Prostate cancer: prediction of extracapsular extension with endorectal MR imaging and three-dimensional proton MR spectroscopic imaging

Deformable image registration for the use of magnetic resonance spectroscopy in prostate treatment planning

PURPOSE

There is now convincing evidence that prostate cancer cells lack the ability to produce and accumulate citrate. Using magnetic resonance spectroscopy imaging (MRSI), regions of absent or low citrate concentration in the prostate can be visualized at a resolution of a few mm. This new advancement provides not only a tool for early diagnosis and screening but also the opportunity for preferential targeting of radiation to regions of high tumor burden in the prostate. The differences in the shape and location of the prostate between MRSI imaging and treatment have been the major obstacle in integrating MRSI in radiation therapy treatment planning. The purpose of this study is to develop a reliable method for deforming the prostate and surrounding regions from the geometry of MRSI imaging to the geometry of treatment planning, so that the regions of high tumor burden identified by the MRSI study can be faithfully transferred to the images used for treatment planning.

METHODS AND MATERIALS

Magnetic resonance spectroscopy imaging studies have been performed on 2 prostate cancer patients using a commercial MRSI system with an endorectal coil and coupling balloon. At the end of each study, we also acquired the MRI of the pelvic region at both the deformed state where the prostate is distorted by the endorectal balloon and the resting state with the endorectal balloon deflated and removed. The task is to find a three-dimensional matrix of transformation vectors for all volume elements that links the two image sets. We have implemented an optimization method to iteratively optimize the transformation vectors using a Newton-Ralphson algorithm. The objective function is based on the mutual information. The distorted images using the transformation vectors are compared with the images acquired at the resting conditions.

RESULTS AND DISCUSSION

The algorithm is capable of performing the registration automatically without the need for intervention. It does not require manual contouring of the organs. By applying the algorithm to multiple image sets of different patients, we found a good agreement between the images transformed from those acquired at the deformed state and those acquired at resting conditions. The computation time required for achieving the registration is in the range of a half-hour (for image size: 256 pixels x 256 pixels x 25 slices). However, the space of registration can be restricted to speed up the process.

CONCLUSION

In this article, we described a three-dimensional deformable image registration method to automatically transform images from the deformed imaging state to resting state. Our examples show that this method is feasible and useful to the treatment planning system.

Proton HR-MAS spectroscopy and quantitative pathologic analysis of MRI/3D-MRSI-targeted postsurgical prostate tissues

Proton high-resolution magic angle spinning ((1)H HR-MAS) NMR spectroscopy and quantitative histopathology were performed on the same 54 MRI/3D-MRSI-targeted postsurgical prostate tissue samples. Presurgical MRI/3D-MRSI targeted healthy and malignant prostate tissues with an accuracy of 81%. Even in the presence of substantial tissue heterogeneity, distinct (1)H HR-MAS spectral patterns were observed for different benign tissue types and prostate cancer. Specifically, healthy glandular tissue was discriminated from prostate cancer based on significantly higher levels of citrate (P = 0.04) and polyamines (P = 0.01), and lower (P = 0.02) levels of the choline-containing compounds choline, phosphocholine (PC), and glycerophosphocholine (GPC). Predominantly stromal tissue lacked both citrate and polyamines, but demonstrated significantly (P = 0.01) lower levels of choline compounds than cancer. In addition, taurine, myo-inositol, and scyllo-inositol were all higher in prostate cancer vs. healthy glandular and stromal tissues. Among cancer samples, larger increases in choline, and decreases in citrate and polyamines (P = 0.05) were observed with more aggressive cancers, and a MIB-1 labeling index correlated (r = 0.62, P = 0.01) with elevated choline. The elucidation of spectral patterns associated with mixtures of different prostate tissue types and cancer grades, and the inclusion of new metabolic markers for prostate cancer may significantly improve the clinical interpretation of in vivo prostate MRSI data.

Prostate Cancer Localization with Endorectal MR Imaging and MR Spectroscopic Imaging: Effect of Clinical Data on Reader Accuracy

PURPOSE

To determine the effect of digital rectal examination findings, sextant biopsy results, and prostate-specific antigen (PSA) levels on reader accuracy in the localization of prostate cancer with endorectal magnetic resonance (MR) imaging and MR spectroscopic imaging.

MATERIALS AND METHODS

This was a retrospective study of 37 patients (mean age, 57 years) with biopsy-proved prostate cancer. Transverse T1-weighted, transverse high-spatial-resolution, and coronal T2-weighted MR images and MR spectroscopic images were obtained. Two independent readers, unaware of clinical data, recorded the size and location of suspicious peripheral zone tumor nodules on a standardized diagram of the prostate. Readers also recorded their degree of diagnostic confidence for each nodule on a five-point scale. Both readers repeated this interpretation with knowledge of rectal examination findings, sextant biopsy results, and PSA level. Step-section histopathologic findings were the reference standard. Logistic regression analysis with generalized estimating equations was used to correlate tumor detection with clinical data, and alternative free-response receiver operating characteristic (AFROC) curve analysis was used to examine the overall effect of clinical data on all positive results.

RESULTS

Fifty-one peripheral zone tumor nodules were identified at histopathologic evaluation. Logistic regression analysis showed awareness of clinical data significantly improved tumor detection rate (P <.02) from 15 to 19 nodules for reader 1 and from 13 to 19 nodules for reader 2 (27%-37% overall) by using both size and location criteria. AFROC analysis showed no significant change in overall reader performance because there was an associated increase in the number of false-positive findings with awareness of clinical data, from 11 to 21 for reader 1 and from 16 to 25 for reader 2.

CONCLUSION

Awareness of clinical data significantly improves reader detection of prostate cancer nodules with endorectal MR imaging and MR spectroscopic imaging, but there is no overall change in reader accuracy, because of an associated increase in false-positive findings. A stricter definition of a true-positive result is associated with reduced sensitivity for prostate cancer nodule detection.

The role of preoperative endorectal magnetic resonance imaging in the decision regarding whether to preserve or resect neurovascular bundles during radical retropubic prostatectomy

BACKGROUND

Because the recovery of erectile function and the avoidance of positive surgical margins are important but competing outcomes, the decision to preserve or resect a neurovascular bundle (NVB) during radical prostatectomy (RP) should be based on the most accurate information concerning the location and extent of the tumor. In the current study, the authors determined the incremental value of endorectal magnetic resonance imaging (eMRI) in making this decision.

METHODS

eMRI was performed in 135 patients preoperatively. For each NVB, tumor extension to the NVB and the need for NVB resection was judged by a surgeon on a scale from 1 (definite preservation) to 5 (definite resection) before and after reviewing eMRI with a radiologist. Histopathologic findings were used as the standard of reference. The value of eMRI was assessed using binormal receiver operating characteristic (ROC) analysis adjusted for multiple observations per patient, and a mixed effects ordinal regression model was used for risk stratification.

RESULTS

Histopathologic examination determined that NVB resection was warranted in 44 of 270 NVBs (16%) because of posterolateral extracapsular extension (n = 29), positive surgical margins (n = 7), or both (n = 8). The areas under the ROC curves (AUC) were 0.741 for pre-MRI and 0.832 for post-MRI surgical planning (P < 0.01). MRI findings suggested altering the surgical plan in 39% of NVBs (106 of 270 NVBs). When the surgeon judged that the NVB resection was definitely not necessary (165 NVBs), MRI confirmed that decision in 138 NVBs (84%); the concordant decision was correct in 96% of the cases (133 of 138 NVBs). In 36 high-risk patients (> or = 75% probability of extracapsular extension), MRI findings changed the surgical plan for 28 NVBs (78%); the change was found to be appropriate in 26 cases (93%).

CONCLUSIONS

MRI was found to significantly improve the surgeon's decision to preserve or resect the NVB during radical prostatectomy.

Magnetic Resonance Imaging and Spectroscopic Imaging of Prostate Cancer

PURPOSE

We describe the practical technical aspects of magnetic resonance spectroscopic imaging (MRSI), and summarize the current and potential future status of magnetic resonance imaging (MRI) and MRSI in the diagnosis, localization, staging, treatment planning and post-treatment followup of prostate cancer.

MATERIALS AND METHODS

Contemporary series of patients with prostate cancer evaluated by MRI and MRSI were reviewed, with particular respect to imaging accuracy as evaluated by histopathological correlation, and the relationship between MRI and MRSI and outcome.

RESULTS

MRI and MRSI have a limited role in prostate cancer diagnosis but may be helpful for patients with a high index of suspicion and negative initial biopsy. High specificity can be achieved for sextant localization of cancer when sextant biopsy, MRI and MRSI are all positive. Volumetric localization is of limited accuracy for tumors less than 0.5 cc. Staging by MRI, which is improved by the addition of MRSI, is of incremental prognostic significance for patients with moderate and high risk tumors. MRI and MRSI may assist in surgical and radiation treatment planning, and posttreatment followup. In particular, the use of MRI to assist radiation treatment planning has been shown to improve outcome. Interventional MRI guided biopsy and therapy remain under investigation.

CONCLUSIONS

Only MRI and MRSI allow combined structural and metabolic evaluation of prostate cancer location, aggressiveness and stage. MRI provides clinically and therapeutically relevant anatomical information. The technology remains in evolution, and continued advances in accuracy and use are likely.

Transition zone prostate cancer: metabolic characteristics at 1H MR spectroscopic imaging--initial results

PURPOSE

To determine whether cancers of the prostate transition zone (TZ) possess a unique metabolic pattern by which they may be identified at proton magnetic resonance (MR) spectroscopic imaging.

MATERIALS AND METHODS

Findings in 40 patients who underwent combined endorectal MR imaging and hydrogen 1 MR spectroscopic imaging before radical prostatectomy and who had TZ tumor identified subsequently at step-section pathologic analysis were retrospectively reviewed. Within this population, a subset of 16 patients whose TZ tumor had a largest diameter of 1 cm or greater and was included in the MR spectroscopic imaging excitation volume was identified. In these 16 patients, the ratios of choline-containing compounds (Cho) and creatine/phosphocreatine (Cr) to citrate (Cit) (ie, [Cho + Cr]/Cit), Cho/Cr, and Cho/Cit were compared in tumor and control tissues. The presence of only Cho and the absence of all metabolites were also assessed.

RESULTS

The mean values of (Cho + Cr)/Cit, Cho/Cr, and Cho/Cit were different between TZ cancer and control tissues (P =.001, P =.003, and P =.001, respectively; Wilcoxon signed rank test). Nine (56%) of 16 patients had at least one tumor voxel in which Cho comprised the only detectable peak, while no control voxels showed only Cho (P =.008, McNemar test). The percentage of voxels in which no metabolites were detected did not differ between tumor and control tissues (P =.134, McNemar test).

CONCLUSION

TZ cancer has a metabolic profile that is different from that of benign TZ tissue; however, the broad range of metabolite ratios observed in TZ cancer precludes the use of a single ratio to differentiate TZ cancer from benign TZ tissue.

Molecular imaging in prostate cancer

Prostate cancer (PCa) is the most common non-cutaneous malignancy in men. New ways to diagnose this cancer in its early stages are needed. Unique genetic and biochemical changes in the cell pave the way for tumors to grow and metastasize. Novel imaging approaches attempt to detect pathological processes in cancer cells at the molecular level. This has led to the establishment and development of the field of molecular imaging. Positron emission tomography (PET), magnetic resonance spectroscopic imaging (MRSI), magnetic resonance imaging (MRI), and radiolabeled antibodies are a few of the modalities that can detect abnormal tumor metabolic processes in the clinical setting. Other imaging techniques are still in their early phase of development but hold promise for the future, including bioluminescence imaging (BLI), measurement of tumor oxygenation, and measurement of uptake of iodine by tumors. These techniques are non-invasive and can spare the patient undue morbidity, while potentially providing early diagnosis, accurate follow-up and, finally, valuable prognostic information.

Multicenter phase-II trial of safety and efficacy of NC100150 for steady-state contrast-enhanced peripheral magnetic resonance angiography

The aim of this study was to test the safety and efficacy of NC100150 injection for steady-state contrast-enhanced peripheral MR angiography in a multicentre phase-II trial. Thirty-three patients underwent steady-state NC100150 enhanced MR angiography (5 mg Fe/kg body weight) of the aortoiliac and femoropopliteal arteries. Safety assessment consisted of pre- and post-injection (2, 24 and 72 h) monitoring of vital signs, physical examination as well as laboratory and electrocardiographic parameters. To determine sensitivity and specificity for detection of haemodynamically significant stenoses (HSS; >50% reduction of luminal diameter) MR angiograms were compared with intra-arterial digital subtraction angiography (IA DSA), which was considered the standard of reference. In 33 patients a mean of 12.8 ml NC100150 was injected. Eleven patients reported 13 mild and 2 moderate adverse events. Five mild and one moderate adverse event were considered due to NC100150 injection. There were no significant changes in vital signs, laboratory or electrocardiographic parameters. Sensitivity and specificity (in percent) for detection of HSS were 87 and 64, 56 and 76, and 75 and 84, for iliac, femoral and popliteal arteries, respectively. NC100150 high-resolution steady-state MR angiography can be performed safely and is feasible for the detection of peripheral arterial HSS, but is as yet not a clinically useful alternative to conventional gadolinium-enhanced MR angiography.

Pathologic characterization of human prostate tissue with proton MR spectroscopy

PURPOSE

To assess the accuracy of magnetic resonance (MR) spectroscopy in documenting the chemical features of human prostate tissue and to ascertain if there are chemical criteria of diagnostic importance.

MATERIALS AND METHODS

Seventy-seven prostate tissue specimens (peripheral zone, n = 61; transitional zone, n = 16) from 43 patients were analyzed with MR spectroscopy. Histologic features were compared with MR spectroscopic data. Statistical analysis was undertaken with analysis of variance and computer software.

RESULTS

Histologically identified carcinomas were determined by using MR spectroscopy with a sensitivity of 100% and a specificity of 94%. Histologically benign tissue from patients without carcinoma of the prostate was distinguished from malignant tissue with a sensitivity of 100% and a specificity of 94%. When benign specimens from patients with cancer elsewhere in the prostate were included in the database, MR spectroscopy helped distinguish benign prostatic hyperplasia from adenocarcinoma with a sensitivity of 97% and specificity of 88%. Depleted citrate and elevated choline levels alone were not accurate markers of malignancy, since citrate levels remain high when a small amount of malignant disease is present. Carcinomas missed at routine histologic examination were identified with MR spectroscopy and confirmed with specialized, nonstandard histologic examination.

CONCLUSION

By comparing the intensity of resonances assigned to choline, creatine, lipid, and lysine, MR spectroscopy can depict prostate carcinoma with a high degree of sensitivity and specificity. Citrate and choline resonances alone are not sufficiently accurate markers for distinguishing between various patterns of prostatic disease.

Imaging clinically localized prostate cancer

At this time there is no highly sensitive and specific widespread radiographic test for local staging of prostate cancer. Future developments will likely require a combination of imaging modalities with utilization guided by risk-stratification models (Table 4). Staging data for all imaging tests discussed in this article are summarized in Tables 5 and 6. Clinically, conventional gray-scale TRUS remains the most frequently used tool because of its utility in guiding prostatic biopsies. Modifications of TRUS--including power and color Doppler, 3D imaging, and new ultrasound contrast agents and elastography--show promise in increasing the accuracy of ultrasound. Endorectal MRI may have some value for staging selected patients. The addition of prostatic MRS, which images the differential activity of metabolites, may increase the specificity of MRI. Newer techniques with finer voxel resolution may prove to be clinically useful. A large well-designed study evaluating the utility of MRI/MRS is currently being planned. Cross-sectional imaging of the pelvis with either MRI or CT should be used selectively as should radionuclide bone scans. Similarly, ProstaScint scans should be ordered selectively, either before or after primary therapy, rather than routinely in all patients.

Combined magnetic resonance imaging and spectroscopic imaging approach to molecular imaging of prostate cancer

Magnetic resonance spectroscopic imaging (MRSI) provides a noninvasive method of detecting small molecular markers (historically the metabolites choline and citrate) within the cytosol and extracellular spaces of the prostate, and is performed in conjunction with high-resolution anatomic imaging. Recent studies in pre-prostatectomy patients have indicated that the metabolic information provided by MRSI combined with the anatomical information provided by MRI can significantly improve the assessment of cancer location and extent within the prostate, extracapsular spread, and cancer aggressiveness. Additionally, pre- and post-therapy studies have demonstrated the potential of MRI/MRSI to provide a direct measure of the presence and spatial extent of prostate cancer after therapy, a measure of the time course of response, and information concerning the mechanism of therapeutic response. In addition to detecting metabolic biomarkers of disease behavior and therapeutic response, MRI/MRSI guidance can improve tissue selection for ex vivo analysis. High-resolution magic angle spinning ((1)H HR-MAS) spectroscopy provides a full chemical analysis of MRI/MRSI-targeted tissues prior to pathologic and immunohistochemical analyses of the same tissue. Preliminary (1)H HR-MAS spectroscopy studies have already identified unique spectral patterns for healthy glandular and stromal tissues and prostate cancer, determined the composition of the composite in vivo choline peak, and identified the polyamine spermine as a new metabolic marker of prostate cancer. The addition of imaging sequences that provide other functional information within the same exam (dynamic contrast uptake imaging and diffusion-weighted imaging) have also demonstrated the potential to further increase the accuracy of prostate cancer detection and characterization.

Prostate cancer tumor volume: measurement with endorectal MR and MR spectroscopic imaging

PURPOSE

To determine accuracy of magnetic resonance (MR) and three-dimensional (3D) MR spectroscopic imaging in prostate cancer tumor volume measurement.

MATERIALS AND METHODS

Endorectal MR and 3D MR spectroscopic imaging were performed in 37 patients before radical prostatectomy. Two independent readers recorded peripheral zone tumor nodule location and volume. Results were analyzed with step-section histopathologic tumor localization and volume measurement as the standard. Accuracy of tumor volume measurement was assessed with the Pearson correlation coefficient. P values were calculated with a random effects model. Bland-Altman regression analysis was used to evaluate systematic bias between tumor volumes measured with MR imaging and true tumor volumes. Analyses were performed for all nodules and nodules greater than 0.50 cm(3).

RESULTS

Mean volume of peripheral zone tumor nodules (n = 51) was 0.79 cm(3) (range, 0.02-3.70 cm(3)). Two readers detected 20 (65%) and 23 (74%) of 31 peripheral zone tumor nodules greater than 0.50 cm(3). For these nodules, measurements of tumor volume with MR imaging, 3D MR spectroscopic imaging, and a combination of both were all positively correlated with histopathologic volume (Pearson correlation coefficients of 0.49, 0.59, and 0.55, respectively); only measurements with 3D MR spectroscopic imaging and a combination of MR and 3D MR spectroscopic imaging demonstrated statistical significance (P <.05). Tumor volume estimation with all three methods was more accurate for higher tumor volumes.

CONCLUSION

Addition of 3D MR spectroscopic imaging to MR imaging increases overall accuracy of prostate cancer tumor volume measurement, although measurement variability limits consistent quantitative tumor volume estimation, particularly for small tumors.

Advances in uroradiological imaging

The development of new imaging techniques and the refinement of established methods in uroradiological imaging is proceeding rapidly. In the last few years several important developments have been implemented in the routine diagnostic evaluation of urological patients.A milestone is the recent advent of multidetector helical computed tomography (CT), enabling the radiologist to provide the clinician with high-quality three-dimensional (3-D) reconstructions of the urological organs. Powerful workstations are an indispensable tool in the post-processing of CT and magnetic resonance imaging (MRI)data. Significant advances in imaging were obtained in the fields of oncological imaging (e.g. prostate MRI and spectroscopic imaging), paediatric uroradiology(e.g. MR urography) and the evaluation of stone disease by unenhanced helical CT.

Staging in prostate cancer

This article reviews the conventional current techniques that are used for staging prostate cancer. The advantages and limitations of each modality are described. Attention is focused on the areas in which progress is rapidly being made and is likely to be developed in the future.

Dualband spectral-spatial RF pulses for prostate MR spectroscopic imaging

Although MR spectroscopic imaging (MRSI) of the prostate has demonstrated clinical utility for the staging and monitoring of cancer extent, current acquisition methods are often inadequate in several aspects. Conventional 180 degrees pulses can suffer from chemical shift misregistration, and have high peak-power requirements that can exceed hardware limits in many prostate MRSI studies. Optimal water and lipid suppression are also critical to obtain interpretable spectra. While complete suppression of the periprostatic lipid resonance is desired, controlled partial suppression of water can provide a valuable phase and frequency reference for data analysis and an assessment of experimental success in cases in which all other resonances are undetectable following treatment. In this study, new spectral-spatial RF pulses were developed to negate chemical shift misregistration errors and to provide dualband excitation with partial excitation of the water resonance and full excitation of the metabolites of interest. Optimal phase modulation was also included in the pulse design to provide 40% reduction in peak RF power. Patient studies using the new pulses demonstrated both feasibility and clear benefits in the reliability and applicability of prostate cancer MRSI.

Localized prostate cancer: effect of hormone deprivation therapy measured by using combined three-dimensional 1H MR spectroscopy and MR imaging: clinicopathologic case-controlled study

PURPOSE

To determine the accuracy of combined magnetic resonance (MR) imaging and three-dimensional (3D) proton MR spectroscopic imaging in localizing prostate cancer to a sextant of the gland in patients receiving hormone deprivation therapy.

MATERIALS AND METHODS

Combined MR imaging/3D MR spectroscopic imaging examinations were performed in 16 hormone-treated patients and 48 nontreated matched control patients before radical prostatectomy and step-section histopathologic analysis. At MR imaging, cancer presence within the peripheral zone was assessed on a per sextant basis by two readers. At 3D MR spectroscopic imaging, cancer was identified by using (choline plus creatine)-to-citrate ratios at cutoff values of 2 and 3 SDs above mean normal peripheral zone values. Data were compared by using receiver operating characteristic analysis.

RESULTS

There was no significant difference in the ability of combined MR imaging/3D MR spectroscopic imaging to localize prostate cancer in treated versus control patients. For MR imaging alone, the sensitivity and specificity were 91% and 48% (reader 1) and 75% and 60% (reader 2) in treated patients versus 79% and 60% (reader 1) and 84% and 43% (reader 2) in control patients. For 3D MR spectroscopic imaging alone (>3 SDs cutoff), higher specificity (treated, 80%; controls, 73%) but lower sensitivity (treated, 56%; controls, 53%) was attained. In treated patients, high sensitivity or specificity (up to 92%) was achieved when either or both modalities indicated cancer.

CONCLUSION

When performed within 4 months after initiating hormone deprivation therapy, combined MR imaging/3D MR spectroscopic imaging had the same accuracy in localizing prostate cancer as in nontreated patients.

Assessment of the risk of positive surgical margins with pelvic phased-array magnetic resonance imaging in patients with clinically localized prostate cancer: a prospective study

OBJECTIVES

We assessed magnetic resonance imaging (MRI) performance in the prediction of positive surgical margins (PSMs) before radical prostatectomy in a prospective study correlating the MRI results and pathologic findings.

METHODS

Between January 1995 and December 1999, 176 patients (mean age 64.2 years, range 49 to 75), with localized prostate cancer (49 with Stage T1 and 127 with Stage T2) underwent preoperative MRI with a pelvic phased-array coil (Tesla-1, Siemens) at a mean interval of 35 days after randomized transrectal biopsies. The mean preoperative prostate-specific antigen level was 10.9 ng/mL (range 1.2 to 39). The MRI studies and specimen analysis were performed by one radiologist unaware of the clinical and biopsy findings and by one pathologist, respectively. Multivariate analysis was performed to compare the predictive value of MRI staging, prostate-specific antigen value, and preoperative Gleason score to identify the PSM rate.

RESULTS

Of the 176 patients, 131 (74%) had Stage T2 disease by MRI and 45 (26%) Stage T3 disease by MRI. Pathologic staging showed 103 with pT2 and 73 with pT3. Overall, the PSM rate of the series was 18%. The PSM rate was 13.7% and 31% for patients with T2 and T3 disease by MRI, respectively. For the T3 MRI cases, the PSM rate was 2.32-fold higher. MRI staging, like the prostate-specific antigen value, was a predictive factor of PSMs (P = 0.05).

CONCLUSIONS

The results of this study show that preoperative MRI staging with the phased-array coil may be helpful in predicting the PSM risk in radical prostatectomy candidates with clinically localized prostate cancer.

Time-dependent effects of hormone-deprivation therapy on prostate metabolism as detected by combined magnetic resonance imaging and 3D magnetic resonance spectroscopic imaging

Combined MRI and 3D spectroscopic imaging (MRI/3D-MRSI) was used to study the metabolic effects of hormone-deprivation therapy in 65 prostate cancer patients, who underwent either short, intermediate, or long-term therapy, compared to 30 untreated control patients. There was a significant time-dependent loss of the prostatic metabolites choline, creatine, citrate, and polyamines during hormone-deprivation therapy, resulting in the complete loss of all observable metabolites (total metabolic atrophy) in 25% of patients on long-term therapy. The amount and time-course of metabolite loss during therapy significantly differed for healthy and malignant tissues. Citrate levels decreased faster than choline and creatine levels during therapy, resulting in an increase in the mean (choline + creatine)/citrate ratio with duration of therapy. Due to a loss of all MRSI detectable citrate, this ratio could not be used to identify cancer in 69% of patients on long-term therapy. In the absence of citrate, however, residual prostate cancer could still be detected by elevated choline levels (choline/creatine ratio > or =1.5), or the presence of only choline in the proton spectrum. The loss of citrate and the presence of total metabolic atrophy correlated roughly with decreasing serum prostatic specific antigen levels with increasing therapy. In summary, MRI/3D-MRSI provided both a measure of residual cancer and a time-course of metabolic response following hormone-deprivation therapy. Magn Reson Med 46:49-57, 2001.

Magnetic resonance spectroscopy of the malignant prostate gland after radiotherapy: a histopathologic study of diagnostic validity

PURPOSE

Accurate spatial representation of tumor clearance after conformal radiotherapy is an endpoint of clinical importance. Magnetic resonance spectroscopy (MRS) can diagnose malignancy in the untreated prostate gland through measurements of cellular metabolites. In this study we sought to describe spectral metabolic changes in prostatic tissue after radiotherapy and validate a multivariate analytic strategy (based on MRS) that could identify viable tumor.

METHODS AND MATERIALS

Transrectal ultrasound-guided prostate biopsies from 35 patients were obtained 18-36 months after external beam radiotherapy. One hundred sixteen tissue specimens were subjected to 1H MRS, submitted to histopathology, and analyzed for correlation with a multivariate strategy specifically developed for biomedical spectra.

RESULTS

The sensitivity and specificity of MRS in identifying a malignant biopsy were 88.9% and 92% respectively, with an overall classification accuracy of 91.4%. The diagnostic spectral regions identified by our algorithm included those due to choline, creatine, glutamine, and lipid. Citrate, an important discriminating resonance in the untreated prostate gland, was invisible in all spectra, regardless of histology.

CONCLUSIONS

Although the spectral features of prostate tissue markedly change after radiotherapy, MRS combined with multivariate methods of analysis can accurately identify histologically malignant biopsies. MRS shows promise as a modality that could integrate three-dimensional measures of tumor response.

Magnetic resonance imaging and spectroscopic imaging: Improved patient selection and potential for metabolic intermediate endpoints in prostate cancer chemoprevention trials

In the design of prostate cancer chemoprevention trials there is a clear need for improved patient selection and risk stratification, as well as the use of biomarkers that could provide earlier assessment of therapeutic efficacy. Studies in preprostatectomy patients have indicated that the metabolic information provided by 3-dimensional magnetic resonance spectroscopic imaging (3D-MRSI) combined with the morphologic information provided by magnetic resonance imaging (MRI) can improve the assessment of cancer location and extent within the prostate, extracapsular spread, and cancer aggressiveness. Additionally, pre- and posttherapy studies have demonstrated the potential of MRI/3D-MRSI to provide a direct measure of the presence and spatial extent of prostate cancer after therapy, a measure of the time course of response, and information concerning the mechanism of therapeutic response. These studies suggest that the addition of MRI/3D-MRSI data to prostate-specific antigen and biopsy data may improve patient selection and risk stratification for chemoprevention trials, improve tissue sampling for ex vivo molecular marker analysis, and provide shorter-term endpoints in chemoprevention trials. However, future studies are necessary to establish the ability of MRI/3D-MRSI to accurately assess patients with premalignant or very early malignant changes, to validate metabolic markers as intermediate endpoints in chemoprevention trials, and to correlate metabolic endpoints with other promising intermediate biomarkers.

Magnetic resonance imaging of the prostate

Magnetic resonance imaging has been shown to be more accurate than other imaging modalities in the evaluation of both malignancies and various benign lesions of the prostate. Despite its superiority, because of its cost and low availability, magnetic resonance imaging should play a role as a problem-solver secondary to computed tomography or ultrasonography. The routine use of magnetic resonance imaging in the staging of prostate cancer before surgery cannot be justified on the basis of published data. Magnetic resonance imaging has been proved to be of value in the planning and delivery of different types of radiotherapy to patients with prostate cancer. Through the use of combined magnetic resonance imaging and the new modality, magnetic resonance spectroscopy, the accuracy and specificity of tumour detection and the delineation of tumour extent can be improved. Magnetic resonance technology is rapidly evolving, and in the near future, new possibilities such as biological imaging will have a great impact on magnetic resonance imaging of the prostate.

Limited value of endorectal magnetic resonance imaging and transrectal ultrasonography in the staging of clinically localized prostate cancer

OBJECTIVE

To examine the role of endorectal magnetic resonance imaging (eMRI) and transrectal ultrasonography (TRUS) for clinically localized prostate cancer and to assess interobserver agreement in interpreting MRI studies.

PATIENTS AND METHODS

Fifty-four patients with biopsy-confirmed prostate cancer underwent TRUS and eMRI before radical retropubic prostatectomy. The MR images were prospectively interpreted by two radiologists with special expertise in this field. The criteria evaluated prospectively in each patient were extracapsular extension (ECE) and seminal vesicle invasion (SVI). The results were correlated with the histopathological findings after radical prostatectomy.

RESULTS

At pathology, 27 patients had stage pT2, 15 had stage pT3a and 12 had stage pT3b lesions. The overall accuracy of eMRI in defining local tumour stage was 93% by radiologist A and 56% by radiologist B; the overall accuracy by TRUS was 63%. There was a poor correlation for the MRI studies between observers. The eMRI was more sensitive than TRUS for detecting ECE and SVI in organ-confined prostate cancer. TRUS had a relatively high specificity for ECE and SVI, and was better than eMRI in this regard.

CONCLUSION

Whereas MRI tended to over-stage, TRUS under-staged prostate cancer. This series shows the current limited value of TRUS and eMRI for planning treatment in patients with clinically localized prostate cancer. Treatment decisions should not be altered based on TRUS or eMRI findings alone.

The prostate: MR imaging and spectroscopy. Present and future

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

Clinical application of BASING and spectral/spatial water and lipid suppression pulses for prostate cancer staging and localization by in vivo 3D 1H magnetic resonance spectroscopic imaging

In previous in situ point-resolved spectroscopy (PRESS) three-dimensional (3D) 1H magnetic resonance (MR) spectroscopic imaging studies, it has been demonstrated that the ratio of prostatic metabolites can noninvasively discriminate prostate cancer from surrounding normal tissue. However, in these studies, conventional chemical shift selective suppression (CHESS) and short-time inversion recovery (STIR) techniques often resulted in inadequate water and lipid suppression. To improve suppression and spatial coverage, the newly developed T1 insensitive dual band selective inversion with gradient dephasing (BASING) Bandstop Filter and dual phase-compensating spectral/spatial spin-echo pulses have been implemented in a clinical setting. In phantom studies, no change in metabolic profiles was observed with application of either BASING or spectral/spatial pulses. In a study of 17 prostate cancer patients, the use of either BASING or spectral/spatial pulses allowed for suppression of water (BASING 99.80 +/- 0.14% and spectral/spatial 99.73 +/- 0.47%) and lipid (BASING 98.56 +/- 1.03% and spectral/spatial 98.44 +/- 1.90%) without a significant difference in the prostatic metabolite ratios. Spectral/spatial suppression has the added advantage of reducing the chemical shift dependence of the PRESS volume, but optimal performance requires high-speed gradients with negligible eddy current effects. BASING suppression is less reliant on accurate pulse and gradient timings and can be implemented easily with no loss in performance on clinical MR scanners with conventional gradients.

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

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