Phosphorus ( 31 P) T 1 and T 2 relaxation times in the resting human calf muscle were assessed by interleaved, surface coil localized inversion recovery and frequency-selective spin-echo at 3 and 7 T. The obtained T 1 (mean ؎ SD) decreased significantly (P < 0.05) from 3 to 7 T for phosphomonoesters (PME) (8.1 ؎ 1.7 s to 3.1 ؎ 0.9 s), phosphodiesters (PDE) (8.6 ؎ 1.2 s to 6.0 ؎ 1.1 s), phosphocreatine (PCr) (6.7 ؎ 0.4 s to 4.0 ؎ 0.2 s), ␥-NTP (nucleotide triphosphate) (5.5 ؎ 0.4 s to 3.3 ؎ 0.2 s), ␣-NTP (3.4 ؎ 0.3 s to 1.8 ؎ 0.1 s), and ␤-NTP (3.9 ؎ 0.4 s to 1.8 ؎ 0.1 s), but not for inorganic phosphate (Pi) (6.9 ؎ 0.6 s to 6.3 ؎ 1.0 s). The decrease in T 2 was significant for Pi (153 ؎ 9 ms to 109 ؎ 17 ms), PDE (414 ؎ 128 ms to 314 ؎ 35 ms), PCr (354 ؎ 16 ms to 217 ؎ 14 ms), and ␥-NTP (61.9 ؎ 8.6 ms to 29.0 ؎ 3.3 ms). This decrease in T 1 with increasing field strength of up to 62% can be explained by the increasing influence of chemical shift anisotropy on relaxation mechanisms and may allow shorter measurements at higher field strengths or up to 62% additional signal-to-noise ratio (SNR) per unit time. The fully relaxed SNR increased by ؉96%, while the linewidth increased from 6.5 ؎ 1.2 Hz to 11.2 ؎ 1.9 Hz or ؉72%. Key words: phosphor; spectroscopy; human muscle; relaxation times; 7 Tesla; high field; chemical shift anistrophy Phosphorus ( 31 P) MR spectroscopy (MRS) is a powerful tool for the noninvasive investigation of human muscle metabolism under various physiological and pathological conditions (1). High-field MR systems, i.e., 7 T, offer advantages to 31 P-MRS in terms of sensitivity and spectral resolution, which has recently been shown in the brain (2).To optimize the measurement parameters of clinical spectroscopy protocols, such as echo time (TE) and repetition time (TR), an accurate knowledge of T 1 and T 2 relaxation times is essential. With TR chosen on the order of T 1 , severe saturation effects must be taken into account, in addition to T 2 decay. For absolute quantification of metabolites, it is therefore essential to accurately determine relaxation times to allow subsequent corrections for T 1 and T 2 decay (3,4).Relaxation times vary not only between different metabolites, but also with B 0 . The T 1 and T 2 of 31 P metabolites in the human leg were previously determined only at lower field strengths, i.e., at 1.5 T (5-13), 2.0 T (14), 2.35 T (15), and 3 T (16), while in vivo data at higher fields have been obtained only from animal studies (17,18).Relaxation in 1 H-MRS is dominated by magnetic dipoledipole interactions according to the Bloembergen-Purcell-Pound (BPP) theory (19). Therefore, 1 H-MRS T 1 relaxation times are increasing with B 0 (20). However, for 31 P-MRS, both dipolar relaxation and chemical shift anisotropy (CSA) are the two major, competing relaxation mechanisms (17,(21)(22)(23). In contrast to dipolar interaction, the contributions of CSA to 1/T 1 and 1/T 2 relaxation rates are proportional to the gyromagnetic ratio (␥), B 0 2 , the asymmetry of the magnetic shielding (...

This work describes a new approach for high-spatial-resolution (1)H MRSI of the human brain at 7 T. (1)H MRSI at 7 T using conventional approaches, such as point-resolved spectroscopy and stimulated echo acquisition mode with volume head coils, is limited by technical difficulties, including chemical shift displacement errors, B(0)/B(1) inhomogeneities, a high specific absorption rate and decreased T(2) relaxation times. The method presented here is based on free induction decay acquisition with an ultrashort acquisition delay (TE*) of 1.3 ms. This allows full signal detection with negligible T(2) decay or J-modulation. Chemical shift displacement errors were reduced to below 5% per part per million in the in-slice direction and were eliminated in-plane. The B(1) sensitivity was reduced significantly and further corrected using flip angle maps. Specific absorption rate requirements were well below the limit (~20 % = 0.7 W/kg). The suppression of subcutaneous lipid signals was achieved by substantially improving the point-spread function. High-quality metabolic mapping of five important brain metabolites was achieved with high in-plane resolution (64 × 64 matrix with a 3.4 × 3.4 × 12 mm(3) nominal voxel size) in four healthy subjects. The ultrashort TE* increased the signal-to-noise ratio of J-coupled resonances, such as glutamate and myo-inositol, several-fold to enable the mapping of even these metabolites with high resolution. Four measurement repetitions in one healthy volunteer provided proof of the good reproducibility of this method. The high spatial resolution allowed the visualization of several anatomical structures on metabolic maps. Free induction decay MRSI is insensitive to T(2) decay, J-modulation, B(1) inhomogeneities and chemical shift displacement errors, and overcomes specific absorption rate restrictions at ultrahigh magnetic fields. This makes it a promising method for high-resolution (1)H MRSI at 7 T and above.

Objective. To investigate the pathologic nature of features termed "bone erosion" and "bone marrow edema" (also called "osteitis) on magnetic resonance imaging (MRI) scans of joints affected by rheumatoid arthritis (RA).Methods. RA patients scheduled for joint replacement surgery (metacarpophalangeal or proximal interphalangeal joints) underwent MRI on the day before surgery. The presence and localization of bone erosions and bone marrow edema as evidenced by MRI (MRI bone erosions and MRI bone marrow edema) were documented in each joint (n ‫؍‬ 12 joints). After surgery, sequential sections from throughout the whole joint were analyzed histologically for bone marrow changes, and these results were correlated with the MRI findings.Results. MRI bone erosion was recorded based on bone marrow inflammation adjacent to a site of cortical bone penetration. Inflammation was recorded based on either invading synovial tissue (pannus), formation of lymphocytic aggregates, or increased vascularity. Fatrich bone marrow was replaced by inflammatory tissue, increasing water content, which appears as bright signal enhancement on STIR MRI sequences. MRI bone marrow edema was recorded based on the finding of inflammatory infiltrates, which were less dense than those of MRI bone erosions and localized more centrally in the joint. These lesions were either isolated or found in contact with MRI bone erosions.Conclusion. MRI bone erosions and MRI bone marrow edema are due to the formation of inflammatory infiltrates in the bone marrow of patients with RA. This emphasizes the value of MRI in sensitively detecting inflammatory tissue in the bone marrow and demonstrates that the inflammatory process extends to the bone marrow cavity, which is an additional target structure for antiinflammatory therapy.

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Liver dysfunction correlates with alterations of intracellular concentrations of 31 P metabolites. Localization and absolute quantification should help to trace regional hepatic metabolism. An improved protocol for the absolute quantification of 31 P metabolites in vivo in human liver was developed by employing three-dimensional (3D) k-space weighted spectroscopic imaging (MRSI) with B 1 -insensitive adiabatic excitation. The protocol allowed for high spatial resolution of 17.8 ؎ 0.22 cm 3 in 34 min at 3 T. No pulse adjustment prior to MRSI measurement was necessary due to adiabatic excitation. The protocol geometry was identical for all measurements so that one calibration data set, acquired from phantom replacement measurement, was applied for all quantifications. The protocol was tested in 10 young, healthy volunteers, for whom 57 ؎ 7 spectra were quantified. Concentrations per liter of liver volume (reproducibilities) were 2.24 ؎ 0.10 mmol/L (1.8%) for phosphomonoesters (PME), 1.37 ؎ 0.07 mmol/L (7.9%) for inorganic phosphate (Pi), 11.40 ؎ 0.96 mmol/L (2.9%) for phosphodiesters (PDE), and 2.14 ؎ 0.10 mmol/L (1.6%) for adenosine triphosphate (ATP), respectively. Taken Key words: spectroscopic imaging; 31 P metabolites; human liver; absolute concentration; concentration distribution Alterations in hepatic energy metabolism are typical for inflammatory and neoplastic liver diseases (1-3). Recently, evidence has shown that abnormalities in energy metabolism can also underlie non-alcoholic fatty liver in insulin-resistant and/or type 2 diabetic patients (4). Thus, information on regional alterations in liver metabolism may contribute to early diagnosis of various liver diseases in humans.During the past decade, in vivo phosphorus magnetic resonance spectroscopy ( 31 P-MRS) has been shown to be a valuable non-invasive research tool to investigate metabolic changes in the liver, specifically with regard to diffuse liver disease (5), viral (6) and alcoholic liver disease (7), cirrhosis (8 -11), and liver metastases (12,13). These studies used metabolite peak ratios as a surrogate for energy metabolism in the human liver. 31 P-MRS has also been used as a tool for determining absolute concentrations of metabolites in the healthy human liver (14 -18) and can yield more detailed information on liver function than metabolite peak ratios.Despite the increasing use of this approach there are discrepancies between the reported results (14 -18), which may reflect different signal acquisition schemes, different corrections of partial longitudinal saturation effects, as well as differences in postprocessing and quantification protocols (16). Thus, there is a need for a robust, simple, and reproducible method for acquiring 31 P metabolite concentrations in the human liver.The most promising approach is currently magnetic resonance spectroscopic imaging (MRSI). The main advantage of multivoxel MRSI resides in the ability to provide a measure of the spatial distribution of metabolites. On the other hand, time demands of typical ...