.6%), including 17 of 50 regions and 40 of 125 cores. Five of 21 patients had positive findings on targeted biopsy only and 1 of 21 had positive findings on template biopsy only. An additional case was upgraded from Grade Group 2 to 3 on targeted biopsy. Extraprostatic disease was detected in 8 of 21 men (38.1%) with histological confirmation in all 3 who underwent lesion biopsy.

CONCLUSIONS

Fluciclovine positron emission tomography real-time ultrasound fusion guidance for biopsy is feasible in patients with biochemical failure after nonsurgical therapy for prostate cancer. It identifies more recurrent prostate cancer using fewer cores compared with template biopsy in the same patient. Further study is required to determine in what manner targeted biopsy may augment template biopsy of recurrent prostate cancer.

Photoacoustic tomography for imaging the prostate: a transurethral illumination probe design and application

In vivo imaging of prostate cancer with photoacoustic tomography is currently limited by the lack of sufficient local fluence for deep tissue penetration and the risk of over-irradiation near the laser-tissue contact surface. We propose the design of a transurethral illumination probe that addresses those limitations. A high energy of 50 mJ/pulse is coupled into a 1000-µm-core diameter multimode fiber. A 2 cm diffusing end is fabricated, which delivers light in radial illumination. The radial illumination is then reflected and reshaped by a parabolic cylindrical mirror to obtain nearly parallel side illumination with a doubled fluence. The fiber assembly is housed in a 25 Fr cystoscope sheath to provide protection of the fiber and maintain a minimal laser-tissue contact distance of 5 mm. A large laser-tissue contact surface area of 4 cm² is obtained and the fluence on the tissue surface is kept below the maximum permissible exposure. By imaging a prostate mimicking phantom, a penetration depth of 3.5 cm at 10 mJ/cm² fluence and 700 nm wavelength is demonstrated. The results indicate that photoacoustic tomography with the proposed transurethral probe has the potential to image the entire prostate while satisfying the fluence maximum permissible exposure and delivering a high power to the tissue.

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.

Future Perspectives and Challenges of Prostate MR Imaging

MR imaging is an important part of prostate cancer diagnosis. Variations in quality and skill in general practice mean results are not as impressive as they were in academic centers. This observation provides an impetus to improve the method. Improved quality assurance will likely result in better outcomes. Improved characterization of clinically significant prostate cancer may assist in making MR imaging more useful. Improved methods of registering MR imaging with transrectal ultrasound imaging and robotic arms controlling the biopsy can reduce the impact of inexperienced operators and make the entire system of MR imaging-guided biopsies more robust.

Evaluation of diffusion weighted imaging in the context of multi-parametric MRI of the prostate in the assessment of suspected low volume prostatic carcinoma

Data from a multi-parametric MRI study of patients with possible early-stage prostate cancer was assessed with a view to creating a more efficient clinical protocol. Based on a correlation analysis suggesting that diffusion-weighted imaging (DWI) scores are more strongly correlated with overall PIRADS scores than other modalities such as dynamic contrast enhanced imaging or spectroscopy, we investigate the combination of T2-weighted imaging (T2w) and DWI as a potential diagnostic tool for prostate cancer detection, staging and guided biopsies. Quantification of the noise floor in the DWI images and careful fitting of the data suggests that the mono-exponential model provides a very good fit to the data and there is no evidence of non-Gaussian diffusion for b-values up to 1000s/mm². This precludes the use of kurtosis or other non-Gaussian measures as a biomarker for prostate cancer in our case. However, the ADC scores for healthy and probably malignant regions are significantly lower for the latter in all 20 but one patient. The results suggest that a simplified mp-MRI protocol combining T2w and DWI may be a good compromise for a cost and time efficient, early-stage prostate cancer diagnostic programme, combining robust MR biomarkers for prostate cancer that can be reliably quantified and appear well-suited for general clinical practice.

MRI-directed cognitive fusion-guided biopsy of the anterior prostate tumors

PURPOSE

We aimed to evaluate the efficacy of magnetic resonance imaging (MRI)-directed cognitive fusion transrectal ultrasonography (TRUS)-guided anterior prostate biopsy for diagnosis of anterior prostate tumors and to illustrate this technique.

METHODS

A total of 39 patients with previous negative TRUS biopsy, but high clinical suspicion of occult prostate cancer, prospectively underwent prostate MRI including diffusion-weighted imaging (DWI). Patients with a suspicious anterior lesion on MRI underwent targeted anterior gland TRUS-guided biopsy with cognitive fusion technique using sagittal probe orientation. PIRADS version 1 scores (T2, DWI, and overall), lesion size, prostate-specific antigen (PSA), PSA density, and prostate gland volume were compared between positive and negative biopsy groups and between clinically significant cancer and remaining cases. Logistic regression analysis of imaging parameters and prostate cancer diagnosis was performed.

RESULTS

Anterior gland prostate adenocarcinoma was diagnosed in 18 patients (46.2%) on targeted anterior gland TRUS-guided biopsy. Clinically significant prostate cancer was diagnosed in 13 patients (33.3%). MRI lesion size, T2, DWI, and overall PIRADS scores were significantly higher in patients with positive targeted biopsies and those with clinically significant cancer (P < 0.05). Biopsies were positive in 90%, 33%, and 29% of patients with overall PIRADS scores of 5, 4, and 3 respectively. Overall PIRADS score was an independent predictor of all prostate cancer diagnosis and of clinically significant prostate cancer diagnosis.

CONCLUSION

Targeted anterior gland TRUS-guided biopsy with MRI-directed cognitive fusion enables accurate sampling and may improve tumor detection yield of anterior prostate cancer.

[Role of prostate MRI, TRUS fusion biopsies and new markers in the diagnostic strategy of prostate cancer]

Multiparametric MRI prostate (mp-MRI) is a powerful tool to locate lesions>0.5cm³ (below this threshold tumor volume, prostate cancers are classified as "insignificant"). The detection rate of the mp-MRI for significant cancers of small volume (0.5-1cm³) with a Gleason score≥7 is>85 %. The prostate mp-MRI optimizes the management of cancers classified as low risk of progression by providing aggressive criteria for misclassified lesions, which require an active treatment and enhance the clinicopathological criteria of indolence for subclinical lesions, which can justify of surveillance. MRI-mp coupled to the 3D ultrasound image fusion, optimizes the predictive value of biopsies and improves tumor staging, particularly when benign prostatic hyperplasia (>40cm³) is associated with clinical course. New tissue markers feasible on biopsies allow to define better the risk of progression of the small volume of cancer in order to reinforce the indications of surveillance or delayed curative treatment.

Learning Non-rigid Deformations for Robust, Constrained Point-based Registration in Image-Guided MR-TRUS Prostate Intervention

Accurate and robust non-rigid registration of pre-procedure magnetic resonance (MR) imaging to intra-procedure trans-rectal ultrasound (TRUS) is critical for image-guided biopsies of prostate cancer. Prostate cancer is one of the most prevalent forms of cancer and the second leading cause of cancer-related death in men in the United States. TRUS-guided biopsy is the current clinical standard for prostate cancer diagnosis and assessment. State-of-the-art, clinical MR-TRUS image fusion relies upon semi-automated segmentations of the prostate in both the MR and the TRUS images to perform non-rigid surface-based registration of the gland. Segmentation of the prostate in TRUS imaging is itself a challenging task and prone to high variability. These segmentation errors can lead to poor registration and subsequently poor localization of biopsy targets, which may result in false-negative cancer detection. In this paper, we present a non-rigid surface registration approach to MR-TRUS fusion based on a statistical deformation model (SDM) of intra-procedural deformations derived from clinical training data. Synthetic validation experiments quantifying registration volume of interest overlaps of the PI-RADS parcellation standard and tests using clinical landmark data demonstrate that our use of an SDM for registration, with median target registration error of 2.98 mm, is significantly more accurate than the current clinical method. Furthermore, we show that the low-dimensional SDM registration results are robust to segmentation errors that are not uncommon in clinical TRUS data.

Development and Phantom Validation of a 3-D-Ultrasound-Guided System for Targeting MRI-Visible Lesions During Transrectal Prostate Biopsy

OBJECTIVE

Three- and four-dimensional transrectal ultrasound transducers are now available from most major ultrasound equipment manufacturers, but currently are incorporated into only one commercial prostate biopsy guidance system. Such transducers offer the benefits of rapid volumetric imaging, but can cause substantial measurement distortion in electromagnetic tracking sensors, which are commonly used to enable 3-D navigation. In this paper, we describe the design, development, and validation of a 3-D-ultrasound-guided transrectal prostate biopsy system that employs high-accuracy optical tracking to localize the ultrasound probe and prostate targets in 3-D physical space.

METHODS

The accuracy of the system was validated by evaluating the targeted needle placement error after inserting a biopsy needle to sample planned targets in a phantom using standard 2-D ultrasound guidance versus real-time 3-D guidance provided by the new system.

RESULTS

The overall mean needle-segment-to-target distance error was 3.6 ± 4.0 mm and mean needle-to-target distance was 3.2 ± 2.4 mm.

CONCLUSION

A significant increase in needle placement accuracy was observed when using the 3-D guidance system compared with visual targeting of invisible (virtual) lesions using a standard B-mode ultrasound-guided biopsy technique.

Molecular imaging and fusion targeted biopsy of the prostate

PURPOSE

This paper provides a review on molecular imaging with positron emission tomography (PET) and magnetic resonance imaging (MRI) for prostate cancer detection and its applications in fusion targeted biopsy of the prostate.

METHODS

Literature search was performed through the PubMed database using the keywords "prostate cancer", "MRI/ultrasound fusion", "molecular imaging", and "targeted biopsy". Estimates in autopsy studies indicate that 50% of men older than 50 years of age have prostate cancer. Systematic transrectal ultrasound (TRUS) guided prostate biopsy is considered the standard method for prostate cancer detection and has a significant sampling error and a low sensitivity. Molecular imaging technology and new biopsy approaches are emerging to improve the detection of prostate cancer.

RESULTS

Molecular imaging with PET and MRI shows promising results in the early detection of prostate cancer. MRI/TRUS fusion targeted biopsy has become a new clinical standard for the diagnosis of prostate cancer. PET molecular image-directed, three-dimensional ultrasound-guided biopsy is a new technology that has great potential for improving prostate cancer detection rate and for distinguishing aggressive prostate cancer from indolent disease.

CONCLUSION

Molecular imaging and fusion targeted biopsy are active research areas in prostate cancer research.

The utilization of magnetic resonance imaging in the operating room

Online image guidance in the operating room using ultrasound imaging led to the resurgence of prostate brachytherapy in the 1980s. Here we describe the evolution of integrating MRI technology in the brachytherapy suite or operating room. Given the complexity, cost, and inherent safety issues associated with MRI system integration, first steps focused on the computational integration of images rather than systems. This approach has broad appeal given minimal infrastructure costs and efficiencies comparable with standard care workflows. However, many concerns remain regarding accuracy of registration through the course of a brachytherapy procedure. In selected academic institutions, MRI systems have been integrated in or near the brachytherapy suite in varied configurations to improve the precision and quality of treatments. Navigation toolsets specifically adapted to prostate brachytherapy are in development and are reviewed.

Transperineal prostate biopsy with ECHO-MRI fusion. Biopsee system. Initial experience

OBJECTIVE

The aim of this study is to present our initial experience with the stereotactic echo-MRI fusion system for diagnosing prostate cancer.

MATERIAL AND METHODS

Between September 2014 and January 2015, we performed 50 prostate biopsies using the stereotactic echo-MRI fusion system. The 3-Tesla multiparameter MR images were superimposed using this image fusion system on 3D echo images obtained with the Biopsee system for the exact locating of areas suspected of prostate cancer. The lesions were classified using the Prostate Imaging Report and Date System.

RESULTS

We assessed a total of 50 patients, with a mean age of 63 years (range, 45-79), a mean prostate-specific antigen level of 8 ng/mL (range, 1.9-20) and a mean prostate volume of 52mL (range, 12-118). Prostate cancer was diagnosed in 69% of the patients and intraepithelial neoplasia in 6%. The results of the biopsy were negative for 24% of the patients. The results of the biopsy and MRI were in agreement for 62% of the patients; however, 46% also had a tumour outside of the suspicious lesion. We diagnosed 46% anterior tumours and 33% apical tumours. One patient had a haematuria, another had a haematoma and a third had acute urine retention.

CONCLUSIONS

Multiparametric prostatic MRI helps identify prostate lesions suggestive of cancer. The Biopsee echo-MRI fusion system provides for guided biopsy and increases the diagnostic performance, reducing the false negatives of classical biopsies and increasing the diagnosis of anterior tumours. Transperineal access minimises the risk of prostatic infection and sepsis.

Multiattribute probabilistic prostate elastic registration (MAPPER): application to fusion of ultrasound and magnetic resonance imaging

PURPOSE

Transrectal ultrasound (TRUS)-guided needle biopsy is the current gold standard for prostate cancer diagnosis. However, up to 40% of prostate cancer lesions appears isoechoic on TRUS. Hence, TRUS-guided biopsy has a high false negative rate for prostate cancer diagnosis. Magnetic resonance imaging (MRI) is better able to distinguish prostate cancer from benign tissue. However, MRI-guided biopsy requires special equipment and training and a longer procedure time. MRI-TRUS fusion, where MRI is acquired preoperatively and then aligned to TRUS, allows for advantages of both modalities to be leveraged during biopsy. MRI-TRUS-guided biopsy increases the yield of cancer positive biopsies. In this work, the authors present multiattribute probabilistic postate elastic registration (MAPPER) to align prostate MRI and TRUS imagery.

METHODS

MAPPER involves (1) segmenting the prostate on MRI, (2) calculating a multiattribute probabilistic map of prostate location on TRUS, and (3) maximizing overlap between the prostate segmentation on MRI and the multiattribute probabilistic map on TRUS, thereby driving registration of MRI onto TRUS. MAPPER represents a significant advancement over the current state-of-the-art as it requires no user interaction during the biopsy procedure by leveraging texture and spatial information to determine the prostate location on TRUS. Although MAPPER requires manual interaction to segment the prostate on MRI, this step is performed prior to biopsy and will not substantially increase biopsy procedure time.

RESULTS

MAPPER was evaluated on 13 patient studies from two independent datasets—Dataset 1 has 6 studies acquired with a side-firing TRUS probe and a 1.5 T pelvic phased-array coil MRI; Dataset 2 has 7 studies acquired with a volumetric end-firing TRUS probe and a 3.0 T endorectal coil MRI. MAPPER has a root-mean-square error (RMSE) for expert selected fiducials of 3.36 ± 1.10 mm for Dataset 1 and 3.14 ± 0.75 mm for Dataset 2. State-of-the-art MRI-TRUS fusion methods report RMSE of 3.06-2.07 mm.

CONCLUSIONS

MAPPER aligns MRI and TRUS imagery without manual intervention ensuring efficient, reproducible registration. MAPPER has a similar RMSE to state-of-the-art methods that require manual intervention.

Deformable MR Prostate Segmentation via Deep Feature Learning and Sparse Patch Matching

Automatic and reliable segmentation of the prostate is an important but difficult task for various clinical applications such as prostate cancer radiotherapy. The main challenges for accurate MR prostate localization lie in two aspects: (1) inhomogeneous and inconsistent appearance around prostate boundary, and (2) the large shape variation across different patients. To tackle these two problems, we propose a new deformable MR prostate segmentation method by unifying deep feature learning with the sparse patch matching. First, instead of directly using handcrafted features, we propose to learn the latent feature representation from prostate MR images by the stacked sparse auto-encoder (SSAE). Since the deep learning algorithm learns the feature hierarchy from the data, the learned features are often more concise and effective than the handcrafted features in describing the underlying data. To improve the discriminability of learned features, we further refine the feature representation in a supervised fashion. Second, based on the learned features, a sparse patch matching method is proposed to infer a prostate likelihood map by transferring the prostate labels from multiple atlases to the new prostate MR image. Finally, a deformable segmentation is used to integrate a sparse shape model with the prostate likelihood map for achieving the final segmentation. The proposed method has been extensively evaluated on the dataset that contains 66 T2-wighted prostate MR images. Experimental results show that the deep-learned features are more effective than the handcrafted features in guiding MR prostate segmentation. Moreover, our method shows superior performance than other state-of-the-art segmentation methods.

In-bore MRI interventions: current status and future applications

PURPOSE OF REVIEW

This review discusses the feasibility, recent advances and current status of in-bore MRI-guided interventional techniques for diagnosis and treatment of focal prostate cancer (PCa) and also explores the future applications, highlighting the emerging strategies for the treatment of PCa.

RECENT FINDINGS

Multiparametric MRI has opened up opportunities for diagnosis and targeted therapeutics to the site of disease within the organ wherein minimizing the incidence of treatment-related toxicity of whole gland therapy. MRI-guided targeted biopsy has a higher detection rate for significant cancer and lower rate of detection of insignificant cancer. In comparison to ultrasound-guided focal therapy, in-bore treatment provides the advantage of real time thermal monitoring during treatment and assessment of treatment coverage by an enhanced scan immediately post-treatment. Preliminary results of ongoing phase I and II in-bore focal PCa treatment trials via transperineal, transrectal and transurethral routes, using different energy modalities for the ablation, have shown promising results.

SUMMARY

Advances in multiparametric-MRI has opened up opportunities for in-bore targeted focal treatment of PCa in the correctly selected patient.

MRI-guided core needle biopsy of the prostate: acceptance and side effects

PURPOSE

We aimed to study side effects, complications, and patient acceptance of magnetic resonance imaging-guided real-time biopsy (MRI-GB) of the prostate.

METHODS

Fifty-four men (49-78 years) with elevated prostate-specific antigen after at least one negative systematic transrectal ultrasound-guided biopsy (TRUS-GB) were included in a prospective clinical study. Suspicious areas on images were selectively sampled by obtaining a median of four specimens (range, 1-9 specimens) using MRI-GB. In TRUS-GB, a median of 10 specimens (range, 6-14 specimens) were obtained. Telephone interviews were conducted one week after outpatient MRI-GB, asking patients about pain and side effects (hematuria, hemospermia, rectal bleeding, fever, and chills) of the two biopsy procedures and which of the two procedures they preferred. Multinomial regression analysis and Fisher's exact test was used to test for differences.

RESULTS

MRI-GB was preferred by 65% (35/54), and 82% (44/54) would undergo MRI-GB again. Pain intensity (P = 0.005) and bleeding duration (P = 0.004) were significantly lower for MRI-GB compared with TRUS-GB. Hematuria was less common after MRI-GB compared with TRUS-GB (P = 0.006). A high correlation was given between bleeding intensity and bleeding duration for TRUS-GB (r=0.77) and pain intensity and pain duration for MRI-GB (r=0.65). Although hemospermia, rectal hemorrhage, fever, and chills were less common in MRI, they showed no statistically significant difference.

CONCLUSION

MRI-GB of the prostate seems to have fewer side effects and less pain intensity than TRUS-GB and was preferred by the majority of patients.

Position and orientation measurement of susceptibility markers using spectrally selective spin-echo projections

PURPOSE

To develop an accurate technique for simultaneously measuring the position and orientation of interventional devices using a projection-based spectrally selective refocusing pulse sequence.

METHODS

Projections along physical axes using spectrally selective excitation were acquired to track a catheter. A 9F passive tracking device capable of generating controllable susceptibility artifacts using susceptibility materials (titanium and graphite) was attached to the catheter. A library of projections for different orientations of the device with respect to the main magnetic field were simulated offline. Cross-correlations with these templates were computed to determine the orientation and position of the device. A phantom study was performed to evaluate the accuracy of the tracking technique. The tracking technique was also evaluated in vivo in the carotid artery of a pig.

RESULTS

Simultaneous and accurate measurement of position and orientation of the tracking device was obtained in the phantom and in vivo studies with reasonable temporal resolution. For the phantom study, the average of absolute errors in the Z-, Y-, and X-axes are 0.37, 0.76, and 0.85 mm, respectively. The mean absolute error and standard deviation of orientation measurement are 1.5 and 1.1 degrees, respectively.

CONCLUSION

This positioning technique, in conjunction with a controllable tracking device, can provide accurate tracking of interventional devices in MR-guided interventions. Magn Reson Med 76:1563-1573, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Targeted prostate biopsy: value of multiparametric magnetic resonance imaging in detection of localized cancer

Prostate cancer is the second most common cancer in men, with 1.1 million new cases worldwide reported by the World Health Organization in one recent year. Transrectal ultrasound (TRUS)-guided biopsy has been used for the diagnosis of prostate cancer for over 2 decades, but the technique is usually blind to cancer location. Moreover, the false negative rate of TRUS biopsy has been reported to be as high as 47%. Multiparametric magnetic resonance imaging (mp-MRI) includes T1- and T2-weighted imaging as well as dynamic contrast-enhanced (DCE) and diffusion-weighted imaging (DWI). mp-MRI is a major advance in the imaging of prostate cancer, enabling targeted biopsy of suspicious lesions. Evolving targeted biopsy techniques-including direct in-bore biopsy, cognitive fusion and software-based MRI-ultrasound (MRI-US) fusion-have led to a several-fold improvement in cancer detection compared to the earlier method. Importantly, the detection of clinically significant cancers has been greatly facilitated by targeting, compared to systematic biopsy alone. Targeted biopsy via MRI-US fusion may dramatically alter the way prostate cancer is diagnosed and managed.

MRI-guided biopsies and minimally invasive therapy for prostate cancer

Recent advances in multiparametric magnetic resonance imaging (mp-MRI) have led to a paradigm shift in the diagnosis and management of prostate cancer (PCa). Its sensitivity in detecting clinically significant cancer and the ability to localize the tumor within the prostate gland has opened up discussion on targeted diagnosis and therapy in PCa. Use of mp-MRI in conjunction with prostate-specific antigen followed by targeted biopsy allows for a better diagnostic pathway than transrectal ultrasound (TRUS) biopsy and improves the diagnosis of PCa. Improved detection of PCa by mp-MRI has also opened up opportunities for focal therapy within the organ while reducing the incidence of side-effects associated with the radical treatment methods for PCa. This review discusses the evidence and techniques for in-bore MRI-guided prostate biopsy and provides an update on the status of MRI-guided targeted focal therapy in PCa.

Magnetic Resonance-Guided Prostate Biopsy

The optimal strategy for prostate cancer diagnosis is to avoid overdiagnosis, defined as diagnosis of clinically insignificant disease, and undersampling of the gland, which leads to missing clinically significant disease. Targeted prostate biopsy is a potential solution for decreasing the rate of both overdiagnosis and undersampling of prostate cancer. We focus here on different techniques for targeting prostate lesions identified on multiparametric MR imaging and review different clinical settings in which MR imaging-targeted prostate biopsies are performed.

Repeat Targeted Prostate Biopsy under Guidance of Multiparametric MRI-Correlated Real-Time Contrast-Enhanced Ultrasound for Patients with Previous Negative Biopsy and Elevated Prostate-Specific Antigen: A Prospective Study

OBJECTIVES

To prospectively determine whether multi-parametric MRI (mpMRI) - contrast-enhanced ultrasound (CEUS) correlated, imaging-guided target biopsy (TB) method could improve the detection of prostate cancer in re-biopsy setting of patients with prior negative biopsy.

METHODS

From 2012 to 2014, a total of 42 Korean men with a negative result from previous systematic biopsy (SB) and elevated prostate-specific antigen underwent 3T mpMRI and real-time CEUS guided TB. Target lesions were determined by fusion of mpMRI and CEUS. Subsequently, 12-core SB was performed by a different radiologist. We compared core-based cancer detection rates (CaDR) using the generalized linear mixed model (GLIMMIX) for each biopsy method.

RESULTS

Core-based CaDR was higher in TB (17.92%, 38 of 212 cores) than in SB (6.15%, 31 of 504 cores) (p < 0.0001; GLIMMIX). In the cancer-positive TB cores, CaDR with suspicious lesions by mpMRI was higher than that by CEUS (86.8% vs. 60.5%, p= 0.02; paired t-test) and concordant rate between mpMRI and CEUS was significantly different with discordant rate (48% vs. 52%, p=0.04; McNemar's test).

CONCLUSION

The mpMRI-CEUS correlated TB technique for the repeat prostate biopsy of patients with prior negative biopsy can improve CaDR based on the number of cores taken.

Design of a Dedicated Five Degree-of-Freedom Magnetic Resonance Imaging Compatible Robot for Image Guided Prostate Biopsy

In order to improve the current clinical application of magnetic resonance (MR)-guided prostate biopsies, a new, fully magnetic resonance imaging (MRI)-compatible solution has been developed. This solution consists of a five degree-of-freedom (5DOF) pneumatic robot, a programmable logic controller (PLC), and a software application for visualization and robot control. The robot can be freely positioned on the MR table. For the calibration of the robot and MR coordinate system, the robot’s needle guide (NG) is used. The software application supports the calibration with image segmentation and graphic overlays and guides the user through the interventional planning process. After selecting a target point, the application calculates the needed movements via solving the kinematics of the robot and translating the adjustment into commands for the PLC driving the step motors of the robot. In case further adjustments are required, the software also allows for manual control of the robot, to position the NG according to the acquired MR images.

Magnetic resonance imaging-guided prostate biopsy: present and future

Systemic transrectal ultrasound-guided biopsy (TRUSBx) is the standard procedure for diagnosing prostate cancer (PCa), but reveals a limited accuracy for the detection of cancer. Currently, multiparametric MR imaging (mp-MRI) is increasingly regarded as a promising method to detect PCa with an excellent positive predictive value. The use of mp-MRI during a MRI-guided biopsy (MRGB) procedure improves the quality of a targeted biopsy. The aim of this article is to provide an overview about the MRGB technique for PCa detection, to review the accuracy and clinical indications of MRGB and discuss its current issues and further directions. A MRGB seems accurate and efficient for the detection of clinically significant PCa in men with previous negative TRUSBx. Moreover, it may decrease the detection of clinically insignificant cancers with fewer biopsy cores.

Comparison of magnetic resonance imaging and ultrasound (MRI-US) fusion-guided prostate biopsies obtained from axial and sagittal approaches

OBJECTIVE

To compare cancer detection rates and concordance between magnetic resonance imaging and ultrasound (MRI-US) fusion-guided prostate biopsy cores obtained from axial and sagittal approaches.

PATIENTS AND METHODS

Institutional records of MRI-US fusion-guided biopsy were reviewed. Detection rates for all cancers, Gleason ≥3 + 4 cancers, and Gleason ≥4 + 3 cancers were computed. Agreement between axial and sagittal cores for cancer detection, and frequency where one was upgraded the other was computed on a per-target and per-patient basis.

RESULTS

In all, 893 encounters from 791 patients that underwent MRI-US fusion-guided biopsy in 2007-2013 were reviewed, yielding 4688 biopsy cores from 2344 targets for analysis. The mean age and PSA level at each encounter was 61.8 years and 9.7 ng/mL (median 6.45 ng/mL). Detection rates for all cancers, ≥3 + 4 cancers, and ≥4 + 3 cancers were 25.9%, 17.2%, and 8.1% for axial cores, and 26.1%, 17.6%, and 8.6% for sagittal cores. Per-target agreement was 88.6%, 93.0%, and 96.5%, respectively. On a per-target basis, the rates at which one core upgraded or detected a cancer missed on the other were 8.3% and 8.6% for axial and sagittal cores, respectively. Even with the inclusion of systematic biopsies, omission of axial or sagittal cores would have resulted in missed detection or under-characterisation of cancer in 4.7% or 5.2% of patients, respectively.

CONCLUSION

Cancer detection rates, Gleason scores, and core involvement from axial and sagittal cores are similar, but significant cancer may be missed if only one core is obtained for each target. Discordance between axial and sagittal cores is greatest in intermediate-risk scenarios, where obtaining multiple cores may improve tissue characterisation.

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.

Automated real-time needle-guide tracking for fast 3-T MR-guided transrectal prostate biopsy: a feasibility study

PURPOSE

To assess the feasibility of automatic needle-guide tracking by using a real-time phase-only cross correlation ( POCC phase-only cross correlation ) algorithm-based sequence for transrectal 3-T in-bore magnetic resonance (MR)-guided prostate biopsies.

MATERIALS AND METHODS

This study was approved by the ethics review board, and written informed consent was obtained from all patients. Eleven patients with a prostate-specific antigen level of at least 4 ng/mL (4 μg/L) and at least one transrectal ultrasonography-guided biopsy session with negative findings were enrolled. Regions suspicious for cancer were identified on 3-T multiparametric MR images. During a subsequent MR-guided biopsy, the regions suspicious for cancer were reidentified and targeted by using the POCC phase-only cross correlation -based tracking sequence. Besides testing a general technical feasibility of the biopsy procedure by using the POCC phase-only cross correlation -based tracking sequence, the procedure times were measured, and a pathologic analysis of the biopsy cores was performed.

RESULTS

Thirty-eight core samples were obtained from 25 regions suspicious for cancer. It was technically feasible to perform the POCC phase-only cross correlation -based biopsies in all regions suspicious for cancer in each patient, with adequate biopsy samples obtained with each biopsy attempt. The median size of the region suspicious for cancer was 8 mm (range, 4-13 mm). In each region suspicious for cancer (median number per patient, two; range, 1-4), a median of one core sample per region was obtained (range, 1-3). The median time for guidance per target was 1.5 minutes (range, 0.7-5 minutes). Nineteen of 38 core biopsy samples contained cancer.

CONCLUSION

This study shows that it is feasible to perform transrectal 3-T MR-guided biopsies by using a POCC phase-only cross correlation algorithm-based real-time tracking sequence.

Prostate biopsy for the interventional radiologist

Prostate biopsies are usually performed by urologists in the office setting using transrectal ultrasound (US) guidance. The current standard of care involves obtaining 10-14 cores from different anatomic sections. Biopsies are usually not directed into a specific lesion because most prostate cancers are not visible on transrectal US. Color Doppler, US contrast agents, elastography, magnetic resonance (MR) imaging, and MR imaging/US fusion are proposed as imaging methods to guide prostate biopsies. Prostate MR imaging and fusion biopsy create opportunities for diagnostic and interventional radiologists to play an increasingly important role in the screening, evaluation, diagnosis, targeted biopsy, surveillance, and focal therapy of patients with prostate cancer.

The value of magnetic resonance imaging in the detection of prostate cancer in patients with previous negative biopsies and elevated prostate-specific antigen levels: a meta-analysis

RATIONALE AND OBJECTIVES

To assess the diagnostic performance of magnetic resonance imaging (MRI) for targeting prostate cancer in patients with previous negative biopsies and elevated prostate-specific antigen (PSA) levels.

MATERIALS AND METHODS

Pubmed, Scopus, and Cochrane Library databases were searched to identify suitable studies published from January 2001 to October 2013. Polled estimation and subgroup analysis data were obtained using a random effect model. Summary receiver operating characteristic curves were used to summarize overall test performance.

RESULTS

Fourteen studies involving 698 patients met the included criteria. The mean prostate cancer detection rate was 37.5%. Twelve studies had a pooled sensitivity, specificity, and diagnostic odds ratio (DOR) of 88%, 69%, and 16.84 by patient analysis, respectively. In the subgroup analysis, magnetic resonance imaging spectroscopy (MRSI) provided higher pooled sensitivity (91%) and specificity (69%) compared with T2-weighted imaging (T2WI). MRSI combined with MRI had the highest pooled specificity (73%). By site analysis, the pooled sensitivity, specificity, and DOR in nine studies were 57%, 90%, and 14.34, respectively. In the subgroup analysis, MRSI combined with MRI showed higher pooled sensitivity (58%) and specificity (93%) compared with T2WI. Diffusion-weighted MRI (DWI) showed the highest pooled specificity: 95% but the lowest pooled sensitivity: 38%.

CONCLUSIONS

A limited number of studies suggest that the value of MRI to target prostate cancer in patients with previous negative biopsies and elevated PSA levels appears significant. MRI combined with MRSI is particularly accurate. Further studies are necessary to confirm the eventual role of DWI in this field.

Diffusion-weighted magnetic resonance imaging in the prostate transition zone: histopathological validation using magnetic resonance-guided biopsy specimens

OBJECTIVES

The objective of this study was to evaluate the apparent diffusion coefficient (ADC) of diffusion-weighted magnetic resonance (MR) imaging for the differentiation of transition zone cancer from non-cancerous transition zone with and without prostatitis and for the differentiation of transition zone cancer Gleason grade (GG) using MR-guided biopsy specimens as a reference standard.

MATERIALS AND METHODS

From consecutive MR-guided prostate biopsies (2008-2012) in our referral center, we retrospectively included patients from whom diffusion-weighted MR imaging ADC values were acquired during MR-guided biopsy and whose biopsy cores had a (cancer) core length 10 mm or greater and originated from the transition zone. Two radiologists, who were blinded to the ADC data, annotated regions of interest on biopsy sampling locations of MR-guided biopsy confirmation scans in consensus. Median ADC (mADC) of the regions of interest was related to histopathology outcome in MR-guided biopsy core specimens. Mixed model analysis was used to evaluate mADC differences between 7 histopathology categories predefined as MR-guided biopsy core specimens with primary and secondary GG 4-5 (I), primary GG 4-5 secondary GG 2-3 (II), primary GG 2-3 secondary GG 4-5 (III) and primary and secondary GG 2-3 cancer (IV), and noncancerous tissue without (V) or with degree 1 (VI) or degree 2 prostatitis (VII). Diagnostic accuracy was evaluated using areas under the receiver operating characteristic (AUC) curve.

RESULTS

Fifty-two patients with 87 cancer-containing biopsy cores and 53 patients with 101 non-cancerous biopsy cores were included. Significant mean mADC differences were present between cancers (mean mADC, 0.77-0.86 × 10 mm/s) and noncancerous transition zone without (1.12 × 10 mm/s) and with degree 1 to 2 prostatitis (1.05-1.12 × 10 mm/s; P < 0.0001-0.05). Exceptions were mixed primary and secondary GG cancers versus a degree 2 of prostatitis (P = 0.06-0.09). No significant differences were found between subcategories of primary and secondary GG cancers (P = 0.17-0.91) and between a degree 1 and 2 prostatitis and non-cancerous transition zone without prostatitis (P = 0.48-0.94).The mADC had an AUC of 0.84 to differentiate cancer versus non-cancerous transition zone. AUCs of 0.84 and 0.56 were found for mADC to differentiate prostatitis from cancer and from non-cancerous transition zone. The mADC had an AUC of 0.62 to differentiate a primary GG 4 versus GG 3 cancer.

CONCLUSIONS

The mADC values can differentiate transition zone cancer from non-cancerous transition zone and from a degree 1, and from most cases of a degree 2 prostatitis. However, because of substantial overlap, mADC has a moderate accuracy to differentiate between different primary and secondary GG subcategories and cannot be used to differentiate non-cancerous transition zone from degrees 1 to 2 of prostatitis. Diffusion-weighted imaging ADC may therefore contribute in the detection of transition zone cancers; however, as a single functional MR imaging technique, diffusion-weighted imaging has a moderate diagnostic accuracy in separating higher from lower GG transition zone cancers and in differentiating prostatitis from non-cancerous transition zone.

MRI-guided biopsy for prostate cancer detection: a systematic review of current clinical results

In-bore magnetic resonance-guided biopsy (MRGB) has been increasingly used in clinical practice to detect prostate cancer (PCa). This review summarizes the current clinical results of this biopsy method. A systematic literature search was performed in the PubMed and Embase databases. Of 2,035 identified records, 49 required full review. In all, ten unique studies reporting clinical results of MRGB could be included. Reported PCa detection rates ranged from 8 to 59 % (median 42 %). The majority of tumors detected by MRGB were clinically significant (81-93 %). Most frequent complications of MRGB are transient hematuria (1-24 %) and short-term perirectal bleeding (11-17 %). Major complications are rare. Based on the reviewed literature, MRGB can be regarded an accurate and safe diagnostic tool to detect clinically significant PCa. However, as general availability is limited, this procedure should be reserved for specific patients. Appropriate indications will have to be determined.

1.5-T magnetic resonance-guided transgluteal biopsies of the prostate in patients with clinically suspected prostate cancer: technique and feasibility

OBJECTIVES

The aim of this study was to examine the feasibility and safety of magnetic resonance-guided prostate biopsy (MRGBx) with a transgluteal approach in patients with cancer suspicious prostatic lesions.

MATERIALS AND METHODS

This study was approved by the ethical committee. A total of 25 men with clinically suspected prostate cancer with increased prostate-specific antigen levels and at least 1 previous negative transrectal ultrasound-guided prostatic biopsy (TRUSBx) underwent diagnostic magnetic resonance (MR) imaging of the prostate. Cancer suspicious regions (CSR) were identified, and MRGBx with a transgluteal approach in a large closed-bore 1.5-T MR system was manually performed in coaxial technique, using transversal fat-suppressed T2-weighted true fast imaging with steady-state free precession sequences. Success rate, biopsy findings, side effects, procedure time, number of acquisitions for the repositioning of the needle guide, and length of the biopsy channel were documented. Follow-up was performed 24 months after the procedure.

RESULTS

In diagnostic MR imaging of the prostate, a total of 40 CSRs were detected in 25 patients. All MRGBx procedures were technically successful and all CSRs were biopsied. The mean number of core biopsies per CSR was 3.3 ± 1.5 (range, 1-7). Histopathological analysis revealed adenocarcinoma in 35% (14/40), acute or chronic prostatitis in 30% (12/40), adenofibromyomatous changes in 22.5% (9/40), and no identifiable pathology in 17.5% (7/40) of CSRs, with a pathological overlap for chronic prostatitis and adenofibromyomatous changes in 1 patient with biopsies in 2 CSRs. No missed prostate cancer after MR-guided biopsy in clinical follow-up was detected. Mean procedure time was 31 ± 7 minutes (range, 21-46 minutes). Side effects were hematuria (n = 7), hematospermia (n = 3), combined hematuria/hematospermia (n = 2), and infection (n=1).

CONCLUSION

Magnetic resonance-guided prostate biopsy of the prostate gland with a transgluteal approach is feasible, safe, and a promising technique for histological clarification of cancer suspicious lesions in patients with increased prostate-specific antigen levels after negative TRUSBx. Magnetic resonance-guided prostate biopsy offers a reasonable alternative to repeated TRUSBx for histological clarification of prostate cancer.

Dielectric Elastomer Jet Valve for Magnetic Resonance Imaging-Compatible Robotics

This paper presents the design and experimental characterization of a binary jet valve, specifically developed to control an all-polymer needle manipulator during intramagnetic resonance imaging (MRI) prostate interventions (biopsies and brachytherapies). The key feature of the MRI-compatible valve is its compact dual-stage configuration. The first stage is composed of a low-friction jet nozzle, driven by a small rotary dielectric elastomer actuator (DEA). The second stage provides sufficient air flow and stability for the binary robotic application through an independent air supply, activated by a bistable spool. A hyperelastic stress-strain model is used to optimize the geometrical dimensions of the DEA jet assembly. Fully functional valve prototypes, made with 3M's VHB 4905 films, are monitored with a high-speed camera in order to quantify the system's shifting dynamics. The impact of nozzle clearance, dielectric elastomer film viscoelasticity, mechanical friction, and actuator torque generation on overall dynamic behavior of two different valve setups is discussed. Results show an overall shifting time of 200–300 ms when the friction of the nozzle and DEA actuation stretches are minimized. Low shifting time combined with compactness, simplicity, and low cost suggest that the low friction DEA-driven jet valves have great potential for switching a large number of pneumatic circuits in an MRI environment as well as in traditional pneumatic applications.

Image-guided robotic interventions for prostate cancer

Robotic prostatectomy is a common surgical treatment for men with prostate cancer, with some studies estimating that 80% of prostatectomies now performed in the USA are done so robotically. Despite the technical advantages offered by robotic systems, functional and oncological outcomes of prostatectomy can still be improved further. Alternative minimally invasive treatments that have also adopted robotic platforms include brachytherapy and high-intensity focused ultrasonography (HIFU). These techniques require real-time image guidance--such as ultrasonography or MRI--to be truly effective; issues with software compatibility as well as image registration and tracking currently limit such technologies. However, image-guided robotics is a fast-growing area of research that combines the improved ergonomics of robotic systems with the improved visualization of modern imaging modalities. Although the benefits of a real-time image-guided robotic system to improve the precision of surgical interventions are being realized, the clinical usefulness of many of these systems remains to be seen.