Quantification Of Phosphorus Metabolites Research Articles

Reproducibility and influencing factors of 31p MR spectroscopy in rabbit liver with two-dimensional chemical shift imaging

Objective To investigate the reproducibility and influencing factors of relative quantification of phosphorus metabolites with two-dimensional chemical shift imaging (2D CSI) in rabbit liver. Methods Using 2D CSI MRS, 500 ml phosphate (NaH2PO4) solution phantom with 0. 05 mol/E concentration and one healthy rabbit were scanned 30 times respectively in one day and rescanned 30 times in the next day, and the stability of MR scanner and reproducibility of within-run and between-days in the same individual were analyzed. Each of thirty rabbits was scanned and rescanned one time respectively in different days, and the reproducibility of between-days in one group was analyzed. The data were statistically analyzed with t tests. Results (1) Phosphate solution phantom had a good reproducibility of within-run with the coefficient variation (CV) of 4. 92% and 5. 12% respectively in different two days. No significant change of phosphorus metabolites was detected in between-days, which was 16. 68 ± 0. 82 and 16. 56 ± 0. 85 respectively(t = 0. 665, P > 0. 05 ). (2) The CV of metabolites in one healthy rabbit ranged from 8. 04% to 34. 13%. Among the metabolites, β-ATP had the best reproducibility with the CV less than 10%. PME was 0. 88 ± 0. 28 and 0. 88 ± 0. 30, PDE was 4. 35 ± 0. 66 and 4. 35 ± 0, 66, Pi was 0. 95 ± 0.30 and 0.97±0.28, α-ATP was 5.58±0.60 and 5.61±0.61, β-ATP was 2.70±0.22 and 2.71± 0. 22, γ-ATP was 2. 20±0. 63 and 2. 18±0.44 respectively, no significant changes of metabolites were detected in between-days( P >0. 05 ). (3) The CV of metabolites in 30 healthy rabbits ranged from 8.48% to 36. 21%. Among the metabelites, β-ATP had the best reproducibility with CV less than 10%. PME was 0. 84 ± 0. 30 and 0. 79 ± 0. 28, PDE was 4. 29 ± 0.72 and 3.94 ± 0. 84, Pi was 0. 91 ± 0. 28 and 0. 92 ± 0. 31, α-ATP was 5.65±0. 66 and 5. 36±0. 60, β-ATP was 2. 71±0. 23 and 2. 66±0. 25, γ-ATP was 2. 07±0. 29 and 1.99±0. 37 respectively, no significant changes of metabolites were detected in between-days (P > 0. 05). Conclusions The relative quantification of hepatic β-ATP may be most reliable among the phosphorus metabolites for rabbit liver because of its good reproducibility and small CV. The quantification of phosphorus metabolites by 31p MRS with 2D CSI in rabbit liver is affected by many factors. Key words: Liver; Phosphorus radioisotope; Magnetic resonance spectroscopy ; Animal experimentation

Application of two-dimensional CSI for absolute quantification of phosphorus metabolites in the human liver

Application of two-dimensional CSI for absolute quantification of phosphorus metabolites in the human liver

Application of two-dimensional CSI for absolute quantification of phosphorus metabolites in the human liver

There have recently been a number of studies dealing with the absolute quantification of concentrations of MR-visible phosphorus compounds in different tissues. The use of absolute values rather than intensity ratios may furnish additional information about metabolic changes associated with different diseases. The purpose of this study was to develop a general procedure for measuring molar metabolite concentrations and to apply it with respect to the evaluation of human liver 31P-MRS data measured using a standard slice-selective two-dimensional CSI sequence and commercial 1H/31P surface coil. The experimental determination of all surface coil-related factors influencing signal intensity was undertaken using a gradient echo imaging technique that can be adapted to commercial systems. The resulting values for healthy volunteers (N = 9) showed concentrations of PME = 2.8 +/- 1.3 mM, PDE = 9.9 +/- 2.7 mM, P(i) = 1.7+/-0.7 mM, and ATP = 3.6 +/- 0.9 mM in the human liver. The data are quite consistent with published findings.

Detection and quantification of free cytosolic inorganic phosphate and other phosphorus metabolites in the beating mouse heart muscle in situ.

The aim of this study was the quantification of inorganic phosphate (Pi) and other phosphorus metabolites by (31)P NMR spectroscopy in the mouse heart muscle in situ, beating at around 600 min(-1). Male adult Quacker-bush mice (mean weight 32 +/- 7 g) were anaesthetized, ventilated and placed in a temperature-controlled animal holder. A purpose-built (31)P NMR surface coil was positioned against the exposed left ventricular myocardium. Partial signal overlap of Pi with 2,3-DPG from chamber blood was minimized using a DEPTH pulse sequence (180 degrees -90 degrees -180 degrees -180 degrees -acq.). Quantification of phosphorus metabolites was performed using an external standard positioned directly above the surface coil. We report for the mouse myocardium in situ an intracellular free [Pi] of <0.4 mM, pH of 7.32 +/- 0.1, free [Mg2+] of 0.41 +/- 0.1 mM, free [ADP] of 13 +/- 1.5 microM, [ATP] of 5 +/- 0.5 mM and [PCr] of 14 +/- 1.5 mM. The phosphorylation ratio (ATP/ADP Pi) was 1005 +/- 200 mM (-1) for a PCr/ATP ratio of 2.7 +/- 0.3. It was concluded that the detection of free [Pi] in the mouse myocardium in situ can be greatly enhanced using a DEPTH pulse sequence. Quantification of compounds using an external standard positioned directly above the surface coil gave comparable results to estimations using internal ATP that was quantified enzymatically. The close agreement between the external and internal methods indicates that ATP is 100% NMR visible in the mouse heart in situ.

Quantification of phosphorus metabolites from chemical shift imaging spectra with corrections for point spread effects and B1 inhomogeneity.

A method is described for quantifying phosphorus metabolites in tissue using spectra localized with surface coils and chemical shift imaging (CSI) and assuming that metabolites are uniformly distributed within a well-defined volume. An analytical expression is developed that yields a single numerical correction factor that takes into account the excitation and receiver profiles of the coil, T1 saturation, and point spread effects associated with Fourier transformation of CSI data. An external phosphorus standard is used to calibrate instrument gain and the B1 profile of the coil. For spherical samples, point spread effects can modulate the signal intensities of three-dimensional CSI spectra from -32% to +54%, depending on the voxel size. Measurements of phantoms of known concentrations showed systematic variations of +/- 10% and random errors of +/- 5%. We have used this method to measure the concentration of phosphocreatine in the thigh muscle of normal volunteers.

Quantification of phosphorus metabolites in human calf muscle and soft-tissue tumours from localized MR spectra acquired using surface coils

Metabolite concentrations determined from MR spectra provide more specific information than peak area ratios. This paper presents a method of quantification that allows metabolite concentrations to be determined from in vivo MR spectra acquired using a surface coil and ISIS localization. Corrections for the effects of field inhomogeneity produced by surface coils are based on a measured and calibrated spatial sensitivity field map for the coil. Account is taken of imperfections in pulse performance, coil loading effects and relaxation effects, the latter making use of published metabolite relaxation times. The technique is demonstrated on model solutions. The concentrations of the main metabolites in normal human calf muscle measured using this method are [PCr] = ; [Pi] = ; [NTP] = . Quantification of spectra acquired from soft-tissue tumours in patients both pre- and post-treatment showed that changes in metabolite concentrations are more sensitive to metabolic changes than changes in peak area ratios.