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.

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.

Single-voxel oversampled J-resolved spectroscopy of in vivo human prostate tissue.

Single-voxel J-resolved spectroscopy with oversampling in the F1 dimension was used to obtain water unsuppressed 1H spectra of in situ human prostate tissue in 40 previously untreated prostate cancer patients. Based on T2-weighted MRI and previous biopsy information, voxels were placed in regions of benign or malignant peripheral zone tissue, or in regions of predominantly glandular or stromal benign prostatic hyperplasia (BPH) within the central gland. The addition of a second J-resolved dimension allowed for the observation of the J-modulation of citrate, as well as the resolution of polyamines from overlapping choline and creatine signals. Regions of healthy peripheral zone tissue and glandular BPH all demonstrated high levels of citrate and polyamines, with consistent coupling and J-modulation patterns. Conversely, regions of malignant peripheral zone tissue and stromal BPH demonstrated low levels of citrate and polyamines consistent with prior in vivo and ex vivo studies. Moreover, water T2 relaxation times determined for healthy peripheral zone tissue (mean 128 +/- 15.2 msec) were significantly different than for malignant peripheral zone tissue (mean 88.0 +/- 14.2 msec, P = 0.005), as well as for predominantly glandular (mean 92.4 +/- 12.2 msec, P = 0.009) and stromal BPH (mean 70.9 +/- 12.1 msec, P = 0.003). This preliminary study demonstrates that J-resolved spectroscopy of the in situ prostate can be acquired, and the information obtained from the second spectral dimension can provide additional physiologic information from human prostate tissue in a reasonable amount of time (< 10 min).

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.

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.