Prostate cancer: localization with three-dimensional proton MR spectroscopic imaging--clinicopathologic study

Prostate cancer: accurate determination of extracapsular extension with high-spatial-resolution dynamic contrast-enhanced and T2-weighted MR imaging--initial results

PURPOSE

To prospectively compare the sensitivity and specificity of high-spatial-resolution dynamic contrast material-enhanced magnetic resonance (MR) imaging with those of high-spatial-resolution T2-weighted MR imaging, performed with an endorectal coil (ERC), for assessment of extracapsular extension (ECE) and staging in patients with prostate cancer, with histopathologic findings as reference.

MATERIALS AND METHODS

The study was approved by the institutional internal review board; a signed informed consent was obtained. MR imaging of the prostate at 1.5 T was performed with combined surface coils and ERCs in 32 patients (mean age, 65 years; range, 42-78 years) before radical prostatectomy. High-spatial-resolution T2-weighted fast spin-echo and high-spatial-resolution dynamic contrast-enhanced three-dimensional gradient-echo images were acquired with gadopentetate dimeglumine. Dynamic contrast-enhanced MR images were analyzed with a computer-generated color-coded scheme. Two experienced readers independently assessed ECE and tumor stage. MR imaging-based staging results were compared with histopathologic results. For the prediction of ECE, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Staging accuracy was determined with the area under the receiver operating characteristic curve (AUC) by using the Wilcoxon-Mann-Whitney index of diagnostic accuracy.

RESULTS

The mean sensitivity, specificity, PPV, and NPV for assessment of ECE with the combined data sets for both readers were 86%, 95%, 90%, and 93%, respectively. The sensitivity of MR images for determination of ECE was significantly improved for both readers (>25%) with combined data sets compared with T2-weighted MR images alone. The combined data sets had a mean overall staging accuracy for both readers of 95%, as determined with AUC. Staging results for both readers were significantly improved (P<.05) with the combined data sets compared with T2-weighted MR images alone.

CONCLUSION

The combination of high-spatial-resolution dynamic contrast-enhanced MR imaging and T2-weighted MR imaging yields improved assessment of ECE and better results for prostate cancer staging compared with either technique independently.

Proton MR spectroscopy of the prostate

PURPOSE

To summarize current technical and biochemical aspects and clinical applications of proton magnetic resonance spectroscopy (MRS) of the human prostate in vivo.

MATERIAL AND METHODS

Pertinent radiological and biochemical literature was searched and retrieved via electronic media (medline, pubmed. Basic concepts of MRS of the prostate and its clinical applications were extracted.

RESULTS

Clinical MRS is usually based on point resolved spectroscopy (PRESS) or spin echo (SE) sequences, along with outer volume suppression of signals from outside of the prostate. MRS of the prostate detects indicator lines of citrate, choline, and creatine. While healthy prostate tissue demonstrates high levels of citrate and low levels of choline that marks cell wall turnover, prostate cancer utilizes citrate for energy metabolism and shows high levels of choline. The ratio of (choline+creatine)/citrate distinguishes between healthy tissue and prostate cancer. Particularly when combined with magnetic resonance (MR) imaging, three-dimensional MRS imaging (3D-CSI, or 3D-MRSI) detects and localizes prostate cancer in the entire prostate with high sensitivity and specificity. Combined MR imaging and 3D-MRSI exceed the sensitivity and specificity of sextant biopsy of the prostate. When MRS and MR imaging agree on prostate cancer presence, the positive predictive value is about 80-90%. Distinction between healthy tissue and prostate cancer principally is maintained after various therapeutic treatments, including hormone ablation therapy, radiation therapy, and cryotherapy of the prostate.

CONCLUSIONS

Since it is non-invasive, reliable, radiation-free, and essentially repeatable, combined MR imaging and 3D-MRSI of the prostate lends itself to the planning of biopsy and therapy, and to post-therapeutic follow-up. For broad clinical acceptance, it will be necessary to facilitate MRS examinations and their evaluation and make MRS available to a wider range of institutions.

Current role and future perspectives of magnetic resonance spectroscopy in radiation oncology for prostate cancer

Prostatic neoplasms are not uniformly distributed within the prostate volume. With recent developments in three-dimensional intensity-modulated and image-guided radiation therapy, it is possible to treat different volumes within the prostate to different thresholds of doses. This approach has the potential to adapt the dose to the biologic aggressiveness of various clusters of tumor cells within the gland. The definition of tumor burden volume in prostate cancer can be facilitated by the use of magnetic resonance spectroscopy (MRS). The increasing sensitivity and specificity of MRS to the prostate is causing new interest in its potential role in the definition of target subvolumes at higher risk of failure following radical radiotherapy. Prostate MRS might also play a role as a noninvasive predictive factor for tumor response and treatment outcome. We review the use of MRS in radiation therapy for prostate cancer by evaluating its accuracy in the classification of aggressive cancer regions and target definition; its current role in the radiotherapy planning process, with special interest in technical issues behind the successful inclusion of MRS in clinical use; and available early experiences as a prognostic tool.

Bildgebende Verfahren bei der Diagnose des Prostatakarzinoms

Prostate cancer is one of the most frequent malignant diseases in men. Despite constant progress achieved in imaging procedures, prostate biopsy is the gold standard for diagnosing prostate cancer. For the assessment of lymph node status, only staging lymphadenectomy provides valid information. The aim of this work is to analyze the imaging procedures available in Germany and their value in primary and lymph node staging as well as biochemical recurrence.

Apparent diffusion coefficient of the prostate in men prior to biopsy: determination of a cut-off value to predict malignancy of the peripheral zone

Determination of the apparent diffusion coefficient (ADC) of the prostate in men (n = 60) with raised prostate-specific antigen (PSA) or an abnormal digital rectal examination (DRE) prior to transrectal ultrasound (TRUS) guided biopsy using endorectal DWI is reported. Patients were categorized into different groups based on their PSA levels. The mean ADC was calculated from a number of regions of interest (ROIs) for the whole of the peripheral zone (PZ) and the central gland (CG). A total of 1108 ROIs were analyzed from 60 patients. The mean ADC value of the PZ was higher than that of the CG in controls. A total of 23 out of 60 patients were positive for malignancy on biopsy, and the mean ADC of the PZ was lower in these patients compared with those who were negative. Moreover, the mean ADC obtained for the whole of the PZ of the prostate in different groups of patients and controls showed a decreasing trend. A plot between PSA and mean ADC for the PZ showed non-linear association with logarithmic decrease in ADC. The mean ADC of the CG was not significantly different in patients who were positive or negative for malignancy in biopsy. In addition, a cut-off value of 1.17 x 10(-3) mm2/s (sensitivity = 73% and specificity = 74%, area under the curve = 0.83) for the mean ADC for the whole of the PZ of patients was determined by using the receiver operating characteristic curve (ROC) to predict malignancy of the PZ.

Prostate cancer: sextant localization with MR imaging, MR spectroscopy, and 11C-choline PET/CT

PURPOSE

To retrospectively compare sensitivity and specificity of magnetic resonance (MR) imaging, three-dimensional (3D) MR spectroscopy, combined MR imaging and 3D MR spectroscopy, and carbon 11 (11C)-choline positron emission tomography (PET)/computed tomography (CT) for intraprostatic tumor sextant localization, with histologic findings as reference standard.

MATERIALS AND METHODS

The local ethics committee on human research provided approval and a waiver of informed consent for the retrospective study. MR imaging, 3D MR spectroscopy, and 11C-choline PET/CT results were retrospectively reviewed in 26 men with biopsy-proved prostate cancer (mean age, 64 years; range, 51-75 years) who underwent radical prostatectomy. Cancer was identified as areas of nodular low signal intensity on T2-weighted MR images. At 3D MR spectroscopy, choline-plus-creatine-to-citrate and choline-to-creatine ratios were used to distinguish healthy from malignant voxels. At PET/CT, focal uptake was visually assessed, and maximum standardized uptake values (SUVs) were recorded. Agreement between 3D MR spectroscopic and PET/CT results was calculated, and ability of maximum SUV to help localize cancer was assessed with receiver operating characteristic analysis. Significant differences between positive and negative sextants with respect to mean maximum SUV were calculated with a paired t test.

RESULTS

Sensitivity, specificity, and accuracy were, respectively, 55%, 86%, and 67% at PET/CT; 54%, 75%, and 61% at MR imaging; and 81%, 67%, and 76% at 3D MR spectroscopy. The highest sensitivity was obtained when either 3D MR spectroscopic or MR imaging results were positive (88%) at the expense of specificity (53%), while the highest specificity was obtained when results with both techniques were positive (90%) at the expense of sensitivity (48%). Concordance between 3D MR spectroscopic and PET/CT findings was slight (kappa=0.139).

CONCLUSION

In localizing cancer within the prostate, comparable specificity was obtained with either 3D MR spectroscopy and MR imaging or PET/CT; however, PET/CT had lower sensitivity relative to 3D MR spectroscopy alone or combined with MR imaging.

NMR-based metabolomics approach to target biomarkers for human prostate cancer

In the era of genomics and proteomics, metabolomics offers a unique way to probe the underlying biochemistry of malignant transformations. In the context of oncological metabolomics, the study of the global variation of metabolites involved in the development and progression of cancers, few existing techniques offer as much potential to discover biomarkers as nuclear magnetic resonance techniques. The most fundamental magnetic resonance methodologies with regard to human prostate cancer are magnetic resonance spectroscopy and magnetic resonance spectroscopic imaging. Recent in vivo explorations have examined crucial metabolites that may indicate cancerous lesions and have the potential to direct treatment; while ex vivo studies of prostatic fluids and tissues have defined novel diagnostic parameters and indicated that magnetic resonance methodologies will be paramount in future prostate cancer management.

3D MR spectroscopic imaging in the evaluation of prostate cancer

The management of prostate cancer is a complex issue with a varying range of treatment options available. Magnetic resonance (MR) imaging of the prostate has been available for sometime but has the limitation of only anatomical evaluation. Three-dimensional MR spectroscopy is emerging as a new and sensitive tool in the metabolic evaluation of prostate cancer. This article reviews the principle, techniques, and methods of evaluation of spectroscopy and also discusses the applications of spectroscopy in the current management of prostate cancer.

Transrectal contrast enhanced ultrasound for diagnosis of prostate cancer

The diagnosis of prostate cancer is based on histology. Prostate biopsies are obtained based on the triad of prostate specific antigen (PSA), digital rectal examination (DRE) and transrectal ultrasound. Because prostate biopsies still have a large percentage of negative outcomes, patient selection and biopsy direction need improvement. This paper describes the recent improvements in prostate cancer imaging, especially contrast-enhanced transrectal ultrasound.

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.

[MRI of prostate cancer]

Endorectal MRI, now a fast and reliable examination, is an essential part of the local work-up for prostate cancer, regardless of the treatment envisioned. MRI spectroscopy, an actively maturing technique, makes it possible to combine anatomical and metabolic information that can be used for detection, staging, and posttreatment follow-up of prostate cancer. In patients with repeated negative biopsies, spectroscopy and dynamic gadolinium injection will be able to detect atypical cancer sites that escape routine biopsies. MRI of lymph nodes with ultrasmall superparamagnetic iron oxide (USPIO) injection will improve diagnostic performance in the detection of lymph node metastases. In the planning of conservative treatment, MRI and especially spectroscopic MRI will increasingly replace computed tomography. Finally, endorectal MRI of the prostate, spectroscopy, and dynamic injection will show local recurrences.

11C-Choline positron-emission tomography/computed tomography and transrectal ultrasonography for staging localized prostate cancer

OBJECTIVE

To evaluate and compare the role of (11)C-choline positron emission tomography (PET) and transrectal ultrasonography (TRUS) in the preoperative staging of clinically localized prostate cancer.

PATIENTS AND METHODS

Fifty-five consecutive patients with biopsy-confirmed prostate cancer had TRUS and (11)C-choline PET as a part of their clinical staging programme before radical retropubic prostatectomy (RP). The PET images were prospectively interpreted by a consensus decision of two nuclear medicine physicians and one radiologist with special expertise in the field. The TRUS was done by one experienced urologist. The criteria evaluated prospectively in each patient were extracapsular extension (ECE), seminal vesicle invasion (SVI) and bladder neck invasion (BNI). The results were compared with the histopathological findings after RP.

RESULTS

At pathology, 32 patients were classified pT2, 16 as pT3a and three had pT3b lesions. In four patients the histopathological examination showed pT4 with BNI. The overall accuracy of PET in defining local tumour stage (pT2 and pT3a-4) was 70%; the overall accuracy by TRUS was 26%. PET was more sensitive than TRUS for detecting ECE (pT3a) and SVI (pT3b) in advanced stages, and in pT4 stages. The sensitivity and positive predictive value (PPV) (95% confidence interval) in stages pT3a-pT4 for PET were 36 (17-59)% and 73 (39-89)%. The sensitivity and PPV in stages pT3a-pT4 for TRUS were 14 (3-35)% and 100 (29-100)%.

CONCLUSIONS

(11)C-choline PET and TRUS tended to understage prostate cancer. This series shows the current limited value of TRUS and PET for making treatment decisions in patients with clinically localized prostate cancer, especially if a nerve-sparing RP is considered. Treatment decisions should not be based on TRUS and (11)C-choline PET findings alone. In future studies, the combination of metabolic and anatomical information of PET and endorectal magnetic resonance imaging should be evaluated, as this might optimize the preoperative staging in prostate cancer.

Prostate cancer detection: magnetic resonance (MR) spectroscopic imaging

Magnetic resonance spectroscopic imaging (MRSI) represents a noninvasive technique to extend the diagnostic evaluation of prostatic cancer, beyond the morphologic information provided by MR imaging throughout the detection of cellular metabolites (choline and citrate). MRSI combined with the anatomical information provided by MRI can improve the assessment cancer location and extent within the prostate, extracapsular spread and cancer aggressiveness; both before and after treatment. We review the performance of MRI with MRSI and the role in the detection, localization, staging and management of the patient pre- and posttherapy for prostate cancer.

Imaging prostate cancer: a multidisciplinary perspective

The major goal for prostate cancer imaging in the next decade is more accurate disease characterization through the synthesis of anatomic, functional, and molecular imaging information. No consensus exists regarding the use of imaging for evaluating primary prostate cancers. Ultrasonography is mainly used for biopsy guidance and brachytherapy seed placement. Endorectal magnetic resonance (MR) imaging is helpful for evaluating local tumor extent, and MR spectroscopic imaging can improve this evaluation while providing information about tumor aggressiveness. MR imaging with superparamagnetic nanoparticles has high sensitivity and specificity in depicting lymph node metastases, but guidelines have not yet been developed for its use, which remains restricted to the research setting. Computed tomography (CT) is reserved for the evaluation of advanced disease. The use of combined positron emission tomography/CT is limited in the assessment of primary disease but is gaining acceptance in prostate cancer treatment follow-up. Evidence-based guidelines for the use of imaging in assessing the risk of distant spread of prostate cancer are available. Radionuclide bone scanning and CT supplement clinical and biochemical evaluation (prostate-specific antigen [PSA], prostatic acid phosphate) for suspected metastasis to bones and lymph nodes. Guidelines for the use of bone scanning (in patients with PSA level > 10 ng/mL) and CT (in patients with PSA level > 20 ng/mL) have been published and are in clinical use. Nevertheless, changes in practice patterns have been slow. This review presents a multidisciplinary perspective on the optimal role of modern imaging in prostate cancer detection, staging, treatment planning, and follow-up.

Prostate cancer: value of magnetic resonance spectroscopy 3D chemical shift imaging

The results of recent studies of magnetic resonance imaging (MRI) combined with three-dimensional magnetic resonance spectroscopic imaging (3D-MRSI) demonstrate that the MRI/3D-MRSI exam is a unique method by which to noninvasively study the cellular metabolism and anatomy of the prostate. 3D-MRSI is emerging as the most specificity tool for non-invasive evaluation of the prostate cancer. The results of current MRI/3D-MRSI studies also provide evidence that the magnitude of metabolic changes in regions of cancer before therapy, as well as the extent of the time course of metabolic changes after therapy, may improve our understanding of cancer aggressiveness. Assessment of cancer spread outside the prostate can be significantly improved by combining MRI findings with estimates of metabolic abnormalities provided by 3D-MRSI. Clinically, combined MRI/3D-MRSI has already demonstrated a potential for improved diagnosis, staging, and treatment planning for patients with prostate cancer. This article reviewed the value of 3D-MRS imaging for the diagnosis, localization, staging, aggressiveness, and treatment planning of prostate cancer.

Standardized threshold approach using three-dimensional proton magnetic resonance spectroscopic imaging in prostate cancer localization of the entire prostate

OBJECTIVES

We sought to determine the localization accuracy using 3-dimensional (3D) proton magnetic resonance spectroscopic imaging (MRSI) of the entire prostate with a standardized thresholds approach in prostate cancer patients.

MATERIALS AND METHODS

In a prospective study, 32 consecutive patients were examined. Mean age and prostate specific antigen level were 61 years and 7.8 ng/mL, respectively. Median biopsy Gleason score was 6. T2-weighted MRI and 3D MRSI of the entire prostate were performed. Three readers recorded the location of suspicious peripheral zone and central gland cancer nodules on a standardized division of the prostate (14 regions of interest [ROI]) using a standardized thresholds approach. The degree of diagnostic confidence for each ROI was recorded on a 5-point scale. Reconstructed whole-mount section histopathology was the standard of reference. The sensitivity, specificity, positive, and negative predictive value, overall accuracy and interobserver agreement were calculated. Areas under the ROI-based receiver operating characteristic curve (AUC) and diagnostic performance parameters were determined.

RESULTS

The standardized thresholds approach had an accuracy of 81% and an AUC of 0.85-0.86 for differentiation between benign and malignant ROIs in the peripheral zone and an accuracy of 87% and an AUC of 0.86-0.91 for this differentiation in the central gland, respectively. Specificities of 81% to 88% were achieved with accompanying sensitivities of 75% to 92% for both peripheral zone and central gland, respectively. Moderate to near-perfect interobserver agreement was demonstrated (kappa=0.42-0.91).

CONCLUSION

Our data indicate that a standardized zone-specific threshold approach in MRSI of the prostate is able to prospectively differentiate between benign and malignant tissues in the peripheral zone and the central gland with good accuracy and interobserver agreement.

Impact of stroma on the growth, microcirculation, and metabolism of experimental prostate tumors

In prostate cancers (PCa), the formation of malignant stroma may substantially influence tumor phenotype and aggressiveness. Thus, the impact of the orthotopic and subcutaneous implantations of hormone-sensitive (H), hormone-insensitive (HI), and anaplastic (AT1) Dunning PCa in rats on growth, microcirculation, and metabolism was investigated. For this purpose, dynamic contrast-enhanced magnetic resonance imaging and (1)H magnetic resonance spectroscopy ([(1)H]MRS) were applied in combination with histology. Consistent observations revealed that orthotopic H tumors grew significantly slower compared to subcutaneous ones, whereas the growth of HI and AT1 tumors was comparable at both locations. Histologic analysis indicated that glandular differentiation and a close interaction of tumor cells and smooth muscle cells (SMC) were associated with slow tumor growth. Furthermore, there was a significantly lower SMC density in subcutaneous H tumors than in orthotopic H tumors. Perfusion was observed to be significantly lower in orthotopic H tumors than in subcutaneous H tumors. Regional blood volume and permeability-surface area product showed no significant differences between tumor models and their implantation sites. Differences in growth between subcutaneous and orthotopic H tumors can be attributed to tumor-stroma interaction and perfusion. Here, SMC, may stabilize glandular structures and contribute to the maintenance of differentiated phenotype.

Automated estimation of tumor probability in prostate magnetic resonance spectroscopic imaging: pattern recognition vs quantification

Despite its diagnostic value and technological availability, (1)H NMR spectroscopic imaging (MRSI) has not found its way into clinical routine yet. Prerequisite for the clinical application is an automated and reliable method for the diagnostic evaluation of MRS images. In the present paper, different approaches to the estimation of tumor probability from MRSI in the prostate are assessed. Two approaches to feature extraction are compared: quantification (VARPRO, AMARES, QUEST) and subspace methods on spectral patterns (principal components, independent components, nonnegative matrix factorization, partial least squares). Linear as well as nonlinear classifiers (support vector machines, Gaussian processes, random forests) are applied and discussed. Quantification-based approaches are much more sensitive to the choice and parameterization of the quantification algorithm than to the choice of the classifier. Furthermore, linear methods based on magnitude spectra easily achieve equal performance and also allow for biochemical interpretation in combination with subspace methods. Nonlinear methods operating directly on magnitude spectra achieve the best results but are less transparent than the linear methods.

Diagnosis of Prostate Cancer in Patients with an Elevated Prostate-Specific Antigen Level: Role of Endorectal MRI and MR Spectroscopic Imaging

OBJECTIVE

The objective of our study was to determine the accuracy of endorectal MRI and MR spectroscopic imaging (MRSI) in the diagnosis of prostate cancer in patients with an elevated serum prostate-specific antigen (PSA) level.

MATERIALS AND METHODS

We retrospectively identified 40 patients with an elevated serum PSA level and without a histologic diagnosis of prostate cancer who underwent endorectal MRI and MRSI at our institution. On the basis of MRI findings alone and then combined MRI and MRSI findings, a single experienced observer rated the presence or absence of prostate cancer in each side of the prostate on a 5-point scale (1 = definitely absent, 5 = definitely present). Areas under the receiver operating characteristic (ROC) curve were calculated using the hemiprostate as the unit of analysis. The presence or absence of cancer on subsequent endorectal sonographically guided sextant biopsy was used as the standard of reference.

RESULTS

Biopsy revealed no cancer in 24 patients, bilateral cancer in 11, and unilateral cancer in five. The areas under the ROC curve for the diagnosis of prostate cancer by hemigland was 0.70 for MRI alone and 0.63 for combined MRI and MRSI (no significant difference, p = 0.32).

CONCLUSION

Endorectal MRI and MRSI are reasonably accurate for the diagnosis of prostate cancer in patients with an elevated serum PSA level, but the remaining limitations suggest that MRI and MRSI should be used as a supplement rather than a replacement for biopsy using the current technology and diagnostic criteria.

Validity of prostate-specific antigen as a tumour marker in men with prostate cancer managed by watchful-waiting: correlation with findings at serial endorectal magnetic resonance imaging and spectroscopic imaging

OBJECTIVE

To investigate the validity of prostate-specific antigen (PSA) as a tumour marker in men with clinically localized prostate cancer who have selected watchful waiting, by determining if serial PSA level measurements are correlated with findings of malignancy or benign prostatic hyperplasia (BPH) at serial endorectal magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI).

PATIENTS AND METHODS

We retrospectively identified 69 men with biopsy-proven prostate cancer being managed by watchful waiting, who underwent serial endorectal MRI/MRSI and who had contemporaneous serial PSA measurements. The mean (range) follow-up was 392 (294-571) days. A panel of three experienced readers reviewed the initial and follow-up MRI/MRSI studies, and classified findings of prostate cancer as stable or progressive. Another reader assessed BPH by calculating total gland and central gland volumes on all studies.

RESULTS

At the follow-up MRI/MRSI, 51, 17 and one patient had stable, progressive, or unevaluable prostate cancer, respectively. The mean PSA velocity was significantly greater in patients with radiologically progressive disease (1.42 vs 0.42 ng/mL/year, P = 0.04). A PSA velocity of >0.75 ng/mL/year identified those with radiologically progressive disease with a true-positive fraction of 0.71 and a false-positive fraction of 0.39. PSA levels were not correlated with changes in total or central gland volumes (P > 0.05).

CONCLUSIONS

In men with clinically localized prostate cancer who select watchful waiting, serial PSA levels are correlated with findings of malignancy but not BPH at serial endorectal MRI/MRSI, suggesting that PSA is a useful longitudinal tumour marker in this population.

Contribution of the MR spectroscopic imaging in the diagnosis of prostate cancer in the peripheral zone

PURPOSE

To establish the additional value of 3D magnetic resonance spectroscopy (3D-MRS) imaging to endorectal MR imaging in the diagnosis of prostrate cancer in the peripheral zone.

MATERIALS AND METHODS

MR imaging and MRS imaging were performed in 79 patients with suspicion of prostate cancer on the basis of digital rectal exploration, transrectal ultrasound and PSA level. All the examinations were performed with 1.5 T MR scan using an endorectal coil (transverse and coronal FSE T2-weighted sequences, axial SE T1-weighted and PRESS 3D CSI). MR examinations have been evaluated by two Radiologists blind of the clinical data in a "per patients" analysis. MR imaging and MRS imaging findings were compared with the result of histological data from radical prostatectomy in 53 patients and biopsy in 17 patients.

RESULTS

Nine patients (11.4%) were excluded because of serious artefacts in the MR spectrum. The reported values of sensitivity, specificity, PPV and NPV for MR imaging alone were respectively 84%, 50%, 76% and 63% (LR+ 1.7; LR- 0.3). Instead the reported values of sensitivity, specificity, PPV and NPV for the combination of MR imaging to MRS imaging were respectively 89%, 79%, 89% and 79% (LR+ 4.28; LR- 0.14). We found an incremental benefit of MRS imaging to MR imaging for tumour diagnosis although these results did not show statistically significant differences.

CONCLUSIONS

The MRS imaging improves the accuracy of the endorectal MR imaging in the diagnosis of prostate cancer.

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

Transrectal ultrasound-guided biopsy of prostate voxels identified as suspicious of malignancy on three-dimensional (1)H MR spectroscopic imaging in patients with abnormal digital rectal examination or raised prostate specific antigen level of 4-10 ng/ml

Results of the evaluation of transrectal ultrasound (TRUS) guided needle biopsy of voxels identified as suspicious of malignancy on magnetic resonance spectroscopic imaging (MRSI) in a large cohort of men (n = 83) with abnormal digital rectal examination (DRE) [prostate specific antigen (PSA) 0-4 ng/ml] or PSA less than 10 ng/ml, are reported. Three-dimensional (1)H MRSI was carried out at 1.5 T using a pelvic-phased array coil in combination with an endorectal surface coil. Voxels were classified as suspicious of malignancy based on Cit/(Cho + Cr) metabolite ratio. TRUS-guided biopsy of suspicious voxels was performed using the z- and x-coordinates obtained from MR images and two to three cores were taken from the suspected site. A systematic sextant biopsy was also carried out. MRSI showed voxels suspicious of malignancy in 44 patients while biopsy revealed cancer in 11 patients (25%). Patients who were negative for malignancy on MRSI were also negative on biopsy. An overall sensitivity of 100%, specificity of 54%, negative predictive value of 100% and accuracy of 60% were obtained. The site of biopsy was confirmed (n = 20) as a hypo-intense area on repeat MRI while repeat MRSI revealed high choline and low citrate. The overall success rate of MRI-directed TRUS-guided biopsy of 25% was higher compared with a 9% success rate achieved without MR guidance in another group of 120 patients. Our results indicate that TRUS-guided biopsy of suspicious area identified as malignant from MRSI can be performed using the coordinates of the voxel derived from MR images. This increases the detection rate of prostate cancer in men with PSA level <10 ng/ml or abnormal DRE and also demonstrates the potential of MR in routine clinical practice.

Prostate spectroscopy at 3 Tesla using two-dimensional S-PRESS

Two-dimensional (2D) strong-coupling point-resolved spectroscopy (S-PRESS) is introduced as a novel approach to (1)H MR spectroscopy (MRS) in the prostate. The technique provides full spectral information and allows for an accurate characterization of the citrate (Cit) signal. The method is based on acquiring a series of PRESS spectra with constant total echo time (TE). The indirect dimension is encoded by varying the relative lengths of the first and second TEs (TE(1) + TE(2) = TE). In the resulting 2D spectra, only the signal of strongly coupled spin systems is spread into the second dimension, which leads to more clearly arranged spectra. Furthermore, the spectral parameters of Cit (coupling constant J and chemical shift difference delta of the AB spin system) can be determined with high accuracy in vivo. The sequence is analytically optimized for maximal "strong coupling peaks" of Cit at 3T. 2D S-PRESS spectra are compared with JPRESS spectra in vitro as well as in vivo.

Combined Use of Diffusion-Weighted MRI and 1H MR Spectroscopy to Increase Accuracy in Prostate Cancer Detection

OBJECTIVE

The objective of our study was to establish the sensitivity and specificity for prostate cancer detection using a combined 1H MR spectroscopy and diffusion-weighted MRI approach.

SUBJECTS AND METHODS

Forty-two men (mean age +/- SD, 69.3 +/- 4.7 years) with prostate cancer were studied using endorectal T2-weighted imaging, 2D chemical shift imaging (CSI), and isotropic apparent diffusion coefficient (ADC) maps. Regions of interest (ROIs) were drawn around the entire gland, central gland, and peripheral zone tumor, diagnostically defined as low signal intensity on T2-weighted images within a sextant that was biopsy-positive for tumor. Lack of susceptibility artifact on a gradient-echo B0 map through the slice selected for CSI and no high signal intensity on external array T1-weighted images confirmed the absence of significant hemorrhage after biopsy. CSI voxels were classified as nonmalignant or as tumor (ROI included > or = 30% or > or = 70% tumor). Choline-citrate (Cho/Cit) ratios and average ADCs were calculated for every voxel. A plot of Cho/Cit ratios versus ADCs yielded a line of best separation of tumor voxels from nonmalignant voxels. Receiver operating characteristic (ROC) curves were plotted for Cho/Cit ratios alone, ADCs alone, and a combination of the two.

RESULTS

The Cho/Cit ratios were significantly higher (p < 0.001) and the ADCs were significantly lower (p < 0.006) in tumor-containing voxels than in non-tumor-containing voxels. When voxels containing 30% or more tumor were considered positive, the area under the ROC curves using combined MR spectroscopy and ADC (0.81) was similar to that of Cho/Cit alone (0.79) and better than ADC alone (0.66). When voxels containing 70% or more tumor were considered positive and cutoffs to achieve a 90%-or-greater sensitivity chosen, a combination of Cho/Cit and ADC achieved a significant improvement in specificity compared with Cho/Cit alone (p < 0.0001) or ADC alone (p < 0.0001).

CONCLUSION

When voxels containing > or = 70% tumor are considered positive, the combined use of MR spectroscopy and diffusion-weighted MRI increases the specificity for prostate cancer detection while retaining the sensitivity compared with MR spectroscopy alone or diffusion-weighted MRI alone.

Functional MR Imaging of Prostate Cancer

T2-weighted magnetic resonance (MR) imaging has been widely used for pretreatment work-up for prostate cancer, but its accuracy for the detection and localization of prostate cancer is unsatisfactory. To improve the utility of MR imaging for diagnostic evaluation, various other techniques may be used. Dynamic contrast material-enhanced MR imaging allows an assessment of parameters that are useful for differentiating cancer from normal tissue. The advantages of this technique include the direct depiction of tumor vascularity and, possibly, obviation of an endorectal coil; however, there also are disadvantages, such as limited visibility of cancer in the transitional zone. Diffusion-weighted imaging demonstrates the restriction of diffusion and the reduction of apparent diffusion coefficient values in cancerous tissue. This technique allows short acquisition time and provides high contrast resolution between cancer and normal tissue, but individual variability in apparent diffusion coefficient values may erode diagnostic performance. The accuracy of MR spectroscopy, which depicts a higher ratio of choline and creatine to citrate in cancerous tissue than in normal tissue, is generally accepted. The technique also allows detection of prostate cancer in the transitional zone. However, it requires a long acquisition time, does not directly depict the periprostatic area, and frequently is affected by artifacts. Thus, a comprehensive evaluation in which both functional and anatomic MR imaging techniques are used with an understanding of their particular advantages and disadvantages may help improve the accuracy of MR for detection and localization of prostate cancer.

Per-Sextant Localization and Staging of Prostate Cancer: Correlation of Imaging Findings with Whole-Mount Step Section Histopathology

OBJECTIVE

The objective of our study was to determine the diagnostic accuracy and interobserver agreement of 1.5-T prostatic MRI for per-sextant tumor localization and staging of prostate cancer as compared with whole-mount step section histopathology.

MATERIALS AND METHODS

Combined endorectal-pelvic phased-array prostatic MRI scans obtained at 1.5 T of 106 patients with biopsy-proven prostate cancer who had undergone radical prostatectomy with whole-mount step section histopathology within 28 days of MRI were retrospectively analyzed by three independent abdominal radiologists (reviewers 1, 2, and 3). Sextants of the prostate (right and left base, middle, and apex) were evaluated for the presence of prostate cancer and extracapsular extension (ECE) using a 5-point confidence scale. Data were statistically analyzed using receiver operating characteristic (ROC) analysis. Interobserver variability was assessed by kappa statistics. For calculation of sensitivity and specificity, data from the 5-point confidence scale were dichotomized into negative (score of 1-3) or positive (score of 4 or 5) findings.

RESULTS

Forty-one patients had ECE (tumor stage T3), and 65 patients had organ-confined disease (stage T2). Of 636 prostatic sextants, 417 were positive for prostate cancer and 135 were positive for ECE at histopathology. For prostate cancer localization, ROC analysis yielded area under the ROC curve (AUC) values ranging from 0.776 +/- 0.023 (SD) to 0.832 +/- 0.027. For the detection of ECE, the AUC values ranged from 0.740 +/- 0.054 to 0.812 +/- 0.045. Interobserver agreement (kappa) ranged from 0.49 to 0.60 for prostate cancer localization and from 0.59 to 0.67 for the detection of ECE.

CONCLUSION

Using the sextant framework, independent observers reach similar accuracy with moderate to substantial agreement for the localization of prostate cancer and ECE by means of MRI of the prostate.

Anatomical and metabolic assessment of prostate using a 3-Tesla MR scanner with a custom-made external transceive coil: Healthy volunteer study

PURPOSE

To examine the possibility of using a 3 Tesla (T) magnetic resonance (MR) scanner with a custom-made external coil to obtain ductal details of the prostate, high-quality spectra, and metabolite mapping corresponding to prostate zonal anatomy in healthy volunteers.

MATERIALS AND METHODS

MRI and two-dimensional (2D) chemical shift imaging (CSI) were performed in 16 healthy volunteers using a 3T scanner with a custom-made external transmit-receive (transceive) coil. Visualization of the prostatic duct-like structure was analyzed on T2-weighted (T2W) images. The resolution of the metabolite peaks and the distribution of metabolites in CSI were also assessed.

RESULTS

In the axial plane, 3-mm-thick images were better than 4-mm-thick images with the same voxel volume for assessing duct-like structures and prostatic urethra. Differentiation between inner and outer citrate (Cit) peaks was frequently observed (29 out of 30). The mean peak area ratio of choline (Cho) plus creatine (Cr) over Cit in the peripheral zone (PZ) was significantly lower than in the transition zone (TZ) (P = 0.014).

CONCLUSION

3T MR examinations of the prostate using an external coil allow information to be collected about the details of duct-like structures, the high-quality spectra of Cit, and the zone-specific distribution of metabolites.

In vivo 1H MR spectroscopy in the evaluation of the serial development of hepatocarcinogenesis in an experimental rat model

RATIONALE AND OBJECTIVES

We used a 1.5-T MR scanner to investigate in vivo hydrogen 1 ((1)H) MRS to evaluate metabolic changes in the hepatocarcinogenesis experimental rat model.

MATERIALS AND METHODS

Hepatocellular carcinoma (HCC) was induced by diethylnitrosamine in 70 treated rats with 20 normal rats used as controls. Single-voxel (1)H MRS is performed to obtained the relative choline-to-lipid (Cho/lipid) ratio. The liver and tumor tissues are incised for the histologic examination. Based on the histologic result, the progression of hepatocarcinogenesis of the animal model was divided into three stages: fibrosis stage, cirrhosis stage, and HCC stage. The mean (+/-SD) ratio values are calculated and compared at various stages between the treated group and the control group.

RESULTS

In control group, the calculated mean (+/-SD) Cho/lipid ratio was 0.15 +/- 0.05. With the progression of hepatocarcinogenesis, the Cho/lipid ratio increased significantly, to 0.18 +/- 0.05, 0.24 +/- 0.07, and 0.38 +/- 0.19, respectively.

CONCLUSION

The (1)H MRS is technically feasible for evaluation of the metabolic changes in the animal model. A significant increase in choline-containing compounds level was observed in the HCC stage in the treated group.

Pitfalls with MRI Evaluation of Prostate Cancer Detection

INTRODUCTION

To assess differences between MRI findings and histopathologically defined prostate cancer localization, we compared clinical results with mapping of radical prostatectomy specimens, and conducted a retrospective MRI cancer localization re-assessment by a urologist-technician after surgery.

METHODS

We performed MRI for a total of 37 suspected prostate cancer patients. Subsequently, all underwent retropubic radical prostatectomy after prostate biopsy for confirmation of the diagnosis. All the specimens were studied histopathologically with serial sectioning using a whole organ approach.

RESULTS

Of the 37 patients, 26 had positive MRI findings. All the surgical specimens contained cancerous lesions, and 23 had multiple foci. Twenty-four of the MRI-positive cases (92.3%) demonstrated coincidence of both MRI and histopathologically defined lesions. In the single focus cases, 78.6% (11/14) demonstrated exact coincidence, but in the multifocal cases there were no cases with exact coincidence of MRI and histopathological findings (0/23).

CONCLUSION

MRI evaluation cannot be considered an effective diagnostic tool in itself for detection of prostate cancers because sensitivity is far from satisfactory, especially in multi-focal cases.

Prostate dynamic contrast-enhanced MRI with simple visual diagnostic criteria: is it reasonable?

The purpose of this study was to evaluate the accuracy of prostate cancer localization with simple visual diagnostic criteria using dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). A total of 46 consecutive patients with biopsy-proven prostate cancer underwent prostate 1.5 T MRI with pelvic phased-array coils before prostatectomy. Besides the usual T2-weighted sequences, a 30-s DCE sequence was acquired three times after gadoterate injection. On DCE images, all early enhancing lesions of the peripheral zone were considered malignant. In the central gland, only early enhancing lesions appearing homogeneous or invading the peripheral zone were considered malignant. Three readers specified the presence of cancer in 20 prostate sectors and the location of distinct tumors. Results were compared with histology; p < 0.05 was considered significant. For localization of cancer in the sectors, DCE imaging had a significantly higher sensitivity [logistic regression, odds ratio (OR): 3.9, p < 0.0001] and a slightly but significantly lower specificity (OR: 0.57, p < 0.0001). Of the tumors >0.3 cc, 50-60% and 78-81% were correctly depicted with T2-weighted and DCE imaging, respectively. For both techniques, the depiction rate of tumors >0.3 cc was significantly influenced by the Gleason score (most Gleason </=6 tumors were overlooked), but not by the tumor volume.

CONCLUSION

DCE-MRI using pelvic phased-array coils and simple visual diagnostic criteria is more sensitive for tumor localization than T2-weighted imaging.

Clinical role of proton magnetic resonance spectroscopy in oncology: brain, breast, and prostate cancer

Standardised proton magnetic resonance spectroscopic imaging (MRSI) was initially developed for routine in-situ clinical assessment of human brain tumours, and its use was later extended for examination of prostate and breast cancers. MRSI coupled with both routine and functional MRI techniques provides more detailed information about a tumour's location and extent of its infiltration than any other modality alone. Information obtained by adding MRSI data to anatomical and functional MRI findings aid in clinical management decisions (such as watchful waiting vs immediate intervention). In this Review, we discuss the current status of proton MRSI, with emphasis on its clinical use to map the location and extent of tumour processes for spectroscopic image-guided biopsy procedures and to monitor treatment paradigms for brain, prostate, and breast cancer.

Applications of magnetic resonance spectroscopy in radiotherapy treatment planning

Following advances in conformal radiotherapy, a key problem now facing radiation oncologists is target definition. While MRI and CT provide images of excellent spatial resolution, they do not always provide sufficient contrast to identify tumour extent or to identify regions of high cellular activity that might be targeted with boost doses. Magnetic resonance spectroscopy (MRS) is an alternative approach that holds great promise for aiding target definition for radiotherapy treatment planning, and for evaluation of response and recurrence. MRS is able to detect signals from low molecular weight metabolites such as choline and creatine that are present at concentrations of a few mM in tissue. Spectra may be acquired from single voxels, or from a 2D or 3D array of voxels using spectroscopic imaging. The current state of the art achieves a spatial resolution of 6-10 mm in a scan time of about 10-15 min. Co-registered MR images are acquired in the same examination. The method is currently under evaluation, in particular in brain (where MRS has been shown to differentiate between many tumour types and grades) and in prostate (where cancer may be distinguished from normal tissue and benign prostatic hypertrophy). The contrast achieved with MRS, based on tissue biochemistry, therefore provides a promising alternative for identifying tumour extent and regions of high metabolic activity. It is anticipated that MRS will become an essential tool for treatment planning where other modalities lack the necessary contrast.

Quantitative analysis of prostate metabolites using 1H HR-MAS spectroscopy

A method was developed to quantify prostate metabolite concentrations using (1)H high-resolution magic angle spinning (HR-MAS) spectroscopy. T(1) and T(2) relaxation times (in milliseconds) were determined for the major prostate metabolites and an internal TSP standard, and used to optimize the acquisition and repetition times (TRs) at 11.7 T. At 1 degrees C, polyamines (PAs; T(1mean) = 100 +/- 13, T(2mean) = 30.8 +/- 7.4) and citrate (Cit; T(1mean) = 237 +/- 39, T(2mean) = 68.1 +/- 8.2) demonstrated the shortest relaxation times, while taurine (Tau; T(1mean) = 636 +/- 78, T(2mean) = 331 +/- 71) and choline (Cho; T(1mean) = 608 +/- 60, T(2mean) = 393 +/- 81) demonstrated the longest relaxation times. Millimolal metabolite concentrations were calculated for 60 postsurgical tissues using metabolite and TSP peak areas, and the mass of tissue and TSP. Phosphocholine plus glycerophosphocholine (PC+GPC), total choline (tCho), lactate (Lac), and alanine (Ala) concentrations were higher in prostate cancer ([PC+GPC](mean) = 9.34 +/- 6.43, [tCho](mean) = 13.8 +/- 7.4, [Lac](mean) = 69.8 +/- 27.1, [Ala](mean) = 12.6 +/- 6.8) than in healthy glandular ([PC+GPC](mean) = 3.55 +/- 1.53, P < 0.01; [tCho](mean) = 7.06 +/- 2.36, P < 0.01; [Lac](mean) = 46.5 +/- 17.4, P < 0.01; [Ala](mean) = 8.63 +/- 4.91, P = 0.051) and healthy stromal tissues ([PC+GPC](mean) = 4.34 +/- 2.46, P < 0.01; [tCho](mean) = 7.04 +/- 3.10, P < 0.01; [Lac](mean) = 45.1 +/- 18.6, P < 0.01; [Ala](mean) = 6.80 +/- 2.95, P < 0.01), while Cit and PA concentrations were significantly higher in healthy glandular tissues ([Cit](mean) = 43.1 +/- 21.2, [PAs](mean) = 18.5 +/- 15.6) than in healthy stromal ([Cit](mean) = 16.1 +/- 5.6, P < 0.01; [PAs](mean) = 3.15 +/- 1.81, P < 0.01) and prostate cancer tissues ([Cit](mean) = 19.6 +/- 12.7, P < 0.01; [PAs](mean) = 5.28 +/- 5.44, P < 0.01). Serial spectra acquired over 12 hr indicated that the degradation of Cho-containing metabolites was minimized by acquiring HR-MAS data at 1 degree C compared to 20 degrees C.

New horizons in genitourinary oncologic imaging

In the management of prostate cancer, combined anatomic and metabolic imaging is already in clinical use. In daily clinical practice, fusion of magnetic resonance imaging and magnetic resonance spectroscopic imaging is improving the evaluation of cancer location, size, and extent and is simultaneously providing assessment of tumor aggressiveness. Pretreatment knowledge of these prognostic variables is essential if minimally invasive, patient-specific cancer therapy is to be achieved. This report discusses the changes that are occurring in oncologic imaging and in genitourinary oncologic imaging in particular. It presents an overview of the applications of magnetic resonance imaging and magnetic resonance spectroscopic imaging for prostate cancer that is intended to illustrate the evolution of state-of-the-art imaging in a clinical setting. It also provides a short review of molecular imaging probes from the field of ongoing prostate cancer research. It concludes with a broader discussion of the nature of molecular imaging and the benefits it offers for cancer research and clinical care, which include noninvasive, in vivo imaging of specific cellular and molecular processes, nearly simultaneous monitoring of multiple molecular events, real-time imaging of the trafficking and targeting of cells, optimal patient-specific adjustment of drug and gene therapy, and assessment of disease progression at a molecular pathologic level.

Prostate cancer localization with dynamic contrast-enhanced MR imaging and proton MR spectroscopic imaging

PURPOSE

To prospectively determine the accuracies of T2-weighted magnetic resonance (MR) imaging, dynamic contrast material-enhanced MR imaging, and quantitative three-dimensional (3D) proton MR spectroscopic imaging of the entire prostate for prostate cancer localization, with whole-mount histopathologic section findings as the reference standard.

MATERIALS AND METHODS

This study was approved by the institutional review board, and informed consent was obtained from all patients. Thirty-four consecutive men with a mean age of 60 years and a mean prostate-specific antigen level of 8 ng/mL were examined. The median biopsy Gleason score was 6. T2-weighted MR imaging, dynamic contrast-enhanced MR imaging, and 3D MR spectroscopic imaging were performed, and on the basis of the image data, two readers with different levels of experience recorded the location of the suspicious peripheral zone and central gland tumor nodules on each of 14 standardized regions of interest (ROIs) in the prostate. The degree of diagnostic confidence for each ROI was recorded on a five-point scale. Localization accuracy and ROI-based receiver operating characteristic (ROC) curves were calculated.

RESULTS

For both readers, areas under the ROC curve for T2-weighted MR, dynamic contrast-enhanced MR, and 3D MR spectroscopic imaging were 0.68, 0.91, and 0.80, respectively. Reader accuracy in tumor localization with dynamic contrast-enhanced imaging was significantly better than that with quantitative spectroscopic imaging (P < .01). Reader accuracy in tumor localization with both dynamic contrast-enhanced imaging and spectroscopic imaging was significantly better than that with T2-weighted imaging (P < .01).

CONCLUSION

Compared with use of T2-weighted MR imaging, use of dynamic contrast-enhanced MR imaging and 3D MR spectroscopic imaging facilitated significantly improved accuracy in prostate cancer localization.

Combined MRI and MR Spectroscopy of the Prostate Before Radical Prostatectomy

OBJECTIVE

The purpose of this study was to evaluate a routine protocol for combined MR and spectroscopic imaging of the prostate for staging accuracy.

SUBJECTS AND METHODS

Fifty patients with biopsy-proven prostate carcinoma were examined with our sequence protocol, which consisted of T2-weighted fast spin-echo sequences and a pelvic T1-weighted spin-echo sequence. For spectroscopy, we used a 3D chemical shift imaging (CSI) spin-echo sequence. Image interpretation was performed by two radiologists. The total number of tumor voxels and tumor voxels per slice were counted to estimate the tumor volume in every patient. The potential of MR spectroscopy to differentiate between T2 and T3 tumors, based on the estimated tumor volumes, was compared with the staging performance of MRI.

RESULTS

The MR measurement time was 19.01 minutes, and the total procedure time averaged 35 minutes. Seventy-six percent of the spectroscopic examinations were successful. Statistically significant differences in the number of tumor voxels per slice and tumor volumes were found between T2 and T3 tumors. The descriptive parameters of MRI and MR spectroscopy did not differ significantly; sensitivity and specificity were 75% and 87%, respectively, for MRI and 88% and 70%, respectively, for MR spectroscopy. The combination of both methods resulted in only a slight improvement in staging performance and was not statistically significant.

CONCLUSION

Combined MRI and MR spectroscopy of the prostate has no diagnostic advantage in staging performance over MRI alone. The mean tumor volumes, estimated by MR spectroscopy, differ statistically significantly between T2 and T3 tumors.

Prostate Cancer Imaging—What the Urologic Oncologist Needs to Know

Appropriate imaging for prostate cancer patients depends on the clinical disease state of the patient and the question being asked. For patients who do not have a cancer diagnosis, ultrasound is the standard approach, in combination with a sextant biopsy. In the future, contrast-enhanced ultrasound and MR imaging-directed biopsy may improve biopsy yield and decrease biopsy number. For clinically localized disease, endorectal coil MR imaging and bone scanning may play a role in patients who have risk factors for extracapsular extension, but more data are needed to define the role of MR spectroscopy and lymphtrophic nanoparticle MR imaging. In the rising prostate-specific antigen (PSA) setting after definitive local therapy, endorectal coil MR imaging may help define local recurrence, whereas bone scanning can be useful in the setting of higher PSA or rapid PSA velocity.

New Clinical Imaging Modalities in Prostate Cancer

In all prostate cancer disease states, exciting novel imaging technology is being tested that may affect the future care of our patients. New US, MRI, and nuclear medicine techniques are improving both the ability to stage patients and to follow treatment-related changes. See Table 3 for a summary of these novel imaging techniques. Important issues still need to be resolved, including standardizing patient populations within trials, demonstrating the reproducibility of these techniques between different centers, and understanding how information gained from these techniques should influence patient care. We eagerly await answers to these questions.

How good is MRI at detecting and characterising cancer within the prostate?

OBJECTIVES

As well as detecting prostate cancer, it is becoming increasingly important to estimate its location, size and grade. We aim to summarise current data on the efficacy of magnetic resonance imaging (MRI) in this setting.

METHODS

Literature review of original research correlating MRI and histologic appearances.

RESULTS

Estimates of the sensitivity of MRI for the detection of cancer vary widely depending on method of analysis used and the definition of significant disease. Recent estimates using T2-weighted sequences and endorectal coils vary from 60% to 96%. Several groups have convincingly shown that dynamic contrast enhancement and spectroscopy each improve detection and that the sensitivity of MRI is comparable to and may exceed that of transrectal biopsy. Specificity is not yet good enough to consider the use of MRI in screening. High-grade and large tumours are detected significantly more often with both T2 sequences and spectroscopy. Estimation of size is improved by dynamic contrast and spectroscopy, but errors of >25% are common.

CONCLUSIONS

The sensitivity of MRI has improved to the point that it has potential in several new areas: targeting of biopsies, monitoring of disease burden both during active surveillance and after focal therapy, and exclusion of cancer in patients with a raised prostate-specific antigen level.

MR-Techniken zur nicht-invasiven Diagnostik des Prostatakarzinoms

The diagnosis of prostate cancer is suggested on the basis of an elevated PSA level, abnormal digital exam, and abnormal transrectal ultrasound. US-guided biopsy is used to confirm the diagnosis, but up to 30% of prostate cancer may be missed with this approach. Meanwhile MR imaging and proton MR spectroscopy have emerged as the most sensitive additional tools for the noninvasive evaluation of prostate cancer. This article reviews the clinical indications for MRI of the prostate and summarizes new techniques such as high field strength (3 tesla) and dynamic contrast-enhanced MRI.

IMRT boost dose planning on dominant intraprostatic lesions: Gold marker-based three-dimensional fusion of CT with dynamic contrast-enhanced and 1H-spectroscopic MRI

PURPOSE

To demonstrate the theoretical feasibility of integrating two functional prostate magnetic resonance imaging (MRI) techniques (dynamic contrast-enhanced MRI [DCE-MRI] and 1H-spectroscopic MRI [MRSI]) into inverse treatment planning for definition and potential irradiation of a dominant intraprostatic lesion (DIL) as a biologic target volume for high-dose intraprostatic boosting with intensity-modulated radiotherapy (IMRT).

METHODS AND MATERIALS

In 5 patients, four gold markers were implanted. An endorectal balloon was inserted for both CT and MRI. A DIL volume was defined by DCE-MRI and MRSI using different prostate cancer-specific physiologic (DCE-MRI) and metabolic (MRSI) parameters. CT-MRI registration was performed automatically by matching three-dimensional gold marker surface models with the iterative closest point method. DIL-IMRT plans, consisting of whole prostate irradiation to 70 Gy and a DIL boost to 90 Gy, and standard IMRT plans, in which the whole prostate was irradiated to 78 Gy were generated. The tumor control probability and rectal wall normal tissue complication probability were calculated and compared between the two IMRT approaches.

RESULTS

Combined DCE-MRI and MRSI yielded a clearly defined single DIL volume (range, 1.1-6.5 cm3) in all patients. In this small, selected patient population, no differences in tumor control probability were found. A decrease in the rectal wall normal tissue complication probability was observed in favor of the DIL-IMRT plan versus the plan with IMRT to 78 Gy.

CONCLUSION

Combined DCE-MRI and MRSI functional image-guided high-dose intraprostatic DIL-IMRT planned as a boost to 90 Gy is theoretically feasible. The preliminary results have indicated that DIL-IMRT may improve the therapeutic ratio by decreasing the normal tissue complication probability with an unchanged tumor control probability. A larger patient population, with more variations in the number, size, and localization of the DIL, and a feasible mechanism for treatment implementation has to be studied to extend these preliminary tumor control and toxicity estimates.

[MR spectroscopic imaging for evaluation of prostate cancer]

MR spectroscopic imaging (MRSI) provides a noninvasive method of evaluating metabolic markers of prostate cancer or healthy prostatic tissue (the metabolites choline and citrate), and is performed in conjunction with high-resolution MR anatomic imaging. Multiple studies have showed the incremental role of MRSI combined with the anatomical information provided by MRI for assessment of cancer location and extent within the prostate, staging, and cancer aggressiveness. In addition, MRSI has a potential role for pre- and post-treatment evaluation in non surgical patients. Ongoing technical developments show the potential role of MRSI for guidance of biopsies or focal treatment. Further developments - including new 3T technology - will likely provide improved spectral resolution for better prostate cancer detection and characterization.

Quantification of prostate MRSI data by model-based time domain fitting and frequency domain analysis

This paper compares two spectral processing methods for obtaining quantitative measures from in vivo prostate spectra, evaluates their effectiveness, and discusses the necessary modifications for accurate results. A frequency domain analysis (FDA) method based on peak integration was compared with a time domain fitting (TDF) method, a model-based nonlinear least squares fitting algorithm. The accuracy of both methods at estimating the choline + creatine + polyamines to citrate ratio (CCP:C) was tested using Monte Carlo simulations, empirical phantom MRSI data and in vivo MRSI data. The paper discusses the different approaches employed to achieve the quantification of the overlapping choline, creatine and polyamine resonances. Monte Carlo simulations showed induced biases on the estimated CCP:C ratios. Both methods were successful in identifying tumor tissue, provided that the CCP:C ratio was greater than a given (normal) threshold. Both methods predicted the same voxel condition in 94% of the in vivo voxels (68 out of 72). Both TDF and FDA methods had the ability to identify malignant voxels in an artifact-free case study using the estimated CCP:C ratio. Comparing the ratios estimated by the TDF and the FDA, the methods predicted the same spectrum type in 17 out of 18 voxels of the in vivo case study (94.4%).

Early response of hepatocellular carcinoma to transcatheter arterial chemoembolization: choline levels and MR diffusion constants--initial experience

PURPOSE

To prospectively investigate the apparent diffusion coefficient (ADC) and choline levels measured at hydrogen 1 ((1)H) magnetic resonance (MR) spectroscopy, to monitor therapeutic responses of hepatocellular carcinoma (HCC) to transcatheter arterial chemoembolization (TACE).

MATERIALS AND METHODS

Institutional review board approval was obtained, and all patients and control subjects provided informed consent. Histologically proved large HCCs (>3 cm in diameter) were evaluated in 20 patients (16 men and four women; mean age, 59 years; range, 34-80 years) before TACE and 2-3 days after TACE. A control group of eight adults (five men and three women; mean age, 43 years; range, 24-76 years) with normal livers was examined by using the same protocol. Hepatic choline levels were measured by means of an external phantom replacement method, quantifying the peak at 3.2 ppm at (1)H MR spectroscopy. ADCs were measured for all lesions. A Wilcoxon rank sum test was used to compare absolute choline concentrations and ADCs at baseline between HCCs and normal liver parenchyma. Changes in choline levels and ADCs in the tumors before and after TACE were analyzed by using the Wilcoxon signed rank test.

RESULTS

The median preoperative choline level in patients with HCC (measured in 18 of the 20 patients) was 4.0 mmol/L (range, 0.0-17.2 mmol/L), which was significantly higher than that in patients with normal livers (n = 8) (median, 1.6 mmol/L; range, 0.0-2.1 mmol/L; P < .01). Among 18 patients with HCC, choline levels decreased significantly from before TACE to after TACE (P < .01). A significant increase in ADC from before TACE to after TACE in the 20 patients with HCC was also found (P < .01).

CONCLUSION

Hepatic choline levels and ADCs may allow monitoring of therapeutic responses of HCC to TACE although larger, more definitive and quantitative studies with clinical end points are needed.

Three-dimensional conformal external beam radiotherapy compared with permanent prostate implantation in low-risk prostate cancer based on endorectal magnetic resonance spectroscopy imaging and prostate-specific antigen level

PURPOSE

To evaluate the metabolic response by comparing the time to resolution of spectroscopic abnormalities (TRSA) and the time to prostate-specific antigen level in low-risk prostate cancer patients after treatment with three-dimensional conformal external beam radiotherapy (3D-CRT) compared with permanent prostate implantation (PPI). Recent studies have suggested that the treatment of low-risk prostate cancer yields similar results for patients treated with 3D-CRT or PPI.

METHODS AND MATERIALS

A total of 50 patients, 25 in each group, who had been treated with 3D-CRT or PPI, had undergone endorectal magnetic resonance spectroscopy imaging before and/or at varying times after therapy. The 3D-CRT patients had received radiation doses of > or =72 Gy compared with 144 Gy for the PPI patients. The spectra from all usable voxels were examined for detectable levels of metabolic signal, and the percentages of atrophic and cancerous voxels were tabulated.

RESULTS

The median time to resolution of the spectroscopic abnormalities was 32.2 and 24.8 months and the time to the nadir prostate-specific antigen level was 52.4 and 38.0 months for the 3D-CRT and PPI patients, respectively. Of the 3D-CRT patients, 92% achieved negative endorectal magnetic resonance spectroscopy imaging findings, with 40% having complete metabolic atrophy. All 25 PPI patients had negative endorectal magnetic resonance spectroscopy imaging findings, with 60% achieving complete metabolic atrophy.

CONCLUSION

The results of this study suggest that metabolic and biochemical responses of the prostate are more pronounced after PPI. Our results have not proved PPI is more effective at curing prostate cancer, but they have demonstrated that it may be more effective at destroying prostate metabolism.

Registration of MR prostate images with biomechanical modeling and nonlinear parameter estimation

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) have been shown to be very useful for identifying prostate cancers. For high sensitivity, the MRI/MRSI examination is often acquired with an endorectal probe that may cause a substantial deformation of the prostate and surrounding soft tissues. Such a probe is removed prior to radiation therapy treatment. To register diagnostic probe-in magnetic resonance (MR) images to therapeutic probe-out MR images for treatment planning, a new deformable image registration method is developed based on biomechanical modeling of soft tissues and estimation of uncertain tissue parameters using nonlinear optimization. Given two-dimensional (2-D) segmented probe-in and probe-out images, a finite element method (FEM) is used to estimate the deformation of the prostate and surrounding tissues due to displacements and forces resulting from the endorectal probe. Since FEM requires tissue stiffness properties and external force values as input, the method estimates uncertain parameters using nonlinear local optimization. The registration method is evaluated using images from five balloon and five rigid endorectal probe patient cases. It requires on average 37 s of computation time on a 1.6 GHz Pentium-M PC. Comparing the prostate outline in deformed probe-out images to corresponding probe-in images, the method obtains a mean Dice Similarity Coefficient (DSC) of 97.5% for the balloon probe cases and 98.1% for the rigid probe cases. The method improves significantly over previous methods (P < 0.05) with greater improvement for balloon probe cases with larger tissue deformations.

Localization of Prostate Cancer Using 3T MRI

OBJECTIVE

To compare dynamic contrast-enhanced imaging and T2-weighted imaging using a 3T MR unit for the localization of prostate cancer.

METHODS

Twenty consecutive patients with biopsy-proven prostate cancer underwent both T2-weighted imaging and dynamic contrast-enhanced imaging. At T2-weighted imaging and dynamic contrast-enhanced imaging, the presence or absence of prostate cancer confined within the prostate without extracapsular or adjacent organ invasion was evaluated in the peripheral zones of base, mid-gland, and apex on each side. Final decisions on prostate cancer localization were made by consensus between two radiologists. Degrees of depiction of tumor borders were graded as poor, fair, or excellent.

RESULTS

Prostate cancer was pathologically detected in 64 (53%) of 120 peripheral zone areas. The sensitivity, specificity, and accuracy for prostate cancer detection were 55%, 88% and 70% for T2-weighted imaging and 73%, 77%, and 75% for dynamic contrast-enhanced imaging, respectively. Three cancer areas were detected only by T2-weighted imaging, 15 only by dynamic contrast-enhanced imaging, and 34 by both T2-weighted imaging and dynamic contrast-enhanced imaging. A fair or excellent degree at depicting tumor border was achieved in 67% by T2-weighted imaging and in 90% by dynamic contrast-enhanced imaging (P<0.05).

CONCLUSIONS

Dynamic contrast-enhanced imaging at 3T MRI is superior to T2-weighted imaging for the detection and depiction of prostate cancer and thus is likely to be more useful for preoperative staging.