[MR tomography in prostatic carcinoma: comparison of conventional and endorectal MRT]

Impact of an endorectal coil for 1H-magnetic resonance spectroscopy of the prostate at 3.0T in comparison to 1.5T: Do we need an endorectal coil?

OBJECTIVES

To evaluate the influence of endorectal coil (ERC) regarding spectral quality and diagnostic suitability and diagnostic performance in 3.0T 1H-magnetic resonance spectroscopy imaging (MRSI) compared to 1.5T MRSI.

MATERIALS AND METHODS

The study was approved by the Institutional Review Board. MRSI of the prostate was performed on 19 patients at 1.5T with ERC (protocol 1), at 3.0T with a disabled ERC (protocol 2) and at 3.0T with ERC (protocol 3). Age, weight, body size, body-mass-index, prostate volume, time between measurements, diagnostic suitability of spectra, histopathological results after biopsy of cancer suspect lesions (CSL), sensitivity and specificity were evaluated. Signal-to-noise ratio (SNR) was calculated and compared using semiparametrical multiple Conover-comparisons. Correlations between SNR and prostate volume and BMI were indicated using Pearson correlation coefficient. Distribution of SNR was evaluated for prostate quadrants.

RESULTS

Diagnostic suitable spectra were achieved in 76 % (protocol 1, 100% in CSL), 32 % (protocol 2, 59% in CSL) and 50 % (protocol 3, 80% in CSL) of the voxels. SNR was significantly higher in protocol 3 compared to protocol 2 and 1 (93,729 vs. 27,836 vs. 32,897, p<0.0001) with significant difference between protocol 2 and 1 (p<0.023). Highest SNR was achieved in the dorsal prostate (protocols 1 and 3; p<0.0001). Sensitivity at 3.0T was higher with use of ERC. Specificity was highest at 1.5T with ERC.

CONCLUSION

The ERC improves the diagnostic suitability and the SNR in MRSI at 3.0T. Less voxels at 3.0T with disabled ERC are suitable for diagnosis compared to 1.5T with ERC. MRSI at 3.0T with ERC shows the highest SNR. SNR in dorsal quadrants of the prostate was higher using ERC.

Vascular endothelial growth factor receptor 2-specific microbubbles for molecular ultrasound detection of prostate cancer in a rat model

OBJECTIVES

To investigate whether rat prostate cancer can be detected by means of molecular ultrasound (US) using target-specific microbubbles versus a nonspecific contrast agent.

MATERIALS AND METHODS

A total of 20 Copenhagen rats were randomly examined 75 to 104 days after orthotopic implantation of G-Dunning rat prostatic tumor cells was using a high-end US system and either 1.2 mL/kg of the nonspecific agent A or 0.1 mL/kg of the target-specific agent B, containing vascular endothelial growth factor receptor 2 binding peptide. Contrast inflow (areas under the curve analysis) was determined during the first 30s, and all microbubbles were destroyed in the scan plane by means of the flash technique 20 minutes after intravenous administration to investigate specific accumulation of individual bubbles in tumors. Differences between normal prostate tissue and tumor were analyzed using luminance images. Sonographically determined tumor localization and extent were compared with magnetic resonance imaging and histology.

RESULTS

The median tumor size in the 20 rats determined on US (2.3 mm) and magnetic resonance imaging (2.4 mm) showed a very high correlation (r = 0.92, P = 0.01). Both agent A and agent B demonstrated higher vascularization of tumor periphery compared with normal prostate (P < 0.05) based on contrast inflow and areas under the curve analysis. Twenty minutes after administration, luminance for agent B in the tumor was significantly higher (P = 0.003) compared with nonspecific agent A (11.8-0.1). In consensus reading, the increase in signal intensity of the tumor compared with normal prostate tissue was significantly higher for agent B (P = 0.005), whereas no significant difference was found for agent A (P = 0.180).

CONCLUSIONS

The target-specific contrast agent was superior to the unspecific US contrast agent both with regard to early inflow analysis and specific accumulation in prostate cancer after 20 minutes.

Preliminary results for characterization of pelvic lymph nodes in patients with prostate cancer by diffusion-weighted MR-imaging

OBJECTIVES

In this retrospective feasibility study diffusion-weighted magnetic resonance imaging (DWI) was evaluated as a potential tool for characterization of pelvic lymph nodes in patients with prostate cancer.

METHODS AND MATERIALS

Twenty-nine patients with prostate cancer underwent DWI of the pelvis at 1.5T by a non breath-hold SSEPI sequence using a body phased array coil with b values of 50, 300, and 600 s/mm(2) and an additional T2-weighted sequence. A total of 118 lymph nodes (>6 mm short axis) were analyzed by measuring the ADC-value with a polygon region of interest. Feasibility for ADC-measurement was assessed by comparing the ADC-value from the automatically created ADC-map (ADC(MR_unit)) with a manually calculated ACD-value (ADC(calculated)) and by using a linear-regression model for comparison with size and standard deviation of the ADC-value. Diagnostic performance was estimated by receiver operator characteristic analysis using histologic and/or clinical follow-up as standard of reference.

RESULTS

ADC(MR_unit) and ADC(calculated) showed a high correlation (r = 0.8999) with a mean percentual deviation of 6.33%. There was a highly significant difference between the mean ADC-value (x10(-3) mm(2)/s) of malignant (1.07 +/- 0.23) versus benign (1.54 +/- 0.25) lymph nodes, even in subgroup analysis for lymph nodes smaller versus larger than 10 mm. Receiver operator characteristic-analysis showed a good accuracy of the ADC-value (85.6% [101/118]; sensitivity: 86.0% [43/50]; specificity: 85.3% [53/68]) for differentiation of malignant and benign lymph nodes at a cutoff 1.30 x 10(-3) mm(2)/s. This was superior to a size-based analysis at a cutoff of 8 mm (accuracy: 66.1% [78/118]; sensitivity: 82.0% [41/50]; specificity: 54.4% [37/68]; P < 0.01).

CONCLUSIONS

DWI has the potential of being an accurate technique for analysis of pelvic lymph nodes. Moreover, our preliminary results suggest that the ADC-value might perform significantly superior to size criteria to discriminate between benign and malignant lymph nodes.

Value of magnetic resonance imaging in prostate cancer diagnosis

MRI has shown its potential in prostate cancer (PCa) imaging. MRI is able to demonstrate zonal anatomy with excellent contrast resolution. Furthermore it can detect PCa dependent not only on tumor-size, histological grading, PSA levels, but also on technical equipment and reader's experience. Non-palpable PCas in the inner and outer gland can be detected by this technique. Another potential is that MRI is helpful for tumor staging and treatment planning as well as response evaluation. Besides the morphological information, MRI can give functional information based on metabolic evaluation with proton magnetic resonance spectroscopy and of tumor angiogenesis based on dynamic contrast-material enhanced MRI and diffusion-weighted imaging. In addition MRI can be used for targeted prostate biopsies; however, the clinical practicability is questionable. Furthermore many data about the value of MRI for PCa diagnosis are based on transrectal ultrasound (TRUS) biopsy findings. Since there is lack of accuracy in fusing MRI images with TRUS images these limit the results of MRI for cancer diagnosis. However, in the future MRI may play an additional role in planning and monitoring minimally invasive PCa therapies. Although, MRI of the prostate seems to be useful, nevertheless this method remains expensive and lacks availability regarding the oncoming requirements.

Imaging of prostate cancer

The role of imaging in the diagnosis and management of prostate is reviewed. Transrectal ultrasonography, which can be used to guide biopsy, is most frequently used imaging technique in cancer detection. For determining the extent of disease, CT and MR imaging are the most commonly used modalities; bone scintigraphy and positron emission tomography have roles only in advanced disease. Currently, the role of imaging in prostate cancer is evolving to improve disease detection and staging, to determine the aggressiveness of disease, and to predict outcomes in different patient populations

Combined Endorectal and Phased-Array MRI in the Prediction of Pelvic Lymph Node Metastasis in Prostate Cancer

OBJECTIVE

The objectives of our study were to evaluate the accuracy of combined endorectal and phased-array MRI in detecting pelvic lymph node metastasis (LNM) in patients with prostate cancer and to determine whether radiologists' predictions of LNM improve with the incorporation of Partin nomogram or MRI findings (or both) regarding extracapsular extension or seminal vesicle invasion.

SUBJECTS AND METHODS

Between May 1999 and September 2003, 411 consecutive patients with clinically localized prostate cancer underwent MRI before surgery. Serum prostate-specific antigen (PSA) level, Gleason grade, clinical stage, greatest percentage of cancer and percentage of positive cores in all biopsy cores, presence of perineural invasion on biopsy, and likelihood of LNM based on the Partin tables (2001 version) were recorded. MRI studies were interpreted prospectively, but the risks of LNM, extracapsular extension, and seminal vesicle invasion were scored retrospectively on the basis of the MRI reports. Surgical pathology constituted the standard of reference. The accuracy of LNM prediction was assessed using areas under receiver operating characteristic curves (AUCs) and univariate and multivariate logistic regression analyses. For multivariate models, the jackknife method was used for bias correction. A p value below 0.05 denoted statistical significance.

RESULTS

At surgical pathology, LNM was present in 22 (5%) of 411 patients. MRI was an independent statistically significant predictor of LNM (p = 0.002), with positive and negative predictive values of 50% and 96.36%, respectively. On multivariate analysis, prediction of lymph node status using the model that included all MRI variables (extracapsular extension, seminal vesicle invasion, and LNM) along with the Partin nomogram results had a significantly greater AUC than the univariate model that included only MRI LNM findings (AUC = 0.892 vs 0.633, respectively; p < 0.01).

CONCLUSION

Incorporation of the Partin nomogram results and MRI findings regarding both extracapsular extension and seminal vesicle invasion improves the MR prediction of LNM in patients with prostate cancer.

MRI of prostate cancer at 1.5 and 3.0 T: comparison of image quality in tumor detection and staging

OBJECTIVE

This prospective study was performed to compare the image quality, tumor delineation, and depiction of staging criteria on MRI of prostate cancer at 1.5 and 3.0 T.

SUBJECTS AND METHODS

Twenty-four patients with prostate cancer underwent MRI at 1.5 T using the combined endorectal-body phased-array coil and at 3.0 T using the torso phased-array coil, among them 22 before undergoing radical prostatectomy. The prostate was imaged with T2-weighted sequences in axial and coronal orientations at both field strengths and, in addition, with an axial T1-weighted sequence at 1.5 T. Preoperative analysis of all MR images taken together was compared with the histologic findings to determine the accuracy of MRI for the local staging of prostate cancer. In a retroanalysis, the image quality, tumor delineation, and conspicuity of staging criteria were determined separately for both field strengths and compared. Statistical analysis was performed using Wilcoxon's and the McNemar tests.

RESULTS

In the preoperative analysis, MRI (at both 1.5 and 3.0 T) had an accuracy of 73% for the local staging of prostate cancer. The retroanalysis yielded significantly better results for 1.5-T MRI with the endorectal-body phased-array coil in terms of image quality (p < 0.001) and tumor delineation (p = 0.012) than for 3.0-T MRI with the torso phased-array coil. Analysis of the individual staging criteria for extracapsular disease did not reveal a superiority of either of the two field strengths in the depiction of any of the criteria.

CONCLUSION

Intraindividual comparison shows that image quality and delineation of prostate cancer at 1.5 T with the use of an endorectal coil in a pelvic phased-array is superior to the higher field strength of 3.0 T with a torso phased-array coil alone. As long as no endorectal coil is available for 3-T imaging, imaging at 1.5 T using the combined endorectal-body phased-array coil will continue to be the gold standard for prostate imaging.

Innovative Diagnostik in der Früherkennung und beim Staging des lokalisierten Prostatakarzinoms

Prostate cancer is the most common malignancy in males. Men aged 50 years and older are recommended to undergo an annual digital rectal examination (DRE) and determination of prostate-specific antigen (PSA) in serum for early detection. Fortunately, disease-specific mortality continues to decline as a result of advances in screening, staging, and patient awareness. However, about 30% of men with a clinically organ-confined disease show evidence of extracapsular extension or seminal vesicle invasion on pathological analysis. Consequently, there is a need for more accurate diagnostic tools for planning tailored treatment. A variety of modern imaging techniques has been implemented in an attempt to obtain more precise staging, thereby allowing for more detailed counseling, and instituting optimum therapy. This review highlights developments in prostate cancer imaging that may improve staging and treatment planning for prostate cancer patients.

Reproducibility of image interpretation in MRI of the prostate: application of the sextant framework by two different radiologists

The aim of this study was to reproduce prostate cancer (PCA) localization by MRI based on prostatic sextants (right and left base, middle, and apex) with minimal systematic error. Combined endorectal/body-phased-array-coil MRI of the prostate at 1.5 T was retrospectively evaluated twice, with an interval of more than 1 month, by each of two independent radiologists (R1 readings R11 and R12, and R2 readings R21 and R22) in 23 patients (age 51-75 years) who had radical prostatectomy within 1 month of MRI. PCA stage was pT2 in 14 patients, and pT3 in nine. Median Gleason score was 7 (range 5-9). Histopathology showed 83 sextants with PCA and 55 without. Reproducibility of sextant positions was within one MRI slice (3 mm) in over 80% of cases. For PCA localization, ROC analysis (AUC=0.584+/-0.048-0.724+/-0.043) yielded no significant intra-reader differences. R11 and R21 differed slightly (P=0.035). Intra-observer agreement (kappa=0.52-0.58) exceeded inter-observer agreement (kappa=0.35-0.45). Intra-observer Spearman correlation (r=0.72-0.74) exceeded inter-observer correlation (r=0.43-0.51) for sextants with PCA, but not for sextants without (r=0.69-0.74). Per-sextant localization and reporting provides a highly reliable framework in MRI of the prostate. MRI of the prostate should be followed up by the same radiologists to minimize systematic error of interpretation.

Patients with a history of elevated prostate-specific antigen levels and negative transrectal US-guided quadrant or sextant biopsy results: value of MR imaging

PURPOSE

To determine the role of magnetic resonance (MR) imaging performed with a combined endorectal body phased-array coil for patients with elevated prostate-specific antigen (PSA) levels or suspicious free-to-total PSA ratios in whom prior transrectal ultrasonographically (US) guided biopsy findings were negative for prostate cancer.

MATERIALS AND METHODS

Forty-four patients with PSA levels greater than 4 ng/mL or free-to-total PSA ratios lower than 15% but negative biopsy findings were examined with T1- and T2-weighted MR imaging at 1.5 T with a combined endorectal body phased-array coil. All patients underwent digital rectal examination (DRE) and transrectal US. Thirty-eight patients underwent repeat biopsy after MR imaging. The accuracy of MR imaging for detection of prostate cancer was assessed prospectively. Retrospectively, MR imaging findings were correlated with individual biopsy site findings. MR imaging and biopsy results were correlated by using a cross table to calculate sensitivity, specificity, and positive predictive value (PPV). Retrospective analysis results were evaluated with receiver operating characteristic analysis. A P value of less than.05 indicated significance (chi(2) test according to Pearson).

RESULTS

At prospective analysis, MR imaging had a sensitivity of 83% and a PPV of 50% for detection of prostate cancer; these values were 33% and 67%, respectively, for DRE and 33% and 57%, respectively, for transrectal US. At retrospective site-by-site analysis, MR imaging results did not correlate significantly with individual biopsy site findings (P =.126); sensitivity was 65% and PPV was 12%.

CONCLUSION

In this patient population, MR imaging has higher sensitivity for detection of prostate cancer than DRE or transrectal US.

Indications for pelvic lymphadenectomy in prostate cancer

Clearly, pelvic lymphadenectomy can provide important staging information in the management of prostate cancer, but this benefit is counterbalanced by a modest increase in morbidity and the significant cost of the procedure. It is difficult to provide universal recommendations concerning the indications for pelvic lymphadenectomy. Part of the problem lies in the fact that urologists perform pelvic lymphadenectomy for several different reasons. Some surgeons perform pelvic lymphadenectomy to better counsel patients after radical prostatectomy about their risk for disease progression and for planning adjuvant radiotherapy or hormonal therapy. For these surgeons, preoperative clinical staging parameters do not exclude patients from pelvic lymphadenectomy, and frozen section analysis intraoperatively provides no useful information. Alternatively, the staging information from pelvic lymphadenectomy can be used to justify cancellation of the subsequent prostatectomy should regional spread of prostate cancer be identified, sparing the patient the morbidity of an unnecessary radical prostatectomy. With this approach, despite the false-negative rate of up to 30%, the expense of frozen section analysis seems justified. For this second group of surgeons, the problem becomes balancing the modest morbidity and cost of pelvic lymphadenectomy against the probability that nodal spread of prostate cancer will be missed if the procedure is omitted. The authors consider a greater than 4% risk for missing regional disease to be unacceptable in this setting. Following this assumption, Table 3 outlines parameters for clinical stage, Gleason score, and preoperative PSA within which pelvic lymphadenectomy is indicated. These recommendations are based on [table: see text] predictions from the Partin nomogram, which has been validated using a series of over 4000 patients. For the large number of patients with clinical T1c disease and a preoperative PSA less than 10 ng/mL, bilateral pelvic lymphadenectomy is indicated only if prostate biopsy identifies tumor of Gleason grade 4 or higher. For lower-grade tumors in this patient population, the risk for nodal metastasis was less than 5% in the Johns Hopkins and Mayo Clinic series of over 5800 patients with prostate cancer. For a large pool of patients, the several thousand dollar cost of pelvic lymphadenectomy and the risk for injury to the obturator nerves and vessels, the formation of lymphoceles, and chronic genital edema can be eliminated with low risk. A nomogram-based approach provides only a starting point for a decision analysis framework to determine whether the surgeon should perform lymphadenectomy at the time of radical prostatectomy because current nomograms predict only lymph node positivity. In a decision analysis framework, some patient and physician value is derived from a negative lymphadenectomy. Moreover, the morbidity associated with pelvic lymphadenectomy and the potential inconvenience associated with treating such morbidity also would be factored into the decision. Consequently, a decision analysis framework that takes into account prognostic value, costs, morbidity, and health state uses ultimately will provide the most informative method for determining when pelvic lymphadenectomy is indicated in patients with prostate cancer.