Transrectal quantitative shear wave elastography in the detection and characterisation of prostate cancer. Surg Endosc. 2013;27:3280-3287. [PMID: 23525883 DOI: 10.1007/s00464-013-2906-7]

Clinical practice of the transrectal shear-wave elastography in benign prostatic hyperplasia

OBJECTIVE

To investigate the practical value of the transrectal two-dimensional shear-wave elastography (SWE) in benign prostatic hyperplasia (BPH).

METHODS

Consecutive male participants with and without BPH constituted the BPH and control group respectively were enrolled prospectively between March and December 2022. Transrectal conventional ultrasound and SWE examinations for the prostate were performed on these participants. Data of quantitative stiffness of the transitional zone (TZ) and peripheral zone (PZ) of prostate, volume of prostate (VP) and volume of TZ (VTZ) and prostate specific androgen (PSA), etc., were collected. Linear regression analyses were used to investigate the associations between quantitative stiffness data and other clinical parameters.

RESULTS

There were 200 participants evaluated, including 100 healthy participants and 100 BPH patients. For every one-year increment in age, it was correlated with 0.50 kPa increasement of TZ stiffness. VP and VTZ were correlated with TZ stiffness. Higher TZ stiffness was associated with higher free prostate specific antigen (PSA) and total PSA.

CONCLUSIONS

The prostate is stiffer and larger in BPH group compared to control group. Quantitative stiffness of the TZ was related with age, VP, VTZ and PSA.

A comparative study of histotripsy parameters for the treatment of fibrotic ex-vivo human benign prostatic hyperplasia tissue

Histotripsy is a noninvasive focused ultrasound therapy that mechanically fractionates tissue to create well-defined lesions. In a previous clinical pilot trial to treat benign prostatic hyperplasia (BPH), histotripsy did not result in consistent objective improvements in symptoms, potentially because of the fibrotic and mechanically tough nature of this tissue. In this study, we aimed to identify the dosage required to homogenize BPH tissue by different histotripsy modalities, including boiling histotripsy (BH) and cavitation histotripsy (CH). A method for histotripsy lesion quantification via entropy (HLQE) analysis was developed and utilized to quantify lesion area of the respective treatments. These data were correlated to changes in mechanical stiffness measured by ultrasound shear-wave elastography before and after treatment with each parameter set and dose. Time points corresponding to histologically observed complete lesions were qualitatively evaluated and quantitatively measured. For the BH treatment, complete lesions occurred with >  = 30 s treatment time, with a corresponding maximum reduction in stiffness of -90.9 ± 7.2(s.d.)%. High pulse repetition frequency (PRF) CH achieved a similar reduction to that of BH at 288 s (-91.6 ± 6.0(s.d.)%), and low-PRF CH achieved a (-82.1 ± 5.1(s.d.)%) reduction in stiffness at dose >  = 144 s. Receiver operating characteristic curve analysis showed that a >  ~ 75% reduction in stiffness positively correlated with complete lesions observed histologically, and can provide an alternative metric to track treatment progression.

A Comparative Study of Histotripsy Parameters for the Treatment of Fibrotic ex-vivo Human Benign Prostatic Hyperplasia Tissue

Histotripsy is a noninvasive focused ultrasound therapy that mechanically fractionates tissue to create well-defined lesions. In a previous clinical pilot trial to treat benign prostatic hyperplasia (BPH), histotripsy did not result in consistent objective improvements in symptoms, potentially because of the fibrotic and mechanically tough nature of this tissue. In this study, we aimed to identify the dosage required to homogenize BPH tissue by different histotripsy modalities, including boiling histotripsy (BH) and cavitation histotripsy (CH). A method for histotripsy lesion quantification via entropy (HLQE) analysis was developed and utilized to quantify lesion area of the respective treatments. These data were correlated to changes in mechanical stiffness measured by ultrasound shear-wave elastography before and after treatment with each parameter set and dose. Time points corresponding to histologically observed complete lesions were qualitatively evaluated and quantitatively measured. For the BH treatment, complete lesions occurred with >=30s treatment time, with a corresponding maximum reduction in stiffness of -90.9±7.2(s.d.)%. High pulse repetition frequency (PRF) CH achieved a similar reduction to that of BH at 288s (-91.6±6.0(s.d.)%), and low-PRF CH achieved a (-82.1±5.1(s.d.)%) reduction in stiffness at dose >=144s. Receiver operating characteristic curve analysis showed that a >~75% reduction in stiffness positively correlated with complete lesions observed histologically, and can provide an alternative metric to track treatment progression.

The Performance of Different Parametric Ultrasounds in Prostate Cancer Diagnosis: Correlation with Radical Prostatectomy Specimens

BACKGROUND

Prostate cancer is a prevalent cancer among men. Multiparametric ultrasound [mpUS] is a diagnostic instrument that uses various types of ultrasounds to diagnose it. This systematic review aims to evaluate the performance of different parametric ultrasounds in diagnosing prostate cancer by associating with radical prostatectomy specimens.

METHODOLOGY

A review was performed on various ultrasound parameters using five databases. Systematic review tools were utilized to eliminate duplicates and identify relevant results. Reviewers used the Quality Assessment of Diagnostic Accuracy Results [QUADAS-2] to evaluate the bias and applicability of the study outcomes.

RESULT

Between 2012 and 2023, eleven studies were conducted to evaluate the performance of the different ultrasound parametric procedures in detecting prostate cancer using grayscale TRUS, SWE, CEUS, and mpUS. The high sensitivity of these procedures was found at 55%, 88.6%, 81%, and 74%, respectively. The specificity of these procedures was found to be 93.4%, 97%, 88%, and 59%, respectively. This high sensitivity and specificity may be associated with the large lesion size. The studies revealed that the sensitivity of these procedures in diagnosing clinically significant prostate cancer was 55%, 73%, 70%, and 74%, respectively, while the specificity was 61%, 78.2%, 62%, and 59%, respectively.

CONCLUSIONS

The mpUS procedure provides high sensitivity and specificity in PCa detection, especially for clinically significant prostate cancer.

Multi-Frequency 3D Shear Wave Absolute Vibro-Elastography (S-WAVE) System for the Prostate

This article describes a novel system for quantitative and volumetric measurement of tissue elasticity in the prostate using simultaneous multi-frequency tissue excitation. Elasticity is computed by using a local frequency estimator to measure the three-dimensional local wavelengths of steady-state shear waves within the prostate gland. The shear wave is created using a mechanical voice coil shaker which transmits simultaneous multi-frequency vibrations transperineally. Radio frequency data is streamed directly from a BK Medical 8848 transrectal ultrasound transducer to an external computer where tissue displacement due to the excitation is measured using a speckle tracking algorithm. Bandpass sampling is used that eliminates the need for an ultra-fast frame rate to track the tissue motion and allows for accurate reconstruction at a sampling frequency that is below the Nyquist rate. A roll motor with computer control is used to rotate the transducer and obtain 3D data. Two commercially available phantoms were used to validate both the accuracy of the elasticity measurements as well as the functional feasibility of using the system for in vivo prostate imaging. The phantom measurements were compared with 3D Magnetic Resonance Elastography (MRE), where a high correlation of 96% was achieved. In addition, the system has been used in two separate clinical studies as a method for cancer identification. Qualitative and quantitative results of 11 patients from these clinical studies are presented here. Furthermore, an AUC of 0.87±0.12 was achieved for malignant vs. benign classification using a binary support vector machine classifier trained with data from the latest clinical study with leave one patient out cross-validation.

Associations of Real-Time Ultrasound and Strain and Shear Wave Elastography with Gastrointestinal Organs: A Systematic Review

Ultrasound elastography is gaining attention for its diagnostic potential across various medical fields, and its physical properties make it valuable in modern clinical medicine. However, its specific attributes, especially in the context of recent medical advancements, remain relatively unexplored. This study aimed to identify instrument-specific characteristics and applications of real-time ultrasound elastography, shear wave elastography, and strain elastography, particularly within gastroenterology. Following PRISMA guidelines, the study examined elastography articles on databases like PubMed, resulting in 78 included articles. Data on patient demographics, organ involvement, specificity, sensitivity, accuracy, positive predictive value, and negative predictive value were extracted. Statistical analysis involved SPSS version 21, with significance set at p < 0.05. The majority of patients were male (50.50%), with a mean age of 42.73 ± 4.41 years. Shear wave elastography was the most prevalent technique (48.7%), and liver investigations were predominant in gastroenterology (34.6%). Gastrointestinal applications showed higher sensitivity, positive predictive value, and negative predictive values (p < 0.05) but lower specificity (p < 0.05). Real-time ultrasound elastography exhibited increased specificity, accuracy, and predictive values (p < 0.05). Ultrasound elastography appears more accurate and effective in gastroenterological settings. Nonetheless, its performance depends on instrument-specific and operator-dependent factors. While promising, further studies are necessary to ascertain optimal utilization in both gastrointestinal and non-gastrointestinal conditions.

Variability of Transrectal Shear Wave Elastography in a Phantom Model

Purpose

This study aimed to assess the variability of transrectal shear wave elastography (SWE) using a designed phantom.

Materials and Methods

In a phantom, the SWE values were examined by two radiologists using agarose and emulsion silicone of different sizes (1, 2, and 3 cm) and shapes (round, cubic) at three depths (1, 2, and 3 cm), two region of interest (ROI) and locations (central, peripheral) using two ultrasound machines (A, B from different vendors). Variability was evaluated using the coefficient of variation (CV).

Results

The CVs decreased with increasing phantom size. Significant changes in SWE values included; agarose phantom at 3 cm depth (p < 0.001; machine A), 1 cm depth (p = 0.01; machine B), emulsion silicone at 2 cm depth (p = 0.047, p = 0.020; both machines). The CVs increased with increasing depth. Significant changes in SWE values included; 1 cm agarose (p = 0.037, p = 0.021; both machines) and 2 cm agarose phantom (p = 0.047; machine A). Significant differences in SWE values were observed between the shapes for emulsion silicone phantom (p = 0.032; machines A) and between ROI locations on machine B (p ≤ 0.001). The SWE values differed significantly between the two machines (p < 0.05). The intra-/inter-operator agreements were excellent (intraclass correlation coefficient > 0.9).

Conclusion

The phantom size, depth, and different machines affected the variability of transrectal SWE.

3-D Transducer Mounted Shear Wave Absolute Vibro-Elastography: Proof of Concept

Quantitative tissue stiffness characterization using ultrasound (US) has been shown to improve prostate cancer (PCa) detection in multiple studies. Shear wave absolute vibro-elastography (SWAVE) allows quantitative and volumetric assessment of tissue stiffness using external multifrequency excitation. This article presents a proof of concept of a first-of-a-kind 3-D hand-operated endorectal SWAVE system designed to be used during systematic prostate biopsy. The system is developed with a clinical US machine, requiring only an external exciter that can be mounted directly to the transducer. Subsector acquisition of radio frequency (RF) data allows imaging of shear waves with a high effective frame rate (up to 250 Hz). The system was characterized using eight different quality assurance phantoms. Due to the invasive nature of prostate imaging, at this early stage of development, validation of in vivo human tissue was instead carried out by intercostally scanning the livers of n = 7 healthy volunteers. The results are compared with 3-D magnetic resonance elastography (MRE) and an existing 3-D SWAVE system with a matrix array transducer (M-SWAVE). High correlations were found with MRE (99% in phantoms, 94% in liver data) and with M-SWAVE (99% in phantoms, 98% in liver data).

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.

Application of Multiple Ultrasonic Techniques in the Diagnosis of Prostate Cancer

Methods for diagnosing prostate cancer (PCa) are developing in the direction of imaging. Advanced ultrasound examination modes include micro-Doppler, computerized-transrectal ultrasound, elastography, contrast-enhanced ultrasound and microultrasound. When two or more of these modes are used in PCa diagnosis, the combined technique is called multiparameter ultrasound (mp-US). Mp-US provides complementary information to multiparameter magnetic resonance imaging (mp-MRI) for diagnosing PCa. At present, no study has attempted to combine the characteristics of different ultrasound modes with advanced classification systems similar to the PIRADS system in mpMRI for the diagnosis of PCa. As an imaging method, mp-US has great potential in the diagnosis of PCa.

Multimodality Characterization of Cancer-Associated Fibroblasts in Tumor Microenvironment and Its Correlation With Ultrasound Shear Wave-Measured Tissue Stiffness in Localized Prostate Cancer

Introduction

Growing evidence suggests that the tumor microenvironment (TME) represented by cellular and acellular components plays a key role in the multistep process of metastases and response to therapies. However, imaging and molecular characterization of the TME in prostate cancer (PCa) and its role in predicting aggressive tumor behavior and disease progression is largely unexplored. The study explores the PCa TME through the characterization of cancer-associated fibroblasts (CAFs) using both immunohistochemistry (IHC) and genomics approaches. This is then correlated with transrectal ultrasound shear wave elastography (USWE)-measured tissue stiffness.

Patients and Methods

Thirty patients with clinically localized PCa undergoing radical prostatectomy for different risk categories of tumor (low, intermediate, and high) defined by Gleason score (GS) were prospectively recruited into this study. Prostatic tissue stiffness was measured using USWE prior to surgery. The CAFs within the TME were identified by IHC using a panel of six antibodies (FAP, SMAα, FSP1, CD36, PDGFRα, and PDGFRβ) as well as gene expression profiling using TempO-sequence analysis. Whether the pattern and degree of immunohistochemical positivity (measured by Quick score method) and expression of genes characterizing CAFs were correlated with USWE- and GS-measured tissue stiffnesses were tested using Spearman's rank correlation and Pearson correlation.

Results

There was a statistically significant correlation between GS of cancers, the pattern of staining for CAFs by immunohistochemical staining, and tissue stiffness measured in kPa using USWE (p < 0.001). Significant differences were also observed in immunohistochemical staining patterns between normal prostate and prostatic cancerous tissue. PDGFRβ and SMAα immunostaining scores increased linearly with increasing the USWE stiffness and the GS of PCa. There was a significant positive correlation between increasing tissue stiffness in tumor stroma and SMAα and PDGFRβ gene expression in the fibromuscular stroma (p < 0.001).

Conclusion

USWE-measured tissue stiffness correlates with increased SMAα and PDGFRβ expressing CAFs and PCa GSs. This mechanistic correlation could be used for predicting the upgrading of GS from biopsies to radical surgery and response to novel treatments.

Alternatives for MRI in Prostate Cancer Diagnostics-Review of Current Ultrasound-Based Techniques

The purpose of this review is to present the current role of ultrasound-based techniques in the diagnostic pathway of prostate cancer (PCa). With overdiagnosis and overtreatment of a clinically insignificant PCa over the past years, multiparametric magnetic resonance imaging (mpMRI) started to be recommended for every patient suspected of PCa before performing a biopsy. It enabled targeted sampling of the suspicious prostate regions, improving the accuracy of the traditional systematic biopsy. However, mpMRI is associated with high costs, relatively low availability, long and separate procedure, or exposure to the contrast agent. The novel ultrasound modalities, such as shear wave elastography (SWE), contrast-enhanced ultrasound (CEUS), or high frequency micro-ultrasound (MicroUS), may be capable of maintaining the performance of mpMRI without its limitations. Moreover, the real-time lesion visualization during biopsy would significantly simplify the diagnostic process. Another value of these new techniques is the ability to enhance the performance of mpMRI by creating the image fusion of multiple modalities. Such models might be further analyzed by artificial intelligence to mark the regions of interest for investigators and help to decide about the biopsy indications. The dynamic development and promising results of new ultrasound-based techniques should encourage researchers to thoroughly study their utilization in prostate imaging.

Application of Shear Wave Elastography and Contrast-Enhanced Ultrasound in Transrectal Prostate Biopsy

OBJECTIVE

To explore the clinical value of ultrasound shear wave elastography (SWE) and contrast-enhanced ultrasound (CEUS) in transrectal prostate biopsy.

METHODS

A total of 54 patients (average age: 67.79±12.01 years) in the experimental group underwent transrectal prostate biopsy under the guidance of SWE, while 46 patients (average age: 69.22±11.54 years) in the control group underwent transrectal prostate biopsy guided by CEUS.

RESULTS

There were a total of 451 needles, with an average of 8.35±1.67 needles per patient in the experimental group, and a total of 462 needles, with an average of 10.04±1.33 needles per patient in the control group. The difference in puncture times between the two groups was statistically significant (P<0.05). There was no significant difference in the positive detection rate, sensitivity or specificity between the two groups (P>0.05), but there was a significant difference in the diagnostic accuracy between the two groups (P<0.05). The E_mean and E_max of prostate cancer were significantly higher in the experimental group than in benign prostatic hyperplasia (P<0.05). The receiver operating characteristic curve (ROC) analysis showed that the area under the ROC curve (AUC) of E_mean was 0.752 (S.E. =0.072, 95% CI=0.611-0.894, P=0.007), and the best cutoff value was 47.005 kPa.

CONCLUSION

In summary, both SWE- and CEUS-guided transrectal prostate biopsy can help find the focus and guide the puncture, and improve the positive detection rate.

Ultrasound elastography

Physicians have used palpation as a diagnostic examination to understand the elastic properties of pathology for a long time since they realized that tissue stiffness is closely related to its biological characteristics. US elastography provided new diagnostic information about elasticity comparing with the morphological feathers of traditional US, and thus expanded the scope of the application in clinic. US elastography is now widely used in the field of diagnosis and differential diagnosis of abnormality, evaluating the degree of fibrosis and assessment of treatment response for a range of diseases. The World Federation of Ultrasound Medicine and Biology divided elastographic techniques into strain elastography (SE), transient elastography and acoustic radiation force impulse (ARFI). The ARFI techniques can be further classified into point shear wave elastography (SWE), 2D SWE, and 3D SWE techniques. The SE measures the strain, while the shear wave-based techniques (including TE and ARFI techniques) measure the speed of shear waves in tissues. In this review, we discuss the various techniques separately based on their basic principles, clinical applications in various organs, and advantages and limitations and which might be most appropriate given that the majority of doctors have access to only one kind of machine.

Prostate Cancer Gleason Score From Biopsy to Radical Surgery: Can Ultrasound Shear Wave Elastography and Multiparametric Magnetic Resonance Imaging Narrow the Gap?

Objectives

To investigate the impact of ultrasound shear wave elastography (USWE) and multiparametric magnetic resonance imaging (mpMRI) in predicting a change in biopsy-assigned Gleason Score (GS) after radical surgery for localised prostate cancer (PCa).

Method

A total of 212 men opting for laparoscopic radical prostatectomy (LRP) between September 2013 and June 2017 were recruited into this study. All the participants had 12-core transrectal ultrasound (TRUS) biopsies and imaging using USWE and mpMRI before radical surgery. The predictive accuracy for imaging modalities was assessed in relation to upgrading and downgrading of PCa GS between the biopsies and radical prostatectomy using Student's t-test and multivariable logistic regression analyses. A decision analysis curve was constructed assessing the impact of nomogram on clinical situations using different thresholds of upgrading probabilities.

Results

Most GS 6 diseases on biopsies were upgraded on radical surgery (37/42, 88.1%). Major downgrading was seen in GS 8 category of disease (14/35; 37.1%), whereas no alteration was observed in GS 7 on biopsies in most men (55/75; 73.3%). In univariate analysis, higher preoperative prostate-specific antigen (PSA) (p = 0.001), higher prostate-specific antigen density (PSAD) (p = 0.002), stiffer USWE lesions (p = 0.009), and higher prostate imaging-reporting and data system (PIRADS) (p = 0.002) on mpMRI were significant predictors of upgrading. In multivariate logistic regression analyses, only PSA (p = 0.016) and USWE-measured tissue stiffness (p = 0.029) showed statistical significance in predicting upgrading.

Conclusions

Measurement of tissue stiffness using USWE in clinically localised PCa can predict upgrading of GS and has the potential to improve patient management options.

Characterisation of Collagen Re-Modelling in Localised Prostate Cancer Using Second-Generation Harmonic Imaging and Transrectal Ultrasound Shear Wave Elastography

Prostate cancer has a poor prognosis and high mortality rate due to metastases. Extracellular matrix (ECM) re-modelling and stroma composition have been linked to cancer progression, including key components of cell migration, tumour metastasis, and tissue modulus. Moreover, collagens are one of the most significant components of the extracellular matrix and have been ascribed to many aspects of neoplastic transformation. This study characterises collagen re-modelling around localised prostate cancer using the second harmonic generation of collagen (SHG), genotyping and ultrasound shear wave elastography (USWE) measured modulus in men with clinically localised prostate cancer. Tempo-sequence assay for gene expression of COL1A1 and COL3A1 was used to confirm the expression of collagen. Second-harmonic generation imaging and genotyping of ECM around prostate cancer showed changes in content, orientation, and type of collagen according to Gleason grades (cancer aggressivity), and this correlated with the tissue modulus measured by USWE in kilopascals. Furthermore, there were clear differences between collagen orientation and type around normal and cancer tissues.

Causal contributors to tissue stiffness and clinical relevance in urology

Mechanomedicine is an emerging field focused on characterizing mechanical changes in cells and tissues coupled with a specific disease. Understanding the mechanical cues that drive disease progression, and whether tissue stiffening can precede disease development, is crucial in order to define new mechanical biomarkers to improve and develop diagnostic and prognostic tools. Classically known stromal regulators, such as fibroblasts, and more recently acknowledged factors such as the microbiome and extracellular vesicles, play a crucial role in modifications to the stroma and extracellular matrix (ECM). These modifications ultimately lead to an alteration of the mechanical properties (stiffness) of the tissue, contributing to disease onset and progression. We describe here classic and emerging mediators of ECM remodeling, and discuss state-of-the-art studies characterizing mechanical fingerprints of urological diseases, showing a general trend between increased tissue stiffness and severity of disease. Finally, we point to the clinical potential of tissue stiffness as a diagnostic and prognostic factor in the urological field, as well as a possible target for new innovative drugs.

Prostate Cancer Ultrasound: Is Still a Valid Tool?

Purpose of Review

The main purpose of this paper review is to highlight the latest ultrasound (US) imaging technologies of the prostate gland, an organ increasingly at the center of attention in the field of oncological diseases of the male sex, which needs a 360° evaluation in order to obtain tailored therapeutic planning. Specialist urological evaluation is designated for this purpose, together with integrated prostate imaging which currently tends to focus more and more on the use of US imaging and its state-of-the-art technologies in iconographic diagnosis, biopsy and, sometimes, treatment of prostatic cancer.

Recent Findings

In particular, the main tools to which reference is made, represent a valid aid to basic US technologies already widely known and diffused, like the grayscale US or the Doppler US, for a "multiparametric" evaluation of the prostate cancer. The concept of multiparametricity is explained by the integration of prostate imaging obtained both with the US evaluation of the gland before and after administration of contrast medium, with the elaboration of parametric maps of quantitative measurement of the enhancement, and with elastography that provides information about the tissue consistency, a finding that strongly relates with the degree of cellularity and with the tumor grading.

Summary

Prostate cancer screening consists of dosing serum levels of prostate-specific antigen (PSA) and performing digit-rectal examination (DRE), more or less associated with transrectal prostate ultrasound (TRUS). However, although these are the most common techniques in clinical practice, they have numerous limitations and make the diagnosis of prostate cancer often challenging. The purpose of mp-US is to enrich the clinical-laboratory data and, above all, the standard US imaging with further details to strengthen the suspicion of malignancy of a prostate tumor, which needs to be addressed to diagnostic deepening with biopsy. This review article provides a summary of the current evidence on mp-US imaging in the evaluation of a clinically significant prostate cancer, comparing the data obtained to the imaging of mp-MRI, the reference tool both in diagnosis and staging.

Correlation of Stiffness of Prostate Cancer Measured by Shear Wave Elastography with Grade Group: A Preliminary Study

The aim of study was to explore the correlation between shear wave elastography (SWE) and grade group (GG) of prostate cancer (PCa). This retrospective study involved prostate-specific antigen elevated patients with elevated prostate-specific antigen levels who underwent SWE before transrectal ultrasound-guided needle biopsy. A total of 49 PCa lesions were reviewed after radical prostatectomy; 3-7 regions of interest were placed within the cancerous area on axial view compared with the tumor foci outlined on the slides by pathologist. The maximum SWE value was measured, quantitative SWE parameters (E_max, E_mean, E_min and standard deviation [SD]) were recorded and correlated with GG and then parameters were compared between indolent (≤2) and aggressive (≥3) GGs. The diagnostic value of each parameter was compared with the receiver operating characteristic curve. Forty-nine PCa foci were divided into two groups on the basis of their GGs. All SWE parameters exhibited a significant linear trend with GG. The area under the receiver operating characteristic curve (AUC) was 0.816 for E_max; with a cutoff point of 84 kPa, sensitivity and specificity were 81.3% and 82.4% to differentiate low and high GGs in PCa. The AUC was 0.776 for E_mean; with a cutoff point of 71 kPa, sensitivity and specificity were 78.1% and 76.5%. For E_min, the AUC was 0.739; with a cutoff point of 60 kPa, sensitivity and specificity were 68.8% and 70.6%. For SD, the AUC was 0.681; with a cutoff point of 8.3 kPa, sensitivity and specificity were 46.9% and 94.1%. There were no significant differences between the four SWE parameters (p < 0.05 for all). SWE features were correlated with GGs, and this correlation may have excellent diagnostic performance in predicting high GG in PCa.

Characterisation of Prostate Lesions Using Transrectal Shear Wave Elastography (SWE) Ultrasound Imaging: A Systematic Review

BACKGROUND

ultrasound-based shear wave elastography (SWE) can non-invasively assess prostate tissue stiffness. This systematic review aims to evaluate SWE for the detection of prostate cancer (PCa) and compare diagnostic estimates between studies reporting the detection of all PCa and clinically significant PCa (csPCa).

METHODS

a literature search was performed using the MEDLINE, EMBASE, Cochrane Library, ClinicalTrials.gov, and CINAHL databases. Studies evaluating SWE for the detection of PCa using histopathology as reference standard were included.

RESULTS

16 studies including 2277 patients were included for review. Nine studies evaluated SWE for the detection of PCa using systematic biopsy as a reference standard at the per-sample level, with a pooled sensitivity and specificity of 0.85 (95% CI = 0.74-0.92) and 0.85 (95% CI = 0.75-0.91), respectively. Five studies evaluated SWE for the detection of PCa using histopathology of radical prostatectomy (RP) specimens as the reference standard, with a pooled sensitivity and specificity of 0.71 (95% CI = 0.55-0.83) and 0.74 (95% CI = 0.42-0.92), respectively. Sub-group analysis revealed a higher pooled sensitivity (0.77 vs. 0.62) and specificity (0.84 vs. 0.53) for detection of csPCa compared to all PCa among studies using RP specimens as the reference standard.

CONCLUSION

SWE is an attractive imaging modality for the detection of PCa.

Diagnostic Value of Transrectal Shear Wave Elastography for Prostate Cancer Detection in Peripheral Zone: Comparison with Magnetic Resonance Imaging

Objective: To assess the diagnostic value of transrectal shear wave elastography (SWE) for detecting prostate cancer (PCa) in peripheral zone and compare it with magnetic resonance imaging (MRI). Materials and Methods: Two hundred twenty-one patients suspected of PCa were enrolled, in which 172 patients of them underwent both SWE and MRI. Elastic value was measured in the area prepared for systematic biopsy and suspicious lesion detected on B-mode or SWE, histopathological result was compared for each biopsy. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy were derived by obtaining optimal threshold from receiver operating characteristic (ROC) curve. The correlation between the stiffness of PCa and Gleason scores, prognostic grades, and percentage of cancer in biopsy were evaluated by Spearman rank correlation. Multivariate logistic regression analysis was performed to determine predictors for diagnosing PCa. The diagnostic capacity of MRI and SWE for detecting PCa and clinically significant PCa in the peripheral zone were assessed by comparing area under curve of ROC curve. Results: A value of 42 kPa was used as the cutoff for differentiating benign from malignant prostatic tissue; the sensitivity, specificity, PPV, NPV, and accuracy were 78.97%, 90.67%, 71.30%, 93.66% and 88.03%, respectively. Rank correlation analysis revealed that the stiffness of PCa had a correlation with Gleason score, prognostic grade, and percentage of cancer in biopsy. On multivariate analysis, the age, free prostate-specific antigen (PSA), PSA density, SWE, and MRI were independent predictors for diagnosing PCa. There was no statistical difference for diagnosing PCa between SWE and MRI (p = 0.259). However, for clinically significant PCa, the diagnostic capacity of SWE was a little higher than MRI (p = 0.013). Conclusions: SWE may provide additional information for PCa detection, which could increase the positive rate of PCa in targeted biopsy and reduce unnecessary biopsy. SWE is compatible with MRI for detecting PCa in the peripheral zone.

Advanced ultrasound in the diagnosis of prostate cancer

The diagnosis of prostate cancer (PCa) can be challenging due to the limited performance of current diagnostic tests, including PSA, digital rectal examination and transrectal conventional US. Multiparametric MRI has improved PCa diagnosis and is recommended prior to biopsy; however, mp-MRI does miss a substantial number of PCa. Advanced US modalities include transrectal prostate elastography and contrast-enhanced US, as well as improved B-mode, micro-US and micro-Doppler techniques. These techniques can be combined to define a novel US approach, multiparametric US (mp-US). Mp-US improves PCa diagnosis but is not sufficiently accurate to obviate the utility of mp-MRI. Mp-US using advanced techniques and mp-MRI provide complementary information which will become even more important in the era of focal therapy, where precise identification of PCa location is needed.

Prediction of Postprostatectomy Biochemical Recurrence Using Quantitative Ultrasound Shear Wave Elastography Imaging

Objectives: To determine the prognostic significance of tissue stiffness measurement using transrectal ultrasound shear wave elastography in predicting biochemical recurrence following radical prostatectomy for clinically localized prostate cancer.

Patients and Methods: Eligible male patients with clinically localized prostate cancer and extraperitoneal laparoscopic radical prostatectomy between November 2013 and August 2017 were retrospectively selected. Information of potential biochemical recurrence predictors, including imaging (ultrasound shear wave elastography and magnetic resonance imaging), clinicopathological characteristics, and preoperative prostate specific antigen (PSA) levels were obtained. Recurrence-free survival (Kaplan–Meier curve) and a multivariate model were constructed using Cox regression analysis to evaluate the impact of shear wave elastography as a prognostic marker for biochemical recurrence.

Results: Patients experienced biochemical recurrence in an average of 26.3 ± 16.3 months during their follow-up. A cutoff of 144.85 kPa for tissue stiffness measurement was estimated for recurrence status at follow-up with a sensitivity of 74.4% and a specificity of 61.7%, respectively (p < 0.05). In univariate analysis, shear wave elastography performed well in all preoperative factors compared to biopsy Gleason Score, PSA and magnetic resonance imaging; in multivariate analysis with postoperative pathological factors, shear wave elastography was statistically significant in predicting postoperative biochemical recurrence, which improved the C-index of predictive nomogram significantly (0.74 vs. 0.70, p < 0.05).

Conclusions: The study revealed that quantitative ultrasound shear wave elastography-measured tissue stiffness was a significant imaging marker that enhanced the predictive ability with other clinical and histopathological factors in prognosticating postoperative biochemical recurrence following radical prostatectomy for clinically localized prostate cancer.

Stiffness of prostate gland measured by transrectal real-time shear wave elastography for detection of prostate cancer: a feasibility study

OBJECTIVE

This study aimed to evaluate the value of the Young's modulus obtained by transrectal real-time shear wave elastography (SWE) for detection of prostate cancer (PCa).

METHODS

215 patients underwent SWE in six identical planes before biopsy guided with transrectal ultrasonography. The Young's modulus of the entire prostate gland was defined as the mean of the results in these planes. The measurements were compared with the pathological results, the prostate specific antigen (PSA), and the Gleason score (GS) after biopsy.

RESULTS

The Young's modulus of elasticity, including the maximum Young's modulus (Emax), the mean Young's modulus (Emean), and the minimum Young's modulus (Emin), were significantly higher in malignant lesions than those in benign lesions (all p < 0.05). The optimal cut-off values for PCa were 128.48 kPa, 62.27 kPa, and 20.03 kPa, respectively. The sensitivities were 77.88%, 81.42%, and 60.18%, respectively, and the specificities were 85.33%, 74.51 and 63.73 %, respectively. PSA positively correlated with Emax and Emean (r = 0.686 and 0.678, respectively), as did the GS (r = 0.410 and 0.382, respectively).

CONCLUSION

The Young's modulus of entire prostate gland can be used to differentiate benign from malignant prostatic lesions. There were higher Young's modulus of elasticity and higher risk of malignant lesions. Meanwhile, higher Young's modulus correlated with higher PSA and GS.

ADVANCES IN KNOWLEDGE

This study indicates SWE can detect PCa by quantified the stiffness of entire prostate gland whether the lesions have been visible or not on gray-scale and Doppler ultrasound.

Comparative Diagnostic Accuracy of Contrast-Enhanced Ultrasound and Shear Wave Elastography in Differentiating Benign and Malignant Lesions: A Network Meta-Analysis

Background: We performed a network meta-analysis to compare the diagnostic accuracy of contrast-enhanced ultrasound (CEUS) and shear wave elastography (SWE) in differentiating benign and malignant lesions in different body sites.

Methods: A computerized literature search of Medline, Embase, SCOPUS, and Web of Science was performed using relevant keywords. Following data extraction, we calculated sensitivity, specificity, positive likelihood ratio (LR), negative LR, and diagnostic odds ratio (DOR) for CEUS, and SWE compared to histopathology as a reference standard. Statistical analyses were conducted by MetaDiSc (version 1.4) and R software (version 3.4.3).

Results: One hundred and fourteen studies (15,926 patients) were pooled in the final analyses. Network meta-analysis showed that CEUS had significantly higher DOR than SWE (DOR = 27.14, 95%CI [2.30, 51.97]) in breast cancer detection. However, there were no significant differences between CEUS and SWE in hepatic (DOR = −6.67, 95%CI [−15.08, 1.74]) and thyroid cancer detection (DOR = 3.79, 95%CI [−3.10, 10.68]). Interestingly, ranking analysis showed that CEUS achieved higher DOR in detecting breast and thyroid cancer, while SWE achieved higher DOR in detecting hepatic cancer. The overall DOR for CEUS in detecting renal cancer was 53.44, 95%CI [29.89, 95.56] with an AUROC of 0.95, while the overall DOR for SWE in detecting prostate cancer was 25.35, 95%CI [7.15, 89.89] with an AUROC of 0.89.

Conclusion: Both diagnostic tests showed relatively high sensitivity and specificity in detecting malignant tumors in different organs. Network meta-analysis showed that CEUS had higher diagnostic accuracy than SWE in detecting breast and thyroid cancer, while SWE had higher accuracy in detecting hepatic cancer. However, the results were not statistically significant in hepatic and thyroid malignancies. Further head-to-head comparisons are needed to confirm the optimal imaging technique to differentiate each cancer type.

A Novel Scoring System for Prediction of Prostate Cancer Based on Shear Wave Elastography and Clinical Parameters

OBJECTIVE

To develop a novel scoring system for the prediction of prostate cancer (PCa).

METHODS

We assessed 127 patients who underwent a prostate biopsy. Prior to biopsy, we performed shear wave elastography (SWE), transrectal ultrasound, digital rectal exam, total prostatic specific antigen, PSA density (PSAD), and free PSA/total PSA ratio (F/T). We developed an 11-point scoring system based on SWE and these clinical parameters.

RESULTS

PCa was diagnosed in 51 (40.2%) of 127 patients and 192 (25.2%) of 762 sextants on initial biopsy. ROC curve analyses showed that the cutoff value (COV) for SWE was 40.8 kpa at the sextant level. The AUC of score system based on the SWE and clinical parameters (0.911) was significantly different from scoring systems based on SWE alone (0.842) or clinical parameters alone (0.868). For this 11-point scoring system, the optimal COV, Youden index, sensitivity, specificity, PPV, NPV, and AUC were 3 points, 0.66, 76.5% 89.5%, 82.98%, 85.00%, and 0.911, respectively. There were 68 negative biopsy results in patients with 0-3 points, and the detection rate of PCa was 100% in patients with scores exceeding 6 points.

CONCLUSION

This 11-point scoring system based on SWE and clinical parameters has the good diagnostic performance for predicting PCa. It may be useful in selecting patients for biopsy, substantially reducing the number of unnecessary biopsies while ensuring that few cancers are missed.

Microscale characterization of prostate biopsies tissues using optical coherence elastography and second harmonic generation imaging

Photonics, especially optical coherence elastography (OCE) and second harmonic generation (SHG) imaging are novel high-resolution imaging modalities for characterization of biological tissues. Following our preliminary experience, we hypothesized that OCE and SHG imaging would delineate the microstructure of prostate tissue and aid in distinguishing cancer from the normal benign prostatic tissue. Furthermore, these approaches may assist in characterization of the grade of cancer, as well. In this study, we confirmed a high diagnostic accuracy of OCE and SHG imaging in the detection and characterization of prostate cancer for a large set of biopsy tissues obtained from men suspected to have prostate cancer using transrectal ultrasound (TRUS). The two techniques and methods described here are complementary, one depicts the stiffness of tissues and the other illustrates the orientation of collagen structure around the cancerous lesions. The results showed that stiffness of cancer tissue was ~57.63% higher than that of benign tissue (Young's modulus of 698.43±125.29 kPa for cancerous tissue vs 443.07±88.95 kPa for benign tissue with OCE. Using histology as a reference standard and 600 kPa as a cut-off threshold, the data analysis showed sensitivity and specificity of 89.6 and 99.8%, respectively. Corresponding positive and negative predictive values were 99.5 and 94.6%, respectively. There was a significant difference noticed in terms of Young's modulus for different Gleason scores estimated by OCE (P-value<0.05). For SHG, distinct patterns of collagen distribution were seen for different Gleason grade disease with computed quantification employing a ratio of anisotropic to isotropic (A:I ratio) and this correlated with disease aggressiveness.

Novel application of three-dimensional shear wave elastography in the detection of clinically significant prostate cancer

The present study evaluated three-dimensional shear wave elastography (3D SWE) in the detection of clinically significant prostate cancer. Clinically significant prostate cancer was defined by a minimum of one biopsy core with a Gleason score of 3+4 or 6 with a maximum cancer core length >4 mm. Patients with serum prostate-specific antigen levels of 4.0-20.0 ng/ml who were suspected of having prostate cancer from multi-parametric magnetic resonance imaging (mpMRI) were prospectively recruited. The 3D SWE was performed pre-biopsy, after which patients underwent MRI-transrectal ultrasound image-guided targeted biopsies for cancer-suspicious lesions and 12-core systematic biopsies. The pathological biopsy results were compared with the mpMRI and 3D SWE images. A total of 12 patients who were suspected of having significant cancer on mpMRI were included. The median pre-biopsy PSA value was 5.65 ng/ml. Of the 12 patients, 10 patients were diagnosed as having prostate cancer. In the targeted biopsy lesions, there was a significant difference in Young's modulus between the cancer-detected area (median 64.1 kPa, n=20) and undetected area (median 30.8 kPa, n=8; P<0.0001). On evaluation of receiver operating characteristics, a cut-off value of the Young's modulus of 41.0 kPa was used for the detection of clinically significant cancer, with which the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of cancer detection were 58, 97, 86 and 87%, respectively. When combining this cut-off tissue elasticity value with Prostate Imaging Reporting and Data System (PI-RADS) scores, the sensitivity, specificity, positive predictive value and negative predictive value of cancer detection were improved to 70, 98, 91 and 92%, respectively. In the cancer-detected lesions, a significant correlation was identified between the tissue elasticity value of the lesions and Gleason score (r=0.898, P<0.0001). In conclusion, PI-RADS combined with measurement of Young's modulus by 3D SWE may improve the diagnosis of clinically significant prostate cancer.

Endoscopic ultrasound: Current roles and future directions

Endoscopic ultrasound (EUS), developed in the 1980s, was initially predominantly used for guidance of fine needle aspiration; the last 25 years, however, have witnessed a major expansion of EUS to various applications, both diagnostic and therapeutic. EUS has become much more than a tool to differentiate different tissue densities; tissue can now be characterized in great detail using modalities such as elastography; the extent of tissue vascularity can now be learned with increasing precision. Using these various techniques, targets for biopsy can be precisely pinpointed. Upon reaching the target, tissue can then be examined microscopically in real-time, ensuring optimal targeting and diagnosis. This article provides a comprehensive review of the various current roles of EUS, including drainage of lesions, visualization and characterization of lesions, injection, surgery, and vascular intervention. With EUS technology continuing to develop exponentially, the article emphasizes the future directions of each modality.

Shear-Wave Elastography for Detection of Prostate Cancer: A Systematic Review and Diagnostic Meta-Analysis

OBJECTIVE

The objective of this study is to review the diagnostic performance of shear-wave elastography (SWE) in the detection of prostate cancer (PCa).

MATERIALS AND METHODS

The MEDLINE, EMBASE, and Cochrane library databases were searched up to December 23, 2016. We included diagnostic accuracy studies that used SWE for PCa detection with prostatectomy or biopsy used as the reference standard. The methodologic quality of the studies was evaluated by two independent reviewers using the revised Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. The sensitivity and specificity of all studies were calculated. Results were pooled and plotted in a hierarchical summary ROC plot with further exploration done using meta-regression analysis and subgroup analysis.

RESULTS

Eight studies (a total of 1028 patients) were evaluated. The pooled sensitivity was 0.83 (95% CI, 0.66-0.92) with a specificity of 0.85 (95% CI, 0.78-0.90) for the detection of PCa. Study design (prospective vs retrospective) was the only significant factor affecting heterogeneity (p < 0.01). At subgroup analysis, the pooled sensitivity and specificity were 0.84 (95% CI, 0.64-0.94) and 0.84 (95% CI, 0.76-0.90), respectively, in studies using shear-wave speed imaging and 0.84 (95% CI, 0.64-0.94) and 0.86 (95% CI, 0.78-0.91), respectively, in studies based on per-lesion analysis.

CONCLUSION

SWE shows good performance for the detection of PCa. However, specific recommendations regarding cutoff value cannot be made because of study heterogeneity.

Ultrasound Elastography of the Prostate Using an Unconstrained Modulus Reconstruction Technique: A Pilot Clinical Study

A novel full-inversion-based technique for quantitative ultrasound elastography was investigated in a pilot clinical study on five patients for non-invasive detection and localization of prostate cancer and quantification of its extent. Conventional-frequency ultrasound images and radiofrequency (RF) data (~5 MHz) were collected during mechanical stimulation of the prostate using a transrectal ultrasound probe. Pre and post-compression RF data were used to construct the strain images. The Young's modulus (YM) images were subsequently reconstructed using the derived strain images and the stress distribution estimated iteratively using finite element (FE) analysis. Tumor regions determined based on the reconstructed YM images were compared to whole-mount histopathology images of radical prostatectomy specimens. Results indicated that tumors were significantly stiffer than the surrounding tissue, demonstrating a relative YM of 2.5 ± 0.8 compared to normal prostate tissue. The YM images had a good agreement with the histopathology images in terms of tumor location within the prostate. On average, 76% ± 28% of tumor regions detected based on the proposed method were inside respective tumor areas identified in the histopathology images. Results of a linear regression analysis demonstrated a good correlation between the disease extents estimated using the reconstructed YM images and those determined from whole-mount histopathology images (r² = 0.71). This pilot study demonstrates that the proposed method has a good potential for detection, localization and quantification of prostate cancer. The method can potentially be used for prostate needle biopsy guidance with the aim of decreasing the number of needle biopsies. The proposed technique utilizes conventional ultrasound imaging system only while no additional hardware attachment is required for mechanical stimulation or data acquisition. Therefore, the technique may be regarded as a non-invasive, low cost and potentially widely-available clinical tool for prostate cancer diagnosis.

Second harmonic generation (SHG) imaging of cancer heterogeneity in ultrasound guided biopsies of prostate in men suspected with prostate cancer

Prostate cancer is a multifocal disease with characteristic heterogeneity and foci that can range from low grade indolent to aggressive disease. The latter is characterised by the well-established histopathological Gleason grading system used in the current clinical care. Nevertheless, a large discrepancy exists on initial biopsy and after the final radical prostatectomy. Moreover, there is no reliable imaging modality to study these foci, in particular at the level of the cells and surrounding matrix. Extracellular matrix (ECM) remodelling is significant in cancer progression with collagen as the dominant structural component providing mechanical strength and flexibility of tissue. In this study, the collagen assembly in prostate tissue was investigated with second harmonic generation (SHG) microscopy: malignant foci demonstrated a reticular pattern, with a typical collagen pattern for each Gleason score. The orientation of collagen for each biopsy was computed by applying a ratio of the anisotropic and isotropic collagen fibres. This value was found to be distinct for each Gleason score. The findings suggest that this approach can not only be used to detect prostate cancer, but also can act as a potential biomarker for cancer aggressiveness.

Accuracy of shear wave elastography for the diagnosis of prostate cancer: A meta-analysis

Many studies have established the high diagnostic accuracy of shear wave elastography (SWE) for the detection of prostate cancer (PCa); however, its utility remains a subject of debate. This meta-analysis sought to appraise the overall accuracy of SWE for the detection of PCa. A literature search of the PubMed, Embase, Cochrane Library, Web of Science and CNKI (China National Knowledge Infrastructure) databases was conducted. In all of the included studies, the diagnostic accuracy of SWE was compared with that of histopathology, which was used as a standard. Data were pooled, and the sensitivity, specificity, area under the curve (AUC), positive likelihood ratio (PLR), negative likelihood ratio (NLR), and diagnostic odds ratio (DOR) were calculated to estimate the accuracy of SWE. The pooled sensitivity and specificity for the diagnosis of PCa by SWE were 0.844 (95% confidence interval: 0.696–0.927) and 0.860 (0.792–0.908), respectively. The AUC was 0.91 (0.89–0.94), the PLR was 6.017 (3.674–9.853), and the NLR was 0.182 (0.085–0.389). The DOR was 33.069 (10.222–106.982). Thus, SWE exhibited high accuracy for the detection of PCa using histopathology as a diagnostic standard. Moreover, SWE may reduce the number of core biopsies needed.

Stiffness of benign and malignant prostate tissue measured by shear-wave elastography: a preliminary study

OBJECTIVES

To measure benign and malignant prostate tissue stiffness using shear-wave elastography (SWE).

METHODS

Thirty consecutive patients underwent transrectal SWE in the axial and sagittal planes before prostatectomy. After reviewing prostatectomy specimens, two radiologists measured stiffness in regions corresponding to cancers, lateral and median benign peripheral zone (PZ) and benign transition zone (TZ).

RESULTS

Cancers were stiffer than benign PZ and TZ. All tissue classes were stiffer on sagittal than on axial imaging, in TZ than in PZ, and in median PZ than in lateral PZ. At multivariate analysis, the nature of tissue (benign or malignant; P < 0.00001), the imaging plane (axial or sagittal; P < 0.00001) and the location within the prostate (TZ, median PZ or lateral PZ; P = 0.0065) significantly and independently influenced tissue stiffness. On axial images, the thresholds maximising the Youden index in TZ, lateral PZ and median PZ were respectively 62 kPa, 33 kPa and 49 kPa. On sagittal images, the thresholds were 76 kPa, 50 kPa and 72 kPa, respectively.

CONCLUSIONS

SWE can distinguish prostate malignant and benign tissues. Tissue stiffness is influenced by the imaging plane and the location within the gland.

KEY POINTS

• Prostate cancers were stiffer than the benign peripheral zone • All tissue classes were stiffer on sagittal than on axial imaging • All tissue classes were stiffer in the transition zone than in the peripheral zone • All tissue classes were stiffer in the median than in the lateral peripheral zone • Taking into account imaging plane and zonal anatomy can improve cancer detection.

Utility of Ultrasound in the Diagnosis, Treatment, and Follow-up of Prostate Cancer: State of the Art

Prostate cancer screening currently consists of serum prostate-specific antigen and digital rectal examination, followed by transrectal ultrasound-guided biopsy for diagnostic confirmation. Although the current paradigm of prostate cancer screening has led to a decrease in advanced disease and cancer-related mortality, these techniques have limitations in terms of sensitivity and specificity, resulting in missed cancers that are clinically significant and the overdetection of clinically insignificant cancers. New imaging techniques and technologies are required to improve the detection of prostate cancer. This article summarizes the use of novel ultrasound techniques and technologies in the detection, biopsy, and treatment of prostate cancer.

WFUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography: Part 5. Prostate

The World Federation for Ultrasound in Medicine and Biology (WFUMB) has produced guidelines for the use of elastography techniques, including basic science, breast, liver and thyroid elastography. Here we present elastography in prostate diseases. For each available technique, procedure, reproducibility, results and limitations are analyzed and recommendations are given. Finally, recommendations are given based on the level of evidence of the published literature and on the WFUMB expert group's consensus. This document has a clinical perspective and is aimed at assessing the usefulness of elastography in the management of prostate diseases.

Inability of shear-wave elastography to distinguish malignant from benign prostate tissue - a comparison of biopsy, whole-mount sectioning and shear-wave elastography

Aim

This study was designed to assess the possible usefulness of shear-wave elastography in differentiating between benign and malignant tissue in prostate neoplasia.

Patients and methods

A total of 120 prostate tissue samples were obtained from 10 patients treated by radical prostatectomy and investigated pre-operatively by ultrasound elastography followed by directed biopsy. After resection, whole-mount sectioning and histological examination was performed. The predictions based on shear-wave elastography were compared with biopsy and histological results.

Results

The comparison between the results of shear-wave elastography and those of biopsy was performed by receiver operating characteristic analysis, which suggested an optimum cut-off tissue elasticity value of 50 kPa, in agreement with earlier studies aimed at distinguishing between benign and malignant tissue. However, the diagnostic selectivity (and thus the diagnostic power) was poor (area under the curve 0.527, which hardly differs from the value of 0.500 that would correspond to a complete lack of predictive power); furthermore, application of this cut-off value to the samples led to a sensitivity of only 74% and a specificity of only 43%. An analogous comparison between the results of shear-wave elastography and those of whole-mount histology, which itself is more reliable than biopsy, gave an even poorer diagnostic selectivity (sensitivity of 62%, specificity of 35%). Meaningful association with Gleason score was not found for D’Amico risk groups (p = 0.35).

Conclusions

The (negative) findings of this investigation add to the dissonance among results of studies investigating the possible value of shear-wave elastography as a diagnostic tool to identify malignant neoplasia. There is a clear need for further research to elucidate the diversity of study results and to identify the usefulness, if any, of the method in question.

Deep learning based classification of breast tumors with shear-wave elastography

This study aims to build a deep learning (DL) architecture for automated extraction of learned-from-data image features from the shear-wave elastography (SWE), and to evaluate the DL architecture in differentiation between benign and malignant breast tumors. We construct a two-layer DL architecture for SWE feature extraction, comprised of the point-wise gated Boltzmann machine (PGBM) and the restricted Boltzmann machine (RBM). The PGBM contains task-relevant and task-irrelevant hidden units, and the task-relevant units are connected to the RBM. Experimental evaluation was performed with five-fold cross validation on a set of 227 SWE images, 135 of benign tumors and 92 of malignant tumors, from 121 patients. The features learned with our DL architecture were compared with the statistical features quantifying image intensity and texture. Results showed that the DL features achieved better classification performance with an accuracy of 93.4%, a sensitivity of 88.6%, a specificity of 97.1%, and an area under the receiver operating characteristic curve of 0.947. The DL-based method integrates feature learning with feature selection on SWE. It may be potentially used in clinical computer-aided diagnosis of breast cancer.

The role of imaging in the diagnosis of primary prostate cancer

Ultrasound and magnetic resonance imaging (MRI) are key imaging modalities in prostate cancer diagnosis. MRI offers a range of intrinsic contrast mechanisms (T2, diffusion-weighted imaging (DWI), MR spectroscopy (MRS)) and extrinsic contrast-generating options based on tumour vascular state following injection of weakly paramagnetic agents such as gadolinium. Together these parameters are referred to as multiparametric (mp)MRI and are used for detecting and guiding biopsy and staging prostate cancer. Although sensitivity of mpMRI is <75% for disease detection, specificity is >90% and a standardised reporting system together with MR-guided targeted biopsy is the optimal diagnostic pathway. Shear wave ultrasound elastography is a new technique which also holds promise for future studies. This article describes the developments in imaging the primary site of prostate cancer and reviews their current and future utility for screening, diagnosis and T-staging the disease.

Elastographic Strain Index in the Evaluation of Focal Lesions Detected With Transrectal Sonography of the Prostate Gland

OBJECTIVES

The purpose of this study was to evaluate the value of elastography in evaluating focal lesions detected by transrectal sonography and to suggest a reference strain index.

METHODS

Sixty-nine patients with focal lesions on transrectal sonography were referred to our department for prostate biopsy. Focal lesions were classified as either highly or less suspicious lesions by our criteria. A strain index from elastography was calculated for the focal lesions. Systematic 12-core randomized biopsies plus 2 targeted biopsies were performed. The mean strain indices for malignant and benign focal lesions were compared, and a cutoff strain index was attained to maximize the sensitivity and specificity for prostate cancer. Strain indices were correlated with Gleason scores.

RESULTS

The mean strain index ± SD for malignant focal lesions (3.26 ± 1.77) was significantly higher than that for benign focal lesions (2.16 ± 1.52; P = .008). The sensitivity, specificity, and area under the receiver operating characteristic curve for diagnosing cancer were 66.7%, 71.1%, and 0.701, respectively, at a strain index cutoff value of greater than 2.4. The strain index showed a moderate linear correlation with the Gleason score (r = 0.441; P = .013).

CONCLUSIONS

Any focal lesion on transrectal sonography with a strain index of greater than 2.4 is at risk for prostate cancer.

A urologist's perspective on prostate cancer imaging: past, present, and future

Prostate cancer is unique in that unlike other solid organ malignancies, only recently has imaging been employed to routinely detect and localize disease. The introduction of transrectal ultrasound was a significant development, transitioning digitally guided prostate biopsies to ultrasound guidance. The arrival of multiparametric MRI has become the next major step, transforming the way Urologist's diagnose, stage, and treat prostate cancer. Recent recommendations against PSA screening have changed the landscape of urologic oncology with the changing needs being reflected in the initiation of additional robust imaging techniques at different time points in prostate cancer care. The current review aims to provide a clinical perspective in the history, current standard of care, and novel imaging modalities in the evaluation of prostate cancer.

A Review of Imaging Methods for Prostate Cancer Detection

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

Endoscopic ultrasound elastography: Current status and future perspectives

Elastography is a new ultrasound modality that provides images and measurements related to tissue stiffness. Endoscopic ultrasound (EUS) has played an important role in the diagnosis and management of numerous abdominal and mediastinal diseases. Elastography by means of EUS examination can assess the elasticity of tumors in the proximity of the digestive tract that are hard to reach with conventional transcutaneous ultrasound probes, such as pancreatic masses and mediastinal or abdominal lymph nodes, thus improving the diagnostic yield of the procedure. Results from previous studies have promised benefits for EUS elastography in the differential diagnosis of lymph nodes, as well as for assessing masses with pancreatic or gastrointestinal (GI) tract locations. It is important to mention that EUS elastography is not considered a modality that can replace biopsy. However, it may be a useful adjunct, improving the accuracy of EUS-fine needle aspiration biopsy (EUS-FNAB) by selecting the most suspicious area to be targeted. Even more, it may be useful for guiding further clinical management when EUS-FNAB is negative or inconclusive. In the present paper we will discuss the current knowledge of EUS elastography, including the technical aspects, along with its applications in the differential diagnosis between benign and malignant solid pancreatic masses and lymph nodes, as well as its aid in the differentiation between normal pancreatic tissues and chronic pancreatitis. Moreover, the emergent indication and future perspectives are summarized, such as the benefit of EUS elastography in EUS-guided fine needle aspiration biopsy, and its uses for characterization of lesions in liver, biliary tract, adrenal glands and GI tract.

3D surface-based registration of ultrasound and histology in prostate cancer imaging

Several transrectal ultrasound (TRUS)-based techniques aiming at accurate localization of prostate cancer are emerging to improve diagnostics or to assist with focal therapy. However, precise validation prior to introduction into clinical practice is required. Histopathology after radical prostatectomy provides an excellent ground truth, but needs accurate registration with imaging. In this work, a 3D, surface-based, elastic registration method was developed to fuse TRUS images with histopathologic results. To maximize the applicability in clinical practice, no auxiliary sensors or dedicated hardware were used for the registration. The mean registration errors, measured in vitro and in vivo, were 1.5±0.2 and 2.1±0.5mm, respectively.