Purpose: To process single voxel spectra of the human skeletal muscle by using an advanced method for accurate, robust, and efficient spectral fitting (AMARES) and by linear combination of model spectra (LCModel). To determine absolute concentrations of extra-(EMCL) and intramyocellular lipids (IMCL). Materials and Methods:Single-voxel proton magnetic resonance spectroscopy (PRESS) was used to obtain the spectra of the calf muscles. Unsuppressed water line was used as a concentration reference. A new prior knowledge for AMARES was proposed to estimate the concentrations of EMCL and IMCL. The prior knowledge was derived from the spectrum of vegetable oil. The results were compared with the values estimated by LCModel. Absolute concentrations of total lipid content in millimoles per kilogram wet weight were used for the comparisons.Results: Absolute concentrations of total lipid content in skeletal muscle were estimated by AMARES and LCModel. Very good correlation of the total fat (EMCL ϩ IMCL) and IMCL concentrations was achieved between both data processing approaches. The absolute quantification of EMCL and IMCL based on MRS data is not a trivial problem. It depends on the ability to distinguish the methylene spectral line of IMCL (IMCL CH2 ) from the methylene line of EMCL (EMCL CH2 ), on relaxations corrections and on the accuracy of the biochemical constants that allow the conversion of the EMCL CH2 and IMCL CH2 spectral intensities to the absolute concentration expressed as millimoles per kilogram wet weight (mmol/kg ww). Because of these difficulties, relatively few research groups reported lipid concentrations in the absolute units (6,(11)(12)(13)(14). The majority of these studies avoided absolute quantification and used the relative measures fat-to-total creatine (creatine and phosphocreatine at ϳ3 ppm) ratio (15-18) or fat-to-unsuppressed water ratio (2,3,10,19,20), where the word fat represents EM-CL CH2 and IMCL CH2 spectral intensities. The applicability of these measures is based on the assumption that water in the muscles or total creatine concentration remains constant during the whole study. These not always valid assumptions and the problem of relaxation corrections can be avoided by using fat as the internal or external concentration reference. Yellow bone marrow (5,8,14,21) and vegetable oil (14) were used for this purpose. An advantage of fat reference is that it does not vary and that the conversion to absolute concentration is straightforward if the same lipid composition is assumed (22). ConclusionSpectral overlap with EMCL is probably the most important factor that limits accuracy of IMCL estimation. It has been shown that sophisticated fitting methods are necessary to differentiate IMCL besides overlap-

Purpose: To estimate absolute brain temperature using proton MR spectroscopy ( 1 H-MRS) and mean brain-body temperature difference of healthy human volunteers. Materials and Methods:Chemical shift difference between temperature-dependent water spectral line position and temperature-stable metabolite spectral reference was used for the estimations of absolute brain temperature. Temperature calibrations constants were obtained from the spectra of the N-acetyl aspartate (NAA line at $2.0 ppm), glycero-phosphocholine (GPC line at $3.2 ppm), and creatine (Cr line at $3.0 ppm) aqueous solutions with pH values within physiologically pertinent ranges. Single-voxel PRESS sequence (TR/TE 2000/ 80 ms) was used for this purpose. Brain temperature was determined by averaging the temperatures computed from water-Cho, water-Cr, and water-NAA chemical shift differences. Results:The mean brain temperature of 18 healthy volunteers was 38.1 6 0.4 C and mean brain-body (rectal) temperature difference was 1.3 6 0.4 C.Conclusion: Improved accuracy of the temperature constants and averaging the temperatures computed from water-Cho, water-Cr, and water-NAA chemical shift differences increased the reliability of the brain temperature estimations. CURRENT KNOWLEDGE ABOUT brain temperature in healthy humans is limited because direct and accurate measurements cannot be made without the need for surgery. The importance of brain temperature and its fluctuations due to biochemical and physical processes is, in the meantime, well acknowledged (1).The factors thought responsible for brain temperature regulation are the temperature of incoming arterial blood, metabolic heat production, heat removal by blood flow, heat conductance of the tissues, and heat exchange with the environment. In mammals, the most important factors are the temperature of the incoming arterial blood, brain metabolism, and external temperature (2). It has been theoretically estimated that the normal human brain produces ca 0.66 J of heat every minute per gram of brain tissue (3). The internal heat is removed mainly by blood flow. The cooling effect of external temperature seems to be less important because it is limited to superficial brain regions of several millimeters of thickness and depends on brain size and ambient temperature (4,5). Theoretical simulations (3,6), animal studies (7), and measurements of venous (internal jugular vein) versus arterial (aortic artery) temperatures in healthy volunteers (8) suggest that there is a positive difference 0.3-0.5 C between brain and body. These observations are in the qualitative agreement with direct measurements of injured head or stroke patients that reveal the brain-body temperature difference in the range 1-2 C (9).Because invasive measurement of the brain temperature cannot be made in healthy volunteers, research has focused on noninvasive MR techniques. Proton MR spectroscopy ( 1 H-MRS) and MR spectroscopic imaging (MRSI) are now validated methods that are capable of estimating absolute brain temperatures (10-17). Thes...

The main purpose of the study was to compare proton (1H) single-voxel MR spectroscopy (MRS) with high-spatial-resolution spectroscopic imaging (MRSI) to determine the lipid content in human skeletal muscle. Unsuppressed water line was used as a concentration reference in the processing of singlevoxel spectra. The spectrum from yellow bone marrow with a 100% fat content and probe with the vegetable oil served as internal and external reference for high-spatial-resolution MRSI, respectively. Very good correlation was found between lipid concentrations measured by water referenced singlevoxel MRS and high-spatial-resolution MRSI with yellow bone marrow as the internal standard. Excellent correlation was found between total lipid concentrations estimated by highspatial-resolution MRSI with vegetable oil as the external fat standard and yellow bone marrow as the internal reference. Proton magnetic resonance spectroscopy ( 1 H-MRS) of skeletal muscle provides complex spectra that offer a wealth of information (1-11). Metabolites that are detectable include carnosine (12,13), taurine (14,15), choline-containing compounds (13), creatine/phosphocreatine (16,17), extra-(EMCL), and intramyocellular (IMCL) lipids (1,2). Recently, new knowledge in the field brought the discovery of the effect of muscle fiber orientation (18 -20). MRS of skeletal muscle showed a great potential for investigating physical and biochemical changes induced by disease processes (4,6,9,11,16) or physiological activity (7,21,22) and enhanced understanding of the underlying biophysics.The growing interest in this field raised the issue of absolute quantification of muscular metabolite concentrations to allow for the comparison of different populations and assessment of metabolic flux rates under in vivo conditions.The unsuppressed water line is almost exclusively used as a concentration reference in the processing of muscle spectra. The acquisition of the water line has found widespread use in single-voxel MRS, particularly because it is a simple matter of acquiring a couple of scans from the measured volume of interest (VOI) either immediately before, or after, the water-suppressed acquisition. The most important advantage of water reference is the high spectral intensity. The large water signal provides excellent signalto-noise ratio data that can be used to determine local magnetic field (B 0 ) shifts, to correct for eddy-current distortions, and to assist in phasing of the spectra (23). In contrast, the acquisition of a water MR spectroscopic imaging (MRSI) data set in addition to the water-suppressed is not always done. If performed as an additional acquisition it can lengthen the study undesirably, especially for volumetric (three-dimensional) MRSI. In spectroscopy of the skeletal muscle, the necessity for relaxation correction of water reference is a fundamental disadvantage. This correction complicates the relative wide range of T 2 values (25 Ͻ T 2 Ͻ 35 ms, B 0 ϭ 1.5 T) (7-9,17,21,24 -26), which depend on the age, type, and distribution of m...

BackgroundThere are different opinions of the clinical value of MRS of the brain. In selected materials MRS has demonstrated good results for characterisation of both neoplastic and non-neoplastic lesions. The aim of this study was to evaluate the supplemental value of MR spectroscopy (MRS) in a clinical setting.Material and methodsMRI and MRS were re-evaluated in 208 cases with a clinically indicated MRS (cases with uncertain or insufficient information on MRI) and a confirmed diagnosis. Both single voxel spectroscopy (SVS) and chemical shift imaging (CSI) were performed in 105 cases, only SVS or CSI in 54 and 49 cases, respectively. Diagnoses were grouped into categories: non-neoplastic disease, low-grade tumour, and high-grade tumour. The clinical value of MRS was considered very beneficial if it provided the correct category or location when MRI did not, beneficial if it ruled out suspected diseases or was more specific than MRI, inconsequential if it provided the same level of information, or misleading if it provided less or incorrect information.ResultsThere were 70 non-neoplastic lesions, 43 low-grade tumours, and 95 high-grade tumours. For MRI, the category was correct in 130 cases (62%), indeterminate in 39 cases (19%), and incorrect in 39 cases (19%). Supplemented with MRS, 134 cases (64%) were correct, 23 cases (11%) indeterminate, and 51 (25%) incorrect. Additional information from MRS was beneficial or very beneficial in 31 cases (15%) and misleading in 36 cases (17%).ConclusionIn most cases MRS did not add to the diagnostic value of MRI. In selected cases, MRS may be a valuable supplement to MRI.

Purpose: To measure prostate spectra of healthy volunteers using a surface coil, to demonstrate age-dependent effects, and to investigate diagnostic possibilities for prostate cancer detection. Materials and Methods:Single-voxel and 2D magnetic resonance spectroscopic imaging (MRSI) spectra of 51 healthy volunteers with biopsy-proven prostate carcinoma of 20 patients for comparison were measured and processed using the LCModel. The mean normalized spectra and mean metabolite-to-citrate intensity ratios were computed.Results: Metabolite-to-citrate ratios of healthy volunteers were lower in the older group (>51 years) than in the younger group (<45 years). The peripheral zone (PZ) revealed a lower metabolite-to-citrate intensity ratio than the central gland (CG). Age-related differences in metabolite-to-citrate ratio were insignificant in the voxels with predominantly CG tissue, whereas significant differences were found in the PZ. Sensitivity in detecting prostate cancer by single-voxel spectroscopy (SVS) and 2D MRSI was 75% and 80%, respectively.Conclusion: SVS and 2D MRSI of the prostate at 3 T, using a surface coil, are useful in situations when insertion of the endorectal coil into the rectum is difficult or impossible. Our findings of age-dependent effects may be of importance for the analysis of patient spectra.