[Selection of candidates for prostate biopsy using multiparametric magnetic resonance imaging in patients with persistently raising PSA]

The current diagnosis of prostate cancer is based on randomized prostate biopsies to obtain histological material for study, without introducing any imaging technique in the diagnostic algorithm.

OBJECTIVES

To conduct a literature review of the role of multiparametric MRI ( mMRI ) in the diagnosis of prostate cancer, and present preliminary data from our series of 233 patients undergoing mRMN and transrectal ultrasound (TRUS) prostate biopsy.

MATERIAL AND METHODS

We performed a PubMed search for those articles that refer to the usefulness of mMRI in the follow-up and monitoring of patients with persistently elevated PSA without previous biopsies, and those with a previous negative biopsy, and assess the power of mRMN for detecting PCa in both the peripheral and the central gland. We present the preliminary results of our series, consisting of 233 patients selected between 2008 and 2011 undergoing mMRI and TRUS-guided prostatic biopsy because of elevated PSA levels or suspicious digital rectal examination.

RESULTS

We discuss several articles published from 2003 to 2014. We compare our results with those from the literature.

DISCUSSION

The diagnostic algorithm of prostate cancer to date does not include any imaging technique in the decision-making process. The mMRI is a functional imaging technique that provides increasing evidence in deciding which patients should be biopsied and which patients may avoid it despite persisting high levels of PSA. The advantage of this technique lies not only in its high detection rate in intermediate and high risk lesions, but also in its high specificity. It allows us to avoid diagnosing clinically insignificant tumors and thus, avoids overtreatment.

CONCLUSION

The mRMN is a useful technique not yet incorporated in algorithms of prostate cancer diagnosis in urological societies. Its safety, effectiveness and efficiency are forcing to include its progressive use and with high probability will be soon incorporated into the decision-making charts.

Joint probability of shape and image similarities to retrieve 2D TRUS-MR slice correspondence for prostate biopsy

This paper presents a novel method to identify the 2D axial Magnetic Resonance (MR) slice from a pre-acquired MR prostate volume that closely corresponds to the 2D axial Transrectal Ultrasound (TRUS) slice obtained during prostate biopsy. The method combines both shape and image intensity information. The segmented prostate contours in both the imaging modalities are described by shape-context representations and matched using the Chi-square distance. Normalized mutual information and correlation coefficient between the TRUS and MR slices are computed to find image similarities. Finally, the joint probability values comprising shape and image similarities are used in a rule-based framework to provide the MR slice that closely resembles the TRUS slice acquired during the biopsy procedure. The method is evaluated for 20 patient datasets, of which 18 results match at least one of the two clinical expert choices.

Spectral clustering of shape and probability prior models for automatic prostate segmentation

Imaging artifacts in Transrectal Ultrasound (TRUS) images and inter-patient variations in prostate shape and size challenge computer-aided automatic or semi-automatic segmentation of the prostate. In this paper, we propose to use multiple mean parametric models derived from principal component analysis (PCA) of shape and posterior probability information to segment the prostate. In contrast to traditional statistical models of shape and intensity priors, we use posterior probability of the prostate region determined from random forest classification to build, initialize and propagate our model. Multiple mean models derived from spectral clustering of combined shape and appearance parameters ensure improvement in segmentation accuracies. The proposed method achieves mean Dice similarity coefficient (DSC) value of 0.96±0.01, with a mean segmentation time of 0.67±0.02 seconds when validated with 46 images from 23 datasets in a leave-one-patient-out validation framework.

The value of endorectal MR imaging to predict positive biopsies in clinically intermediate-risk prostate cancer patients

The aim of this study was to assess the effectiveness of endorectal MR imaging in predicting the positive biopsy results in patients with clinically intermediate risk for prostate cancer. We performed a prospective endorectal MR imaging study with 81 patients at intermediate risk to detect prostate cancer between January 1997 and December 1998. Intermediate risk was defined as: prostatic specific antigen (PSA) levels between 4 and 10 ng/ml or PSA levels in the range of 10-20 ng/ml but negative digital rectal examination (DRE) or PSA levels progressively higher (0.75 ng/ml year(-1)). A transrectal sextant biopsy was performed after the endorectal MR exam, and also of the area of suspicion detected by MR imaging. The accuracies were measured, both singly for MR imaging and combined for PSA level and DRE, by calculating the area index of the receiver operating characteristics (ROC) curve. Cancer was detected in 23 patients (28%). Overall sensitivity and specificity of endorectal MRI was 70 and 76%, respectively. Accuracy was 71% estimated from the area under the ROC curve for the total patient group and 84% for the group of patients with PSA level between 10-20 ng/ml. Positive biopsy rate (PBR) was 63% for the group with PSA 10-20 ng/ml and a positive MR imaging, and 15% with a negative MR exam. The PBR was 43% for the group with PSA 4-10 ng/ml and a positive MR study, and 13% with a negative MR imaging examination. We would have avoided 63% of negative biopsies, while missing 30% of cancers for the total group of patients. Endorectal MR imaging was not a sufficient predictor of positive biopsies for patients clinically at intermediate risk for prostate cancer. Although we should not avoid performing systematic biopsies in patients with endorectal MR imaging negative results, as it will miss a significant number of cancers, selected patients with a PSA levels between 10-20 ng/ml or clinical-biopsy disagreement might benefit from endorectal MR imaging.