The role of image guided biopsy targeting in patients with atypical small acinar proliferation.

PURPOSE: Men diagnosed with atypical small acinar proliferation are counseled to undergo early rebiopsy because the risk of prostate cancer is high. However, random rebiopsies may not resample areas of concern. Magnetic resonance imaging/transrectal ultrasound fusion guided biopsy offers an opportunity to accurately target and later retarget specific areas in the prostate. We describe the ability of magnetic resonance imaging/transrectal ultrasound fusion guided prostate biopsy to detect prostate cancer in areas with an initial diagnosis of atypical small acinar proliferation. MATERIALS AND METHODS: Multiparametric magnetic resonance imaging of the prostate and magnetic resonance imaging/transrectal ultrasound fusion guided biopsy were performed in 1,028 patients from March 2007 to February 2014. Of the men 20 met the stringent study inclusion criteria, which were no prostate cancer history, index biopsy showing at least 1 core of atypical small acinar proliferation with benign glands in all remaining cores and fusion targeted rebiopsy with at least 1 targeted core directly resampling an area of the prostate that previously contained atypical small acinar proliferation. RESULTS: At index biopsy median age of the 20 patients was 60 years (IQR 57-64) and median prostate specific antigen was 5.92 ng/ml (IQR 3.34-7.48). At fusion targeted rebiopsy at a median of 11.6 months 5 of 20 patients (25%, 95% CI 6.02-43.98) were diagnosed with primary Gleason grade 3, low volume prostate cancer. On fusion rebiopsy cores that directly retargeted areas of previous atypical small acinar proliferation detected the highest tumor burden. CONCLUSIONS: When magnetic resonance imaging/transrectal ultrasound fusion guided biopsy detects isolated atypical small acinar proliferation on index biopsy, early rebiopsy is unlikely to detect clinically significant prostate cancer. Cores that retarget areas of previous atypical small acinar proliferation are more effective than random rebiopsy cores.

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.

Intravoxel incoherent motion MR imaging for prostate cancer: an evaluation of perfusion fraction and diffusion coefficient derived from different b-value combinations.

There has been a resurgent interest in intravoxel incoherent motion (IVIM) MR imaging to obtain perfusion as well as diffusion information on lesions, in which the diffusion was modeled as Gaussian diffusion. However, it was observed that this diffusion deviated from expected monoexponential decay at high b-values and the reported perfusion in prostate is contrary to the findings in dynamic contrast-enhanced (DCE) MRI studies and angiogenesis. Thus, this work is to evaluate the effect of different b-values on IVIM perfusion fractions (f) and diffusion coefficients (D) for prostate cancer detection. The results show that both parameters depended heavily on the b-values, and those derived without the highest b-value correlated best with the results from DCE-MRI studies; specifically, f was significantly elevated (7.2% vs. 3.7%) in tumors when compared with normal tissues, in accordance with the volume transfer constant (K(trans); 0.39 vs. 0.18 min(-1)) and plasma fractional volume (v(p) ; 8.4% vs. 3.4%). In conclusion, it is critical to choose an appropriate range of b-values in studies or include the non-Gaussian diffusion contribution to obtain unbiased IVIM measurements. These measurements could eliminate the need for DCE-MRI, which is especially relevant in patients who cannot receive intravenous gadolinium-based contrast media.

Utility of multiparametric magnetic resonance imaging suspicion levels for detecting prostate cancer.

PURPOSE: We determine the usefulness of multiparametric magnetic resonance imaging in detecting prostate cancer, with a specific focus on detecting higher grade prostate cancer. MATERIALS AND METHODS: Prospectively 583 patients who underwent multiparametric magnetic resonance imaging and subsequent prostate biopsy at a single institution were evaluated. On multiparametric magnetic resonance imaging, lesions were identified and scored as low, moderate or high suspicion for prostate cancer based on a validated scoring system. Magnetic resonance/ultrasound fusion guided biopsies of magnetic resonance imaging lesions in addition to systematic 12-core biopsies were performed. Correlations between the highest assigned multiparametric magnetic resonance imaging suspicion score and presence of cancer and biopsy Gleason score on the first fusion biopsy session were assessed using univariate and multivariate logistic regression models. Sensitivity, specificity, negative predictive value and positive predictive value were calculated and ROC curves were developed to assess the discriminative ability of multiparametric magnetic resonance imaging as a diagnostic tool for various biopsy Gleason score cohorts. RESULTS: Significant correlations were found between age, prostate specific antigen, prostate volume, and multiparametric magnetic resonance imaging suspicion score and the presence of prostate cancer (p<0.0001). On multivariate analyses controlling for age, prostate specific antigen and prostate volume, increasing multiparametric magnetic resonance imaging suspicion was an independent prognosticator of prostate cancer detection (OR 2.2, p<0.0001). Also, incremental increases in multiparametric magnetic resonance imaging suspicion score demonstrated stronger associations with cancer detection in patients with Gleason 7 or greater (OR 3.3, p<0.001) and Gleason 8 or greater (OR 4.2, p<0.0001) prostate cancer. Assessing multiparametric magnetic resonance imaging as a diagnostic tool for all prostate cancer, biopsy Gleason score 7 or greater, and biopsy Gleason score 8 or greater separately via ROC analyses demonstrated increasing accuracy of multiparametric magnetic resonance imaging for higher grade disease (AUC 0.64, 0.69, and 0.72, respectively). CONCLUSIONS: Multiparametric magnetic resonance imaging is a clinically useful modality to detect and characterize prostate cancer, particularly in men with higher grade disease.

Multiparametric magnetic resonance imaging and ultrasound fusion biopsy detect prostate cancer in patients with prior negative transrectal ultrasound biopsies.

PURPOSE: Patients with negative transrectal ultrasound biopsies and a persistent clinical suspicion are at risk for occult but significant prostate cancer. The ability of multiparametric magnetic resonance imaging/ultrasound fusion biopsy to detect these occult prostate lesions may make it an effective tool in this challenging scenario. MATERIALS AND METHODS: Between March 2007 and November 2011 all men underwent prostate 3 T endorectal coil magnetic resonance imaging. All concerning lesions were targeted with magnetic resonance imaging/ultrasound fusion biopsy. In addition, all patients underwent standard 12-core transrectal ultrasound biopsy. Men with 1 or more negative systematic prostate biopsies were included in our cohort. RESULTS: Of the 195 men with previous negative biopsies, 73 (37%) were found to have cancer using the magnetic resonance imaging/ultrasound fusion biopsy combined with 12-core transrectal ultrasound biopsy. High grade cancer (Gleason score 8+) was discovered in 21 men (11%), all of whom had disease detected with magnetic resonance imaging/ultrasound fusion biopsy. However, standard transrectal ultrasound biopsy missed 12 of these high grade cancers (55%). Pathological upgrading occurred in 28 men (38.9%) as a result of magnetic resonance imaging/ultrasound fusion targeting vs standard transrectal ultrasound biopsy. The diagnostic yield of combined magnetic resonance imaging/ultrasound fusion platform was unrelated to the number of previous negative biopsies and persisted despite increasing the number of previous biopsy sessions. On multivariate analysis only prostate specific antigen density and magnetic resonance imaging suspicion level remained significant predictors of cancer. CONCLUSIONS: Multiparametric magnetic resonance imaging with a magnetic resonance imaging/ultrasound fusion biopsy platform is a novel diagnostic tool for detecting prostate cancer and may be ideally suited for patients with negative transrectal ultrasound biopsies in the face of a persistent clinical suspicion for cancer.

Is apparent diffusion coefficient associated with clinical risk scores for prostate cancers that are visible on 3-T MR images?

PURPOSE: To investigate whether apparent diffusion coefficients (ADCs) derived from diffusion-weighted (DW) magnetic resonance (MR) imaging at 3 T correlate with the clinical risk of prostate cancer in patients with tumors that are visible on MR images, with MR imaging/transrectal ultrasonography (US) fusion-guided biopsy as a reference. MATERIALS AND METHODS: Forty-eight consecutive patients (median age, 60 years; median serum prostate-specific antigen value, 6.3 ng/mL) who underwent DW imaging during 3-T MR imaging with an endorectal coil were included in this retrospective institutional review board-approved study, and informed consent was obtained from each patient. Patients underwent targeted MR imaging/transrectal US fusion-guided prostate biopsy. Mean ADCs of cancerous target tumors were correlated with Gleason and D'Amico clinical risk scores. The true risk group rate and predictive value of the mean ADC for classifying a tumor by its D'Amico clinical risk score was determined by using linear discriminant and receiver operating characteristic analyses. RESULTS: A significant negative correlation was found between mean ADCs of tumors in the peripheral zone and their Gleason scores (P = .003; Spearman ρ = -0.60) and D'Amico clinical risk scores (P < .0001; Spearman ρ = -0.69). ADC was found to distinguish tumors in the peripheral zone with intermediate to high clinical risk from those with low clinical risk with a correct classification rate of 0.73. CONCLUSION: There is a significant negative correlation between ADCs and Gleason and D'Amico clinical risk scores. ADCs may therefore be useful in predicting the aggressiveness of prostate cancer. SUPPLEMENTAL MATERIAL: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10100667/-/DC1.

Accelerated T2 mapping for characterization of prostate cancer.

Prostate T(2) mapping was performed in 34 consecutive patients using an accelerated multiecho spin-echo sequence with 4-fold k-space undersampling leading to a net acceleration factor of 3.3 on a 3T scanner. The mean T(2) values from the accelerated and conventional, unaccelerated sequences demonstrated a very high correlation (r = 0.99). Different prostate segments demonstrated similarly good interscan reproducibility (p = not significant) with slightly larger difference at base: 2.0% ± 1.6% for left base and 2.1% ± 1.1% for right base. In patients with subsequent targeted biopsy, T(2) values of histologically proven malignant tumor areas were significantly lower than the suspicious looking but nonmalignant lesions (p < 0.05) and normal areas (p < 0.001): 100 ± 10 ms for malignant tumors, 114 ± 23 ms for suspicious lesions and 149 ± 32 ms for normal tissues. The proposed method can provide an effective approach for accelerated T(2) quantification for prostate patients.

D'Amico risk stratification correlates with degree of suspicion of prostate cancer on multiparametric magnetic resonance imaging.

PURPOSE: We determined whether there is a correlation between D'Amico risk stratification and the degree of suspicion of prostate cancer on multiparametric magnetic resonance imaging based on targeted biopsies done with our electromagnetically tracked magnetic resonance imaging/ultrasound fusion platform. MATERIALS AND METHODS: A total of 101 patients underwent 3 Tesla multiparametric magnetic resonance imaging of the prostate, consisting of T2, dynamic contrast enhanced, diffusion weighted and spectroscopy images in cases suspicious for or with a diagnosis of prostate cancer. All prostate magnetic resonance imaging lesions were then identified and graded by the number of positive modalities, including low-2 or fewer, moderate-3 and high-4 showing suspicion on multiparametric magnetic resonance imaging. The biopsy protocol included standard 12-core biopsy, followed by real-time magnetic resonance imaging/ultrasound fusion targeted biopsies of the suspicious magnetic resonance lesions. Cases and lesions were stratified by the D'Amico risk stratification. RESULTS: In this screening population 90.1% of men had a negative digital rectal examination. Mean±SD age was 62.7±8.3 years and median prostate specific antigen was 5.8 ng/ml. Of the cases 54.5% were positive for cancer on protocol biopsy. Chi-square analysis revealed a statistically significant correlation between magnetic resonance suspicion and D'Amico risk stratification (p<0.0001). Within cluster resampling demonstrated a statistically significant correlation between magnetic resonance suspicion and D'Amico risk stratification for magnetic resonance targeted core biopsies and magnetic resonance lesions (p<0.01) CONCLUSIONS: Our data support the notion that using multiparametric magnetic resonance prostate imaging one may assess the degree of risk associated with magnetic resonance visible lesions in the prostate.

Magnetic resonance imaging/ultrasound fusion guided prostate biopsy improves cancer detection following transrectal ultrasound biopsy and correlates with multiparametric magnetic resonance imaging.

PURPOSE: A novel platform was developed that fuses pre-biopsy magnetic resonance imaging with real-time transrectal ultrasound imaging to identify and biopsy lesions suspicious for prostate cancer. The cancer detection rates for the first 101 patients are reported. MATERIALS AND METHODS: This prospective, single institution study was approved by the institutional review board. Patients underwent 3.0 T multiparametric magnetic resonance imaging with endorectal coil, which included T2-weighted, spectroscopic, dynamic contrast enhanced and diffusion weighted magnetic resonance imaging sequences. Lesions suspicious for cancer were graded according to the number of sequences suspicious for cancer as low (2 or less), moderate (3) and high (4) suspicion. Patients underwent standard 12-core transrectal ultrasound biopsy and magnetic resonance imaging/ultrasound fusion guided biopsy with electromagnetic tracking of magnetic resonance imaging lesions. Chi-square and within cluster resampling analyses were used to correlate suspicion on magnetic resonance imaging and the incidence of cancer detected on biopsy. RESULTS: Mean patient age was 63 years old. Median prostate specific antigen at biopsy was 5.8 ng/ml and 90.1% of patients had a negative digital rectal examination. Of patients with low, moderate and high suspicion on magnetic resonance imaging 27.9%, 66.7% and 89.5% were diagnosed with cancer, respectively (p <0.0001). Magnetic resonance imaging/ultrasound fusion guided biopsy detected more cancer per core than standard 12-core transrectal ultrasound biopsy for all levels of suspicion on magnetic resonance imaging. CONCLUSIONS: Prostate cancer localized on magnetic resonance imaging may be targeted using this novel magnetic resonance imaging/ultrasound fusion guided biopsy platform. Further research is needed to determine the role of this platform in cancer detection, active surveillance and focal therapy, and to determine which patients may benefit.

Documenting the location of prostate biopsies with image fusion.

OBJECTIVE To develop a system that documents the location of transrectal ultrasonography (TRUS)-guided prostate biopsies by fusing them to MRI scans obtained prior to biopsy, as the actual location of prostate biopsies is rarely known. PATIENTS AND METHODS Fifty patients (median age 61) with a median prostate-specific antigen (PSA) of 5.8 ng/ml underwent 3T endorectal coil MRI prior to biopsy. 3D TRUS images were obtained just prior to standard TRUS-guided 12-core sextant biopsies wherein an electromagnetic positioning device was attached to the needle guide and TRUS probe in order to track the position of each needle pass. The 3D-TRUS image documenting the location of each biopsy was fused electronically to the T2-weighted MRI. Each biopsy needle track was marked on the TRUS images and these were then transposed onto the MRI. Each biopsy site was classified pathologically as positive or negative for cancer and the Gleason score was determined. RESULTS The location of all (n= 605) needle biopsy tracks was successfully documented on the T2-weighted (T2W) MRI. Among 50 patients, 20 had 56 positive cores. At the sites of biopsy, T2W signal was considered 'positive' for cancer (i.e. low in signal intensity) in 34 of 56 sites. CONCLUSION It is feasible to document the location of TRUS-guided prostate biopsies on pre-procedure MRI by fusing the pre-procedure TRUS to an endorectal coil MRI using electromagnetic needle tracking. This procedure may be useful in documenting the location of prior biopsies, improving quality control and thereby avoiding under-sampling of the prostate as well as directing subsequent biopsies to regions of the prostate not previously sampled.

Navigation systems for ablation.

Navigation systems, devices, and intraprocedural software are changing the way interventional oncology is practiced. Before the development of precision navigation tools integrated with imaging systems, thermal ablation of hard-to-image lesions was highly dependent on operator experience, spatial skills, and estimation of positron emission tomography-avid or arterial-phase targets. Numerous navigation systems for ablation bring the opportunity for standardization and accuracy that extends the operator's ability to use imaging feedback during procedures. In this report, existing systems and techniques are reviewed and specific clinical applications for ablation are discussed to better define how these novel technologies address specific clinical needs and fit into clinical practice.

Learning deep similarity metric for 3D MR-TRUS image registration.

PURPOSE: The fusion of transrectal ultrasound (TRUS) and magnetic resonance (MR) images for guiding targeted prostate biopsy has significantly improved the biopsy yield of aggressive cancers. A key component of MR-TRUS fusion is image registration. However, it is very challenging to obtain a robust automatic MR-TRUS registration due to the large appearance difference between the two imaging modalities. The work presented in this paper aims to tackle this problem by addressing two challenges: (i) the definition of a suitable similarity metric and (ii) the determination of a suitable optimization strategy. METHODS: This work proposes the use of a deep convolutional neural network to learn a similarity metric for MR-TRUS registration. We also use a composite optimization strategy that explores the solution space in order to search for a suitable initialization for the second-order optimization of the learned metric. Further, a multi-pass approach is used in order to smooth the metric for optimization. RESULTS: The learned similarity metric outperforms the classical mutual information and also the state-of-the-art MIND feature-based methods. The results indicate that the overall registration framework has a large capture range. The proposed deep similarity metric-based approach obtained a mean TRE of 3.86 mm (with an initial TRE of 16 mm) for this challenging problem. CONCLUSION: A similarity metric that is learned using a deep neural network can be used to assess the quality of any given image registration and can be used in conjunction with the aforementioned optimization framework to perform automatic registration that is robust to poor initialization.

Initial clinical experience with real-time transrectal ultrasonography-magnetic resonance imaging fusion-guided prostate biopsy.

OBJECTIVE: To evaluate the feasibility and utility of registration and fusion of real-time transrectal ultrasonography (TRUS) and previously acquired magnetic resonance imaging (MRI) to guide prostate biopsies. PATIENTS AND METHODS: Two National Cancer Institute trials allowed MRI-guided (with or with no US fusion) prostate biopsies during placement of fiducial markers. Fiducial markers were used to guide patient set-up for daily external beam radiation therapy. The eligible patients had biopsy-confirmed prostate cancer that was visible on MRI. A high-field (3T) MRI was performed with an endorectal coil in place. After moving to an US suite, the patient then underwent TRUS to visualize the prostate. The US transducer was equipped with a commercial needle guide and custom modified with two embedded miniature orthogonal five-degrees of freedom sensors to enable spatial tracking and registration with MR images in six degrees of freedom. The MRI sequence of choice was registered manually to the US using custom software for real-time navigation and feedback. The interface displayed the actual and projected needle pathways superimposed upon the real-time US blended with the prior MR images, with position data updating in real time at 10 frames per second. The registered MRI information blended to the real-time US was available to the physician who performed targeted biopsies of highly suspicious areas. RESULTS: Five patients underwent limited focal biopsy and fiducial marker placement with real-time TRUS-MRI fusion. The Gleason scores at the time of enrollment on study were 8, 7, 9, 9, and 6. Of the 11 targeted biopsies, eight showed prostate cancer. Positive biopsies were found in all patients. The entire TRUS procedure, with fusion, took approximately 10 min. CONCLUSION: The fusion of real-time TRUS and prior MR images of the prostate is feasible and enables MRI-guided interventions (like prostate biopsy) outside of the MRI suite. The technique allows for navigation within dynamic contrast-enhanced maps, or T2-weighted or MR spectroscopy images. This technique is a rapid way to facilitate MRI-guided prostate therapies such as external beam radiation therapy, brachytherapy, cryoablation, high-intensity focused ultrasound ablation, or direct injection of agents, without the cost, throughput, or equipment compatibility issues that might arise with MRI-guided interventions inside the MRI suite.

EM-enhanced US-based seed detection for prostate brachytherapy.

PURPOSE: Intraoperative dosimetry in low-dose-rate (LDR) permanent prostate brachytherapy requires accurate localization of the implanted seeds with respect to the prostate anatomy. Transrectal Ultrasound (TRUS) imaging, which is the main imaging modality used during the procedure, is not sufficiently robust for accurate seed localization. We present a method for integration of electromagnetic (EM) tracking into LDR prostate brachytherapy procedure by fusing it with TRUS imaging for seed localization. METHOD: Experiments were conducted on five tissue mimicking phantoms in a controlled environment. The seeds were implanted into each phantom using an EM-tracked needle, which allowed recording of seed drop locations. After each needle, we reconstructed a 3D ultrasound (US) volume by compounding a series of 2D US images acquired during retraction of an EM-tracked TRUS probe. Then, a difference image was generated by nonrigid registration and subtraction of two consecutive US volumes. A US-only seed detection method was used to detect seed candidates in the difference volume, based on the signature of the seeds. Finally, the EM-based positions of the seeds were used to detect the false positives of the US-based seed detection method and also to estimate the positions of the missing seeds. After the conclusion of the seed implant process, we acquired a CT image. The ground truth for seed locations was obtained by localizing the seeds in the CT image and registering them to the US coordinate system. RESULTS: Compared to the ground truth, the US-only detection algorithm achieved a localization error mean of 1.7 mm with a detection rate of 85%. By contrast, the EM-only seed localization method achieved a localization error mean of 3.7 mm with a detection rate of 100%. By fusing EM-tracking information with US imaging, we achieved a localization error mean of 1.8 mm while maintaining a 100% detection rate without any false positives. CONCLUSIONS: Fusion of EM-tracking and US imaging for prostate brachytherapy can combine high localization accuracy of US-based seed detection with the robustness and high detection rate of EM-based seed localization. Our phantom experiments serve as a proof of concept to demonstrate the potential value of integrating EM-tracking into LDR prostate brachytherapy.

Is visual registration equivalent to semiautomated registration in prostate biopsy?

In magnetic resonance iimaging- (MRI-) ultrasound (US) guided biopsy, suspicious lesions are identified on MRI, registered on US, and targeted during biopsy. The registration can be performed either by a human operator (visual registration) or by fusion software. Previous studies showed that software registration is fairly accurate in locating suspicious lesions and helps to improve the cancer detection rate. Here, the performance of visual registration was examined for ability to locate suspicious lesions defined on MRI. This study consists of 45 patients. Two operators with differing levels of experience (<1 and 18 years) performed visual registration. The overall spatial difference by the two operators in 72 measurements was 10.6 ± 6.0 mm. Each operator showed a spatial difference of 9.4 ± 5.1 mm (experienced; 39 lesions) and 12.1 ± 6.6 mm (inexperienced; 33 lesions), respectively. In a head-to-head comparison of the same 16 lesions from 12 patients, the spatial differences were 9.7 mm ± 4.9 mm (experienced) and 13.4 mm ± 7.4 mm (inexperienced). There were significant differences between the two operators (unpaired, P value = 0.042; paired, P value = 0.044). The substantial differences by the two operators suggest that visual registration could improperly and inaccurately target many tumors, thereby potentially leading to missed diagnosis or false characterization on pathology.

Multiparametric magnetic resonance imaging-transrectal ultrasound fusion-assisted biopsy for the diagnosis of local recurrence after radical prostatectomy.

OBJECTIVE: Approximately 15% of patients who undergo radical prostatectomy (RP) for prostate cancer develop local recurrence, which is heralded by a rise in serum prostate-specific antigen (PSA) levels. Early detection and treatment of recurrence improves the outcome of salvage treatment. We investigated the ability of multiparametric magnetic resonance imaging (mpMRI)-transrectal ultrasound (TRUS) fusion-guided biopsy (FGB) combined with "cognitive biopsy" to confirm local recurrence of prostate cancer after RP. MATERIALS AND METHODS: In this retrospective study conducted between January 2010 and December 2014, patients with rising PSA levels after RP who had no known evidence of distant metastases underwent mpMRI including T2-weighted (T2W) imaging, diffusion-weighted imaging, dynamic contrast-enhanced (DCE) MRI at 3 Tesla, and subsequent MRI-ultrasound fusion biopsy with cognitive assistance. The detection rate of locally recurrent disease was determined. RESULTS: A total of 10 patients (mean age = 67y, mean PSA level = 3.44ng/ml) met the inclusion criteria. Of the 10 patients, all had positive findings suspicious for local recurrence on mpMRI per entrance criterion. The most important features on mpMRI were early enhancement on DCE MR images and hypointensity on T2W images. The average lesion diameter on mpMRI was 1.12cm (range: 0.40-2.20cm). All suspicious lesions (16/16, 100%) were positive on T2W MR images, 14 (89%) showed positive features on apparent diffusion coefficient maps of diffusion-weighted images, and 16 (100%) were positive on DCE MR images. MRI-TRUS FGBs were positive in 10/16 lesions (62.5%) and 8/10 (80%) patients. CONCLUSION: MRI-TRUS FGB with cognitive assistance is able to detect and diagnose locally recurrent lesions after RP, even at low PSA levels. This may facilitate early detection of recurrent disease and improve salvage treatment outcomes.

Electromagnetic tracking for catheter reconstruction in ultrasound-guided high-dose-rate brachytherapy of the prostate.

PURPOSE: The accurate delivery of high-dose-rate brachytherapy is dependent on the correct identification of the position and shape of the treatment catheters. In many brachytherapy clinics, transrectal ultrasound (TRUS) imaging is used to identify the catheters. However, manual catheter identification on TRUS images can be time consuming, subjective, and operator dependent because of calcifications and distal shadowing artifacts. We report the use of electromagnetic (EM) tracking technology to map the position and shape of catheters inserted in a tissue-mimicking phantom. METHODS AND MATERIALS: The accuracy of the EM system was comprehensively quantified using a three-axis robotic system. In addition, EM tracks acquired from catheters in a phantom were compared with catheter positions determined from TRUS and CT images to compare EM system performance to standard clinical imaging modalities. The tracking experiments were performed in a controlled laboratory environment and also in a typical brachytherapy operating room to test for potential EM distortions. RESULTS: The robotic validation of the EM system yielded a mean accuracy of <0.5 mm for a clinically acceptable field of view in a nondistorting environment. The EM-tracked catheter representations were found to have an accuracy of <1 mm when compared with TRUS- and CT-identified positions, both in the laboratory environment and in the brachytherapy operating room. The achievable accuracy depends to a large extent on the calibration of the TRUS probe, geometry of the tracked devices relative to the EM field generator, and locations of surrounding clinical equipment. To address the issue of variable accuracy, a robust calibration algorithm has been developed and integrated into the workflow. The proposed mapping technique was also found to improve the workflow efficiency of catheter identification. CONCLUSIONS: The high baseline accuracy of the EM system, the consistent agreement between EM-tracked, TRUS- and CT-identified catheters, and the improved workflow efficiency illustrate the potential value of using EM tracking for catheter mapping in high-dose-rate brachytherapy.

Magnetic resonance imaging/ultrasound-fusion biopsy significantly upgrades prostate cancer versus systematic 12-core transrectal ultrasound biopsy.

BACKGROUND: Gleason scores from standard, 12-core prostate biopsies are upgraded historically in 25-33% of patients. Multiparametric prostate magnetic resonance imaging (MP-MRI) with ultrasound (US)-targeted fusion biopsy may better sample the true gland pathology. OBJECTIVE: The rate of Gleason score upgrading from an MRI/US-fusion-guided prostate-biopsy platform is compared with a standard 12-core biopsy regimen alone. DESIGN, SETTING, AND PARTICIPANTS: There were 582 subjects enrolled from August 2007 through August 2012 in a prospective trial comparing systematic, extended 12-core transrectal ultrasound biopsies to targeted MRI/US-fusion-guided prostate biopsies performed during the same biopsy session. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The highest Gleason score from each biopsy method was compared. INTERVENTIONS: An MRI/US-fusion-guided platform with electromagnetic tracking was used for the performance of the fusion-guided biopsies. RESULTS AND LIMITATIONS: A diagnosis of prostate cancer (PCa) was made in 315 (54%) of the patients. Addition of targeted biopsy led to Gleason upgrading in 81 (32%) cases. Targeted biopsy detected 67% more Gleason ≥4+3 tumors than 12-core biopsy alone and missed 36% of Gleason ≤3+4 tumors, thus mitigating the detection of lower-grade disease. Conversely, 12-core biopsy led to upgrading in 67 (26%) cases over targeted biopsy alone but only detected 8% more Gleason ≥4+3 tumors. On multivariate analysis, MP-MRI suspicion was associated with Gleason score upgrading in the targeted lesions (p<0.001). The main limitation of this study was that definitive pathology from radical prostatectomy was not available. CONCLUSIONS: MRI/US-fusion-guided biopsy upgrades and detects PCa of higher Gleason score in 32% of patients compared with traditional 12-core biopsy alone. Targeted biopsy technique preferentially detects higher-grade PCa while missing lower-grade tumors.

A statistical model-based technique for accounting for prostate gland deformation in endorectal coil-based MR imaging.

In prostate brachytherapy procedures, combining high-resolution endorectal coil (ERC)-MRI with Computed Tomography (CT) images has shown to improve the diagnostic specificity for malignant tumors. Despite such advantage, there exists a major complication in fusion of the two imaging modalities due to the deformation of the prostate shape in ERC-MRI. Conventionally, nonlinear deformable registration techniques have been utilized to account for such deformation. In this work, we present a model-based technique for accounting for the deformation of the prostate gland in ERC-MR imaging, in which a unique deformation vector is estimated for every point within the prostate gland. Modes of deformation for every point in the prostate are statistically identified using a set of MR-based training set (with and without ERC-MRI). Deformation of the prostate from a deformed (ERC-MRI) to a non-deformed state in a different modality (CT) is then realized by first calculating partial deformation information for a limited number of points (such as surface points or anatomical landmarks) and then utilizing the calculated deformation from a subset of the points to determine the coefficient values for the modes of deformations provided by the statistical deformation model. Using a leave-one-out cross-validation, our results demonstrated a mean estimation error of 1mm for a MR-to-MR registration.

Multimodality image fusion-guided procedures: technique, accuracy, and applications.

Personalized therapies play an increasingly critical role in cancer care: Image guidance with multimodality image fusion facilitates the targeting of specific tissue for tissue characterization and plays a role in drug discovery and optimization of tailored therapies. Positron-emission tomography (PET), magnetic resonance imaging (MRI), and contrast-enhanced computed tomography (CT) may offer additional information not otherwise available to the operator during minimally invasive image-guided procedures, such as biopsy and ablation. With use of multimodality image fusion for image-guided interventions, navigation with advanced modalities does not require the physical presence of the PET, MRI, or CT imaging system. Several commercially available methods of image-fusion and device navigation are reviewed along with an explanation of common tracking hardware and software. An overview of current clinical applications for multimodality navigation is provided.