(31)P MR spectroscopic imaging of the human prostate provides information about phosphorylated metabolites that could be used for prostate cancer characterization. The sensitivity of a magnetic field strength of 7 T might enable 3D (31)P MR spectroscopic imaging with relevant spatial resolution in a clinically acceptable measurement time. To this end, a (31)P endorectal coil was developed and combined with an eight-channel (1)H body-array coil to relate metabolic information to anatomical location. An extensive safety validation was performed to evaluate the specific absorption rate, the radiofrequency field distribution, and the temperature distribution of both coils. This validation consisted of detailed Finite Integration Technique simulations, confirmed by MR thermometry and B 1+ measurements in a phantom and in vivo temperature measurements. The safety studies demonstrated that the presence of the (31)P endorectal coil had no influence on the specific absorption rate levels and temperature distribution of the external eight-channel (1)H array coil. To stay within a 10 g averaged local specific absorption rate of 10 W/kg, a maximum time-averaged input power of 33 W for the (1)H array coil was allowed. For transmitting with the (31)P endorectal coil, our safety limit of less than 1°C temperature increase in vivo during a 15-min MR spectroscopic imaging experiment was reached at a time-averaged input power of 1.9 W. With this power setting, a second in vivo measurement was performed on a healthy volunteer. Using adiabatic excitation, 3D (31)P MR spectroscopic imaging produced spectra from the entire prostate in 18 min with a spatial resolution of 4 cm(3). The spectral resolution enabled the separate detection of phosphocholine, phosphoethanolamine, inorganic phosphate, and other metabolites that could play an important role in the characterization of prostate cancer.

High quality T2w TSE prostate imaging can be performed routinely and within specific absorption rate limits at 7 T with an external transceive body array.

Knowledge of T1 relaxation times and NOE enhancements enables protocol optimization for (31) P MRSI of the prostate at 7 T. With a strongly reduced (31) P flip angle (≤ 45°), a (31) P MRSI dataset with optimal signal-to-noise ratio per unit time can be obtained within 15 minutes. The NOE enhancement can improve fitting accuracy, but its variability requires further investigation.

An often employed strategy to enhance signals in 31P MR spectroscopy is the generation of the nuclear Overhauser effect (NOE) by saturating the water resonance. However, NOE allegedly increases the variability of the 31P data, because variation is reported in NOE enhancements. This would negate the SNR gain it generates. We hypothesized that variation in NOE enhancement values is not due to variability in the NOE itself, but that it is attributable to measurement uncertainties in the values used to calculate the enhancement. If true, the expected increase in SNR with NOE would improve the repeatability of 31P MR spectroscopy measurements. To verify this hypothesis, a repeatability study of native and NOE-enhanced 31P MRSI was performed in the brain of 7 healthy volunteers at 7T. The repeatability coefficient (RC) and the coefficient of variation in repeated measurements (CoVrepeat) were determined per method, and the 95% limits of agreement (LoA) between native and NOE-enhanced signals were calculated. The variation between the methods, defined by the LoA, is at least as great as that predicted by the RC of each method. The sources of variation in NOE enhancements were determined using variance component analysis. In the 7 metabolites with a positive NOE enhancement (9 metabolite resonances assessed), CoVrepeat improved on average by 15%. The LoAs could be explained by the RCs of the individual methods for the majority of the metabolites, generally confirming our hypothesis. Variation in NOE enhancement was mainly attributable to the factor repeat, but between-voxel effects were also present for phoshpoethanolamine and (glycero)phosphocholine. CoVrepeat and fitting error were strongly correlated and improved with positive NOE. Our findings generally indicate that NOE enhances the signal of the metabolites, improving the repeatability of metabolite measurements. Additional variability due to NOE was minimal. These findings encourage the use of NOE-enhanced 31P MRSI.

Purpose:To assess metabolite levels in peritumoral edematous (PO) and surrounding apparently normal (SAN) brain regions of glioblastoma, metastasis, and meningioma in humans with 1H‐MRSI to find biomarkers that can discriminate between tumors and characterize infiltrative tumor growth.Materials and Methods:Magnetic resonance (MR) spectra (semi‐LASER MRSI, 30 msec echo time, 3T) were selected from regions of interest (ROIs) under MRI guidance, and after quality control of MR spectra. Statistical testing between patient groups was performed for mean metabolite ratios of an entire ROI and for the highest value within that ROI.Results:The highest ratios of the level of choline compounds and the sum of myo‐inositol and glycine over N‐acetylaspartate and creatine compounds were significantly increased in PO regions of glioblastoma versus that of metastasis and meningioma. In the SAN region of glioblastoma some of these ratios were increased. Differences were less prominent for metabolite levels averaged over entire ROIs.Conclusion:Specific metabolite ratios in PO and SAN regions can be used to discriminate glioblastoma from metastasis and meningioma. An analysis of these ratios averaged over entire ROIs and those with most abnormal values indicates that infiltrative tumor growth in glioblastoma is inhomogeneous and extends into the SAN region. J. Magn. Reson. Imaging 2012;36:1072–1082. © 2012 Wiley Periodicals, Inc.