The contribution of strain patterns in characterization of prostate peripheral zone lesions at transrectal ultrasonography

Elastography Targeted Prostate Biopsy in Patients under Active Surveillance

OBJECTIVE

The aim of this study was to examine elastography-based prostate biopsy in prostate cancer (PCa) patients under active surveillance.

PATIENTS AND METHODS

We relied on PCa patients who opted for active surveillance and underwent elastography targeted and systematic follow-up biopsy at the Braunschweig Prostate Cancer Center between October 2009 and February 2015. Each prostate sextant was considered as an individual case. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy (ACC) for elastography to predict follow-up biopsy results were analyzed, respectively, and 95 % confidence intervals (CIs) were carried out by using 2000 bootstrapping sample analyses.

RESULTS

Overall, 50 men and 300 sextants were identified. Overall, 27 (54%) men and 66 (22%) sextants harbored PCa at follow-up biopsy. Sensitivity, specificity, PPV, NPV, and ACC for elastography to predict follow-up biopsy results were: 19.7 (95% CI: 11.9-27.3), 86.8 (95% CI: 82.7-90.3), 29.6 (95% CI: 14.6-46.0), 79.3 (95% CI: 71.6-86.5), and 72.0% (95% CI: 65.7-78.3), respectively.

CONCLUSIONS

We recorded limited reliability of elastography-based prediction of follow-up biopsy results in active surveillance patients. Based on our analyses, we can neither recommend to rely exclusively on elastography-based targeted biopsies nor to delay or to omit follow-up biopsies based on elastography results during active surveillance.

Evaluation of the Performance of the Ultrasound (US) Elastographic Q-Analysis Score Combined With the Prostate Imaging Reporting and Data System for Malignancy Risk Stratification in Prostate Nodules Based on Transrectal US-Magnetic Resonance Imaging Fusion Imaging

OBJECTIVES

This study retrospectively evaluated the prognostic performance of the ultrasound elastographic Q-analysis score (EQS) combined with the Prostate Imaging Reporting and Data System (PI-RADS) for malignancy risk stratification in prostate nodules based on transrectal ultrasound-magnetic resonance imaging fusion imaging.

METHODS

Sixty-two patients who were suspected to have PCa between October 2017 and May 2018 in our hospital were retrospectively evaluated. The performance of the EQS and PI-RADS was evaluated by patients' receiver operating characteristic curves in differentiating malignant and benign prostate nodules. The combination of the EQS and PI-RADS methods for prostate imaging was evaluated.

RESULTS

Sixty-two prostate nodules in 62 patients were included. All of the patients underwent biopsy; 29 cases were prostate cancer, and the rest were benign prostate lesions. Both the EQS and PI-RADS were significantly higher in malignant nodules than in benign nodules. The sensitivity, specificity, area under the curve, positive likelihood ratio, negative likelihood ratio, positive predictive value, negative predictive value, and Youden index of an EQS cutoff of 2.05 were 86.2%, 81.8%, 85.9%, 4.73, 0.169, 80.6%, 87.1%, and 68%, respectively. The corresponding numbers for a PI-RADS cutoff of 4 were 82.7%, 69.7%, 84.2%, 2.72, 0.25, 70.6%, 82.1%, and 52.4%. The "tandem" method had a higher diagnostic specificity (87.9%), positive likelihood ratio (6.55), and positive predictive value (85.1%). The "parallel" method had a higher diagnostic sensitivity (96.5%), negative likelihood ratio (0.06), and negative predictive value (95.2%).

CONCLUSIONS

both the EQS and PI-RADS had good diagnostic performance in differentiating between malignant and benign prostate lesions. The combination of the EQS and PI-RADS improved the diagnostic performance to a certain degree.

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.

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.

Additional Targeted Biopsy in Clinically Suspected Prostate Cancer: Prospective Randomized Comparison between Contrast-Enhanced Ultrasound and Sonoelastography Guidance

Our aim was to improve the detection of prostate cancer by evaluating whether contrast-enhanced ultrasound (CEUS) or sonoelastography (SE) is more helpful in guiding targeted biopsy (TB) performed before systematic biopsy (SB). A total of 52 patients suspected of having prostate cancer were prospectively included and randomly assigned to either the CEUS or SE group. Different, independent radiologists performed TB and twelve-core SB. Within each group, cancer detection rates based on core number were compared between SB and TB. We evaluated the effect of TB on core-based cancer detection rates between the CEUS and SE groups. Cancer detection was higher in overall TB cores 16.4% (28/171) than SB cores 11.4% (71/624) in both groups. In the SE group, TB cores revealed higher cancer detection than did SB cores from 4.49% (14/312) to 12.86% (9/70) (p = 0.01). Compared with CEUS, SE may improve detection rates when considering additional TB guidance methods.

Detection and characterisation of biopsy tissue using quantitative optical coherence elastography (OCE) in men with suspected prostate cancer

We present first quantitative three-dimensional (3D) data sets recorded using optical coherence elastography (OCE) for the diagnosis and detection of prostate cancer (PCa). 120 transrectal ultrasound guided prostate biopsy specimens from 10 men suspected with prostate cancer were imaged using OCE. 3D quantitative mechanical assessment of biopsy specimens obtained in kilopascals (kPa) at an interval of 40 µm was compared with histopathology. Sensitivity, specificity, and positive and negative predictive values were calculated for OCE in comparison to histopathology. The results show OCE imaging could reliably differentiate between benign prostate tissue, acinar atypical hyperplasia, prostatic intraepithelial neoplasia and malignant PCa. The sensitivity and specificity of OCE for the detection of prostate cancer was 0.98 and 0.91 with AUC > 0.99. Quantitative 3D OCE based on the assessment of mechanical properties of tissues can reliably differentiate prostate tissue specimen in an ex-vivo setting. This is a promising imaging modality for characterising different grades of cancers.

Transrectal real-time tissue elastography - an effective way to distinguish benign and malignant prostate tumors

BACKGROUND

To investigate the relationship between extracellular matrix parameters and texture of prostatic lesions evaluated by transrectal real-time tissue elastography (TRTE).

METHODS

120 patients suspicious for prostate cancer underwent TRTE. Targeted biopsies were carried out after 12-core systematic biopsy. Epithelia were stained with hematoxylin-eosin, and Victoria blue and Ponceau S were used to stain elastic-collagen fibers, and picric acid-sirius red for visualization of collagen type I (Col1) and III (Col3). Smooth muscles were visualized by immunohistochemistry. All image analyses were performed in a blind manner using Image Pro Plus 6.0, and the area ratios of epithelium, elastic fibers, collagen fibers and Col1/Col3 were determined.

RESULTS

42 patients with typical elastograms were included in the final data analysis. Significant differences were detected between the benign and malignant groups in the area ratios of epithelium (P = 0.01), smooth muscles and Col1/Col3 (P = 0.04, P = 0.02, respectively). There were no significant differences in the area ratios of epithelium, smooth muscle and elastic fibers between the stiff and soft lesion groups. The area ratio of Col1 was (0.05 ± 0.03) in the stiff group, and (0.02 ± 0.01) in the soft group (P= 0.00). However, the area ratio of Col3 was (0.03 ± 0.02) in the stiff group, and (0.05 ± 0.04) in the soft group (P = 0.16). Col1/Col3 in the stiff group (1.99 ± 1.59) was greater than in the soft group (0.71 ± 0.64) (P = 0.01).

CONCLUSIONS

Tissue hardness of prostatic tumors was mainly dependent on the Col1 content, Col1/Col3 being higher in malignant than in benign lesions, so the prostate tissue texture can be used as a target for distinguishing between the two with TRTE.

Elastic modulus of the prostate: a new non-invasive feature to diagnose bladder outlet obstruction in patients with benign prostatic hyperplasia

The purpose of our study was to develop a reliable method for the non-invasive evaluation of bladder outlet obstruction (BOO) caused by benign prostate hyperplasia (BPH). In our study, the International Prostate Symptom Score was assessed in, and trans-rectal ultrasound (TRUS) and shear wave sonoelastography (SWE) were performed on, 55 patients with BPH who had undergone urodynamic evaluation (the gold standard diagnostic procedure for BOO). The results indicated that the elastic modulus of the transitional zone was the indicator most strongly correlated with BOO stage (r = 0.666, p < 0.001), and had the largest area under the receiver operating characteristic curve, 0.826 (95% confidence interval: 0.717-0.934, p = 0.001). An elastic modulus of the transitional zone ≥ 32.4 kPa or a total prostate volume ≥ 54.4 mL was diagnostic of BOO, with a sensitivity, specificity, positive predictive value, negative predictive value and accuracy for BOO of 97.2%, 62.5%, 85.4%, 90.9% and 86.5%, respectively. The elastic modulus of the transitional zone is a promising indicator in the assessment of the severity of BOO. In addition, the combination of elastic modulus and total prostate volume was the most accurate indicator in the non-invasive diagnosis of BOO in patients with BPH.

Alterations in mechanical properties are associated with prostate cancer progression

Cancer progression and metastasis have been shown to be accompanied by alterations in the mechanical properties of tissues, but the relationship between the mechanical properties and malignant behavior in prostate cancer (Pca) is less clear. The aims of this study were to detect the mechanical properties of benign prostatic hyperplasia (BPH) and Pca tissues on both the macro- and micro-scales, to explore the relationships between mechanical properties and malignant behavior and, finally, to identify the important molecules in the mechanotransduction signaling pathway. We demonstrated that the strain index of Pca tissue was significantly higher than that of BPH tissue on the macro-scale but the Young's modulus of the Pca tissues, especially in advanced Pca, was lower than that of BPH tissues on the micro-scale. These two seemingly contradictory results can be explained by the excessive proliferation of tumor cells (Ki-67) and the degradation of scaffold proteins (collagens). These data indicate that alterations of the macro- and micro-mechanical properties of Pca tissues with malignant behavior are contradictory. The mechanical properties of tissues might be useful as a new risk factor for malignancy and metastasis in Pca. Furthermore, collagens, matrix metalloproteinase, fibronectin, and integrins might be the important molecules in the mechanotransduction signaling pathway.

Prostatic elasticity: a new non-invasive parameter to assess bladder outlet obstruction caused by benign prostatic hyperplasia (a canine experiment)

OBJECTIVE

To evaluate the change of prostatic elasticity during the development of benign prostatic hyperplasia (BPH) and its correlation with the degree of bladder outlet obstruction (BOO) in the canine model of BOO caused by BPH.

MATERIALS AND METHODS

Ten male beagle dogs were selected in this study. To establish canine model of BOO caused by BPH, each beagle underwent castration surgery followed by encapsulating the prostate with a double layer of nylon mesh and then treating the beagles with a combination of steroids for 12 weeks. Transrectal ultrasound (TRUS) examination and urodynamic evaluation were performed before and at 4, 8, and 12 weeks of hormone administration. Prostatic volume, Young modulus of prostatic tissue, and urodynamic parameters were compared at each time instance, and the correlation between the Young modulus of the prostatic tissue and urodynamic parameters were evaluated.

RESULTS

All beagles developed BOO caused by BPH over the time period of the study. Prostatic volume, Young modulus of prostatic tissue, and urodynamic parameters had statistically significant differences before and after 4, 8, and 12 weeks of hormone administration (P <.05). Young modulus of prostatic tissue showed a very significant correlation with urodynamic parameters, including maximum urine flow (Qmax) (r = -0.802, P <.01), Qave (r = -0.711, P <.01), Pves@open (r = 0.638, P <.01), Pves@Qmax (r = 0.699, P <.01), Pdet@Qmax (r = 0.757, P <.01), and Pdetmax (r = 0.739, P <.01).

CONCLUSION

Young modulus of prostatic tissue increased during the development of the BPH. There was a significant correlation between Young modulus of prostatic tissue and the degree of BOO.

Towards ultrasound probe positioning optimization during prostate needle biopsy using pressure feedback

PURPOSE

Accurate Transrectal Ultrasound (TRUS)-guided prostate needle biopsy requires registering preoperative 3D TRUS or MR image, in which tumors and other suspicious areas are visible, to intraoperative 2D TRUS images. Such image registration is time-consuming while its real-time implementation is yet to be developed. To bypass this registration step, robotic needle biopsy systems can be used to place the US probe at the same position relative to the prostate during the 3D and 2D image acquisition to ensure similar prostate deformation. To have such similar deformation, only visual feedback is not sufficient as such feedback can be used to only guarantee that the whole prostate is within the field of view irrespective of the probe's orientation. As such, contact pressure feedback can be utilized to ensure consistent minimum contact between the probe and prostate.

METHOD

A robotic system is proposed where a TRUS probe with pressure sensor array is used. The contact pressure can be measured during imaging and used to provide feedback in conjunction with an optimization algorithm for consistent probe positioning. The robotic system is driven by the feedback to position the probe such that pressure pattern of the sensors during 2D image acquisition is similar to the pressure pattern during 3D image acquisition. The proposed method takes into account the patient's body movement expected during image acquisition. In this study, an in silico phantom is used where the simulated contact pressure distribution required in the optimization algorithm is obtained using a prostate finite element model.

RESULT

Starting from an arbitrary position where the probe contacts the phantom, this position was varied systematically until a position corresponding to maximum pressure pattern similarity between contact pressure patterns corresponding to the 2D and 3D imaging was achieved successfully.

CONCLUSION

Results obtained from the in silico phantom study indicate that the proposed technique is capable of ensuring having only minimal relative prostate deformation between preoperative image acquisition and intraoperative imaging used for guiding needle biopsy, paving the way for faster and more accurate registration.