Imaging of prostate cancer

Sensitivity and specificity evaluation of endorectal magnetic resonance imaging and transrectal sonography in the staging of prostate cancer

Objectives

Nowadays endorectal probes for Magnetic Resonance Imaging (MRI) have better resolutions, which allows to acquire high-level images of prostate and to improve the MRI sensitivity and specificity to determine the cancer volume and the extraprostatic extension. The objective of the present study is to evaluate the sensitivity and diagnostic accuracy of endorectal MRI for identifying the local extension of prostate carcinoma compared to transrectal sonography (TRUS) of prostate.

Materials and Methods

The study included 81 patients with clinical suspect of cancer and/or elevated values of serum prostate specific antigen (PSA), who underwent endorectal MRI with 1.5 T endorectal probe before transrectal biopsy. Patients with localized prostate cancer underwent radical surgery. The results of endorectal MRI were compared to those of TRUS and histopathological examination outcomes.

Results

15 of the 81 enrolled patients had extraprostatic localization of cancer, which was assessed through TRUS in 4 cases only (26%), and through MRI in 7 cases (46%). A seminal vesicle involvement was present in 10 patients, detected by MRI in 5 cases and in no cases by TRUS.

Discussion and Conclusions

Data are similar to the findings collected by several Authors. The endorectal MRI has a better accuracy in staging prostate cancer compared to TRUS. Nevertheless, this procedure has some limits: little availability of equipment in hospitals, physicians’ little experience, and higher costs compared to TRUS.

Follow-up of the transrectal ultrasonographic features of the prostate after biopsy: does any ultrasonographically detectable lesion form secondary to the first biopsy?

OBJECTIVE

The purpose of this study was to evaluate the transrectal ultrasonographic features of the prostate after biopsy and to find out whether any ultrasonographically detectable lesion forms secondary to biopsy.

METHODS

Prebiopsy transrectal ultrasonographic findings in 60 consecutive patients who underwent repeated biopsies were evaluated. Detected lesions that were not defined before the first biopsy were considered postbiopsy-formed lesions and were sampled during the second biopsy. All transrectal ultrasonographically detected lesions were correlated with histopathologic results in the same locations.

RESULTS

There were 7 (11.6%) patients with new hypoechoic lesions formed after the first biopsy. Histopathologic analysis of postbiopsy-detected lesions showed that 38.5% were cancer; 62.5% of the detected benign lesions were prostatitis foci.

CONCLUSIONS

Prostate biopsy does not give rise to formation of fibrotic scar tissue in the peripheral zone. Most postbiopsy-detected lesions are prostatitis foci, but all hypoechoic lesions must be sampled during repeated prostate biopsies because of the 38.5% cancer detection rate.

The value of endorectal MRI in the early diagnosis of prostate cancer

OBJECTIVE

Assess the value of endorectal MR imaging (EMRI) in the early diagnosis of prostate cancer (PCa) and compare this test to prostate specific antigen (PSA) and digital rectal examination (DRE) in the prediction of negative biopsies.

MATERIAL AND METHODS

92 patients with elevated PSA (>4 ng/ml) and/or abnormal DRE were studied. All patients underwent an EMRI previous to transrectal ultrasound guided needle sextant biopsies (3 cores in each peripheral zone), and were followed up. We performed a total of 184 biopsies: 92 patients underwent 1 biopsy; out of them, 61 patients underwent 2 biopsies, 27 patients 3 biopsies, 3 patients 4 biopsies and 1 patient 5 biopsies. 67 patients had a final negative biopsy and 25 had a final positive biopsy. Mean PSA was 10.44 ng/ml, and the mean % fPSA/tPSA was 0.20. Uni- and multivariate analysis and ROC curves were used to compare the accuracy of the different tests. The probability of positive biopsy with each technique was also assessed.

RESULTS

EMRI had a high negative predictive value (91.07%) and the highest accuracy (77%) of all tests, higher than PSA (62%). Mean PSA was not statistically different in patients with negative biopsies (9.44 ng/ml) and positive biopsies (11.8 ng/ml) (p=0.064). The association of EMRI-DRE-PSA had the highest accuracy (83%) significantly higher than DRE-PSA (70%). The probability of positive biopsy in patients with negative DRE and EMRI, and PSA values between 5 and 15 ng/ml was 5-10% at first and second biopsies, but decreased progressively on subsequent biopsies (<8% at third biopsy, <5% at fourth biopsy and <3% at fifth biopsy).

CONCLUSION

In patients with elevated PSA and/or abnormal DRE with two previous negative biopsies, an EMRI is a useful test to rule out PCa, when negative, and avoid subsequent biopsies, as they have a low chance of positive biopsy.

The prostate: MR imaging and spectroscopy. Present and future

The applications of combined MR imaging and MR spectroscopic imaging of prostate cancer have expanded significantly over the past 10 years and have reached the point of clinical trial results to test robustness and clinical significance. MR spectroscopic imaging extends the diagnostic evaluation of prostate cancer beyond the morphologic information provided by MR imaging throughout the detection of cellular metabolites. The combined metabolic and anatomic information provided by MR imaging and MR spectroscopic imaging has allowed a more accurate assessment of the presence, location, extent, and aggressiveness of prostate cancer both before and after treatment. This information has already demonstrated the ability to improve therapeutic planning for individual prostate cancer patients and shows great promise in the assessment of therapeutic response and the evaluation of new treatment regimes.

Three-dimensional magnetic resonance spectroscopic imaging of brain and prostate cancer

Clinical applications of magnetic resonance spectroscopic imaging (MRSI) for the study of brain and prostate cancer have expanded significantly over the past 10 years. Proton MRSI studies of the brain and prostate have demonstrated the feasibility of noninvasively assessing human cancers based on metabolite levels before and after therapy in a clinically reasonable amount of time. MRSI provides a unique biochemical "window" to study cellular metabolism noninvasively. MRSI studies have demonstrated dramatic spectral differences between normal brain tissue (low choline and high N-acetyl aspartate, NAA) and prostate (low choline and high citrate) compared to brain (low NAA, high choline) and prostate (low citrate, high choline) tumors. The presence of edema and necrosis in both the prostate and brain was reflected by a reduction of the intensity of all resonances due to reduced cell density. MRSI was able to discriminate necrosis (absence of all metabolites, except lipids and lactate) from viable normal tissue and cancer following therapy. The results of current MRSI studies also provide evidence that the magnitude of metabolic changes in regions of cancer before therapy as well as the magnitude and time course of metabolic changes after therapy can improve our understanding of cancer aggressiveness and mechanisms of therapeutic response. Clinically, combined MRI/MRSI has already demonstrated the potential for improved diagnosis, staging and treatment planning of brain and prostate cancer. Additionally, studies are under way to determine the accuracy of anatomic and metabolic parameters in providing an objective quantitative basis for assessing disease progression and response to therapy.

Elastic moduli of breast and prostate tissues under compression

To evaluate the dynamic range of tissue imaged by elastography, the mechanical behavior of breast and prostate tissue samples subject to compression loading has been investigated. A model for the loading was validated and used to guide the experimental design for data collection. The model allowed the use of small samples that could be considered homogeneous; this assumption was confirmed by histological analysis. The samples were tested at three strain rates to evaluate the viscoelastic nature of the material and determine the validity of modeling the tissue as an elastic material for the strain rates of interest. For loading frequencies above 1 Hz, the storage modulus accounted for over 93 percent of the complex modulus. The data show that breast fat tissue has a constant modulus over the strain range tested while the other tissues have a modulus that is dependent on the strain level. The fibrous tissue samples from the breast were found to be 1 to 2 orders of magnitude stiffer than fat tissue. Normal glandular breast tissue was found to have an elastic modulus similar to that of fat at low strain levels, but the modulus of the glandular tissue increased by an order of magnitude above fat at high strain levels. Carcinomas from the breast were stiffer than the other tissues at the higher strain level; intraductal in situ carcinomas were like fat at the low strain level and much stiffer than glandular tissue at the high strain level. Infiltrating ductal carcinomas were much stiffer than any of the other breast tissues. Normal prostate tissue has a modulus that is lower than the modulus of the prostate cancers tested. Tissue from prostate with benign prostatic hyperplasia (BPH) had modulus values significantly lower than normal tissue. There was a constant but not significant difference in the modulus of tissues taken from the anterior and posterior portions of the gland.

Source localization following permanent transperineal prostate interstitial brachytherapy using magnetic resonance imaging

PURPOSE

Dosimetric evaluation of completed brachytherapy implant procedures is crucial in developing proper technique and has prognostic implications. Accurate definition of the prostate gland and localization of the implanted radioactive sources are critical to attain meaningful dosimetric data. Methods using radiographs and CT accurately localize sources, but poorly delineate the prostate gland. MRI has been recognized as a superior imaging modality in delineating the prostate gland, but poor in localizing sources due to lack of source visibility. The purpose of this study was to optimize the visualization of sources using MRI and compare to CT derived source localization.

METHODS AND MATERIALS

Multiple MRI scanning techniques were attempted until an acceptable sequence to visualize both the prostate gland and the implanted sources was found. The exams were performed using a pelvic coil only in approximately 15 min. The CT and MRI scans of 20 consecutive patients who had received TRUS-guided permanent transperineal interstitial prostate 125Iodine or 103Palladium brachytherapy were evaluated using an in-house dosimetry system. To eliminate anatomical dependence, the MRI-derived DVHs for the entire calculation volume were then compared to those derived from the CT scans.

RESULTS

The differences in isodose volumes, of the calculation volumes, for all implants at all dose levels were not statistically significant at the 95% confidence level. Calculation volume isodose volumes derived from MR images were statistically similar to those derived from CT images at the prescription dose for both 125Iodine (p < 0.01) and 103Palladium (p < 0.026).

CONCLUSION

This study presents the first evidence that MRI may be reliably used to identify permanently implanted 125Iodine and 103Palladium sources. Given the advantage of target definition characteristics of MRI, substantially more accurate dosimetric analysis of prostate implants is now possible. The cost of the optimized and abbreviated MR scanning sequence used in this study is comparable to a pelvic CT scan. Postimplant MRI allows more accurate volumetric and anatomically relevant evaluation of permanent prostate implants, which may provide useful clinical correlation.