Free magnesium levels in normal human brain and brain tumors: 31P chemical-shift imaging measurements at 1.5 T.

Abstract

We have studied a series of normal subjects and patients with brain tumors, by using 31p three-dimensional chemical shift imaging to obtain localized 31p spectra of the brain. A significant proportion of brain cytosolic ATP in normal brain is not complexed to Mg , as indicated by the chemical shift 6 of the f-P resonance of ATP. The ATP (3-P METHODS Imaging/31p Chemical-Shift Imaging (CSI) Spectroscopy. Combined proton imaging/31P spectroscopic examinations of patients and healthy volunteers were done on a standard clinical imager [1.5 T Siemens (Iselin, NJ) Magnetom]. Positioning and proton imaging required 20 min; the 8 x 8 x 8 3D-CSI spectroscopic data required 17 min per twoacquisition block. For patients A, B, and C, 31P spectra were acquired by using 5-or 10-cm-diameter 31p surface coils and a 3D-CSI sequence with a sin/cos adiabatic half-passage pulse (17). For volunteers and patients D and E, spectra were acquired with a quadrature low-pass birdcage resonator and 3D-CSI with a 250-,us rectangular pulse with a low-tip angle as described (16); no spatial filtering was done. Retrospective alignment of the CSI voxels (16,18) was used to position the voxels symmetrically with respect to the falx cerebri and to place the central axial slice below the corpus callosum for normal subjects. For patients B through E, a CSI voxel was centered on the tumor. For patient A, whose tumor contained large cystic regions, the CSI voxel was centered on the viable portion of the tumor, as assessed from Gd contrast-enhanced proton images. After shifting, the data were Fouriertransformed in time and k-space domains, and all spectra were phased with the same corrections (obtained from the nonlocalized spectrum) to produce a three-dimensional array of 512 spectra. The 3D-CSI spectra were corrected for the missing initial time points of the free induction decay (FID) (16,19) to produce baseline-corrected spectra that are visually easier to inspect.Patients. Three male and two female patients with brain tumors, aged 36-70 years, were examined. All examination procedures were approved by the Investigational Review Board. The histories of the patients were as follows: case A, recurrent oligodendroglioma in the left temporal lobe, treated

Magnesium abnormalities of skeletal muscle in dermatomyositis and juvenile dermatomyositis

“…Therefore, free magnesium concentrations are low in most cell types. In skeletal muscle, free Mg 2ϩ has been estimated to be between 0.5 and 1.5 mmoles/kg using various methods including P-31 MRS (16,18,(30)(31)(32). In the present investigation, free Mg 2ϩ levels in the muscles of normal control subjects (mean Ϯ SEM 0.83 Ϯ 0.09 mmoles/kg for adults and 0.78 Ϯ 0.06 mmoles/kg for children) were within the reported range during rest (Tables 5 and 6).…”

“…Levels of intracellular free Mg 2ϩ and Mg-ATP have been determined with P-31 MRS in a variety of human tissues, including red blood cells, brain, liver, and muscle (14,(16)(17)(18). Magnesium deficiency has been reported in involved tissues in a number of clinical conditions, including hypertension, arteriosclerosis, cardiac arrhythmias, diabetes mellitus, and eosinophilia-myalgia syndrome (19)(20)(21).…”

Magnesium in the Central Nervous System

“…This result is likely related to the lower ATP concentration of brain tissue (3 mM) compared to that of skeletal muscle (8 mM), ATP being the major binding site present in the cellular milieu. Nevertheless, the value found of 0.182 mM is lower than that obtained by others (Taylor et al, 1991;Halvorson et al, 1992). This is not a surprising result as the model considered in building this calibration curve contains more species that bind Mg 2+ than in all other approaches published.…”

“…Membrane perturb--ations that are typically associated with the neoplastic phenotype determine the release of intracellularly bound Mg. Accordingly, a seminal study showed a significant increase of intra--cellular Mg in human brain tumours by 31P--NMR (Taylor et al, 1991). Having high intracellular Mg might represent a selective advantage for the transformed cells.…”

“…In particular, the calibration curve should take into account: i) other ions present in the cell cytosol competing with Mg 2+ in binding ATP such as H + , Na + , K + , and ii) other ligands such as ADP, PCr and Pi competing with ATP in binding Mg 2+ (Iotti et al, 1996). Operatively, [Mg 2+ ] is assessed by 31 P--MRS from the chemical shift of β--ATP being measured from the signal of either α--ATP (Gupta et al, 1984;Williams and Smith, 1995) or PCr (Taylor et al, 1991;Halvorson et al, 1992). The reliability of the in vivo measurements depends on the availability of an appropriate in vitro calibration method to determine the limits of chemical shifts of unbound ATP and Mg--ATP complexes.…”