Quantification of metabolites from single-voxelin vivo 1H NMR data of normal human brain by means of time-domain data analysis

We present here a combination of time-domain signal analysis procedures for quantification of human brainin vivo ¹H NMR spectroscopy (MRS) data. The method is based on a separate removal of a residual water resonance followed by a frequency-selective time-domain line-shape fitting analysis of metabolite signals. Calculation of absolute metabolite concentrations was based on the internal water concentration as a reference. The estimated average metabolite concentrations acquired from six regions of normal human brain with a single-voxel spin-echo technique for theN-acetylaspartate, creatine, and choline-containing compounds were 11.4±1.0,6.5±0.5, and 1.7±0.2 mmol kg^–1 wet weight, respectively. The time-domain analyses ofin vivo ¹H MRS data from different brain regions with their specific characteristics demonstrate a case in which the use of frequency-domain methods pose serious difficulties.     

In vivo localized1 H spectroscopy of the rat eye at 7 T: preliminary studies

Preliminaryin vivo proton spectroscopic studies of the posterior chamber of the rat eye have been undertaken at 7 T. The Spatial and Chemical shift encoded Excitation (SPACE) localization sequence was used to acquire signals from 10-µl voxels and demonstrate the presence of metabolites associated with the vitreous humor, lens, retina, and the optic nerve. LocalizedT ₂ andT ₁ measurements of water in the vitreous humor indicate a relatively fluid environment. Susceptibility maps are used to demonstrate the difficulties ofin vivo spectroscopic investigations in the anterior regions of the eye. Comments are made concerning the implications for spectral resolution in these regions.     

In vivo1H-MR spectroscopy of the human heart

4. Conclusions Combined respiratory and cardiac triggering improves the localization accuracy and spectral quality in cardiac¹H-MRS dramatically leading to substantially increased spectral reproducibility. The best practical realization of double triggering turned out to be the use of the ECG amplitude when making use of the fact that it is modulated by respiration. In spite of the spectral quality achieved in most subjects, we still fail to record satisfactory spectra in a minority of subjects. The reasons for this are not understood at present but must be some particulars of either a given subject or the experimental setup. The cardiac¹H-MR spectra contain quantifiable contributions from creatine, TMA, lipids, and probably taurine. It is possible that the spectral contributions of creatine are subject to dipolar coupling similar to the observations for skeletal muscle.     

Application of LCModel for quality control and quantitative in vivo1H MR spectroscopy by short echo time STEAM sequence

The linear combination of model spectra (LCModel) calculation of a parameter for long-term quality control,k _T, was introduced, representing the ratio of the temporal and nominal intensities of CH₃ groups of lactate and acetate in a quality control phantom. This procedure is a part of the quality assurance of the scanner using fully automatic measurement and calculation ofk _T parameters, and utilizing Shewhart regulation control charts for continuous evaluation of the magnetic resonance (MR) scanner setting. The application of thek _T parameter for the correction of in vivo data increases the precision of molar concentration determination by about 4%. This was tested by the quantitative in vivo MR determination of the molar concentrations of 13 prominent metabolites (N-acetylaspartate (NAA),N-acetylaspartylgutamate, creatine and phosphocreatine (Cr), choline-containing compounds (Cho), myo-inositol, scyllo-inositol., γ-aminobutyric acid, glutamine, glutamate, glucose, lactate, alanine, taurine) in the white matter and hippocampus of the brain in groups of volunteers, using a short echo time stimulated echo acquisition mode sequence (echo time =10 ms) and the LCModel technique. The repeatability of the measurement of prominent metabolites such as NAA, Cr and Cho was found to be around 10% (relative standard deviation,n=6); precision in a group of volunteers (n=20 and 28, respectively) was in the range of approximately 13–20%. For other metabolites, which are measured with a lower signal-to-noise ratio, the precision can be much lower.     

Two-dimensional MR spectroscopy of healthy and cancerous prostates in vivo

Objectives  A major goal of this article is to summarize the current status of evaluating prostate metabolites non-invasively using spatially resolved two-dimensional (2D) MR Spectroscopy (MRS). Materials and Methods  Due to various technical challenges, the spatially resolved versions of 2D MRS techniques are currently going through the developmental stage. During the last decade, four different versions of 2D MRS sequences have been successfully implemented on 3T and 1.5T MRI scanners manufactured by three different vendors. These sequences include half and maximum echo sampled J-resolved spectroscopy (JPRESS), S-PRESS and L-COSY, which are single volume localizing sequences, and the multi-voxel based JPRESS sequence. Results  Even though greater than 1ml voxels have been used, preliminary evaluations of 2D JPRESS, S-PRESS and L-COSY sequences have demonstrated unambiguous detection of citrate, creatine, choline, spermine and more metabolites in human prostates. ProFIT-based quantitation of JPRESS and L-COSY data clearly shows the superiority of 2D MRS over conventional one-dimensional (1D) MRS and more than six metabolites have been successfully quantified. These sequences have been evaluated in a small group of prostate pathologies and pilot investigations using these sequences show promising results in prostate pathologies. Conclusion  Implementation of the state-of-the-art 2D MRS techniques and preliminary evaluation in prostate pathologies are discussed in this review. Even though these techniques are going through developmental and early testing phases, it is evident that 2D MRS can be easily added on to any clinical Magnetic Resonance Imaging (MRI) protocol to non-invasively record the biochemical contents of the prostate.     

1H MR spectroscopic imaging with short and long echo time to discriminate glycine in glial tumours

OBJECT: To investigate glycine (Gly) concentrations in low- and high-grade gliomas based on (1)H MR spectroscopic imaging (MRSI) with short and long echo time (TE). Myoinositol (MI) and Gly appear at the same resonance frequency of 3.56 ppm, but due to strong coupling the MI signal dephases more rapidly. Therefore, their contribution to the 3.56 ppm signal should be distinguishable comparing MRSI data acquired at short and long TE. MATERIALS AND METHODS: (1)H MRSI (TE = 30 and 144 ms) was performed at 3 T in 29 patients with histopathological confirmed World Health Organization (WHO) grade II-IV gliomas and in FIVE healthy subjects. All spectra from the gliomas revealed increase of the 3.56 ppm resonance in the short TE spectra. Signal intensities of Gly and MI were differentiated either by analysing the short to long TE ratio of the resonance or by performing a weighted difference. Gly concentrations were compared between high-grade (WHO III-IV) and low-grade gliomas. RESULTS: High-grade gliomas showed significantly higher Gly concentrations compared to low-grade gliomas. CONCLUSION: Appropriate data processing of short and long TE (1)H MRSI provides a tool to distinguish and to quantify Gly and MI concentrations in gliomas. As Gly seems to be a marker of malignancy, more dedicated spectroscopic methods to differentiate these metabolites are justified.     

Transmit/receive headcoil for optimal <Superscript>1</Superscript>H MR spectroscopy of the brain in paediatric patients at 3 T

¹H magnetic resonance (MR) spectroscopy is a useful tool to obtain metabolic information from the brain in paediatric patients. To detect signals of metabolites at low concentrations or from small volumes, the signal-to-noise ratio (SNR) has to be optimized. The SNR can be increased by going to higher field strengths. However, this leads to higher spectral bandwidths, which increases the chemical shift artefact. Here we present a transmit/receive headcoil which is adapted to the dimensions of the paediatric head and enables PRESS localization with high radio-frequency (RF) bandwidths that minimize the chemical shift displacement to only 5%. In addition, since the pulse lengths are shorter with higher RF bandwidths, the echo time can be reduced to 10 ms improving SNR as well.Parts of this work have been presented at the European Society for Magnetic Resonance in Medicine and Biology in Rotterdam in 2003     

In vivo1H MR spectra analysis by means of second derivative method

Short echo time (TE) in vivo PRESS¹H MR spectra (2 T. TE = 35 ms) of normal brain were fitted in the frequency domain using the second derivative method. In this approach, local maxima and hidden peaks are found as local minima of spectrum second derivative. The Lorentzian robust minimisation procedure (referred to as maximum likelihood or m-estimate fitting) using Levenburg -Marquardt non-linear fitting engine was applied. Spectral lines were approximated under the assumption of the mixed Lorentzian/Gaussian lineshapes. The same procedure was applied to 18 proton spectra. The number of peaks found within the range of 0.74/4.2 parts per million (ppm) was 52 ± 3 and their positions were almost the same. The fitted lines were assigned on the basis of the J-pattern recalculated for the field strength of 2 T and by comparing the chemical shifts with the shifts in the single compound spectra. The ratios of main metabolites, such as NAA/Cr, Cho/Cr, Cho/NAA and ml/Cr, are in accord with those obtained earlier using the software supplied with the MR imager and the absolute concentrations ofN-acetylaspartate (NAA). choline containing compounds (Cho),myo Inositol (ml), glucose (Gle) and glutamate (Glu) obtained from the fit agree with those reported in literature, which confirms the usefulness of the second derivative method in routine analyses of¹H MR brain spectra.     

1H magnetic resonance spectroscopy of the brains of normal infants and after perinatal hypoxia-ischemia

The aims of this study were to define proton (¹H) metabolite peak-area ratios in the brains of normal infants and to investigate abnormalities after perinatal hypoxia-ischemia. Point-resolved spectroscopy (PRESS) data were collected at 2.4 T with an echo time (TE) of 270 ms from 8-ml voxels located in the thalamus or occipito-parietal region. Fourteen normal and 9 asphyxiated infants were studied. The gestational plus postnatal ages (GPA) of these two groups were 31–41 (median 36) and 27–41 (37) weeks, respectively, and the asphyxiated infants were studied aged 0–10 (2) days. Peak-area ratios were determined in the normal infants for choline-containing compounds (Cho), creatine plus phosphocreatine (Cr),N-acetylaspartate (NAA) and lactate (Lac). Lactate was detected in all the normal infants and Lac/NAA was higher in the occipito-parietal region than in the thalamus (p<0.005). Lac/NAA decreased with increasing GPA in both the thalamus (p=0.014) and the occipito-parietal region (p=0.033). In six of the nine asphyxiated infants, Lac/NAA was above 95% confidence intervals for either the thalamus and/or the occipito-parietal region. Of these six infants, two died and three were neurologically abnormal aged 2 months, indicating that elevated Lac/NAA after perinatal hypoxia-ischemia may convey a poor prognosis. Propan-l,2-diol (the phenobarbitone injection medium) was detected at 1.1 ppm in three infants.     

31P-NMR spectroscopy of human blood and serum: first results from volunteers and patients with congestive heart failure,diabetes mellitus and hyperlipidaemia

³¹P-containing metabolites in human blood, serum and erythrocytes were measured or calculated. Phosphodiesters were found in serum, but not in erythrocytes. 2,3-diphosphoglycerate and 2,3-diphosphoglycerate/ATP ratios were increased in patients with congestive heart failure (2,3-diphosphoglycerate by 13% in mild to moderate, 31% in severe congestive heart failure, 2,3-diphosphoglycerate/ATP ratio by 9% in mild to moderate, 38% in severe congestive heart failure); phosphodiesters were increased in diabetes mellitus (by 26%) and even more so in hyperlipidaemia (by 57%). Changes of blood³¹P compounds with disease states may have diagnostic potential and should be recognized for correction of organ spectra.     

The role of relaxation time corrections for the evaluation of long and short echo time <Superscript>1</Superscript>H MR spectra of the hippocampus by NUMARIS and LCModel techniques

1H MR spectroscopy is routinely used for lateralization of epileptogenic lesions. The present study deals with the role of relaxation time corrections for the quantitative evaluation of long (TE=135 ms) and short echo time (TE=10 ms) 1H MR spectra of the hippocampus using two methods (operator-guided NUMARIS and LCModel programs). Spectra of left and right hippocampi of 14 volunteers and 14 patients with epilepsy were obtained by PRESS (TR/TE=5000/135 ms) and STEAM (TR/TE=5000/10 ms) sequences with a 1.5-T imager. Evaluation was carried out using Siemens NUMARIS software and the results were compared with data from LCModel processing software. No significant differences between the two methods of processing spectra with TE=135 ms were found. The range of relaxation corrections was determined. Metabolite concentrations in hippocampi calculated from spectra with TE=135 ms and 10 ms after application of correction coefficients did not differ in the range of errors and agreed with published data (135 ms/10 ms: NAA=10.2±0.6/10.4±1.3 mM, Cho=2.4±0.1/2.7±0.3 mM, Cr=12.2±1.3/11.3±1.3 mM). When relaxation time corrections were applied, quantitative results from short and long echo time evaluation with LCModel were in agreement. Signal intensity ratios obtained from long echo time spectra by NUMARIS operator-guided processing also agreed with the LCModel results.     

Assignment of the 2.03 ppm resonance in in vivo <Superscript>1</Superscript>H MRS of human brain tumour cystic fluid: contribution of macromolecules

MRI and MRS are established techniques for the evaluation of intracranial mass lesions and cysts. The 2.03 ppm signal recorded in their ¹H-MRS spectra is often assigned to NAA from outer volume contamination, although it has also been detected in non-infiltrating tumours and large cysts. We have investigated the molecular origin of this resonance in ten samples of cystic fluids from human brain tumours. The NMR detected content of the 2.03 ppm resonance in 136 ms echo time spectra, assuming an N- CH₃ origin, was 3.19 ± 1.01 mM. Only one third (34 ± 12%) of the N-acetyl containing compound (NAC) signal could be extracted by perchloric acid (PCA) indicating that most of it originated in a macromolecular PCA-insoluble component. Chemical analysis of the cyst fluids showed that sialic acid bound to macromolecules would account for 64.3% and hexuronic containing compounds for 29.2% of the NMR-detectable ex vivo signal, 93.4% of the signal at TE 136 ms. Lactate content measured by NMR (6.4 ± 4.4 mM) and the predominance of NAC originating in sialic acid point to a major origin from tumour rather than from plasma for this 2.03 ppm resonance.     

Signal enhancement through heteronuclear polarisation transfer in in-vivo <Superscript>31</Superscript>P MR spectroscopy of the human brain

Significant ³¹P NMR signal enhancement through heteronuclear polarisation transfer was obtained in model solutions and in vivo on a 1.5-T whole-body MR scanner equipped with two RF channels. The much higher population differences involved in proton Zeeman energy levels can be transferred to the ³¹P levels with the refocused INEPT (insensitive nucleus enhancement by polarisation transfer) double-resonance experiment by means of a series of simultaneously applied broadband RF pulses. INEPT achieves a polarisation transfer from ¹H to ³¹P spin states by directly reordering the populations in spin systems with heteronuclear scalar coupling. Thus, only the ³¹P NMR signal of metabolites with scalar ¹H–³¹P coupling is amplified, while the other metabolite signals in the spectra are suppressed. Compared to Ernst-angle excitation, a repetition-time-dependent signal enhancement of η=(29±3)% for methylene diphosphonic acid (MDPA) and η=(56±1)% for phosphorylethanolamine (PE) was obtained on model solutions through optimisation of the temporal parameters of the pulse experiment. The results are in good agreement with numerical calculations of the theoretical model for the studied spin systems. With optimised echo times, in-vivo ³¹P signal enhancement of the same order was obtained in studies of the human brain.     

Combined 1H and 31P MR spectroscopic imaging: impaired energy metabolism in severe carotid stenosis and changes upon treatment

OBJECT: To evaluate if combined (1)H and (31)P MR spectroscopic imaging (MRSI) before and after treatment of severe internal carotid artery (ICA) stenosis detects significant changes in energy metabolism in the basal ganglia of both hemispheres. MATERIALS AND METHODS: A group of 14 patients with high-grade ICA stenosis and 11 healthy control subjects were examined with 2D (1)H MRSI and 3D (31)P MRSI at 3 T before and after treatment of severe ICA stenosis. Spectroscopic data were processed with LCModel and jMRUI software. Changes of the phosphorylated metabolites, pH, N-acetyl-acetate, creatine and choline-containing compounds prior/post intervention were analyzed and patients' data were compared with that of control subjects. RESULTS: Untreated patients had significantly higher Adenosindiphosphate (ADP) in basal ganglia ipsi- and contralateral to the side of ACI stenosis compared to controls. After treatment, ADP of both hemispheres significantly decreased by approximately 20% compared to the pre-treatment values. Further, significant decreases of phosphorylated metabolites prior/post intervention were found for patients compared to controls. CONCLUSION: This spectroscopic study reveals that unilateral high-grade ICA stenosis has an effect on cerebral high-energy metabolism of both hemispheres, which is at least partially reversible after treatment. Therefore the restoration of blood flow in high-grade ICA stenosis recovers the impaired energy balance of the brain.     

Large increases in1H metaboliteT 2's after cerebral hypoxia-ischemia correlate with ATP depletion

In vivo proton (¹H) magnetic resonance spectroscopy (MRS) can measure cerebral metabolite concentrations and nuclear relaxation times. Function of the sodium (Na⁺)/potassium (K⁺) pump in cell membranes depends on adequate adenosine triphosphate (ATP) levels: intracellular Na⁺ is normally extruded in exchange for extracellular K⁺. Low ATP will cause pump dysfunction and loss of K⁺ accompanied by influx of Na⁺and water. Raised intracellular water may increase molecular mobility and this might be detectable as increased apparent transverse relaxation times (T ₂'s).¹H-MRS of the brains of newborn piglets during acute hypoxia-ischemia revealed enigmatic increases in the peak area of creatine + phosphocreatine (Cr) relative to those of choline-containing compounds (Cho) andN-acetylaspartate (NAA). Interleaved¹H and phosphorus (³¹P) MRS showed that theT ₂'s of both Cr and lactate (Lac) increased during acute hypoxia-ischemia and these changes correlated with reductions in nucleotide triphosphate (NTP; largely ATP). Within 50 h of metabolic recovery from the primary insult, as delayed energy failure developed, theT ₂'s of Cho, Cr, NAA, and Lac increased greatly. TheseT ₂ changes also correlated with NTP depletion. These observations demonstrate important relationships betweenT ₂'s and function of the ATP-dependent Na⁺/K⁺ pump.     

Investigation of multidrug resistance in cultured human renal cell carcinoma cells by 31P-NMR spectroscopy and treatment survival assays

KTCTL-26 and KTCTL-2 are renal cell carcinoma (RCC) lines with high and lowexpression of P-170 glycoprotein, respectively. Inherent differences between the two cell lines in terms of phosphate metabolites and growth characteristics in culture were examined for possible association with multidrug resistance (MDR). Differences in response to drug treatment were investigated for 40 h incubations with various doses of vinblastine (VBL) alone or as cotreatments with various concentrations of the calcium antagonist diltiazem (DIL) and/or interferon–α (IFN-α). Treatment effects were quantitated using the MTT survival assay and ³¹P magnetic resonance spectroscopy (MRS) to determine phosphate metabolite profiles in intact cells. KTCTL-2 and KTCTL-26 cells exhibited significant inherent differences in phosphocholine, glycerophosphocholine, glycerophosphoethanolamine, and phosphocreatine levels. KTCTL-26 cells were more sensitive than KTCTL-2 to 0.011μM VBL alone (87% vs. 102% survival) or to 0.011μM BL + 10μM DIL (55% vs. 80% survival). The latter treatment resulted in a significant decrease in the ratio of phosphocholine to glycerophosphocholine in KTCTL-26 cells but no significant changes in phosphate metabolites in KTCTL-2 cells. Metabolomic ³¹P MRS detects different metabolite profiles for RCC cell lines with different MDR phenotypes and may be useful for noninvasive characterization of tumors in a clinical setting.This revised version was published online in August 2005 with a corrected sequence of authors.     

A continuous-flow perfusion system for the maintenance and NMR study of small tissue samples in vitro

To describe and evaluate a novel perfusion system developed to maintain excised tissue in a flowing, oxygenated bathing solution during acquisition of nuclear magnetic resonance (NMR) data, and in addition allow precise data to be acquired continuously while altering the composition of the bathing solution surrounding the tissue. A chamber to house the tissue sample was constructed of interlocking sections of polyethylene tubing, and had approximate internal dimensions of 4 mm in diameter and 4 mm in height. Temperature-controlled, physiologically appropriate buffer solution was pumped via an infusion pump through the chamber, entering and exiting by way of small openings on either end. Immediately surrounding the polyethylene chamber was a tight-fitting four-loop solenoid RF coil. Measured proton NMR parameters were found to be fairly insensitive to the flow rate of the buffer if this coil was used only for reception and a larger-volume transmit-only coil was used for excitation. Temperature control of the sample was successfully implemented between 25 and 40°C. The perfusion system was found to be resistant to the effects of flow rate, as well as a useful tool for the administration of drugs or agents to the tissue. Changes in buffer composition could be performed on the fly without the need to reposition the sample each time a change was made. This avoidance of repositioning was found to yield a fivefold improvement in the precision of T₂ spectral parameters (using frog sciatic nerve as a sample).The authors wish to acknowledge the Canadian Institutes of Health Research (CIHR) for funding and the In Vivo NMR Facility of the University of Alberta for infrastructural support     

An iron-based T 1 contrast agent made of iron-phosphate complexes: In vitro and in vivo studies

A new iron-based T ₁ contrast agent consisting of a complex of iron ions coordinated to phosphate and amine ligands (Fe_(phos) in short) has been characterized by spectroscopic and magnetic measurements. NMR relaxation studies showed r ₁ values to be dependent on the phosphate salt concentration, K₂HPO₄, present in the medium. r ₁ reaches a maximum value of 2.5 mM^?1 s^?1 for measurements carried out at 7 T and 298 K. ³¹P MRS, Mössbauer spectroscopy and magnetic measurements of Fe_(phos) solutions suggest paramagnetic Fe³⁺ ions present in the studied iron–phosphate complex. In vitro and in vivo toxicity experiments with C6 cells and CD1 mice, respectively, demonstrated lack of toxicity for Fe_(phos) at the highest dose tested in the MRI experiments (12 mM iron for C6 cells and 0.32 mmol iron/kg for mice). Finally, T ₁ weighted images of brain tumours in mice have shown positive contrast enhancement of Fe_(phos) for tumour afflicted regions in the brain.