In vitro high resolution 1H-spectroscopy of the human prostate: benign prostatic hyperplasia, normal peripheral zone and adenocarcinoma

Developments in proton MR spectroscopic imaging of prostate cancer

In this paper, we review the developments of 1H-MR spectroscopic imaging (MRSI) methods designed to investigate prostate cancer, covering key aspects such as specific hardware, dedicated pulse sequences for data acquisition and data processing and quantification techniques. Emphasis is given to recent advancements in MRSI methodologies, as well as future developments, which can lead to overcome difficulties associated with commonly employed MRSI approaches applied in clinical routine. This includes the replacement of standard PRESS sequences for volume selection, which we identified as inadequate for clinical applications, by sLASER sequences and implementation of 1H MRSI without water signal suppression. These may enable a new evaluation of the complementary role and significance of MRSI in prostate cancer management.

Metabolism of prostate cancer by magnetic resonance spectroscopy (MRS)

Understanding the metabolism of prostate cancer (PCa) is important for developing better diagnostic approaches and also for exploring new therapeutic targets. Magnetic resonance spectroscopy (MRS) techniques have been shown to be useful in the detection and quantification of metabolites. PCa illustrates metabolic phenotype, showing lower levels of citrate (Cit), a key metabolite of oxidative phosphorylation and alteration in several metabolic pathways to sustain tumor growth. Recently, dynamic nuclear polarization (DNP) studies have documented high rates of glycolysis (Warburg phenomenon) in PCa. High-throughput metabolic profiling strategies using MRS on variety of samples including intact tissues, biofluids like prostatic fluid, seminal fluid, blood plasma/sera, and urine have also played a vital role in understanding the abnormal metabolic activity of PCa patients. The enhanced analytical potential of these techniques in the detection and quantification of a large number of metabolites provides an in-depth understanding of metabolic rewiring associated with the tumorigenesis. Metabolomics analysis offers dual advantages of identification of diagnostic and predictive biomarkers as well as in understanding the altered metabolic pathways which can be targeted for inhibiting the cancer progression. This review briefly describes the potential applications of in vivo ¹H MRS, high-resolution magic angle spinning spectroscopy (HRMAS) and in vitro MRS methods in understanding the metabolic changes of PCa and its usefulness in the management of PCa patients.

NMR quantification of lactate production and efflux and glutamate fractional enrichment in living human prostate biopsies cultured with [1,6-13 C2 ]glucose

PURPOSE

Image-guided prostate biopsies are routinely acquired in the diagnosis and treatment monitoring of prostate cancer, yielding useful tissue for identifying metabolic biomarkers and therapeutic targets. We developed an optimized biopsy tissue culture protocol in combination with [1,6-¹³ C₂ ]glucose labeling and quantitative high-resolution NMR to measure glycolysis and tricarboxcylic acid (TCA) cycle activity in freshly acquired living human prostate biopsies.

METHODS

We acquired 34 MRI-ultrasound fusion-guided prostate biopsies in vials on ice from 22 previously untreated patients. Within 15 min, biopsies were transferred to rotary tissue culture in 37°C prostate medium containing [1,6-¹³ C₂ ]glucose. Following 24 h of culture, tissue lactate and glutamate pool sizes and fractional enrichments were quantified using quantitative ¹ H high resolution magic angle spinning Carr-Purcell-Meiboom-Gill (CPMG) spectroscopy at 1°C with and without ¹³ C decoupling. Lactate effluxed from the biopsy tissue was quantified in the culture medium using quantitative solution-state high-resolution NMR.

RESULTS

Lactate concentration in low-grade cancer (1.15 ± 0.78 nmol/mg) and benign (0.74 ± 0.15 nmol/mg) biopsies agreed with prior published measurements of snap-frozen biopsies. There was substantial fractional enrichment of [3-¹³ C]lactate (≈70%) and [4-¹³ C]glutamate (≈24%) in both low-grade cancer and benign biopsies. Although a significant difference in tissue [3-¹³ C]lactate fractional enrichment was not observed, lactate efflux was significantly higher (P < 0.05) in low-grade cancer biopsies (0.55 ± 0.14 nmol/min/mg) versus benign biopsies (0.31 ± 0.04 nmol/min/mg).

CONCLUSION

A protocol was developed for quantification of lactate production-efflux and TCA cycle activity in single living human prostate biopsies, allowing metabolic labeling on a wide spectrum of human tissues (e.g., metastatic, post-non-surgical therapy) from patients not receiving surgery.

Metabolomic Biomarkers of Prostate Cancer: Prediction, Diagnosis, Progression, Prognosis, and Recurrence

Metabolite profiling is being increasing employed in the study of prostate cancer as a means of identifying predictive, diagnostic, and prognostic biomarkers. This review provides a summary and critique of the current literature. Thirty-three human case-control studies of prostate cancer exploring disease prediction, diagnosis, progression, or treatment response were identified. All but one demonstrated the ability of metabolite profiling to distinguish cancer from benign, tumor aggressiveness, cases who recurred, and those who responded well to therapy. In the subset of studies where biomarker discriminatory ability was quantified, high AUCs were reported that would potentially outperform the current gold standards in diagnosis, prognosis, and disease recurrence, including PSA testing. There were substantial similarities between the metabolites and the associated pathways reported as significant by independent studies, and important roles for abnormal cell growth, intensive cell proliferation, and dysregulation of lipid metabolism were highlighted. The weight of the evidence therefore suggests metabolic alterations specific to prostate carcinogenesis and progression that may represent potential metabolic biomarkers. However, replication and validation of the most promising biomarkers is currently lacking and a number of outstanding methodologic issues remain to be addressed to maximize the utility of metabolomics in the study of prostate cancer. Cancer Epidemiol Biomarkers Prev; 25(6); 887-906. ©2016 AACR.

NMR-based metabolomics of prostate cancer: a protagonist in clinical diagnostics

Advances in the application of NMR spectroscopy-based metabolomic profiling of prostate cancer comprises a potential tactic for understanding the impaired biochemical pathways arising due to a disease evolvement and progression. This technique involves qualitative and quantitative estimation of plethora of small molecular weight metabolites of body fluids or tissues using state-of-the-art chemometric methods delivering an important platform for translational research from basic to clinical, to reveal the pathophysiological snapshot in a single step. This review summarizes the present arrays and recent advancements in NMR-based metabolomics and a glimpse of currently used medical imaging tactics, with their role in clinical diagnosis of prostate cancer.

Contribution of Histopathologic Tissue Composition to Quantitative MR Spectroscopy and Diffusion-weighted Imaging of the Prostate

PURPOSE

To determine associations of metabolite levels derived from magnetic resonance (MR) spectroscopic imaging (ie, hydrogen 1 [(1)H] MR spectroscopic imaging) and apparent diffusion coefficients (ADCs) from diffusion-weighted imaging with prostate tissue composition assessed by digital image analysis of histologic sections.

MATERIALS AND METHODS

Institutional ethical review board approved this retrospective study and waived informed consent. Fifty-seven prostate cancer patients underwent an MR examination followed by prostatectomy. One hematoxylin and eosin-stained section of the resected prostate per patient was digitized and computationally segmented into nuclei, lumen, and combination of epithelial cytoplasm and stroma. On each stained section, regions of interest (ROIs) were chosen and matched to the corresponding ADC map and (1)H MR spectroscopic imaging voxels. ADC and two metabolite ratios (citrate [Cit], spermine [Spm], and creatine [Cr] to choline [Cho] and Cho to Cr plus Spm) were correlated with percentage areas of nuclei, lumen, and cytoplasm and stroma for peripheral zone (PZ), transition zone (TZ), and tumor tissue in both zones of the prostate by using a linear mixed-effect model and Spearman correlation coefficient (ρ).

RESULTS

ADC and (Cit + Spm + Cr)/Cho ratio showed positive correlation with percentage area of lumen (ρ = 0.43 and 0.50, respectively) and negative correlation with percentage area of nuclei (ρ = -0.29 and -0.26, respectively). The Cho/(Cr + Spm) ratio showed negative association with percentage area of lumen (ρ = -0.40) and positive association with area of nuclei (ρ = 0.26). Percentage areas of lumen and nuclei, (Cit + Spm + Cr)/Cho ratio, and ADC were significantly different (P < .001) between benign PZ (23.7 and 7.7, 8.83, and 1.58 × 10(-3) mm(2)/sec, respectively) and tumor PZ tissue (11.4 and 12.5, 5.13, and 1.20 × 10(-3) mm(2)/sec, respectively). These parameters were also significantly different between benign TZ (20.0 and 8.2, 6.50, and 1.26 × 10(-3) mm(2)/sec, respectively) and tumor TZ tissue (9.8 and 11.2, 4.36, and 1.03 × 10(-3) mm(2)/sec, respectively).

CONCLUSION

The observed correlation of (Cit + Spm + Cr)/Cho ratio and ADC of the prostate with its tissue composition indicates that components of this composition, such as percentage luminal area, contribute to the value of these MR parameters.

Recent Advances in Metabolic Profiling And Imaging of Prostate Cancer

Cancer is a metabolic disease. Cancer cells, being highly proliferative, show significant alterations in metabolic pathways such as glycolysis, respiration, the tricarboxylic acid (TCA) cycle, oxidative phosphorylation, lipid metabolism, and amino acid metabolism. Metabolites like peptides, nucleotides, products of glycolysis, the TCA cycle, fatty acids, and steroids can be an important read out of disease when characterized in biological samples such as tissues and body fluids like urine, serum, etc. The cancer metabolome has been studied since the 1960s by analytical techniques such as mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Current research is focused on the identification and validation of biomarkers in the cancer metabolome that can stratify high-risk patients and distinguish between benign and advanced metastatic forms of the disease. In this review, we discuss the current state of prostate cancer metabolomics, the biomarkers that show promise in distinguishing indolent from aggressive forms of the disease, the strengths and limitations of the analytical techniques being employed, and future applications of metabolomics in diagnostic imaging and personalized medicine of prostate cancer.

High-resolution NMR spectroscopy of human body fluids and tissues in relation to prostate cancer

High-resolution NMR spectroscopic studies of prostate tissue extracts, prostatic fluid, seminal fluid, serum and urine can be used for the detection of prostate cancer, based on the differences in their metabolic profiles. Useful diagnostic information is obtained by the detection or quantification of as many metabolites as possible and comparison with normal samples. Only a few studies have shown the potential of high-resolution in vitro NMR of prostate tissues. A survey of the literature has revealed that studies on body fluids, such as urine and serum, in relation to prostate cancer are rare. In addition, the potential of NMR of nuclei other than (1)H, such as (13)C and (31)P, has not been exploited fully. The metabolomic analysis of metabolites, detected by high-resolution NMR, may help to identify metabolites which could serve as useful biomarkers for prostate cancer detection. Such NMR-derived biomarkers would not only help in prostate cancer detection and in understanding the in vivo MRS metabolic profile, but also to investigate the biochemical and metabolic changes associated with cancer. Here, we review the published research work on body fluids in relation to prostate and prostate tissue extracts, and highlight the potential of such studies for future work.

High-resolution magic angle spinning 1H MRS in prostate cancer

Prostate cancer (PCa) is the most frequently diagnosed malignancy in men worldwide, largely as a result of the increased use of the annual serum prostate-specific antigen (PSA) screening test for detection. PSA screening has saved lives, but it has also resulted in the overtreatment of many patients with PCa because of a limited ability to accurately localize and characterize PCa lesions through imaging. High-resolution magic angle spinning (HRMAS) (1)H MRS has proven to be a strong potential clinical tool for PCa diagnosis and prognosis. The HRMAS technique allows valuable metabolic information to be obtained from ex vivo intact tissue samples and also enables the performance of histopathology on the same tissue specimens. Studies have found that the quantification of individual metabolite levels and metabolite ratios, as well as metabolomic profiles, shows strong potential to improve accuracy in PCa detection, diagnosis and monitoring. Ex vivo HRMAS is also a valuable tool for the interpretation of in vivo results, including the localization of tumors, and thus has the potential to improve in vivo diagnostic tests used in the clinic. Here, we primarily review publications of HRMAS (1)H MRS and its use for the study of intact human prostate tissue.

In vivo (1) H MR spectroscopic imaging of aggressive prostate cancer: can we detect lactate?

PURPOSE

A semi-LASER sequence was optimized for in vivo lactate detection in the prostate.

METHODS

The ethical committee waived the need for informed consent to measure 17 patients with high grade prostate cancer on a 3T system. A semi-LASER sequence was used with an echo time of 144 ms and optimized interpulse timing for a spectral citrate shape with high signal intensity. An LCModel basis set was developed for fitting choline, creatine, spermine, citrate, and lactate and was used to fit all spectra in tumor-containing voxels. For patients without detectable lactate, the minimal detectable lactate concentration was determined by adding in all spectra of tumor tissue a simulated lactate signal. The amplitude of the simulated lactate signal was iteratively decreased until its fit reached a Cramér Rao lower bound >20%, which was then set as the patient-specific detection limit.

RESULTS

In none of the patients a convincing lactate signal was found. We estimated that on average the lactate levels in high grade prostate cancer are below 1.5 mM (range 0.9-3.5 mM), Interestingly, in one patient with extensive necrosis in the tumor biopsy samples (Gleason score 5+5), large lipid resonances were observed, which originated from the tumor.

CONCLUSION

The minimal detectable lactate concentration of 1.5 mM in high grade prostate cancer indicates that if lactate is increased it remains at low concentrations.

Recent advances in metabolomics in oncology

The burden of cancer is growing worldwide and with it a more desperate need for better tools to detect, diagnose and monitor the disease is required. It is well recognized that cancer cells are characterized by distinct metabolic perturbations. The metabolomics approach involves the comprehensive profiling of the full complement of low MW compounds in a biological system. By applying advanced analytical and statistical tools, the 'metabolome' is mined for biomarkers that are associated with the state of cancer. This review presents an introduction to the main analytical platforms used in metabolomics analyses, such as NMR spectroscopy and MS, as well as the statistical tools used to mine these datasets. The discussion focuses on 'state-of-the-art' investigations on the four cancer types that have received the most study by metabolomics, namely breast, prostate, colorectal and liver cancer.

A decade in prostate cancer: from NMR to metabolomics

Over the past 30 years, continuous progress in the application of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance spectroscopic imaging (MRSI) to the detection, diagnosis and characterization of human prostate cancer has turned what began as scientific curiosity into a useful clinical option. In vivo MRSI technology has been integrated into the daily care of prostate cancer patients, and innovations in ex vivo methods have helped to establish NMR-based prostate cancer metabolomics. Metabolomic and multimodality imaging could be the future of the prostate cancer clinic--particularly given the rationale that more accurate interrogation of a disease as complex as human prostate cancer is most likely to be achieved through paradigms involving multiple, instead of single and isolated, parameters. The research and clinical results achieved through in vivo MRSI and ex vivo NMR investigations during the first 11 years of the 21st century illustrate areas where these technologies can be best translated into clinical practice.

Metabolomic Characterization of Ovarian Epithelial Carcinomas by HRMAS-NMR Spectroscopy

Objectives. The objectives of the present study are to determine if a metabolomic study by HRMAS-NMR can (i) discriminate between different histological types of epithelial ovarian carcinomas and healthy ovarian tissue, (ii) generate statistical models capable of classifying borderline tumors and (iii) establish a potential relationship with patient's survival or response to chemotherapy. Methods. 36 human epithelial ovarian tumor biopsies and 3 healthy ovarian tissues were studied using (1)H HRMAS NMR spectroscopy and multivariate statistical analysis. Results. The results presented in this study demonstrate that the three histological types of epithelial ovarian carcinomas present an effective metabolic pattern difference. Furthermore, a metabolic signature specific of serous (N-acetyl-aspartate) and mucinous (N-acetyl-lysine) carcinomas was found. The statistical models generated in this study are able to predict borderline tumors characterized by an intermediate metabolic pattern similar to the normal ovarian tissue. Finally and importantly, the statistical model of serous carcinomas provided good predictions of both patient's survival rates and the patient's response to chemotherapy. Conclusions. Despite the small number of samples used in this study, the results indicate that metabolomic analysis of intact tissues by HRMAS-NMR is a promising technique which might be applicable to the therapeutic management of patients.

Post-processing correction of the endorectal coil reception effects in MR spectroscopic imaging of the prostate

PURPOSE

To develop and validate a post-processing correction algorithm to remove the effect of the inhomogeneous reception profile of the endorectal coil on MR spectroscopic imaging (MRSI) data.

MATERIALS AND METHODS

A post-processing algorithm to correct for the endorectal coil reception effects on MRSI data was developed based upon theoretical modeling of the endorectal coil reception profile and of the spatial saturation pulse profiles. This algorithm was evaluated on three-dimensional (3D) MRSI data acquired at 3T from a uniform phantom and from 18 patients with known or suspected prostate cancer.

RESULTS

For the phantom data, the coefficient of variation of metabolite peak areas decreased 16% to 46% and the peak area distributions became more Gaussian with correction, as demonstrated by higher Q-Q plot linear correlations (R(2) = 0.98 +/- 0.007 vs. R(2) = 0.89 +/- 0.066). Across the 18 patients, the mean coefficient of variation for suppressed water decreased significantly, from 0.95 +/- 0.18, to 0.66 +/- 0.11, (P < 10(-6), paired t-test) and the linear correlations of the Q-Q plots for the suppressed water increased from R(2) = 0.91 to R(2) = 0.95 (P = 0.0083, paired t-test) with correction.

CONCLUSION

An algorithm for reducing the effect of the inhomogeneous reception profile in endorectal coil acquired 3D MRSI prostate data was demonstrated, illustrating increased homogeneity and more Gaussian peak area distributions.

N-acetyl resonances in in vivo and in vitro NMR spectroscopy of cystic ovarian tumors

An unassigned and prominent resonance in the region from delta 2.0-2.1 ppm has frequently been found in the in vivo MR spectra of cancer patients. We demonstrated the presence of this resonance with in vivo MRS in the cyst fluid of a patient with an ovarian tumor. (1)H-NMRS on the aspirated cyst fluid of this patient confirmed the observation. A complex of resonances was observed between 2.0 and 2.1 ppm. It was also present in 11 additional ovarian cyst fluid samples randomly chosen from our biobank. The resonance complex was significantly more prominent in samples from mucinous tumors than in samples from other histological subtypes. A macromolecule (>10 kDa) was found responsible for this complex of resonances. A correlation spectroscopy (COSY) experiment revealed cross peaks of two different types of bound sialic acid suggesting that N-glycans from glycoproteins and/or glycolipids cause this resonance complex. In the literature, plasma alpha-1 acid glycoprotein (AGP), known for its high content of N-linked glycans, has been suggested to contribute to the delta 2.0-2.1 spectral region. The AGP cyst fluid concentration did not correlate significantly with the peak height of the delta 2.0-2.1 resonance complex in our study. AGP may be partly responsible for the resonance complex but other N-acetylated glycoproteins and/or glycolipids also contribute. After deproteinization of the cyst fluid, N-acetyl-L-aspartic acid (NAA) was found to contribute significantly to the signal in this spectral region in three of the 12 samples. GC-MS independently confirmed the presence of NAA in high concentration in the three samples, which all derived from benign serous tumors. We conclude that both NAA and N-acetyl groups from glycoproteins and/or glycolipids may contribute to the delta 2.0-2.1 ppm resonance complex in ovarian cyst fluid. This spectral region seems to contain resonances from biomarkers that provide relevant clinical information on the type of ovarian tumor.

Diffusion-weighted imaging with apparent diffusion coefficient mapping and spectroscopy in prostate cancer

Prostate cancer is a major health problem, and the exploration of noninvasive imaging methods that have the potential to improve specificity while maintaining high sensitivity is still critically needed. Tissue changes induced by tumor growth can be visualized by magnetic resonance imaging (MRI) methods. Current MRI methods include conventional T2-weighted imaging, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping and magnetic resonance spectroscopy (MRS). Techniques such as DWI/ADC provide functional information about the behavior of water molecules in tissue; MRS can provide biochemical information about the presence or absence of certain metabolites, such as choline, creatine, and citrate. Finally, vascular parameters can be investigated using dynamic contrast-enhanced MRI. Moreover, with whole-body MRI and DWI, metastatic disease can be evaluated in 1 session and may provide a way to monitor treatment. Therefore, when combining these various methods, a multiparametric data set can be built to assist in the detection, localization, assessment of prostate cancer aggressiveness, and tumor staging. Such a comprehensive approach offers more power to evaluate prostate disease than any single measure alone. In this article, we focus on the role of DWI/ADC and MRS in the detection and characterization using both in vivo and ex vivo imaging of prostate pathology.

Evaluation of lactate and alanine as metabolic biomarkers of prostate cancer using 1H HR-MAS spectroscopy of biopsy tissues

The goal of this study was to investigate the use of lactate and alanine as metabolic biomarkers of prostate cancer using (1)H high-resolution magic angle spinning (HR-MAS) spectroscopy of snap-frozen transrectal ultrasound (TRUS)-guided prostate biopsy tissues. A long-echo-time rotor-synchronized Carr-Purcell-Meiboom-Gill (CPMG) sequence including an electronic reference to access in vivo concentrations (ERETIC) standard was used to determine the concentrations of lactate and alanine in 82 benign and 16 malignant biopsies (mean 26.5% +/- 17.2% of core). Low concentrations of lactate (0.61 +/- 0.28 mmol/kg) and alanine (0.14 +/- 0.06 mmol/kg) were observed in benign prostate biopsies, and there was no significant difference between benign predominantly glandular (N = 54) and stromal (N = 28) biopsies between patients with (N = 38) and without (N = 44) a positive clinical biopsy. In biopsies containing prostate cancer there was a highly significant (P < 0.0001) increase in lactate (1.59 +/- 0.61 mmol/kg) and alanine (0.26 +/- 0.07 mmol/kg), and minimal overlap with lactate concentrations in benign biopsies. This study demonstrates for the first time very low concentrations of lactate and alanine in benign prostate biopsy tissues. The significant increase in the concentration of both lactate and alanine in biopsy tissue containing as little as 5% cancer could be exploited in hyperpolarized (13)C spectroscopic imaging (SI) studies of prostate cancer patients.

High resolution magic angle spinning NMR spectroscopy for metabolic assessment of cancer presence and Gleason score in human prostate needle biopsies

OBJECTIVES

Histopathology of prostate needle biopsies (PNBs) is an important part in the diagnosis, prognosis and treatment evaluation of prostate cancer. The determination of metabolite levels in the same biopsies may have additional clinical value. Here, we demonstrate the use of non-destructive high resolution magic angle spinning (HRMAS) proton NMR Spectroscopy for the assessment of metabolic profiles of prostate tissue in PNBs as commonly obtained in standard clinical practice.

MATERIALS AND METHODS

PNBs that were taken routinely from 48 patients suspected of having prostate cancer were subjected to HRMAS proton NMR spectroscopy. Subsequent histopathology of the same biopsies classified the tissue either as cancer (n = 10) or benign (n = 30).

RESULTS

Some practical aspects of this assessment were evaluated, such as typical spectral contamination caused by the PNB procedure. Significant metabolic differences were found between malignant and benign tissue using a small set of ratio's involving signals of choline compounds, citrate and lactate. Moreover, significant correlations were observed between choline, total choline, and citrate over creatine signal ratios and the Gleason scores of tumor in PNBs and of tumor in the whole prostate.

CONCLUSION

This preliminary study indicates that HRMAS NMR of routinely obtained PNBs can provide detailed metabolic information of intact prostate tissue with clinical relevance.

Quantitative J-resolved prostate spectroscopy using two-dimensional prior-knowledge fitting

Two-dimensional (2D) prior-knowledge fitting (ProFit) was adapted and applied for the quantification of J-resolved (JPRESS) spectra acquired at a field strength of 3T from the human prostate in vivo. In contrast to methods based on simple line fitting and peak integration, commonly applied for metabolite quantification in the prostate, ProFit yields metabolite concentration ratios that are independent of sequence and field strength, since it is based on the linear combination of 2D basis spectra. It is demonstrated that ProFit benefits from the increased information content and reduced baseline distortion in JPRESS prostate spectra, in particular for the quantification of coupled metabolites like citrate (Cit), spermine (Spm), and myo-inositol (mI). The method is validated with 10 repetitive prostate measurements on the same subject. Furthermore, a study carried out on 10 healthy subjects shows that the six prostate metabolites creatine (Cr), total choline (Cho), Cit, Spm, mI, and scyllo-inositol (sI) can be reliably detected in vivo, some of which--especially total Cho and Cit--have proven to be useful markers for the detection of prostate cancer.

[Prostate MRI spectroscopy]

MRI spectroscopy is a non invasive method for detecting active metabolites used as markers. Chorine and citrate are used for analyzing prostate cancer. MRI spectroscopy combines morphologic imaging and metabolic cartography. This combination allows a new approach for the diagnosis of prostate cancer in patients with negative biopsy and high Levels of PSA. With MRI spectroscopy the Local staging of prostate cancer has a better accuracy than with MRI alone. It can also be used for the diagnosis of residual disease and recurrence in patients treated with conservative therapy.

Correlation between metabolite ratios and ADC values of prostate in men with increased PSA level

Proton magnetic resonance spectroscopic imaging (MRSI) and diffusion-weighted imaging (DWI) were carried out in men with increased prostate-specific antigen (PSA) level. Forty subjects [controls (Group I) and patients (Groups II and III with PSA >20 and 4-20 ng/ml, respectively)] were investigated using endorectal coil at 1.5 T prior to transrectal ultrasound (TRUS)-guided biopsy. Metabolite ratio [citrate/(choline+creatine)] and apparent diffusion coefficient (ADC) were calculated for identical voxels. In patients, voxels that showed lower metabolite ratio showed reduced ADC in the peripheral zone (PZ) of the prostate, and voxels with increased metabolite ratio showed higher ADC. Metabolite ratios were used to predict areas of malignancy if the ratio was <1.4 and if ADC value was <1.17 x 10(-3) mm(2)/s. Patients in Group II had lower metabolite ratio and ADC in the PZ compared to controls and Group III. All 13 were positive for malignancy in MR, while 12 of 13 were positive on TRUS-guided sextant biopsy. In Group III, certain voxels of PZ that showed reduced metabolite ratio also showed lower ADC. A positive correlation was observed between metabolite ratio and ADC. MR predicted areas of malignancy in PZ in 15 of 20 patients; however, only six were positive on TRUS-guided biopsy perhaps due to high false-negative rate of TRUS-guided biopsy. Results show positive correlation between MRSI and DWI and their potential in detection of malignancy, thereby improving the diagnosis especially in patients with PSA level of 4-20 ng/ml.

Magnetic resonance in surgical oncology: II - literature review

Ex vivo and in vivo applications of magnetic resonance spectroscopy have been developed which aid in distinguishing malignant from normal tissues. Studies of breast, colon, cervix, oesophageal and prostate cancer reveal both the successes and failings of present technology. Verification that these non-invasive tests might supplant conventional histology in obtaining spatial diagnostic and chemical prognostic information remains for the time being illusive.

Comparisons of brain metabolites observed by HRMAS 1H NMR of intact tissue and solution 1H NMR of tissue extracts in SIV-infected macaques

The objective of this study was to compare ex vivo proton high-resolution magic angle spinning magnetic resonance spectra of intact tissue with those spectra obtained by solution (1)H NMR of brain extracts of the same sample. Sixteen brain tissue samples from simian immunodeficiency virus-infected rhesus macaques from both frontal cortex and putamen were evaluated by comparing brain metabolite quantities of N-acetylaspartate (NAA), choline-containing compounds (Cho), myo-inositol (MI), creatine (Cr), lactate (Lac), glutamate (Glu) and acetate (Ace). The ratios of the individual NMR peak areas of all metabolites relative to the creatine peak area were calculated. Linear regression analysis revealed significant correlations between measurements using the two methods. The strength of the correlations varied depending on the metabolite studied. We found highly significant correlations for NAA/Cr (r2 = 0.77; p < 0.0001), NAA + Ace/Cr (r2 = 0.73; p < 0.0001) and MI/Cr (r2 = 0.75; p < 0.0001). We observed somewhat less strong correlations for Glu/Cr (r2 = 0.54; p < 0.002) and Lac/Cr (r2 = 0.54; p < 0.002). There was a substantially weaker correlation for Cho/Cr (r2 = 0.32; p = 0.02). When plotting the metabolite ratios obtained by 1H HRMAS NMR of the intact tissue sample on the ordinate vs 1H NMR of the tissue extract on the abscissa, most metabolites exhibited a slope close to unity, and a positive intercept probably due to macromolecular contributions to the MAS spectra. The slope for Cho/Cr was substantially less than unity. Generally, samples from the frontal cortex showed a better correlation between intact and extracted tissue samples than putamen. This is most prominent in the cases of NAA/Cr and Cho/Cr. We conclude that both methods provide substantially the same information for most major brain metabolites, with the exception of the Cho resonance.

Ex vivo proton MR spectroscopy (1H-MRS) for evaluation of human gastric carcinoma

The present study was performed to determine the characteristics of the biochemical metabolites related to gastric cancer using ex vivo (1)H magnetic resonance spectroscopy (MRS), and to assess the clinical usefulness. A total of 35 gastric specimens resected during surgery for gastric cancer were used to compare MR spectra. A 1.5-T (64-MHz) clinical MR imager equipped with facilities for spectroscopy was used to obtain MR spectra from 33 gastric specimens. High-resolution (1)H nuclear magnetic resonance (NMR) spectra of the remains of two specimens were also examined with a 9.4-T (400-MHz) NMR spectrometer. Localized spectroscopic measurements were performed in two layers of gastric tissue, the proper muscle layer and the composite mucosa/submucosa layer. T(2) FSE and 3D SPGR images were used to determine the voxel size and the location for MRS data collection. MR spectra were obtained using the single-voxel PRESS technique with parameters of TR/TE = 2000/30 ms, NA = 256, and voxel size = 3 x 3 x 3 mm(3) (27 microL). Cancerous and noncancerous gastric tissues in the voxel were determined by histopathological analysis. On 9.4-T ex vivo NMR spectroscopy, the following metabolite peaks were found: lipids at 0.9 ppm (CH(3)) and 1.3 ppm (CH(2)); alanine (beta-CH(3)) at 1.58 ppm; N-Acetyl neuraminic acid (NANA: sialic acid) at 2.03 ppm; and glutathione at 2.25 ppm in normal gastric tissue layers. In the 1.5-T MR system, broad and featureless spectral peaks of the various metabolites in normal human gastric tissue were observed at 0.9 ppm, 1.3 ppm, 2.0 ppm, and 2.2 ppm regardless of gastric tissue layer. In specimens (Borrmann type III) with tubular adenocarcinoma, resonance peaks were observed at 1.26 ppm, 1.36 ppm (doublet of lactate), and 3.22 ppm (choline). Cancer lesions showed decreased levels of lipid peaks, showing the significant lactate doublet peaks, and increased intensity of the choline peak as compared with noncancerous gastric tissue. We found that decreased levels of lipids and increases in lactate and choline peaks in gastric tissue were markers for malignancy in gastric lesions. Information provided by ex vivo (1)H MRS, together with the development of in vivo (1)H MRS with high field strength and high resolution, may be very useful for the diagnosis of gastric cancer in clinical situation.

Chronic prostatitis: MR imaging and 1H MR spectroscopic imaging findings--initial observations

PURPOSE

To determine whether chronic prostatitis affects three-dimensional proton magnetic resonance (MR) spectroscopic imaging in evaluation of disease in the peripheral zone.

MATERIALS AND METHODS

Combined MR imaging and three-dimensional MR spectroscopic imaging data were examined retrospectively in 12 patients with radical prostatectomy specimens that contained regions of chronic prostatitis larger than 6 mm in the peripheral zone. The 6-mm restriction was based on MR spectroscopic imaging spatial resolution of 6.25 mm. Transverse T2-weighted MR images were reviewed for changes in signal intensity (SI): normal, suspicious for cancer (nodular focal low SI), or indeterminate (focal low SI that was not nodular or contour deforming or diffuse low SI). At MR spectroscopic imaging, proton spectra were considered suspicious for cancer if the ratio of choline plus creatine to citrate was more than 2 SDs above normal mean peripheral zone values.

RESULTS

In the 12 patients, mean pretreatment prostate-specific antigen level was 5.77 +/- 2.07 (SD), and median biopsy Gleason score for the gland was 6. At MR imaging in the area of histopathologically confirmed chronic prostatitis, seven of 12 patients had focal low SI that was not nodular (contour deforming) over a region in and around the pathologically defined focus of chronic prostatitis. MR imaging in one patient showed diffuse low SI that correlated with a diffuse area of chronic prostatitis at pathologic examination. MR imaging in another patient showed nodular focal low SI that was suspicious for cancer and corresponded to a focus of chronic prostatitis at pathologic examination. The remaining three patients had no MR imaging abnormality in the region of chronic prostatitis. In the pathologically identified regions of chronic prostatitis, MR spectroscopic imaging data in nine of 12 patients demonstrated elevated choline peak and reduced or no citrate, findings that mimic those of cancer. In two patients, the spectra were normal, and in the remaining patient, the spectra were nondiagnostic.

CONCLUSION

At MR spectroscopic imaging, pathologically confirmed chronic prostatitis may demonstrate metabolic abnormality that leads to false-positive diagnosis of cancer. The most common MR imaging finding in chronic prostatitis was focal low SI that was not specific for cancer. In one patient, the MR imaging diagnosis of cancer could not be excluded.

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.

1H magnetic resonance spectroscopy of invasive cervical cancer: an in vivo study with ex vivo corroboration

The objective of this study was to establish in vivo (1)H-magnetic resonance (MR) spectroscopic appearances of cervical cancer using an endovaginal receiver coil and corroborate findings with magic angle spinning (MAS) MR spectroscopy of tissue samples. Fifty-three women (14 controls and 39 with cervical cancer) underwent endovaginal coil MR imaging at 1.5 T with T(1)- and T(2)-weighted scans sagittal and transverse to the cervix. Localized (1)H MR spectra (PRESS technique, TR 1600 ms, TE 135 ms) were accumulated in all controls and 29 cancer patients whose tumour filled > 50% of a single 3.4 cm(3) voxel. Peaks from triglyceride-CH(2) and -CH(3) were defined as present and in-phase (with the choline resonance), present but out-of-phase, or not present. Peak areas of choline-containing compounds were standardized to the area of unsuppressed tissue water resonance. Comparisons in observed resonances between groups were made using Fisher's exact test (qualitative data) and a t-test (quantitative data). Biopsies from these women analysed using MAS-MR spectroscopy and normalized to the intensity of an external standard of silicone rubber were similarly compared. Adequate water suppression permitted spectral analysis in 11 controls and 27 cancer patients. In-phase triglyceride-CH(2) resonances (1.3 ppm) were observed in 74% of tumours but in no control women (p < 0.001). No differences were observed in the presence of a 2 ppm resonance, choline-containing compounds or creatine in cancer compared with control women. However, ex vivo analysis showed significant differences not only in -CH(2), but also in -CH(3), a 2 ppm resonance, choline-containing compounds and creatine between tissues from control women and cancer tissue (p < 0.001, = 0.001, = 0.036, < 0.001 and = 0.004 respectively). On in vivo (1)H-MR spectroscopy, the presence of positive triglyceride-CH(2) resonances can be used to detect and confirm the presence of cervical cancer. However, technical improvements are required before routine clinical use.

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.

Leakage of metabolites from tissue biopsies can result in large errors in quantitation by MRS

The leakage of metabolites from frozen and thawed tissue biopsies was measured semi-quantitatively by high-field (8.5 T) proton MRS. Human prostate and rat brain tissue specimens, frozen within 1 min of collection, lost significant and variable amounts of diagnostic metabolites immediately upon thawing. For prostate tissue 30-50% of initial total choline compounds, total creatines and citrate were detected in the collection buffer immediately after thawing. The widely used protocol for MR assessment of tissue biopsies, which involves washing of thawed tissue samples in fresh buffer, results in loss of large and unpredictable amounts of possibly diagnostic metabolites prior to MRS. This reduces the reproducibility of MR analysis of tissue biopsies and compromises the reliable identification of MR spectral patterns diagnostic of tissue pathology. The problem can be avoided by minimizing the volume of storage buffer, omitting tissue washing and performing MRS measurements on the tissue immersed in the original storage buffer.

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.

In-vivo proton magnetic resonance spectroscopy in adnexal lesions

OBJECTIVE

To explore the in-vivo 1H- MR spectral features of adnexal lesions and to characterize the spectral patterns of various pathologic entities.

MATERIALS AND METHODS

Thirty-one patients with surgically and histopathologically confirmed adnexal lesions underwent short echo-time STEAM (stimulated echo acquisition method) 1H- MR spectroscopy, and the results obtained were analysed.

RESULTS

The methylene present in fatty acid chains gave rise to a lipid peak of 1.3 ppm in the 1H- MR spectra of most malignant tumors and benign teratomas. This same peak was not observed, however, in the spectra of benign ovarian epithelial tumors: in a number of these, a peak of 5.2 ppm, due to the presence of the olefine group (-CH=CH-) was noted. The ratios of lipid peak at 1.3 ppm to water peak (lipid/water ratios) varied between disease groups, and in some benign teratomas was characteristically high.

CONCLUSION

An intense lipid peak at 1.3 ppm is observed in malignant ovarian tumors but not in benign epithelial tumors. 1H- MRS may therefore be helpful in the differential diagnosis of adnexal lesions.

In vivo proton (H1) magnetic resonance spectroscopy for cervical carcinoma

Proton magnetic resonance spectroscopy (MRS) may be a useful tool in both the initial diagnosis of cervical carcinoma and the subsequent surveillance after radiation therapy, particularly when other standard diagnostic methods are inconclusive. Single voxel magnetic resonance (MR) spectral data were acquired from 8 normal volunteers, 16 patients with cervical cancer before radiation therapy, and 18 patients with cervical cancer after radiation therapy using an external pelvic coil at a 1.5-T on a Signa system. The presence or absence of various resonances within each spectrum was evaluated for similarities within each patient group and for spectral differences between groups. Resonances corresponding to lipid and creatine dominated the spectrum for the eight normal volunteers without detection of a choline resonance. Spectra from 16 pretreatment patients with biopsy-proven cervical cancer revealed strong resonances at a chemical shift of 3.25 ppm corresponding to choline. Data acquired from the 18 posttreatment setting studies was variable, but often correlated well with the clinical findings. Biopsy confirmation was obtained in seven patients. H1 MRS of the cervix using a noninvasive pelvic coil consistently demonstrates reproducible spectral differences between normal and neoplastic cervical tissue in vivo. However, signal is still poor for minimal disease recurrence. Further study is needed at intervals before, during, and after definitive irradiation with biopsy confirmation to validate the accuracy of MRS in distinguishing persistence or recurrence of disease from necrosis and fibrosis.

Non-destructive quantitation of spermine in human prostate tissue samples using HRMAS 1H NMR spectroscopy at 9.4 T

We present the results of a study of human prostate specimens evaluated by high resolution magic angle spinning (1)H nuclear magnetic resonance (NMR) spectroscopy at 400 MHz (9.4 T) and by quantitative histopathology. We demonstrate that NMR and pathology data can be obtained from the same intact specimens, and report for the first time a linear correlation between the NMR measured concentration of spermine, a proposed endogenous inhibitor to prostate cancer growth, and the volume percentage of normal prostatic epithelial cells as quantified by histopathology. Our results show that NMR may serve as a critical tool for the investigation of the inhibitory mechanism of spermine in human subjects.

The prostate: MR imaging and spectroscopy. Present and future

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

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

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

Human prostate: multisection proton MR spectroscopic imaging with a single spin-echo sequence--preliminary experience

The authors investigated the feasibility of a multisection proton magnetic resonance (MR) spectroscopic imaging technique for the acquisition of metabolic information in the human prostate. Multisection MR spectroscopic imaging was performed of a citrate phantom and of the prostates of eight adult volunteers. High-quality proton MR spectra and citrate metabolite maps of the prostate were obtained with this method.

In vivo proton magnetic resonance spectroscopy of diseased prostate: spectroscopic features of malignant versus benign pathology

In vivo Proton Magnetic Resonance Spectroscopy appears potentially useful for non-invasive discrimination between benign prostatic hyperplasia (BPH) and prostate carcinoma (PC). Aiming to delimit the range within which spectra from one or the other pathology should occur, and establish extreme spectroscopic features of malignant versus benign prostate disease, we performed endorectal proton MR spectroscopy on 20 patients severely affected of either benign prostatic hyperplasia (BPH) (n = 10) or prostate cancer (PC) (n = 10). They were selected on the basis of the large volume and homogeneity of their lesions, which were histologically confirmed after spectroscopy. Consequently, high-quality short-TE proton spectra with well-resolved metabolite signals, and practically free of volume averaging issues were obtained in all cases. Apart from the typical citrate, creatine, and choline signals of prostate spectra, both BPH and PC spectra showed a peak centered at 3.6 ppm which was assigned to myo-inositol. The intensity of this contribution was found significantly increased in PC cases compared to BPH. Possible relationships between neoplastic transformation and the metabolic pathways in which myo-inositol participates are discussed. Average spectroscopic profiles were calculated for both advanced pathologies, and showed obvious differentiated features. In quantitative terms, the ratio of citrate to choline peak areas as well as that of creatine to myo-inositol appeared as the most convenient to discriminate between advanced PC cases (both ratios below 1.0) and advanced BPH cases (both ratios above 1.0).

Citrate in the diagnosis of prostate cancer

BACKGROUND

One of the major current problems involved in prostate cancer (PCa) is the unavailability of sensitive, accurate, and preferably noninvasive procedures for the diagnosis of PCa. Moreover, procedures are needed which will permit the early detection, staging, location, and estimation of the volume of malignancy, and preferably a mapping of the prostate for follow-up of progression and regression of the malignancy.

METHODS

The unique citrate relationships of the prostate, coupled with recent developments and technological advancements in magnetic resonance spectroscopy (MRS) for the in situ determination of citrate levels, now provides an excellent diagnostic procedure which can achieve all these goals. There exist strong, compelling basic and clinical studies in support of the employment of 1H MRS measurements of citrate and other associated metabolites in the diagnosis of PCa.

RESULTS

This review provides the background leading to the current status of MRS citrate analysis, summarizes the data from clinical trials, and describes the applications of the procedure for the diagnosis of PCa and follow-up of patients. The use of MRS studies in defining the functional, as well as pathological relationships of the prostate, is also discussed.

CONCLUSIONS

This review is intended to be informative to the prostate- and oncology-interested community, and, hopefully, to engender much-needed interest and support in future research regarding the prostate relationships described in this report.

In vivo differential diagnosis of prostate cancer and benign prostatic hyperplasia: localized proton magnetic resonance spectroscopy using external-body surface coil

Localized proton-stimulated echo acquisition mode (STEAM) spectroscopy was performed in seven patients with benign prostatic hyperplasia (BPH), six patients with prostate cancer, and seven healthy volunteers to determine whether citrate levels detected using a saddle-type external-body surface coil (two loops of 13 cm x 17 cm) could reliably discriminate BPH from prostatic cancer. Relative area ratios of citrate level to choline plus creatine or citrate to lipid signal were compared with postoperative pathologic histology findings. The metabolic signals were well detectable as much as the line width of water resonance was ranging from 5 to 9 hz. Average SNRs of citrate in BPH and prostate cancer were 11.4 and 1.9, respectively. The major finding was consistently lower citrate levels in prostate cancer compared with BPH and normal prostate central gland. This was significantly (p < 0.01) reflected by lower mean citrate/[creatine+choline] peak area ratio and citrate/lipid peak area ratio observed for region of cancer (0.446 +/- 0.063, 0.097 +/- 0.030) compared with BPH (1.458 +/- 0.107, 0.786 +/- 0.162) and normal central gland (1.418 +/- 0.129, 0.175 +/- 0.011), respectively. These studies demonstrate the potential of citrate spectrum detected by an external-body surface coil as an in vivo marker for discriminating prostate cancer from BPH.

Novel role of zinc in the regulation of prostate citrate metabolism and its implications in prostate cancer

The prostate gland of humans and many other animals has the major function of accumulating and secreting extraordinarily high levels of citrate. This specialized metabolic process of "net citrate production" is the result of unique metabolic capabilities of the secretory epithelial cells. Most importantly, in prostate cancer (Pca) the capability for net citrate production is lost. In addition to citrate, the normal and BPH (benign prostatic hyperplasia) prostate also accumulates the highest levels of zinc in the body. As with citrate, in Pca the ability for high zinc accumulation is diminished. These and other correlations between zinc and citrate in the prostate have been indicative of an important role of zinc in the regulation of citrate metabolism in normal and malignant prostate epithelial cells. The link between zinc and citrate metabolism has now been established. The intramitochondrial accumulation of high zinc levels inhibits mitochondrial (m-) aconitase activity, which inhibits citrate oxidation. This essentially truncates the Krebs cycle and markedly decreases the cellular energy (ATP) production normally coupled to citrate oxidation. It is also clear that zinc accumulation in citrate-producing prostate epithelial cells is regulated by testosterone and by prolactin. These relationships form the basis for a new concept of the role of zinc and citrate-related energy metabolism in prostate malignancy. The inability of malignant prostate cells to accumulate high zinc levels results in increased citrate oxidation and the coupled ATP production essential for the progression of malignancy. The concept offers new approaches to the treatment of Pca.

In vivo quantification of citrate concentration and water T2 relaxation time of the pathologic prostate gland using 1H MRS and MRI

We have previously reported a striking correlation between water T2 relaxation time and citrate concentration in the normal prostate (Liney G.P.; Lowry M.; Turnbull L.W.; Manton D.J.; Knowles A.J.; Blackband S.J.; Horsman A. Proton MR T2 maps correlate with the citrate concentration in the prostate. NMR Biomed. 9:59-64; 1996). In this study we present data from similar studies of the pathologic gland. The findings support the hypothesis that measurement of both citrate concentration and water T2 relaxation time in vivo may aid the differentiation of prostatic carcinoma from benign disease and normal tissue.

Proton MR spectroscopy of the normal human prostate with an endorectal coil and a double spin-echo pulse sequence

This report describes the use of an endorectal coil and a double spin-echo pulse sequence for localized 1H MR spectroscopy of the normal prostate in volunteers. The spectra showed well-resolved signals for citrate, (phospho)choline, and creatine protons. Additional signals were assigned to taurine and myoinositol protons. J modulation of the main and outer peaks of citrate could be monitored in vivo. Apparent relaxation times T1 and T2 have been estimated for the methyl protons of cholines and creatine. An effective T1 relaxation time was estimated for the main peaks of the citrate multiplet. Ratios of the integrals of these resonances have been evaluated, and tissue contents of choline and creatine were estimated using the H2O signal as an internal reference. Spectroscopic imaging experiments revealed a lower relative citrate signal in central parts of the prostate than in peripheral parts.

Citrate signal enhancement with a homonuclear J-refocusing modification to double-echo PRESS sequences

The citrate signal at field strengths of whole body imagers arises from two sets of two strongly coupled methylene protons. This causes citrate spectra acquired with standard in vivo localization schemes like the double-echo point resolved echo spectroscopy (PRESS) sequence to have complicated dependencies on timing parameters. A homonuclear J-refocused version of the double-echo PRESS sequence that has previously been shown to completely remove J-modulations from weakly coupled AX systems is considered for its potential in acquiring signal from the strongly coupled AB system of citrate. An analytic solution to the problem is derived with the density matrix formalism and verified both numerically and experimentally for 7 T conditions. The general expression for the AB signal is applied to study the 1.5 T citrate signal where a substantial signal enhancement over conventional double-echo PRESS sequences is predicted and verified for echo times in the 150 to 300 ms range.

Quantification of citrate concentration in the prostate by proton magnetic resonance spectroscopy: zonal and age-related differences

A commercial phased-array multicoil was used to acquire water-suppressed localized proton spectra of the two major anatomical regions of the prostate. The signal-to-noise ratio and spectral resolution allowed identification of peaks from choline and creatine, as well as a major peak from citrate. Quantification of the citrate peak using experimentally determined relaxation parameters with tissue water as an internal concentration reference revealed a marked variability between different volunteers. Nevertheless, in each case, the citrate concentration was up to fourfold greater in the peripheral zone than in the central gland. Furthermore, the difference in citrate concentration between these two regions was positively correlated with the subjects age. The results indicate a consistent difference in cellular function between the major anatomical regions within the prostate and may have important consequences for the application of magnetic resonance spectroscopy to the diagnosis of prostatic pathology.