Determination of saturation factors in 31P NMR spectra of the developing human brain

Deciphering the Role of Klf10 in the Cerebellum

Recent studies have demonstrated a new role for Klf10, a Krüppel-like transcription factor, in skeletal muscle, specifically relating to mitochondrial function. Thus, it was of interest to analyze additional tissues that are highly reliant on optimal mitochondrial function such as the cerebellum and to decipher the role of Klf10 in the functional and structural properties of this brain region. In vivo (magnetic resonance imaging and localized spectroscopy, behavior analysis) and in vitro (histology, spectroscopy analysis, enzymatic activity) techniques were applied to comprehensively assess the cerebellum of wild type (WT) and Klf10 knockout (KO) mice. Histology analysis and assessment of locomotion revealed no significant difference in Klf10 KO mice. Diffusion and texture results obtained using MRI revealed structural changes in KO mice characterized as defects in the organization of axons. These modifications may be explained by differences in the levels of specific metabolites (myo-inositol, lactate) within the KO cerebellum. Loss of Klf10 expression also led to changes in mitochondrial activity as reflected by a significant increase in the activity of citrate synthase, complexes I and IV. In summary, this study has provided evidence that Klf10 plays an important role in energy production and mitochondrial function in the cerebellum.

Mr Spectroscopy in Clinical Research

MR spectroscopy (MRS) offers unique possibilities for non-invasive evaluation of biochemistry in vivo. During recent years there has been a growing body of evidence from clinical research studies on human beings using 31P and 1H MRS. The results indicate that it is possible to evaluate phosphorous energy metabolism, loss of neurones, and lactate production in a large number of brain diseases. Furthermore, 31P and 1H MRS may be particularly clinically useful in evaluation of various disorders in skeletal muscle. In the heart 31P MRS seems at the moment the most suitable for evaluation of global affections of the myocardium. In the liver 31P MRS appears to be rather insensitive and non-specific, but absolute quantification of metabolite concentrations and using metabolic “stress models” may prove useful in the future. The clinical role of MRS in oncology is still unclear, but it may be useful for noninvasive follow-up of treatment.

Taken together, the evidence obtained so far certainly shows some trends for clinical applications of MRS. Methods are now available for the clinical research necessary for establishing routine clinical MRS examinations.

In vivo31P NMR spectroscopy shows an increase in glycerophosphorylcholine concentration without alterations in mitochondrial function in the prefrontal cortex of medicated schizophrenic patients at rest

The (31)P NMR localised method was used to study the metabolism of phospholipid and high energy phosphate in the prefrontal cortex. The spectra were taken from patients with schizophrenia (11 males) receiving neuroleptic medication, and were compared to normal controls (15 males). Their spectral intensities were analysed using a non-linear least-squares method with a prior knowledge of the fixed chemical shifts and linewidths, leading to further resolution into resonances of glycerophosphorylethanolamine (GPE), glycerophosphorylcholine (GPC), phosphorylethanolamine (PE) and phosphorylcholine (PC). The metabolite concentrations were calculated referring to the spectral intensities of phosphate phantoms with known concentrations. T1 values of phantom and cerebrum were estimated from a series of localised inversion recovery spectra to correct for the signal saturation effects. The schizophrenic patients showed an increased concentration of GPC but not GPE, PE or PC. Furthermore, no difference was observed regarding the concentration of high-energy phosphates such as phosphocreatine, inorganic phosphate and ATP. The patients did not show any differences in mitochondrial function such as phosphorylation potential and the ratio of the rate of ATP synthesis. Thus, an increase in GPC concentration in the prefrontal cortex could be characteristic of the pathophysiology of schizophrenia with mild negative symptoms.

Study of the maturation of the child's brain using 31P-MRS

The maturation of human cerebrum and cerebellum in 37 normal children aged 4 months to 13 years 8 months was evaluated by 31P-magnetic resonance spectroscopy using two different conditions of repetition time (TR) (TR = 3 seconds and 15 seconds) in each region. The results were as follows. First, the PME/PDE, PCr/gamma-ATP and Pi/PCr ratios differed between the cerebrum and the cerebellum. The PME/PDE and PCr/gamma-ATP ratios were greater in the cerebellum than in the cerebrum. However, the Pi/PCr ratio was smaller in the cerebellum than in the cerebrum. At TR = 3 seconds, the ratio of (PME/PDE ratio in the cerebellum)/(PME/PDE ratio in the cerebrum) and the ratio of (PCr/gamma-ATP ratio in the cerebellum)/(PCr/gamma-ATP ratio in the cerebrum) manifested a nearly constant value independent of age. Second, the phosphomonoester peak in the cerebrum contained a substance with a longer relaxation time than 3 seconds; this substance was present in large amounts in the early period, then gradually decreased during maturation.

Axonal dysfunction and disability in a relapse of multiple sclerosis: longitudinal study of a patient

In a 6-year longitudinal study of a patient with relapsing progressive multiple sclerosis (MS), we used proton magnetic resonance spectroscopy to assess N-acetylaspartate (NAA) from a large central brain volume to evaluate the relationship between this marker of neuronal integrity and clinical disability. During the follow-up period, there was one major relapse and its subsequent partial remission. Changes in the brain NAA to creatine ratio correlated strongly with clinical disability (Spearman rank coefficient = -0.73, p < 0.001). We interpret this as evidence that axonal dysfunction or loss contributes to functional impairment of patients with MS. Because the NAA signal in the large volume of interest originated predominantly from white matter that appeared normal on conventional MRI, these results also suggest that some degree of axonal dysfunction may be widespread in acute, severe relapses.

In vivo phosphorus polarization transfer and decoupling from protons in three-dimensional localized nuclear magnetic resonance spectroscopy of human brain

Refocused insensitive nucleus enhancement by polarization transfer (RINEPT) from protons (1H) to a J-coupled phosphorus (31P) has been incorporated into three-dimensional (3D) chemical-shift-imaging (CSI) sequence on a clinical imager. The technique is demonstrated on a phantom and in in vivo human brain. The polarization-transfer efficiency (approximately 1.2) is lower than the theoretical maximum of gamma1H/gamma31P approximately 2.4 resulting from 1H-1H homonuclear J couplings of similar magnitude competing with the 1H --> 31P transfer. Nevertheless, compared with direct 31P Ernst-angle excitation, signal gains of up to x1.8 were obtained mainly as a result of T1 differences between 31P and the 1H. Spectral interpretation is simplified by editing out all non-proton-coupled 31P signals. The duration, approximately 50 min, and power deposition, approximately 1 W x kg(-1), make the application suitable for human studies.

Changes in 31P-relaxation times during organ preservation: observations on cold stored human donor livers

During cold preservation for transplantation the tissue hydration state changes. It is not known whether such changes lead to altered relaxation times of 31P nuclei with potential consequences for the quantification of tissue metabolites. Therefore, 31P spectroscopic and proton T1 relaxometric measurements were performed on 42 isolated human donor livers shortly before implantation. The results demonstrate that 31P T1 relaxation times change during preservation for clinical transplantation, thus quantification of tissue metabolites in cold stored donor livers may be in part dependent on the tissue hydration state. Furthermore, it appeared that changes in tissue hydration state especially affect the physico-chemical characteristics of the intracellular fluid compartment. This study indicates that reliable spectroscopic quantification of tissue metabolites, particularly during sequential spectroscopic measurements in cold stored donor organs is best warranted under fully relaxed conditions.

Measurement of spin-lattice relaxation times and kinetic rate constants in rat muscle using progressive partial saturation and steady-state saturation transfer

31P spin-lattice relaxation times (T1) of metabolites in rat calf muscle at 1.9 Tesla and the forward rate through the creatine kinase (CK) reaction have been measured using a new method based on modeling progressive saturation explicitly incorporating the effect of chemical exchange. In a separate series of experiments, we compared our method with inversion recovery both in vitro and in vivo, finding agreement between the techniques. We found that the T1 values of phosphocreatine (PCr) (6.6 +/- 0.3 s), gamma-ATP (2.6 +/- 0.6 s), alpha-ATP (2.4 +/- 0.4 s) and beta-ATP (2.2 +/- 0.2 s) are unchanged by stimulation of sufficient intensity to induce a 32% drop in PCr level. The errors in T1 values which arise when chemical exchange is neglected are calculated. These are found to be on the order of 20% for PCr and 30-50% for gamma-ATP under typical conditions. Use of longer repetition times results in larger errors in measured values of T1. This source of error can be effectively eliminated by use of sufficiently short repetition times. We found that the rate constant of the forward CK reaction was increased 60% by stimulation, from 0.20 +/- 0.03 s-1 to 0.32 +/- 0.03 s-1, but that the phosphorus flux did not change.

Heteronuclear multivoxel spectroscopy of in vivo human brain: two-dimensional proton interleaved with three-dimensional 1H-decoupled phosphorus chemical shift imaging

Multivoxel, heteronuclear interleaved two-dimensional proton and three-dimensional 1H-decoupled 31P CSI of human brain is demonstrated. This method offers efficient use of limited examination time as patient preparation, coil tuning, shimming and imaging are done only once and the CSI data sets from both nuclei are obtained concurrently. Effective interleaving of 31P and 1H is possible due to the shorter T1s of proton brain metabolites, allowing a 1H acquisition cycle to be inserted into each 31P TR. This way, the entire MRS time is available to both nuclei, increasing their SNR per-unit-time by approximately 12% for 31P and approximately 80% for 1H, compared with sequential detection of equal (45-50 min) length. The spectral resolution and SNR of 31P are further increased through bi-level 1H-decoupling and NOE.

[Nuclear magnetic resonance spectroscopy: methodology and applications to the study of asphyxia neonatorum]

Cerebral metabolism has been extensively studied by magnetic resonance spectroscopy (MRS). MRS allows the study of neonates brain maturation as well as the onset and the evolution of brain injury. The use of phosphorous spectroscopy allows the quantification of phosphorylated metabolites. Thus, the measurement of the relative concentrations of creatine-phosphate and inorganic-phosphate is a prognostic factor of the outcome of a neonate after birth asphyxia. Absolute concentrations have more recently been studied and seem to be more significant. Proton MRS gives access to brain metabolites such as choline, lactate, N-acetyl aspartate and taurine. Its use is more recent than the phosphorous spectroscopy but first results already show its potential in neonatology.

Metabolite concentrations in the developing brain estimated with proton MR spectroscopy

The purpose of the present study was to estimate absolute concentrations and relaxation time constants of metabolites that were detectable with proton magnetic resonance (MR) spectroscopy in the healthy preterm, term, and infant brain. Five MR spectra were recorded for each infant by using STEAM (stimulated-echo acquisition mode) sequences with different TEs and TRs. Water was used as an internal standard. The T1 of choline-containing compounds (Cho) and the T1 of phosphocreatine plus creatine (PCr+Cr) decreased. The T2 of the N-acetyl-L-aspartate (NAA) resonance increased, probably because of a relatively larger signal overlap with glutamate in the most immature brains. The concentration of NAA almost doubled, whereas the Cho concentration showed only a nonsignificant tendency to decrease; therefore, the well-known increase in the ratio of NAA to Cho appears to be due mostly to an increase in NAA concentration. The concentration of PCr+Cr increased rapidly and reached adolescent values at approximately 4 months of age.

Dual interleaved 1H and proton-decoupled-31P in vivo chemical shift imaging of human brain

A technique is demonstrated to obtain interleaved proton (1H) and 1H-decoupled phosphorus (31P) spectra of human brain using 2D CSI. A modified commercial full-body imager and a dual-tuned birdcage head-coil were employed. Because proton relaxation times are shorter than those of phosphorus, TR(1H) can be chosen to be shorter than TR(31P), thus permitting a 1H acquisition to be inserted in each 31P cycle. The scheme results in significant time savings as both CSI data sets are obtained concurrently with patient loading, coil tuning, shimming, and imaging needed to be done only once.

Phosphorus-31 magnetic resonance spectroscopy and ventricular enlargement in bipolar disorder

Phosphorus-31 magnetic resonance spectroscopy (31P-MRS) was used to examine whether reduced levels of phosphomonoesters (PME) were correlated with ventricular enlargement in 40 patients with bipolar disorder and 60 age-matched normal control subjects. Ventricular enlargement was assessed by magnetic resonance imaging (1H-MRI) using the following three methods: Evans ratio (ER), Huckman number (HN), and minimum distance of caudate nuclei (MDCN). Although MDCN and ER were significantly larger in the patient group, no significant correlations were found between 31P-MRS and 1H-MRI. PME was negatively correlated with age in bipolar disorder. Decreased levels of PME were found only in bipolar I disorder. Intracellular pH was positively correlated with duration of lithium treatment. These results suggest that the observed PME reduction was not related to ventricular enlargement, but the issue should be further studied with volumetric MRI analysis.