Clinical application of a 3D ultrasound-guided prostate biopsy system

Reliable Prostate Cancer Risk Mapping From MRI Using Targeted and Systematic Core Needle Biopsy Histopathology

OBJECTIVE

To compute a dense prostate cancer risk map for the individual patient post-biopsy from magnetic resonance imaging (MRI) and to provide a more reliable evaluation of its fitness in prostate regions that were not identified as suspicious for cancer by a human-reader in pre- and intra-biopsy imaging analysis.

METHODS

Low-level pre-biopsy MRI biomarkers from targeted and non-targeted biopsy locations were extracted and statistically tested for representativeness against biomarkers from non-biopsied prostate regions. A probabilistic machine learning classifier was optimized to map biomarkers to their core-level pathology, followed by extrapolation of pathology scores to non-biopsied prostate regions. Goodness-of-fit was assessed at targeted and non-targeted biopsy locations for the post-biopsy individual patient.

RESULTS

Our experiments showed high predictability of imaging biomarkers in differentiating histopathology scores in thousands of non-targeted core-biopsy locations (ROC-AUCs: 0.85-0.88), but also high variability between patients (Median ROC-AUC [IQR]: 0.81-0.89 [0.29-0.40]).

CONCLUSION

The sparseness of prostate biopsy data makes the validation of a whole gland risk mapping a non-trivial task. Previous studies i) focused on targeted-biopsy locations although biopsy-specimens drawn from systematically scattered locations across the prostate constitute a more representative sample to non-biopsied regions, and ii) estimated prediction-power across predicted instances (e.g., biopsy specimens) with no patient distinction, which may lead to unreliable estimation of model fitness to the individual patient due to variation between patients in instance count, imaging characteristics, and pathologies.

SIGNIFICANCE

This study proposes a personalized whole-gland prostate cancer risk mapping post-biopsy to allow clinicians to better stage and personalize focal therapy treatment plans.

BioPrev-C - development and validation of a contemporary prostate cancer risk calculator

Objectives

To develop a novel biopsy prostate cancer (PCa) prevention calculator (BioPrev-C) using data from a prospective cohort all undergoing mpMRI targeted and transperineal template saturation biopsy.

Materials and methods

Data of all men who underwent prostate biopsy in our academic tertiary care center between 11/2016 and 10/2019 was prospectively collected. We developed a clinical prediction model for the detection of high-grade PCa (Gleason score ≥7) based on a multivariable logistic regression model incorporating age, PSA, prostate volume, digital rectal examination, family history, previous negative biopsy, 5-alpha-reductase inhibitor use and MRI PI-RADS score. BioPrev-C performance was externally validated in another prospective Swiss cohort and compared with two other PCa risk-calculators (SWOP-RC and PBCG-RC).

Results

Of 391 men in the development cohort, 157 (40.2%) were diagnosed with high-grade PCa. Validation of the BioPrev C revealed good discrimination with an area under the curve for high-grade PCa of 0.88 (95% Confidence Interval 0.82-0.93), which was higher compared to the other two risk calculators (0.71 for PBCG and 0.84 for SWOP). The BioPrev-C revealed good calibration in the low-risk range (0 - 0.25) and moderate overestimation in the intermediate risk range (0.25 - 0.75). The PBCG-RC showed good calibration and the SWOP-RC constant underestimation of high-grade PCa over the whole prediction range. Decision curve analyses revealed a clinical net benefit for the BioPrev-C at a clinical meaningful threshold probability range (≥4%), whereas PBCG and SWOP calculators only showed clinical net benefit above a 30% threshold probability.

Conclusion

BiopPrev-C is a novel contemporary risk calculator for the prediction of high-grade PCa. External validation of the BioPrev-C revealed relevant clinical benefit, which was superior compared to other well-known risk calculators. The BioPrev-C has the potential to significantly and safely reduce the number of men who should undergo a prostate biopsy.

Targeted Prostate Biopsies-What the Radiologist Needs to Know

The emergence of multiparametric MR imaging has enabled a more reliable targeted approach to diagnosis of prostate cancer. Targeted biopsies are central to the MR imaging-dependent pathway to prostate cancer diagnosis and potentially improve the detection of clinically significant prostate cancers. In a targeted biopsy, tissue samples are obtained from suspicious regions identified on a prebiopsy diagnostic MR imaging. This article describes and compares principles, advantages, and disadvantages of the different strategies available for targeting an MR imaging-visible suspicious lesion.

Preoperative imaging accuracy in size determination of prostate cancer in men undergoing radical prostatectomy for clinically localised disease

OBJECTIVES

To compare the accuracy of pre-surgical prostate size measurements using mpMRI and USWE with imaging-based 3D-printed patient-specific whole-mount moulds facilitated histopathology, and to assess whether size assessment varies between clinically significant and non-significant cancerous lesions including their locations in different zones of the prostate.

METHODS

The study population included 202 men with clinically localised prostate cancer opting for radical surgery derived from two prospective studies. Protocol-based imaging data was used for measurement of size of prostate cancer in clinically localised disease using MRI (N = 106; USWE (N = 96). Forty-eight men overlapped between two studies and formed the validation cohort. The primary outcome of this study was to assess the accuracy of pre-surgical prostate cancerous size measurements using mpMRI and USWE with imaging-based 3D-printed patient-specific whole-mount moulds facilitated histopathology as a reference standard. Independent-samples T-tests were used for the continuous variables and a nonparametric Mann-Whitney U test for independent samples was applied to examine the distribution and median differences between mpMRI and USWE groups.

RESULTS

A significant number of men had underestimation of prostate cancer using both mpMRI (82.1%; 87/106) and USWE (64.6%; 62/96). On average, tumour size was underestimated by a median size of 7 mm in mpMRI, and 1 mm in USWE. There were 327 cancerous lesions (153 with mpMRI and 174 for USWE). mpMRI and USWE underestimated the majority of cancerous lesions (108/153; 70.6%) and (88/174; 50.6%), respectively. Validation cohort data confirmed these findings MRI had a nearly 20% higher underestimation rate than USWE (χ² (1, N = 327) = 13.580, p = 0.001); especially in the mid and apical level of the gland. Clinically non-significant cancers were underestimated in significantly higher numbers in comparison to clinically significant cancers.

CONCLUSIONS

Size measurement of prostate cancers on preoperative imaging utilising maximum linear extent technique, underestimated the extent of cancer. Further research is needed to confirm our observations using different sequences, methods and approaches for cancer size measurement.

Cryotherapy for partial gland ablation of prostate cancer: Oncologic and safety outcomes

BACKGROUND

Partial gland ablation (PGA) is a new option for treatment of prostate cancer (PCa). Cryotherapy, an early method of PGA, has had favorable evaluations, but few studies have employed a strict protocol using biopsy endpoints in men with clinically significant prostate cancer (csPCa).

METHODS

143 men with unilateral csPCa were enrolled in a prospective, observational trial of outpatient PGA-cryotherapy. Treatment was a 2-cycle freeze of the affected prostate part. Participants were evaluated with MRI-guided biopsy (MRGB) at baseline and at 6 months and 18 months after treatment. Absence of csPCa upon MRGB was the primary endpoint; quality-of-life at baseline and at 6 months after treatment was assessed by EPIC-CP questionnaires in the domains of urinary and sexual function.

RESULTS

Of the 143 participants, 136 (95%) completed MRGB at 6 months after treatment. In 103/136 (76%), the biopsy revealed no csPCa. Of the 103, 71 subsequently had an 18-month comprehensive biopsy; of the 71 with 18-month biopsies, 46 (65%) were found to have no csPCa. MRI lesions became undetectable in 96/130 (74%); declines in median serum PSA levels (6.9 to 2.5 ng/mL), PSA density (0.15 to 0.07), and prostate volume (42 to 34cc) were observed (all p < 0.01). Neither lesion disappearance on MRI nor PSA decline correlated with biopsy outcome. Urinary function was affected only slightly and sexual function moderately.

CONCLUSION

In the near to intermediate term, partial gland ablation with cryotherapy was found to be a safe and moderately effective treatment of intermediate-risk prostate cancer. Eradication of cancer was better determined by MRI-guided biopsy than by MRI or PSA.

Landmarks in the evolution of prostate biopsy

Approaches and techniques used for diagnostic prostate biopsy have undergone considerable evolution over the past few decades: from the original finger-guided techniques to the latest MRI-directed strategies, from aspiration cytology to tissue core sampling, and from transrectal to transperineal approaches. In particular, increased adoption of transperineal biopsy approaches have led to reduced infectious complications and improved antibiotic stewardship. Furthermore, as image fusion has become integral, these novel techniques could be incorporated into prostate biopsy methods in the future, enabling 3D-ultrasonography fusion reconstruction, molecular targeting based on PET imaging and autonomous robotic-assisted biopsy.

Detection of prostate cancer using diffusion-relaxation correlation spectrum imaging with support vector machine model - a feasibility study

BACKGROUND

To evaluate the performance of diffusion-relaxation correlation spectrum imaging (DR-CSI) with support vector machine (SVM) in detecting prostate cancer (PCa).

METHODS

In total, 114 patients (mean age, 66 years, range, 48-87 years) who received a prostate MRI and underwent biopsy were enrolled in three stages. Thirty-nine were assigned for the exploration stage to establish the model, 18 for the validation stage to choose the appropriate scale for mapping and 57 for the test stage to compare the diagnostic performance of the DR-CSI and PI-RADS.

RESULTS

In the exploration stage, the DR-CSI model was established and performed better than the ADC and T₂ values (both P < 0.001). The validation result shows that at least 2 pixels were required for both the long-axis and short-axis in the mapping procedure. In the test stage, DR-CSI had higher accuracy than PI-RADS ≥ 3 as a positive finding based on patient (84.2% vs. 63.2%, P = 0.004) and lesion (78.8% vs. 57.6%, P = 0.001) as well as PI-RADS ≥ 4 on lesion (76.5% vs. 64.7%, P = 0.029), while there was no significant difference between DR-CSI and PI-RADS ≥ 4 based on patient (P = 0.508). For clinically significant PCa, DR-CSI had higher accuracy than PI-RADS ≥ 3 based on patients (84.2% vs. 63.2%, P = 0.004) and lesions (62.4% vs. 48.2%, P = 0.036). There was no significant difference between DR-CSI and PI-RADS ≥ 4 (P = 1.000 and 0.845 for the patient and lesion levels, respectively).

CONCLUSIONS

DR-CSI combined with the SVM model may improve the diagnostic accuracy of PCa.

TRIAL REGISTRATION

This study was approved by the Ethics Committee of our institute (Approval No. KY2018-213). Written informed consent was obtained from all participants.

Partial Gland Ablation of Prostate Cancer: Effects of Repeat Treatment

OBJECTIVE

To evaluate the near-term clinical and pathological effects of repeat partial gland ablation (PGA) in men with intermediate-risk prostate cancer (PCa).

MATERIALS AND METHODS

One hundred seventy men with focal lesions of PCa (all GG2 or GG3) underwent PGA with high-intensity focused ultrasound (HIFU) or cryotherapy (CRYO) in prospective trials. Residual PCa in or near the ablation zone was found in 37 men after a first PGA; 30 went on to receive a second PGA and were the subjects of study. At 3 timepoints, baseline and 6 months after first and second ablations, quality-of-life (QOL) questionnaires (IIEF, IPSS) and MRI-guided biopsies (MRGB) were performed. Biopsies were targeted and systematic at baseline and in follow-up, comprehensively about the ablation zone.

RESULTS

All 30 patients completed QOL questionnaires and 26 had MRGB at the 3 timepoints. Mean QOL scores were not significantly different from the baseline after the first or second PGA. No operative complications were encountered; and "decisional regret" was reported in only 2/29 men after the repeat ablation. A decrease in semen volume was reported by 25% of patients. Repeat ablation was successful (absence of csPCa on MRGB) in 14/26 (53%) of men. PSA levels decreased and MRI lesions resolved after ablations, but neither was a reliable predictor of biopsy outcomes.

CONCLUSION

When initial PGA fails, repeat PGA is a reasonable consideration, because in near-term follow-up, secondary procedures appear to be safe, causing only minimal detriment to urinary and sexual function, with csPCa becoming undetectable by MRGB in approximately half the patients.

Recent Advances in Tracking Devices for Biomedical Ultrasound Imaging Applications

With the rapid advancement of tracking technologies, the applications of tracking systems in ultrasound imaging have expanded across a wide range of fields. In this review article, we discuss the basic tracking principles, system components, performance analyses, as well as the main sources of error for popular tracking technologies that are utilized in ultrasound imaging. In light of the growing demand for object tracking, this article explores both the potential and challenges associated with different tracking technologies applied to various ultrasound imaging applications, including freehand 3D ultrasound imaging, ultrasound image fusion, ultrasound-guided intervention and treatment. Recent development in tracking technology has led to increased accuracy and intuitiveness of ultrasound imaging and navigation with less reliance on operator skills, thereby benefiting the medical diagnosis and treatment. Although commercially available tracking systems are capable of achieving sub-millimeter resolution for positional tracking and sub-degree resolution for orientational tracking, such systems are subject to a number of disadvantages, including high costs and time-consuming calibration procedures. While some emerging tracking technologies are still in the research stage, their potentials have been demonstrated in terms of the compactness, light weight, and easy integration with existing standard or portable ultrasound machines.

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.

Training deep neural networks with noisy clinical labels: toward accurate detection of prostate cancer in US data

PURPOSE

Ultrasound is the standard-of-care to guide the systematic biopsy of the prostate. During the biopsy procedure, up to 12 biopsy cores are randomly sampled from six zones within the prostate, where the histopathology of those cores is used to determine the presence and grade of the cancer. Histopathology reports only provide statistical information on the presence of cancer and do not normally contain fine-grain information of cancer distribution within each core. This limitation hinders the development of machine learning models to detect the presence of cancer in ultrasound so that biopsy can be more targeted to highly suspicious prostate regions.

METHODS

In this paper, we tackle this challenge in the form of training with noisy labels derived from histopathology. Noisy labels often result in the model overfitting to the training data, hence limiting its generalizability. To avoid overfitting, we focus on the generalization of the features of the model and present an iterative data label refinement algorithm to amend the labels gradually. We simultaneously train two classifiers, with the same structure, and automatically stop the training when we observe any sign of overfitting. Then, we use a confident learning approach to clean the data labels and continue with the training. This process is iteratively applied to the training data and labels until convergence.

RESULTS

We illustrate the performance of the proposed method by classifying prostate cancer using a dataset of ultrasound images from 353 biopsy cores obtained from 90 patients. We achieve area under the curve, sensitivity, specificity, and accuracy of 0.73, 0.80, 0.63, and 0.69, respectively.

CONCLUSION

Our approach is able to provide clinicians with a visualization of regions that likely contain cancerous tissue to obtain more accurate biopsy samples. The results demonstrate that our proposed method produces superior accuracy compared to the state-of-the-art methods.

Head-to-Head Comparison of 68Ga-PSMA-11 PET/CT and mpMRI with a Histopathology Gold Standard in the Detection, Intraprostatic Localization, and Determination of Local Extension of Primary Prostate Cancer: Results from a Prospective Single-Center Imaging Trial

The role of prostate-specific membrane antigen (PSMA)-targeted PET in comparison to multiparametric MRI (mpMRI) in the evaluation of intraprostatic cancer foci is not well defined. The aim of our study was to compare the diagnostic performance of ⁶⁸Ga-PSMA-11 PET/CT (PSMA PET/CT), mpMRI, and PSMA PET/CT + mpMRI using 3 independent masked readers for each modality and with histopathology as the gold standard in the detection, intraprostatic localization, and determination of local extension of primary prostate cancer. Methods: Patients with intermediate- or high-risk prostate cancer who underwent PSMA PET/CT as part of a prospective trial (NCT03368547) and mpMRI before radical prostatectomy were included. Each imaging modality was interpreted by 3 independent readers who were unaware of the other modality result. A central majority rule was applied (2:1). Pathologic examination of whole-mount slices was used as the gold standard. Imaging scans and whole-mount slices were interpreted using the same standardized approach on a segment level and a lesion level. A "neighboring" approach was used to define imaging-pathology correlation for the detection of individual prostate cancer foci. Accuracy in determining the location, extraprostatic extension (EPE), and seminal vesicle invasion (SVI) of prostate cancer foci was assessed using receiver-operating-characteristic curve analysis. Interreader agreement was calculated using intraclass correlation coefficient analysis. Results: The final analysis included 74 patients (14 [19%] with intermediate risk and 60 [81%] with high risk). The cancer detection rate (lesion-based analysis) was 85%, 83%, and 87% for PSMA PET/CT, mpMRI, and PSMA PET/CT + mpMRI, respectively. The change in AUC was statistically significant between PSMA PET/CT + mpMRI and the 2 imaging modalities alone for delineation of tumor localization (segment-based analysis) (P < 0.001) but not between PSMA PET/CT and mpMRI (P = 0.093). mpMRI outperformed PSMA PET/CT in detecting EPE (P = 0.002) and SVI (P = 0.001). In the segment-level analysis, intraclass correlation coefficient analysis showed moderate reliability among PSMA PET/CT and mpMRI readers using a 5-point Likert scale (range, 0.53-0.64). In the evaluation of T staging, poor reliability was found among PSMA PET/CT readers and poor to moderate reliability was found for mpMRI readers. Conclusion: PSMA PET/CT and mpMRI have similar accuracy in the detection and intraprostatic localization of prostate cancer foci. mpMRI performs better in identifying EPE and SVI. For the T-staging evaluation of intermediate to high-risk prostate cancer, mpMRI should still be considered the imaging modality of reference. Whenever available, PSMA PET/MRI or the coregistration or fusion of PSMA PET/CT and mpMRI (PSMA PET/CT + mpMRI) should be used as it improves tumor extent delineation.

Magnetic Resonance Imaging-Guided Biopsy in Active Surveillance of Prostate Cancer

PURPOSE

The underlying premise of prostate cancer active surveillance (AS) is that cancers likely to metastasize will be recognized and eliminated before cancer-related disease can ensue. Our study was designed to determine the prostate cancer upgrading rate when biopsy guided by magnetic resonance imaging (MRGBx) is used before entry and during AS.

MATERIALS AND METHODS

The cohort included 519 men with low- or intermediate-risk prostate cancer who enrolled in prospective studies (NCT00949819 and NCT00102544) between February 2008 and February 2020. Subjects were preliminarily diagnosed with Gleason Grade Group (GG) 1 cancer; AS began when subsequent MRGBx confirmed GG1 or GG2. Participants underwent confirmatory MRGBx (targeted and systematic) followed by surveillance MRGBx approximately every 12 to 24 months. The primary outcome was tumor upgrading to ≥GG3.

RESULTS

Upgrading to ≥GG3 was found in 92 men after a median followup of 4.8 years (IQR 3.1-6.5) after confirmatory MRGBx. Upgrade-free probability after 5 years was 0.85 (95% CI 0.81-0.88). Cancer detected in a magnetic resonance imaging lesion at confirmatory MRGBx increased risk of subsequent upgrading during AS (HR 2.8; 95% CI 1.3-6.0), as did presence of GG2 (HR 2.9; 95% CI 1.1-8.2) In men who upgraded ≥GG3 during AS, upgrading was detected by targeted cores only in 27%, systematic cores only in 25% and both in 47%. In 63 men undergoing prostatectomy, upgrading from MRGBx was found in only 5 (8%).

CONCLUSIONS

When AS begins and follows with MRGBx (targeted and systematic), upgrading rate (≥GG3) is greater when tumor is initially present within a magnetic resonance imaging lesion or when pathology is GG2 than when these features are absent.

Bi-parametric MRI/TRUS fusion targeted repeat biopsy after systematic 10-12 core TRUS-guided biopsy reveals more significant prostate cancer especially in anteriorly located tumors

Background

MRI and fusion guided biopsy have an increased role in the diagnosis of prostate cancer.

Purpose

To demonstrate the possible advantages with Bi-parametric MRI fusion-guided repeat biopsy over systematic 10–12-core biopsy for the diagnosis of prostate cancer.

Material and Methods

Four hundred and twenty-three consecutive men, with previous systematic 10–12-core TRUS-guided biopsy, and with suspicion of, or diagnosis of, low-risk prostate cancer underwent fusion-guided prostate biopsy between February 2015 and February 2017. The material was retrospectively assessed. In 220 cases no previous cancer was diagnosed, and in 203 cases confirmatory fusion guided biopsy was performed prior to active monitoring. MRI was classified according to PI-RADS. Systematic biopsy was compared to fusion guided biopsy for the detection of cancer, and PI-RADS was compared to the Gleason score.

Results

Fusion guided biopsy detected significantly more cancers than systematic (p < .001). Gleason scores were higher in the fusion biopsy group (p < .001). Anterior tumors were present in 54% of patients. Fusion biopsy from these lesions showed cancer in 53% with previously negative biopsy in systematic biopsies and 66% of them were upgraded from low risk to intermediate or high-risk cancers.

Conclusion

These results show superior detection rate and grading of bi-parametric MRI/TRUS fusion targeted repeat biopsy over systematic 10–12 core biopsies. Fusion guided biopsy detects more significant cancers despite using fewer cores. The risk group was changed for many patients initially selected for active surveillance due to upgrading of tumors. Bi-parametric MRI shows promising results in detecting anterior tumors in patients with suspected prostate cancer.

Towards targeted ultrasound-guided prostate biopsy by incorporating model and label uncertainty in cancer detection

PURPOSE

Systematic prostate biopsy is widely used for cancer diagnosis. The procedure is blind to underlying prostate tissue micro-structure; hence, it can lead to a high rate of false negatives. Development of a machine-learning model that can reliably identify suspicious cancer regions is highly desirable. However, the models proposed to-date do not consider the uncertainty present in their output or the data to benefit clinical decision making for targeting biopsy.

METHODS

We propose a deep network for improved detection of prostate cancer in systematic biopsy considering both the label and model uncertainty. The architecture of our model is based on U-Net, trained with temporal enhanced ultrasound (TeUS) data. We estimate cancer detection uncertainty using test-time augmentation and test-time dropout. We then use uncertainty metrics to report the cancer probability for regions with high confidence to help the clinical decision making during the biopsy procedure.

RESULTS

Experiments for prostate cancer classification includes data from 183 prostate biopsy cores of 41 patients. We achieve an area under the curve, sensitivity, specificity and balanced accuracy of 0.79, 0.78, 0.71 and 0.75, respectively.

CONCLUSION

Our key contribution is to automatically estimate model and label uncertainty towards enabling targeted ultrasound-guided prostate biopsy. We anticipate that such information about uncertainty can decrease the number of unnecessary biopsy with a higher rate of cancer yield.

A System for Co-Registration of High-Resolution Ultrasound, Magnetic Resonance Imaging, and Whole-Mount Pathology for Prostate Cancer

In order to evaluate the diagnostic accuracy of high-resolution ultrasound (HRUS) for detection of prostate cancer, it must be validated against whole-mount pathology. An ex-vivo HRUS scanning system was developed and tested in phantom and human tissue experiments to allow for in-plane computational co-registration of HRUS with magnetic resonance imaging (MRI) and whole-mount pathology. The system allowed for co-registration with an error of 1.9mm±1.4mm, while also demonstrating an ability to allow for lesion identification.Clinical Relevance- Using this system, a workflow can be established to co-register HRUS with MRI and pathology to allow for the diagnostic accuracy of HRUS to be determined with direct comparison to MRI.

In vivo assessment of prostate cancer response using quantitative ultrasound characterization of ultrasonic scattering properties

Background

The study here investigated quantitative ultrasound (QUS) parameters to assess tumour response to ultrasound-stimulated microbubbles (USMB) and hyperthermia (HT) treatment in vivo. Mice bearing prostate cancer xenografts were exposed to various treatment conditions including 1% (v/v) Definity microbubbles stimulated at ultrasound pressures 246 kPa and 570 kPa and HT duration of 0, 10, 40, and 50 min. Ultrasound radiofrequency (RF) data were collected using an ultrasound transducer with a central frequency of 25 MHz. QUS parameters based on form factor models were used as potential biomarkers of cell death in prostate cancer xenografts.

Results

The average acoustic concentration (AAC) parameter from spherical gaussian and the fluid-filled spherical models were the most efficient imaging biomarker of cell death. Statistical significant increases of AAC were found in the combined treatment groups: 246 kPa + 40 min, 246 kPa + 50 min, and 570 kPa + 50 min, in comparison with control tumours (0 kPa + 0 min). Changes in AAC correlates strongly (r² = 0.62) with cell death fraction quantified from the histopathological analysis.

Conclusion

Scattering property estimates from spherical gaussian and fluid-filled spherical models are useful imaging biomarkers for assessing tumour response to treatment. Our observation of changes in AAC from high ultrasound frequencies was consistent with previous findings where parameters related to the backscatter intensity (AAC) increased with cell death.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08706-7.

MRI-Targeted Prostate Biopsy Techniques: AJR Expert Panel Narrative Review

Prostate cancer is the second most common malignancy in men worldwide. Systematic transrectal prostate biopsy is commonly used to obtain tissue to establish the diagnosis. However, in recent years, MRI-targeted biopsy (based on an MRI examination performed prior to consideration of biopsy) has been shown to detect more clinically significant cancer and less clinically insignificant cancer compared to systematic biopsy. This approach of performing MRI prior to biopsy has become, or is becoming, a standard of practice in centers throughout the world. This growing use of an MRI-directed pathway is leading to performance of a larger volume of MRI-targeted prostate biopsies. The three common MRI-targeted biopsy techniques are cognitive biopsy, MRI-ultrasound software fusion biopsy, and MRI in-bore guided biopsy. These techniques for using MRI information at the time of biopsy can be performed via a transrectal or transperineal approach. This narrative review presents the three MRI-targeted biopsy techniques along with their advantages and shortcomings. Comparisons among the techniques are summarized based on the available evidence. Studies to date have provided heterogeneous results, and the preferred technique remains debated.

Magnetic resonance imaging-guided prostate biopsy-A review of literature

Objective

Multiparametric magnetic resonance imaging (MP-MRI) helps to identify lesion of prostate with reasonable accuracy. We aim to describe the various uses of MP-MRI for prostate biopsy comparing different techniques of MP-MRI guided biopsy.

Materials and methods

A literature search was performed for "multiparametric MRI", "MRI fusion biopsy", "MRI guided biopsy", "prostate biopsy", "MRI cognitive biopsy", "MRI fusion biopsy systems", "prostate biopsy" and "cost analysis". The search operation was performed using the operator "OR" and "AND" with the above key words. All relevant systematic reviews, original articles, case series, and case reports were selected for this review.

Results

The sensitivity of MRI targeted biopsy (MRI-TB) is between 91%-93%, and the specificity is between 36%-41% in various studies. It also has a high negative predictive value (NPV) of 89%-92% and a positive predictive value (PPV) of 51%-52%. The yield of MRI fusion biopsy (MRI-FB) is similar, if not superior to MR cognitive biopsy. In-bore MRI-TB had better detection rates compared to MR cognitive biopsy, but were similar to MR fusion biopsy.

Conclusions

The use of MRI guidance in prostate biopsy is inevitable, subject to availability, cost, and experience. Any one of the three modalities (i.e. MRI cognitive, MRI fusion and MRI in-bore approach) can be used. MRI-FB has a fine balance with regards to accuracy, practicality and affordability.

Real-time interleaved spectroscopic photoacoustic and ultrasound (PAUS) scanning with simultaneous fluence compensation and motion correction

For over two decades photoacoustic imaging has been tested clinically, but successful human trials have been limited. To enable quantitative clinical spectroscopy, the fundamental issues of wavelength-dependent fluence variations and inter-wavelength motion must be overcome. Here we propose a real-time, spectroscopic photoacoustic/ultrasound (PAUS) imaging approach using a compact, 1-kHz rate wavelength-tunable laser. Instead of illuminating tissue over a large area, the fiber-optic delivery system surrounding an US array sequentially scans a narrow laser beam, with partial PA image reconstruction for each laser pulse. The final image is then formed by coherently summing partial images. This scheme enables (i) automatic compensation for wavelength-dependent fluence variations in spectroscopic PA imaging and (ii) motion correction of spectroscopic PA frames using US speckle tracking in real-time systems. The 50-Hz video rate PAUS system is demonstrated in vivo using a murine model of labelled drug delivery.

Tips to start an MR-US fusion biopsy program

There is growing evidence that MRI-ultrasound (MR-US)-targeted biopsy (TB) has high detection rates of clinically significant prostate cancer (PCa) compared to standard transrectal ultrasound (TRUS)-guided biopsy. A radiologist plays a significant role in MR-US fusion biopsy planning. Here, we discuss six simple steps that can help set up a successful MR-US fusion biopsy program in collaboration with the urologist.

PI-RADS: what is new and how to use it

The prostate imaging reporting and data system (PI-RADS) has revolutionized the use of magnetic resonance imaging (MRI) for the management of prostate cancer (PCa). The most recent version 2.1, PI-RADS v2.1, provides specific refinements in the performance, relaxing some recommendations which were not found to be helpful, while reinforcing and clarifying others. The interpretation of T2-weighted imaging (T2WI) in the transition zone (TZ), and the overall assessment of TZ nodules, now allows for a clearer distinction between those which are clearly benign and those which might warrant tissue sampling. Additional changes also resolve discrepancies in T2WI and diffusion-weighted imaging (DWI) of the peripheral zone (PZ). PI-RADS v2.1 is a simpler, more straightforward, and more reproducible method to better communicate between physicians regarding findings on prostate MRI.

Determination of Gleason score discrepancy for risk stratification in magnetic resonance-ultrasound fusion prostate biopsy

BACKGROUND

Magnetic resonance imaging (MRI)-ultrasound (US) fusion biopsy remains challenging and highlights the need towards standardization.

PURPOSE

To characterize the clinical and MRI features of clinically significant prostate cancer (csPCa) with discrepant Gleason score (GS) in MRI-US fusion biopsy.

MATERIAL AND METHODS

A total of 400 consecutive patients with suspected cancer lesions who underwent MRI-US fusion biopsy and subsequent prostatectomy were included. In the comparison of biopsy GS with pathology GS, matched lesions were defined as a GS, and discrepant lesions were defined as an upgrade of the GS. Descriptive statistics were used to define clinical characteristics, including age, prostate-specific antigen (PSA), PSA density, and maximal cancer core length (MCCL). Differences between lesions with matched and discrepant GS were determined considering the location and PI-RADS v2 score. A paired comparison of the volumes between the two groups was performed.

RESULTS

There were 130 lesions with discrepant GS in 124 patients. There was no significant difference in the age, PSA, and PSA density between the two groups, except for the MCCL (P = 0.028). The lesions were distributed in the peripheral (n = 88) and transition (n = 42) zones; 33, 50, and 47 lesions were at the apex, mid-gland, and base levels, respectively. PI-RADS scores were as follows: 2 (n = 5), 3 (n = 8), 4 (n = 68), and 5 (n = 39). In comparison with matched lesions, discrepant lesions had significantly smaller multiparametric MRI-measured cancer volumes (P < 0.05).

CONCLUSION

Knowledge of discrepant GS in MRI-US fusion biopsy is important, and a careful approach is needed to reduce this discrepancy.

Comparison of Targeted vs Systematic Prostate Biopsy in Men Who Are Biopsy Naive: The Prospective Assessment of Image Registration in the Diagnosis of Prostate Cancer (PAIREDCAP) Study

Importance

Magnetic resonance imaging (MRI) guidance improves the accuracy of prostate biopsy for the detection of clinically significant prostate cancer, but the optimal use of such guidance is not yet clear.

Objective

To determine the cancer detection rate (CDR) of targeting MRI-visible lesions vs systematic prostate sampling in the diagnosis of clinically significant prostate cancer in men who were biopsy naive.

Design, Setting, and Participants

This paired cohort trial, known as the Prospective Assessment of Image Registration in the Diagnosis of Prostate Cancer (PAIREDCAP) study, was conducted in an academic medical center from January 2015 to April 2018. Men undergoing first-time prostate biopsy were enrolled. Paired-cohort participants were a consecutive series of men with MRI-visible lesions (defined by a Prostate Imaging Reporting & Data System version 2 score  ≥ 3), who each underwent 3 biopsy methods at the same sitting: first, a systematic biopsy; second, an MRI-lesion biopsy targeted by cognitive fusion; and third, an MRI-lesion targeted by software fusion. Another consecutive series of men without MRI-visible lesions underwent systematic biopsies to help determine the false-negative rate of MRI during the trial period.

Main Outcomes and Measures

The primary end point was the detection rate of clinically significant prostate cancer (Gleason grade group ≥2) overall and by each biopsy method separately. The secondary end points were the effects of the Prostate Imaging Reporting & Data System version 2 grade, prostate-specific antigen density, and prostate volume on the primary end point. Tertiary end points were the false-negative rate of MRI and concordance of biopsy-method results by location of detected cancers within the prostate.

Results

A total of 300 men participated; 248 had MRI-visible lesions (mean [SD] age, 65.5 [7.7] years; 197 were white [79.4%]), and 52 were control participants (mean [SD] age, 63.6 [5.9] years; 39 were white [75%]). The overall CDR was 70% in the paired cohort group, achieved by combining systematic and targeted biopsy results. The CDR by systematic sampling was 15% in the group without MRI-visible lesions. In the paired-cohort group, CDRs varied from 47% (116 of 248 men) when using cognitive fusion biopsy alone, to approximately 60% when using systematic biopsy (149 of 248 men) or either fusion method alone (154 of 248 men), to 70% (174 of 248 men) when combining systematic and targeted biopsy. Discordance of tumor locations suggests that the different biopsy methods detect different tumors. Thus, combining targeting and systematic sampling provide greatest sensitivity for detection of clinically significant prostate cancer. For all biopsy methods, the Prostate Imaging Reporting & Data System version 2 grade and prostate-specific antigen density were directly associated with CDRs, and prostate volume was inversely associated.

Conclusions and Relevance

An MRI-visible lesion in men undergoing first-time prostate biopsy identifies those with a heightened risk of clinically significant prostate cancer. Combining targeted and systematic biopsy offers the best chances of detecting the cancer.

3-T Multiparametric MRI Followed by In-Bore MR-Guided Biopsy for Detecting Clinically Significant Prostate Cancer After Prior Negative Transrectal Ultrasound-Guided Biopsy

OBJECTIVE. The purpose of this study was to evaluate the rate of detection of clinically significant prostate cancer (csPCa), as assessed on the basis of Prostate Imaging Reporting and Data System version 2.1 (PI-RADSv2.1) guidelines, using 3-T in-bore MR-guided biopsy (MRGB) for a cohort of patients suspected of having csPCa despite having a history of recent negative transrectal ultrasound-guided biopsy results. MATERIALS AND METHODS. The cohort in this retrospective, single-center study was derived from a database of 330 patients who underwent multiparametric MRI (mpMRI) followed by in-bore transrectal 3-T MRGB. Seventy-nine patients (mean [± SD] age, 64.1 ± 8.6 years) with prior negative transrectal ultrasound-guided biopsy results and positive pre-MRGB mpMRI results (PI-RADS score ≥ 3) composed the final cohort. The rate of detection of PCa and csPCa (the latter of which was defined by a Gleason score of 3 + 4 or higher) was stratified according to updated PI-RADSv2.1 assessment. RESULTS. MRGB detected PCa in 36 patients (45.6%), 30 (83.3%) of whom had csPCa. The PI-RADSv2.1 score was a strong predictor (odds ratio, 3.97; 95% CI, 1.93-7.47) of csPCa detection. We found two benign transition zone target lesions that were downgraded from PI-RADSv2 category 3 to PI-RADSv2.1 category 2. PCa was detected in 18.4% (7/38), 65.2% (15/23), and 87.5% (14/16) of individuals with PI-RADSv2.1 category 3, 4, and 5 lesions, respectively, with 85.7% (6/7), 86.7% (13/15), and 78.6% (11/14) of these cases found to be csPCa, respectively. Of the seven PI-RADSv2.1 category 3 csPCa lesions, six had prostate-specific antigen density greater than 0.10 ng/mL/cc. CONCLUSION. With the use of 3-T in-bore MRGB, csPCa was detected in 38% of individuals with prior negative transrectal ultrasound-guided biopsy results. PI-RADSv2.1 was a strong predictor of csPCa detection. On the basis of our results, patients with PI-RADSv2.1 category 4 or 5 lesions and patients with PI-RADSv2.1 category 3 lesions and a prostate-specific antigen density greater than or equal to 0.10 ng/mL/cc may benefit from in-bore MRGB.

Prostate MRI-TRUS fusion biopsy: a review of the state of the art procedure

Prostate cancer is the fourth most common cancer and population-based screening programmes are being increasingly adopted worldwide. Screening-positive patients undergo routine transrectal ultrasound (TRUS)-guided systematic biopsy, which is the current diagnostic standard for prostate cancer. However, systematic biopsies suffer from poor sensitivity, especially for the tumors of the anterior prostate and apex as well as in large volume glands. In the past decade, MRI-guided targeted biopsies have come up, which utilize the multiparametric capability of MRI to target lesions for sampling. MRI/TRUS fusion biopsies combine the advantages of MRI-targeting with that of real-time guidance made possible by TRUS. MRI-TRUS fusion biopsies are being increasingly used in men with high clinical suspicion of prostate cancer who have had prior negative systematic biopsies. A large number of fusion biopsy platforms are currently available commercially. Although the basic workflow is similar, there are differences in the operational software, biopsy routes offered, TRUS acquisition technique, type of correction applied at the time of fusion and in the probe tracking hardware. The article describes the current role and indications of MRI-TRUS fusion biopsy followed by a discussion on the workflow, patient preparation, biopsy procedure and complications.

Multiple instance learning combined with label invariant synthetic data for guiding systematic prostate biopsy: a feasibility study

PURPOSE

Ultrasound imaging is routinely used in prostate biopsy, which involves obtaining prostate tissue samples using a systematic, yet, non-targeted approach. This approach is blinded to individual patient intraprostatic pathology, and unfortunately, has a high rate of false negatives.

METHODS

In this paper, we propose a deep network for improved detection of prostate cancer in systematic biopsy. We address several challenges associated with training such network: (1) Statistical labels: Since biopsy core's pathology report only represents a statistical distribution of cancer within the core, we use multiple instance learning (MIL) networks to enable learning from ultrasound image regions associated with those data; (2) Limited labels: The number of biopsy cores are limited to at most 12 per patient. As a result, the number of samples available for training a deep network is limited. We alleviate this issue by effectively combining Independent Conditional Variational Auto Encoders (ICVAE) with MIL. We train ICVAE to learn label-invariant features of RF data, which is subsequently used to generate synthetic data for improved training of the MIL network.

RESULTS

Our in vivo study includes data from 339 prostate biopsy cores of 70 patients. We achieve an area under the curve, sensitivity, specificity, and balanced accuracy of 0.68, 0.77, 0.55 and 0.66, respectively.

CONCLUSION

The proposed approach is generic and can be applied to several other scenarios where unlabeled data and noisy labels in training samples are present.

Pre-clinical evaluation of an image-guided in-situ Raman spectroscopy navigation system for targeted prostate cancer interventions

PURPOSE

Transrectal ultrasound (TRUS) image guidance is the standard of care for diagnostic and therapeutic interventions in prostate cancer (PCa) patients, but can lead to high false-negative rates, compromising downstream effectiveness of therapeutic choices. A promising approach to improve in-situ detection of PCa lies in using the optical properties of the tissue to discern cancer from healthy tissue. In this work, we present the first in-situ image-guided navigation system for a spatially tracked Raman spectroscopy probe integrated in a PCa workflow, capturing the optical tissue fingerprint. The probe is guided with fused TRUS/MR imaging and tested with both tissue-simulating phantoms and ex-vivo prostates. The workflow was designed to be integrated the clinical workflow for trans-perineal prostate biopsies, as well as for high-dose rate (HDR) brachytherapy.

METHODS

The proposed system developed in 3D Slicer includes an electromagnetically tracked Raman spectroscopy probe, along with tracked TRUS imaging automatically registered to diagnostic MRI. The proposed system is tested on both custom gelatin tissue-simulating optical phantoms and biological tissue phantoms. A random-forest classifier was then trained on optical spectrums from ex-vivo prostates following prostatectomy using our optical probe. Preliminary in-human results are presented with the Raman spectroscopy instrument to detect malignant tissue in-situ with histopathology confirmation.

RESULTS

In 5 synthetic gelatin and biological tissue phantoms, we demonstrate the ability of the image-guided Raman system by detecting over 95% of lesions, based on biopsy samples. The included lesion volumes ranged from 0.1 to 0.61 cc. We showed the compatibility of our workflow with the current HDR brachytherapy setup. In ex-vivo prostates of PCa patients, the system showed a 81% detection accuracy in high grade lesions.

CONCLUSION

Pre-clinical experiments demonstrated promising results for in-situ confirmation of lesion locations in prostates using Raman spectroscopy, both in phantoms and human ex-vivo prostate tissue, which is required for integration in HDR brachytherapy procedures.

Using spatial tracking with magnetic resonance imaging/ultrasound-guided biopsy to identify unilateral prostate cancer

OBJECTIVES

To create reliable predictive metrics of unilateral disease using spatial tracking from a fusion device, thereby improving patient selection for hemi-gland ablation of prostate cancer.

PATIENTS AND METHODS

We identified patients who received magnetic resonance imaging (MRI)/ultrasound-guided biopsy and radical prostatectomy at a single institution between 2011 and 2018. In addition to standard clinical features, we extracted quantitative features related to biopsy core and MRI target locations predictive of tumour unilaterality. Classification and Regression Tree (CART) analysis was used to create a decision tree (DT) for identifying cancer laterality. We evaluated concordance of model-determined laterality with final surgical pathology.

RESULTS

A total of 173 patients were identified with biopsy coordinates and surgical pathology available. Based on CART analysis, in addition to biopsy- and MRI-confirmed disease unilaterality, patients should be further screened for cancer detected within 7 mm of midline in a 40 mL prostate, which equates to the central third of any-sized prostate by radius. The area under the curve for this DT was 0.82. Standard diagnostics and the DT correctly identified disease laterality in 73% and 80% of patients, respectively (P = 0.13). Of the patients identified as unilateral by standard diagnostics, 47% had undetected contralateral disease or were otherwise incorrectly identified. This error rate was reduced to 17% (P = 0.01) with the DT.

CONCLUSION

Using spatial tracking from fusion devices, a DT was more reliable for identifying laterality of prostate cancer compared to standard diagnostics. Patients with cancer detected within the central third of the prostate by radius are poor hemi-gland ablation candidates due to the risk of midline extension of tumour.

IDEAL Stage 2a experience with in-office, transperineal MRI/ultrasound software fusion targeted prostate biopsy

Objective

Although the feasibility of transperineal biopsy under local anesthesia has been demonstrated, little is known regarding the application of MRI/ultrasound software fusion targeted biopsy for transperineal biopsy under local anesthesia. The objective of our study is to describe our initial experience with in-office transperineal MRI/ultrasound software fusion targeted biopsy (Idea, Development, Exploration, Assessment, Long-term Follow-up [IDEAL] Stage 2a).

Methods

Between October 2017 and July 2019, 33 men underwent in-office transperineal MRI-targeted biopsy using the Artemis (Eigen, Grass Valley, CA, USA) fixed-robotic arm system. The indication for biopsy was elevated prostate specific antigen (PSA) (n=14), prior negative biopsy (n=10), active surveillance (n=6), and surveillance after partial gland cryoablation (n=3). We prospectively captured patient demographic and clinical characteristics, biopsy outcomes, and complications. Complications were classified according to Common Terminology Criteria for Adverse Events (CTCAE) V.5.0.

Results

The median patient age was 67 years (IQR 61–71) and the median serum PSA level was 7.0 ng/mL (IQR 5.1–11.4). The median duration of in-office MRI-targeted transperineal biopsy was 26 min (IQR 23–28). Overall, transperineal MRI-targeted biopsy detected prostate cancer in 18 (54.6%) men, with 8 (24.2%) being clinically significant (Gleason Score ≥3+4, Grade Group ≥2). Clinically significant prostate cancer was detected in four (28.6%) biopsy naïve men, two (20.0%) men with a prior negative, one (16.7%) man on active surveillance and one (33.3%) man following partial gland ablation. Three (9.1%) men experienced complications: two hematuria and one urinary retention.

Conclusion

Our findings demonstrate the feasibility of the fixed-robotic arm fusion platform for in-office transperineal MRI-targeted biopsy and a low rate of adverse events. However, larger prostate size precludes MRI/ultrasound software fusion and pubic arch interference hindered the transperineal MRI-targeted approach in 9.1% of men. Pubic arch interference was overcome by a free-hand approach with software fusion guidance.

Magnetic Resonance Imaging-Guided Confirmatory Biopsy for Initiating Active Surveillance of Prostate Cancer

IMPORTANCE

Transrectal, ultrasonography-guided prostate biopsy often fails to disclose the severity of underlying pathologic findings for prostate cancer. Magnetic resonance imaging (MRI)-guided biopsy may improve the characterization of prostate pathologic results, but few studies have examined its use for the decision to enter active surveillance.

OBJECTIVE

To evaluate whether confirmatory biopsy findings by MRI guidance are associated with the risk of pathologic disease upgrading among patients with prostate cancer during active surveillance.

DESIGN, SETTINGS, AND PARTICIPANTS

This retrospective cohort study used prospectively obtained registry data from 332 men with prostate cancer of Gleason grade group (GG) 2 or lower who were referred for active surveillance at a large academic medical center from January 1, 2009, through December 31, 2017.

EXPOSURES

All confirmatory and follow-up biopsies were performed using MRI guidance with an MRI-ultrasonography fusion device. Patients underwent repeated MRI-guided biopsies every 12 to 24 months. At follow-up sessions, in addition to obtaining systematic samples, lesions seen on MRI were targeted and foci of low-grade prostate cancer were obtained again using tracking technology. Active surveillance was terminated with detection of at least GG3 disease or receipt of treatment.

MAIN OUTCOMES AND MEASURES

The primary outcome was upgrading to at least GG3 disease during active surveillance. Secondary outcomes were the associations of MRI lesion grade, prostate-specific antigen (PSA) level, PSA density, and biopsy method (targeted, systematic, or tracked) with the primary outcome.

RESULTS

Of 332 patients (mean [SD] age, 62.8 [7.6] years), 39 (11.7%) upgraded to at least GG3 disease during follow-up. The incidence of upgrading was 7.9% (9 of 114) when the confirmatory biopsy finding was normal, 11.4% (20 of 175) when the finding showed GG1 disease, and 23.3% (10 of 43) when the finding was GG2 disease (P = .03). Men with GG2 disease were almost 8 times more likely to upgrade during surveillance compared with those with normal findings but only among those with low PSA density (hazard ratio [HR], 7.82; 95% CI, 2.29-26.68). A PSA density of at least 0.15 ng/mL/mL was associated with increased risk of upgrading among patients with normal findings (HR, 7.21; 95% CI, 1.98-26.24) or GG1 disease (HR, 2.86; 95% CI, 1.16 to 7.03) on confirmatory biopsy. A total of 46% of pathologic disease upgrades would have been missed if only the targeted biopsy was performed and 65% of disease upgrades were detected only with tracked biopsy.

CONCLUSIONS AND RELEVANCE

The findings suggest that confirmatory biopsy with MRI guidance is significantly associated with future disease upgrading of prostate cancer, especially when combined with PSA density, and should be considered as an appropriate entry point for active surveillance. Systematic and targeted biopsies were additive in detection of clinically significant cancers. Repeated biopsy at sites at which findings were previously abnormal (tracking biopsy) facilitated detection of cancers not suitable for continued active surveillance.

A comparison of magnetic resonance imaging techniques used to secure biopsies in prostate cancer patients

Introduction: Prostate cancer (PCa) is the most common diagnosed malignancy among the male population in the United States. The incidence is increasing with an estimated amount of 175.000 cases in 2019. Areas covered: Primarily, PCa is generally detected by an elevated or rising serum prostate-specific antigen (PSA) and digital rectal examination (DRE) followed by pathological examination. Histopathology ultimately confirms the presence of PCa and determines a Gleason score. However, PSA and DRE have low specificity and sensitivity, respectively. Subsequently, accurate assessment of the aggressiveness of PCa is essential to prevent overdiagnosis and thus overtreatment of low-risk or indolent cancers. By visualizing PCa suspicious lesions and sampling them during the targeted biopsy, it is likely that the diagnostic accuracy of significant PCa improves. This article reviews the current imaging techniques used to secure biopsies in patients with a suspicion of PCa. The advantages and limitations of each technique are described. Expert opinion: Multiparametric magnetic resonance imaging (mpMRI) and subsequent-targeted biopsy have improved the diagnostic accuracy of PCa detection in men with an elevated or rising serum PSA. Prostate lesions visible on mpMRI are easily targeted during either in-bore MRI-guided biopsy, cognitive fusion biopsy or MRI-TRUS fusion biopsy.

Deformable registration of PET/CT and ultrasound for disease-targeted focal prostate brachytherapy

We propose a deformable registration algorithm for prostate-specific membrane antigen (PSMA) PET/CT and transrectal ultrasound (TRUS) fusion. Accurate registration of PSMA PET to intraoperative TRUS will allow physicians to customize dose planning based on the regions involved. The inputs to the registration algorithm are the PET/CT and TRUS volumes as well as the prostate segmentations. PET/CT and TRUS volumes are first rigidly registered by maximizing the overlap between the segmented prostate binary masks. Three-dimensional anatomical landmarks are then automatically extracted from the boundary as well as within the prostate. Then, a deformable registration is performed using a regularized thin plate spline where the landmark localization error is optimized between the extracted landmarks that are in correspondence. The proposed algorithm was evaluated on 25 prostate cancer patients treated with low-dose-rate brachytherapy. We registered the postimplant CT to TRUS using the proposed algorithm and computed target registration errors (TREs) by comparing implanted seed locations. Our approach outperforms state-of-the-art methods, with significantly lower ( mean ± standard deviation ) TRE of 1.96 ± 1.29    mm while being computationally efficient (mean computation time of 38 s). The proposed landmark-based PET/CT-TRUS deformable registration algorithm is simple, computationally efficient, and capable of producing quality registration of the prostate boundary as well as the internal gland.

Magnetic resonance imaging-guided targeted biopsy in risk classification among patients on active surveillance: A diagnostic meta-analysis

BACKGROUND

The aim of this study was to assess the sensitivity and accuracy of magnetic resonance imaging-guided targeted biopsy (MRI-TB) in patients undergoing active surveillance (AS) procedure.

METHODS

We searched databases to identify relevant studies which compared MRI-TB with systemic biopsy for diagnosing prostate cancer in patients on AS. Outcomes included sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), area under the curve (AUC) and publication bias of AS group, confirmatory biopsy group and follow-up biopsy group.

RESULTS

Fourteen articles involving 1693 patients were included. In AS group, the sensitivity was 0.62 (95% confidence interval [CI], 0.57-0.68), specificity was 0.89 (95% CI, 0.87-0.90), NLR was 0.43 (0.31-0.60), PLR was 4.90 (3.50-6.86), DOR was 12.75 (7.22-22.51), and AUC was 0.8645. In confirmatory biopsy group, the sensitivity was 0.67 (0.59-0.74), specificity was 0.89 (0.86-0.91), NLR was 0.42 (0.27-0.65), PLR was 4.94 (3.88-6.30), DOR was 14.54 (9.60-22.02), and AUC was 0.8812. In follow-up biopsy group, the sensitivity was 0.35 (0.22-0.51), specificity was 0.88 (0.82-0.92), NLR was 0.76 (0.52-1.11), PLR was 3.06 (1.71-5.50), DOR was 4.41 (2.15-9.03), and AUC was 0.8367.

CONCLUSION

MRI-TB has a moderate-to-high diagnostic accuracy for diagnosing and reclassifying patients on AS with high specificity and AUC value under the SROC curve.

Targeted Prostate Biopsy Gleason Score Heterogeneity and Implications for Risk Stratification

OBJECTIVES

To quantify Gleason score (GS) heterogeneity within multiparametric magnetic resonance imaging (MRI)-targeted prostate biopsies and to determine impact on National Comprehensive Cancer Network (NCCN) risk stratification.

METHODS

An Institutional Review Board-approved retrospective study was performed on men who underwent Artemis (MRI-transrectal-ultrasound fusion) targeted biopsy (TB) for suspected prostate cancer between 2012 and 2015. Intratarget heterogeneity was defined as a difference in GS between 2 cores within a single target in patients with ≥2 positive cores. Prostate specific antigen, maximum tumor diameter, apparent diffusion coefficient, MRI suspicion score, prostate volume, systematic biopsy (SB) GS, and T-stage were analyzed for correlation with heterogeneity. Changes in NCCN risk based on high versus low GS on TB, SB alone, and SB+TB were compared.

RESULTS

Fifty-three patients underwent TB of 73 suspected lesions. Seventy percent (51/73) had ≥2 positive cores, thus meeting inclusion criteria for heterogeneity analysis. Fifty-five percent (28/51) of qualifying targets showed GS heterogeneity. None of the evaluated factors showed a significant relationship with heterogeneity. NCCN low-risk, intermediate-risk, and high-risk groups were 30%, 49%, and 21%, respectively, with SB alone. Adding low GS TB to SB resulted in 17%, 55%, 28% in each risk group, while using high GS+SB resulted in 4%, 54%, and 42%. Overall, the addition of TB resulted in higher NCCN risk groups in 38% of cases.

CONCLUSIONS

Over half of multiparametric MRI-defined targets demonstrated GS heterogeneity. The addition of high GS from TB leads to risk inflation compared with using SB alone. Further research is needed on how to integrate these findings into current risk stratification models and clinical practice.

Deep neural maps for unsupervised visualization of high-grade cancer in prostate biopsies

Prostate cancer (PCa) is the most frequent noncutaneous cancer in men. Early detection of PCa is essential for clinical decision making, and reducing metastasis and mortality rates. The current approach for PCa diagnosis is histopathologic analysis of core biopsies taken under transrectal ultrasound guidance (TRUS-guided). Both TRUS-guided systematic biopsy and MR-TRUS-guided fusion biopsy have limitations in accurately identifying PCa, intraoperatively. There is a need to augment this process by visualizing highly probable areas of PCa. Temporal enhanced ultrasound (TeUS) has emerged as a promising modality for PCa detection. Prior work focused on supervised classification of PCa verified by gold standard pathology. Pathology labels are noisy, and data from an entire core have a single label even when significantly heterogeneous. Additionally, supervised methods are limited by data from cores with known pathology, and a significant portion of prostate data is discarded without being used. We provide an end-to-end unsupervised solution to map PCa distribution from TeUS data using an innovative representation learning method, deep neural maps. TeUS data are transformed to a topologically arranged hyper-lattice, where similar samples are closer together in the lattice. Therefore, similar regions of malignant and benign tissue in the prostate are clustered together. Our proposed method increases the number of training samples by several orders of magnitude. Data from biopsy cores with known labels are used to associate the clusters with PCa. Cancer probability maps generated using the unsupervised clustering of TeUS data help intuitively visualize the distribution of abnormal tissue for augmenting TRUS-guided biopsies.

Characteristics of missed prostate cancer lesions on 3T multiparametric-MRI in 518 patients: based on PI-RADSv2 and using whole-mount histopathology reference

PURPOSE

To determine the characteristics of missed prostate cancer (PCa) lesions on 3T multiparametric-MRI (mpMRI) based on PI-RADSv2 with whole-mount histopathology (WMHP) correlation.

MATERIALS AND METHODS

This IRB-approved, HIPAA-compliant study, included 614 consecutive men with 3T mpMRI prior to prostatectomy at a single tertiary center between 12/2009 and 4/2017. Clinical, mpMRI, and pathologic features were obtained. PI-RADSv2-based MRI detected lesions were matched with previously finalized WMHP by a genitourinary (GU) radiologist and a GU pathologist. Patients with no mpMRI detected PCa lesion, but with at least one lesion ≥ 1 cm on WMHP, were reviewed retrospectively and assigned a PI-RADSv2 score. Tumor characteristics were compared between missed and detected lesions.

RESULT

The final cohort included 518 patients with 1085 WMHP lesions. 51.9% (563/1085) of lesions were missed on 3T mpMRI. 71.4% (402/563), 21.7% (122/563), 4.4% (25/563), and 2.5% (14/563) of the missed lesions were Gleason scores (GS) 3 + 3, 3 + 4, 4 + 3, and 8 - 10, respectively. Missed PCa lesions had significantly lower proportion of GS ≥ 7 (p < 0.001) and smaller size for overall (p < 0.001) and index subcohorts (p < 0.001), as compared to detected lesions. 34.5% (194) of overall and 71.2% (79) index missed lesions were larger than 1 cm. In 13.7% (71/518) of patients without MR detected PCa, 149 lesions were detected on WMHP, with 70 (47%) lesions ≥ 1 cm. In retrospective review of these lesions, 42.9% (30), 18.6% (13), 21.5% (15), 10% (7), and 7% (5) were PI-RADSv2 1, 2, 3, 4, and 5, respectively.

CONCLUSION

3T mpMRI has an excellent per patients diagnostic performance for PCa and majority of missed lesions are clinically nonsignificant.

The added value of systematic biopsy in men with suspicion of prostate cancer undergoing multiparametric MRI-targeted biopsy

PURPOSE

Incorporation of multiparametric magnetic resonance imaging (mpMRI) and targeted biopsy (TBx) in the diagnostic pathway for prostate cancer (CaP) is rapidly becoming common practice. In men with a prebiopsy positive mpMRI a TBx only approach, thereby omitting transrectal ultrasound-guided systematic biopsy (SBx), has been postulated. In this study we evaluated the additional clinical relevance of SBx in men with a positive prebiopsy mpMRI (Prostate Imaging Reporting and Data System [PI-RADS] ≥ 3) undergoing TBx for CaP detection, Gleason grading and CaP localization.

MATERIAL AND METHODS

Prospective data of 255 consecutive men with a prebiopsy positive mpMRI (PI-RADS ≥ 3) undergoing 12-core SBx and subsequent MRI-transrectal ultrasound fusion TBx in 2 institutions between 2015 and 2018 was obtained. The detection rate for significant CaP (Gleason score [GS] ≥ 3 + 4) for TBx and SBx were compared. The rate of potentially missed significant CaP by a TBx only approach was determined and GS concordance and CaP localization by TBx and SBx was evaluated.

RESULTS

TBx yielded significant CaP in 113 men (44%) while SBx yielded significant CaP in 110 men (43%) (P = 0.856). Insignificant CaP was found in 21 men (8%) by TBx, while SBx detected 34 men (13%) with insignificant CaP (P = 0.035). A TBx only approach, omitting SBx, would have missed significant CaP in 13 of the 126 men (10%) with significant CaP on biopsy. Ten of the 118 men (8%), both positive on TBx and SBx, were upgraded in GS by SBx while 11 men (9%) had higher maximum tumor core involvement on SBx. Nineteen of the 97 men (20%) with significant CaP in both TBx and SBx were diagnosed with unilateral significant CaP on mpMRI and TBx while SBx demonstrated bilateral significant CaP.

CONCLUSIONS

In men with a prebiopsy positive mpMRI, TBx detects high-GS CaP while reducing insignificant CaP detection as compared to SBx. SBx and TBx as stand-alone missed significant CaP in 13% and 10% of the men with significant CaP on biopsy, respectively. A combination of SBx and TBx remains necessary for the most accurate assessment of detection, grading, tumor core involvement, and localization of CaP.

Use of MRI-Guided Biopsy for Selection and Follow-up of Men Undergoing Hemi-gland Cryoablation of Prostate Cancer

OBJECTIVE

To investigate safety, efficacy, and quality of life impact of hemi-gland cryotherapy for clinically-significant prostate cancer (CaP), when patient selection and follow-up includes MRI-guided biopsy.

METHODS

Twenty-nine men with unilateral CaP (all clinically significant with prostate volume <60 cc) were enrolled in a prospective observational trial of hemi-gland cryotherapy. Mean patient age was 68.7 years. Median prostate-specific antigen (PSA) was 6.6 ng/mL. MRI-guided biopsy (3T-MRI, Artemis US fusion) was used for diagnosis and repeated at 6-month follow-up in all men. Treatment was under general anesthesia using the BTG/Galil system. Validated questionnaires were used to determine effects of treatment on urinary and sexual function and quality of life.

RESULTS

Cryotherapy was completed satisfactorily in all 29 cases in <60 minutes with no intraoperative complications. Significant decreases in PSA (median decrease 5.6 ng/mL) and PSA density (median decrease 0.14 ng/mL/cc) were observed (P < .01). At 6 months, 23 patients (79%) demonstrated no residual cancer on follow-up MRI-guided biopsy of the treated side. Three patients (10%) revealed micro-residual disease. Three patients (10%) had residual cancer and underwent further treatment. Ipsilateral MRI lesions were present before treatment in 26 patients and after treatment in only 2, reflecting the gross ablative effect; however, MRI showed disappearance of lesions in 4 patients with residual tumor on biopsy. The single complication was 1 case of transient urinary retention; 85% of men who were sexually active continued without change after treatment. Voiding function was unchanged.

CONCLUSION

Hemi-gland cryoablation for clinically-significant CaP is well-tolerated, and when patients are selected and followed by MRI/US fusion biopsy, cancer control appears promising at 6 months.

Association of training level and outcome of software-based image fusion-guided targeted prostate biopsies

PURPOSE

The aim of this study was to assess the impact of experience on the outcome of image fusion-guided prostate biopsies performed by urologists working at a high-volume medical center.

METHODS

The first 210 consecutive fusion biopsies were analyzed following installation of the software-based biopsy platform Artemis™ (Eigen, USA). The impact of training was measured in terms of changes in prostate cancer detection rates and biopsy duration over time. We sought to identify a threshold of experience for urologists, which predicts higher detection rates of targeted biopsies. The influence of various factors on prostate cancer detection rates was evaluated using bi- and multivariate analysis.

RESULTS

Twenty-two urologists (n = 9 senior urologists, n = 13 urological residents) performed targeted biopsies followed by systematic 12-core biopsies. Overall, targeted biopsies yielded a positive result in 39.6% of 260 suspicious MRI lesions. A subgroup analysis of the six urologists who performed more than ten biopsies was then conducted, and their level of experience (i.e., performance of more than eight biopsies) was found to be associated with higher detection rates than those with less experience (49.0% and 23.0%, respectively; p < 0.001) in the targeted biopsies. Experience was likewise a significant and independent predictor of a cancer-positive targeted biopsy (p = 0.002). Experienced senior physicians did not outperform residents in their targeted biopsy results. Further, biopsy duration correlated negatively (r = - 0.5931, p < 0.001) with the total number of biopsies performed for all subgroups during the period of assessment.

CONCLUSIONS

Experience is an important predictor of the rate of detection in targeted biopsies using software-based biopsy platforms with semi-robotic assistance. Moreover, the performance of just a few procedures appears sufficient to increase biopsy effectiveness significantly. Lastly, supervision by experts is recommended during the training phase.

Real-Time FEM-Based Registration of 3-D to 2.5-D Transrectal Ultrasound Images

We present a novel technique for real-time deformable registration of 3-D to 2.5-D transrectal ultrasound (TRUS) images for image-guided, robot-assisted laparoscopic radical prostatectomy (RALRP). For RALRP, a pre-operatively acquired 3-D TRUS image is registered to thin-volumes comprised of consecutive intra-operative 2-D TRUS images, where the optimal transformation is found using a gradient descent method based on analytical first and second order derivatives. Our method relies on an efficient algorithm for real-time extraction of arbitrary slices from a 3-D image deformed given a discrete mesh representation. We also propose and demonstrate an evaluation method that generates simulated models and images for RALRP by modeling tissue deformation through patient-specific finite-element models (FEM). We evaluated our method on in-vivo data from 11 patients collected during RALRP and focal therapy interventions. In the presence of an average landmark deformation of 3.89 and 4.62 mm, we achieved accuracies of 1.15 and 0.72 mm, respectively, on the synthetic and in-vivo data sets, with an average registration computation time of 264 ms, using MATLAB on a conventional PC. The results show that the real-time tracking of the prostate motion and deformation is feasible, enabling a real-time augmented reality-based guidance system for RALRP.].

Cost and efficacy comparison of five prostate biopsy modalities: a platform for integrating cost into novel-platform comparative research

BACKGROUND

The cornerstone of prostate cancer diagnosis remains the transrectal ultrasound-guided biopsy (TRUS-BX), which most frequently occurs in the office setting under local anesthesia. However, there are now other techniques of prostate biopsy aimed at improving outcomes such as patient comfort, significant cancer detection, and infectious complications. The purpose of the present study is to compare the cost and efficacy outcomes of five different approaches.

METHODS

We compared the comprehensive costs of a random sample size of 20-30 cases from each of the following: (1) local anesthesia TRUS-BX (reference), (2) sedation TRUS-BX, (3) general anesthesia transperineal template biopsy (TP), (4) sedation MRI-TRUS fusion biopsy (FB), and (5) sedation in-bore MRI biopsy (IB-MRI). Cost categories included pre-procedure, anesthesia pharmacy and recovery, and the technical/professional costs from urology, radiology, and pathology services. For procedure outcomes, we compared the larger cohorts of TRUS-BX, TP, and FB in terms of indication, cancer yield, and downstream decision impact.

RESULTS

Compared with standard TRUS-BX, the total costs of sedation TRUS-BX, TP, FB, and IB-MRI increased significantly ×1.9 (90%), ×2.5 (153%), ×2.5 (150%), and ×2.2 (125%), respectively (p < 0.001). Although there was no statistical difference between the total costs of TP, FB, and IB-MRI, these costs were significantly higher than those of TRUS-BX under either local anesthesia or sedation (p < 0.05). The cost of TRUS-BX under sedation was significantly higher than that of TRUS-BX under local anesthesia (p < 0.001). Compared to TRUS-BX, more significant cancers were detected in FB (16% vs. 36%) and TP (16% vs. 34%) groups (p < 0.001).

CONCLUSIONS

Compared with standard TRUS-BX, the additions of imaging, sedation anesthesia, and transperineal template increase costs significantly, and can be considered along with known improvements in accuracy and side effects. Ongoing efforts to combine imaging and transperineal biopsy, especially in an outpatient/local anesthesia setting may lead to a higher cost/benefit.

Defining the target prior to prostate fusion biopsy: the effect of MRI reporting on cancer detection

PURPOSE

Definition of targets in multiparametric MRI (mpMRI) prior to MRI/TRUS fusion prostate biopsy either by urologist or radiologist, as a prose report or by illustration is crucial for accurate targeted biopsies (TB). The objective was to analyze the effect of MRI reporting on target definition and cancer detection.

METHODS

202 patients underwent MRI/TRUS fusion biopsy with Artemis™ (Eigen, USA). mpMRI results were submitted in written form to urologists, who marked the targets in the proprietary software. An expert uroradiologist reviewed and marked mpMRI targets blinded to biopsy data. We compared number, localization and volume of targets between the observers and analyzed whether variations impaired TB results by bivariate and logistic regression models.

RESULTS

Interobserver variability was moderate regarding number and low regarding localization of targets. Urologists overestimated target volumes significantly compared to radiologists (p = 0.045) and matching target volume between both observers was only 43.9%. Overall cancer detection rate was 69.8 and 52.0% by TB. A higher matching target volume was a significant predictor of cancer in TB (p < 0.001). Logistic regression revealed prostate volume and PI-RADS as independent predictors. Defining targets in incorrect T2w slices in the cranio-caudal axis are one presumable reason for missing cancer in TB.

CONCLUSIONS

A high concordance of the target definition between radiologist and urologist is mandatory for accurate TB. Optimized ROI definition is recommended to improve TB results, preferably as contouring in MRI sequences by the radiologist or, if not feasible, by precise MRI reports including specific localization in sequence and slice as well as an illustration. High prostate volume and low PI-RADS score have to be considered as limiting factors for target definition.