Comparative review of algorithms and methods for chemical-shift-encoded quantitative fat-water imaging

PURPOSE

To propose a standardized comparison between state-of-the-art open-source fat-water separation algorithms for proton density fat fraction (PDFF) andR 2 * $$ {R}_2^{\ast } $$ quantification using an open-source multi-language toolbox.

METHODS

Eight recent open-source fat-water separation algorithms were compared in silico, in vitro, and in vivo. Multi-echo data were synthesized with varying fat-fractions, B0 off-resonance, SNR and TEs. Experimental evaluation was conducted using calibrated fat-water phantoms acquired at 3T and multi-site open-source phantoms data. Algorithms' performances were observed on challenging in vivo datasets at 3T. Finally, reconstruction algorithms were investigated with different fat spectra to evaluate the importance of the fat model.

RESULTS

In silico and in vitro results proved most algorithms to be not sensitive to fat-water swaps andB 0 $$ {\mathrm{B}}_0 $$ offsets with five or more echoes. However, two methods remained inaccurate even with seven echoes and SNR = 50, and two other algorithms' precision depended on the echo spacing scheme (p < 0.05). The remaining four algorithms provided reliable performances with limits of agreement under 2% for PDFF and 6 s-1 forR 2 * $$ {R}_2^{\ast } $$ . The choice of fat spectrum model influenced quantification of PDFF mildly (<2% bias) and ofR 2 * $$ {R}_2^{\ast } $$ more severely, with errors up to 20 s-1 .

CONCLUSION

In promoting standardized comparisons of MRI-based fat and iron quantification using chemical-shift encoded multi-echo methods, this benchmark work has revealed some discrepancies between recent approaches for PDFF andR 2 * $$ {R}_2^{\ast } $$ mapping. Explicit choices and parameterization of the fat-water algorithm appear necessary for reproducibility. This open-source toolbox further enables the user to optimize acquisition parameters by predicting algorithms' margins of errors.

Combining sodium MRI, proton MR spectroscopic imaging, and intracerebral EEG in epilepsy

Whole brain ionic and metabolic imaging has potential as a powerful tool for the characterization of brain diseases. We combined sodium MRI (²³ Na MRI) and ¹ H-MR Spectroscopic Imaging (¹ H-MRSI), assessing changes within epileptogenic networks in comparison with electrophysiologically normal networks as defined by stereotactic EEG (SEEG) recordings analysis. We applied a multi-echo density adapted 3D projection reconstruction pulse sequence at 7 T (²³ Na-MRI) and a 3D echo-planar spectroscopic imaging sequence at 3 T (¹ H-MRSI) in 19 patients suffering from drug-resistant focal epilepsy who underwent presurgical SEEG. We investigated ²³ Na MRI parameters including total sodium concentration (TSC) and the sodium signal fraction associated with the short component of T₂ * decay (f), alongside the level of metabolites N-acetyl aspartate (NAA), choline compounds (Cho), and total creatine (tCr). All measures were extracted from spherical regions of interest (ROIs) centered between two adjacent SEEG electrode contacts and z-scored against the same ROI in controls. Group comparison showed a significant increase in f only in the epileptogenic zone (EZ) compared to controls and compared to patients' propagation zone (PZ) and non-involved zone (NIZ). TSC was significantly increased in all patients' regions compared to controls. Conversely, NAA levels were significantly lower in patients compared to controls, and lower in the EZ compared to PZ and NIZ. Multiple regression analyzing the relationship between sodium and metabolites levels revealed significant relations in PZ and in NIZ but not in EZ. Our results are in agreement with the energetic failure hypothesis in epileptic regions associated with widespread tissue reorganization.

Grey-matter sodium concentration as an individual marker of multiple sclerosis severity

OBJECTIVE

Quantification of brain injury in patients with variable disability despite similar disease duration may be relevant to identify the mechanisms underlying disability in multiple sclerosis (MS). We aimed to compare grey-matter sodium abnormalities (GMSAs), a parameter reflecting neuronal and astrocyte dysfunction, in MS patients with benign multiple sclerosis (BMS) and non-benign multiple sclerosis (NBMS).

METHODS

We identified never-treated BMS patients in our local MS database of 1352 patients. A group with NBMS was identified with same disease duration. All participants underwent ²³Na magnetic resonance imaging (MRI). The existence of GMSA was detected by statistical analysis.

RESULTS

In total, 102 individuals were included (21 BMS, 25 NBMS and 56 controls). GMSA was detected in 10 BMS and 19 NBMS (11/16 relapsing-remitting multiple sclerosis (RRMS) and 8/9 secondary progressive multiple sclerosis (SPMS) patients) (p = 0.05). On logistic regression including the presence or absence of GMSA, thalamic volume, cortical grey-matter volume and T2-weighted lesion load, thalamic volume was independently associated with BMS status (odds ratio (OR) = 0.64 for each unit). Nonetheless, the absence of GMSA was independently associated when excluding patients with significant cognitive alteration (n = 7) from the BMS group (OR = 4.6).

CONCLUSION

Detection of GMSA in individuals and thalamic volume are promising to differentiate BMS from NBMS as compared with cortical or whole grey-matter atrophy and T2-weighted lesions.

Respiratory-triggered quantitative MR spectroscopy of the human cervical spinal cord at 7 T

PURPOSE

Ultra-high field 1 H MR spectroscopy (MRS) is of great interest to help characterizing human spinal cord pathologies. However, very few studies have been reported so far in this small size structure at these fields due to challenging experimental difficulties caused by static and radiofrequency field heterogeneities, as well as physiological motion. In this work, in line with the recent developments proposed to strengthen spinal cord MRS feasibility at 7 T, a respiratory-triggered acquisition approach was optimized to compensate for dynamic B 0 field heterogeneities and to provide robust cervical spinal cord MRS data.

METHODS

A semi-LASER sequence was purposely used, and a dedicated raw data processing algorithm was developed to enhance MR spectral quality by discarding corrupted scans. To legitimate the choices done during the optimization stage, additional tests were carried out to determine the impact of breathing, voluntary motion, body mass index, and fitting algorithm. An in-house quantification tool was concomitantly designed for accurate estimation of the metabolite concentration ratios for choline, N-acetyl-aspartate (NAA), myo-inositol and glutathione. The method was tested on a cohort of 14 healthy volunteers.

RESULTS

Average water linewidth and NAA signal-to-noise ratio reached 0.04 ppm and 11.01, respectively. The group-average metabolic ratios were in good agreement with previous studies and showed intersession reproducibility variations below 30%.

CONCLUSION

The developed approach allows a rise of the acquired MRS signal quality and of the quantification robustness as compared to previous studies hence offering strengthened possibilities to probe the metabolism of degenerative and traumatic spinal cord pathologies.

Comparison of single-voxel 1H-cardiovascular magnetic resonance spectroscopy techniques for in vivo measurement of myocardial creatine and triglycerides at 3T

BACKGROUND

Single-voxel proton cardiovascular magnetic resonance spectroscopy (1H-CMRS) benefits from 3 T to detect metabolic abnormalities with the quantification of intramyocardial fatty acids (FA) and creatine (Cr). Conventional point resolved spectroscopy (PRESS) sequence remains the preferred choice for CMRS, despite its chemical shift displacement error (CSDE) at high field (≥ 3 T). Alternative candidate sequences are the semi-adiabatic Localization by Adiabatic SElective Refocusing (sLASER) recommended for brain and musculoskeletal applications and the localized stimulated echo acquisition mode (STEAM). In this study, we aim to compare these three single-voxel 1H-CMRS techniques: PRESS, sLASER and STEAM for reproducible quantification of myocardial FA and Cr at 3 T. Sequences are compared both using breath-hold (BH) and free-breathing (FB) acquisitions.

METHODS

CMRS accuracy and theoretical CSDE were verified on a purposely-designed fat-water phantom. FA and Cr CMRS data quality and reliability were evaluated in the interventricular septum of 10 healthy subjects, comparing repeated BH and free-breathing with retrospective gating.

RESULTS

Measured FA/W ratio deviated from expected phantom ratio due to CSDE with all sequences. sLASER supplied the lowest bias (10%, vs -28% and 27% for PRESS and STEAM). In vivo, PRESS provided the highest signal-to-noise ratio (SNR) in FB scans (27.5 for Cr and 103.2 for FA). Nevertheless, a linear regression analysis between the two BH showed a better correlation between myocardial Cr content measured with sLASER compared to PRESS (r = 0.46; p = 0.03 vs. r = 0.35; p = 0.07) and similar slopes of regression lines for FA measurements (r = 0.94; p < 0.001 vs. r = 0.87; p < 0.001). STEAM was unable to perform Cr measurement and was the method with the lowest correlation (r = 0.59; p = 0.07) for FA. No difference was found between measurements done either during BH or FB for Cr, FA and triglycerides using PRESS, sLASER and STEAM.

CONCLUSION

When quantifying myocardial lipids and creatine with CMR proton spectroscopy at 3 T, PRESS provided higher SNR, while sLASER was more reproducible both with single BH and FB scans.

Quantitative assessment of sciatic nerve changes in Charcot-Marie-Tooth type 1A patients using magnetic resonance neurography

BACKGROUND AND PURPOSE

Nerve tissue alterations have rarely been quantified in Charcot-Marie-Tooth type 1A (CMT1A) patients. The aim of the present study was to quantitatively assess the magnetic resonance imaging (MRI) anomalies of the sciatic and tibial nerves in CMT1A disease using quantitative neurography MRI. It was also intended to seek for correlations with clinical variables.

METHODS

Quantitative neurography MRI was used in order to assess differences in nerve volume, proton density and magnetization transfer ratio in the lower limbs of CMT1A patients and healthy controls. Disease severity was evaluated using the Charcot-Marie-Tooth Neuropathy Score version 2, Charcot-Marie-Tooth examination scores and Overall Neuropathy Limitations Scale scores. Electrophysiological measurements were performed in order to assess the compound motor action potential and the Motor Unit Number Index. Clinical impairment was evaluated using muscle strength measurements and Charcot-Marie-Tooth examination scores.

RESULTS

A total of 32 CMT1A patients were enrolled and compared to 13 healthy subjects. The 3D nerve volume, magnetization transfer ratio and proton density were significantly different in CMT1A patients for the whole sciatic and tibial nerve volume. The sciatic nerve volume was significantly correlated with the whole set of clinical scores whereas no correlation was found between the tibial nerve volume and the clinical scores.

CONCLUSION

Nerve injury could be quantified in vivo using quantitative neurography MRI and the corresponding biomarkers were correlated with clinical disability in CMT1A patients. The sensitivity of the selected metrics will have to be assessed through repeated measurements over time during longitudinal studies to evaluate structural nerve changes under treatment.

Evaluation of the Sensitivity of Inhomogeneous Magnetization Transfer (ihMT) MRI for Multiple Sclerosis

BACKGROUND AND PURPOSE

Inhomogeneous magnetization transfer is a new endogenous MR imaging contrast mechanism that has demonstrated high specificity for myelin. Here, we tested the hypothesis that inhomogeneous magnetization transfer is sensitive to pathology in a population of patients with relapsing-remitting MS in a way that both differs from and complements conventional magnetization transfer.

MATERIALS AND METHODS

Twenty-five patients with relapsing-remitting MS and 20 healthy volunteers were enrolled in a prospective MR imaging research study, whose protocol included anatomic imaging, standard magnetization transfer, and inhomogeneous magnetization transfer imaging. Magnetization transfer and inhomogeneous magnetization transfer ratios measured in normal-appearing brain tissue and in MS lesions of patients were compared with values measured in control subjects. The potential association of inhomogeneous magnetization transfer ratio variations with the clinical scores (Expanded Disability Status Scale) of patients was further evaluated.

RESULTS

The magnetization transfer ratio and inhomogeneous magnetization transfer ratio measured in the thalami and frontal, occipital, and temporal WM of patients with MS were lower compared with those of controls (P < .05). The mean inhomogeneous magnetization transfer ratio measured in lesions was lower than that in normal-appearing WM (P < .05). Significant (P < .05) negative correlations were found between the clinical scores and inhomogeneous magnetization transfer ratio measured in normal-appearing WM structures. Weaker nonsignificant correlation trends were found for the magnetization transfer ratio.

CONCLUSIONS

The sensitivity of the inhomogeneous magnetization transfer technique for MS was highlighted by the reduction in the inhomogeneous magnetization transfer ratio in MS lesions and in normal-appearing WM of patients compared with controls. Stronger correlations with the Expanded Disability Status Scale score were obtained with the inhomogeneous magnetization transfer ratio compared with the standard magnetization transfer ratio, which may be explained by the higher specificity of inhomogeneous magnetization transfer for myelin.

Distribution of brain sodium long and short relaxation times and concentrations: a multi-echo ultra-high field 23Na MRI study

Sodium (²³Na) MRI proffers the possibility of novel information for neurological research but also particular challenges. Uncertainty can arise in in vivo ²³Na estimates from signal losses given the rapidity of T2* decay due to biexponential relaxation with both short (T₂*_short) and long (T₂*_long) components. We build on previous work by characterising the decay curve directly via multi-echo imaging at 7 T in 13 controls with the requisite number, distribution and range to assess the distribution of both in vivo T₂*_short and T₂*_long and in variation between grey and white matter, and subregions. By modelling the relationship between signal and reference concentration and applying it to in vivo ²³Na-MRI signal, ²³Na concentrations and apparent transverse relaxation times of different brain regions were measured for the first time. Relaxation components and concentrations differed substantially between regions of differing tissue composition, suggesting sensitivity of multi-echo ²³Na-MRI toward features of tissue composition. As such, these results raise the prospect of multi-echo ²³Na-MRI as an adjunct source of information on biochemical mechanisms in both physiological and pathophysiological states.

Creatine, Glutamine plus Glutamate, and Macromolecules Are Decreased in the Central White Matter of Premature Neonates around Term

Preterm birth represents a high risk of neurodevelopmental disabilities when associated with white-matter damage. Recent studies have reported cognitive deficits in children born preterm without brain injury on MRI at term-equivalent age. Understanding the microstructural and metabolic underpinnings of these deficits is essential for their early detection. Here, we used diffusion-weighted imaging and single-voxel 1H magnetic resonance spectroscopy (MRS) to compare brain maturation at term-equivalent age in premature neonates with no evidence of white matter injury on conventional MRI except diffuse excessive high-signal intensity, and normal term neonates. Thirty-two infants, 16 term neonates (mean post-conceptional age at scan: 39.8±1 weeks) and 16 premature neonates (mean gestational age at birth: 29.1±2 weeks, mean post-conceptional age at scan: 39.2±1 weeks) were investigated. The MRI/MRS protocol performed at 1.5T involved diffusion-weighted MRI and localized 1H-MRS with the Point RESolved Spectroscopy (PRESS) sequence. Preterm neonates showed significantly higher ADC values in the temporal white matter (P<0.05), the occipital white matter (P<0.005) and the thalamus (P<0.05). The proton spectrum of the centrum semiovale was characterized by significantly lower taurine/H2O and macromolecules/H2O ratios (P<0.05) at a TE of 30 ms, and reduced (creatine+phosphocreatine)/H2O and (glutamine+glutamate)/H2O ratios (P<0.05) at a TE of 135 ms in the preterm neonates than in full-term neonates. Our findings indicate that premature neonates with normal conventional MRI present a delay in brain maturation affecting the white matter and the thalamus. Their brain metabolic profile is characterized by lower levels of creatine, glutamine plus glutamate, and macromolecules in the centrum semiovale, a finding suggesting altered energy metabolism and protein synthesis.

MRI/MRS of corpus callosum in patients with clinically isolated syndrome suggestive of multiple sclerosis

A trophy of corpus callosum (C C) related to axonal loss has previously been observed in patients at the early stage of clinically definite multiple sclerosis (CDMS). Atrophy increases with the progression of the disease. Nevertheless, no data concerning the onset of atrophy of C C are currently available. The purpose of this study is to determine if damage in callosal tissue was present at the earliest stage of MS, in a subgroup of patients presenting with a clinically isolated syndrome suggestive of MS (C ISSMS), fulfilling the dissemination in space criteria according to McDonald. Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) techniques were applied to measure C C volume, magnetization transfer ratio (MTR), mean diffusivity (MD), N-acetyl aspartate/choline-containing compounds (NAA/C ho) ratio, N-acetyl aspartate/total creatine (NA A/C r) ratio and C ho/C r ratio inside the C C of 46 C ISSMS patients and 24 sexand age-matched controls. No atrophy of C C was observed in the C ISSMS group. C C of patients was character ized by decreased MTR and increased MD. No change in the NA A/C r ratio was observed while the NA A/C ho ratio decreased and C ho/C r ratio increased in the splenium and the central anterio r part of C C. These abnormalities were present in patients with, but also without, macroscopic lesions inside the C C. O ur results indicate that diffuse structural and metabolic changes, which may be interpreted as representing predominantly myelin patho logy, occur in the C C at the earliest stage of MS before any atrophy is detected.

Onset and underpinnings of white matter atrophy at the very early stage of multiple sclerosis - a two-year longitudinal MRI/MRSI study of corpus callosum

Backgrounds Atrophy of corpus callosum (CC), a white matter structure linking the two hemispheres, is commonly observed in multiple sclerosis (MS). However, the occurrence and processes leading to this alteration are not yet determined.

Goal and methods To better characterize the onset and progression of CC atrophy from the early stage of MS, we performed a two-year follow-up magnetic resonance imaging/magnetic resonance spectroscopic imaging (MRI/MRSI) exploration of CC in 24 patients with clinically isolated syndrome. These patients were explored using the same protocol at month (M)6, M12 and M24. MRI/MRSI techniques were applied to measure CC volume, and relative concentrations of N-acetylaspartate (NAA), creatine/phosphocreatine (Cr) and choline-containing compounds (Cho). A group of matched controls was also explored.

Results Atrophy of CC, not present at baseline, was observed at M12 and progressed over the second year (M24). At baseline, a decrease in relative NAA level was observed in the anterior and posterior body of CC, with normalization during the follow-up period. In the anterior body, an increase in relative Cho level was observed, with normalization at M6. Normal relative Cr levels were observed at all time points in all sub-regions. The rate of CC atrophy was correlated with the change in the Expanded Disability Status Scale (EDSS) during the follow-up period.

Conclusion These results suggest that CC atrophy appears over a period of one year after the first acute inflammatory episode, and that this atrophy is accompanied, especially in the anterior body of CC, by a normalization of the relative Cho levels, marker of acute inflammation, and NAA levels, marker of neuronal dysfunction and/or loss.

Distribution of brain sodium accumulation correlates with disability in multiple sclerosis: a cross-sectional 23Na MR imaging study

PURPOSE

To quantify brain sodium accumulations and characterize for the first time the spatial location of sodium abnormalities at different stages of relapsing-remitting (RR) multiple sclerosis (MS) by using sodium 23 ((23)Na) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

This study was approved by the local committee on ethics, and written informed consent was obtained from all participants. Three-dimensional (23)Na MR imaging data were obtained with a 3.0-T unit in two groups of patients with RR MS-14 with early RR MS (disease duration <5 years) and 12 with advanced RR MS (disease duration >5 years)-and 15 control subjects. Quantitative assessment of total sodium concentration (TSC) levels within compartments (MS lesions, white matter [WM], and gray matter [GM]) as well as statistical mapping analyses of TSC abnormalities were performed.

RESULTS

TSC was increased inside demyelinating lesions in both groups of patients, whereas increased TSC was observed in normal-appearing WM and GM only in those with advanced RR MS. In patients, increased TSC inside GM was correlated with disability (as determined with the Expanded Disability Status Scale [EDSS] score; P = .046, corrected) and lesion load at T2-weighted imaging (P = .003, corrected) but not with disease duration (P = .089, corrected). Statistical mapping analysis showed confined TSC increases inside the brainstem, cerebellum, and temporal poles in early RR MS and widespread TSC increases that affected the entire brain in advanced RR MS. EDSS score correlated with TSC increases inside motor networks.

CONCLUSION

TSC accumulation dramatically increases in the advanced stage of RR MS, especially in the normal-appearing brain tissues, concomitant with disability. Brain sodium MR imaging may help monitor the occurrence of tissue injury and disability.

Epileptogenic brain lesions in children: the added-value of combined diffusion imaging and proton MR spectroscopy to the presurgical differential diagnosis

PURPOSE

Focal cortical dysplasia (FCD), dysembryoplastic neuroepithelial tumors (DNTs), and gangliogliomas (GGs) share many clinical features, and the presurgical differential diagnosis of these lesions using conventional magnetic resonance imaging (MRI) is challenging in some cases. The purpose of this work was thus to evaluate the capacity of diffusion-weighted imaging (DWI) and proton magnetic resonance spectroscopy (MRS) to distinguish each lesion from the others.

METHODS

Seventeen children (mean age 9.0 ± 4.7 years), who had been referred for epilepsy associated with a brain tumor and operated, were selected. Preoperative MRI examinations were performed on a 1.5 T system and included anatomical images [T2-weighted, fluid-attenuated inversion recovery (FLAIR) and T1 pre- and post-injection images] as well as DWI and MRS [echo time (TE) = 30 and 135 ms]. Apparent diffusion coefficient (ADC) values were calculated in the lesion and healthy control. MRS relative quantification consisted in normalizing each metabolite by the sum (S) of all metabolites (S(TE=135 ms) = NAA+Cr+Cho; S(TE=30 ms) = NAA+Cr+Cho+Glx+mI). Univariate and multivariate analyses were performed in order to determine which criteria could differentiate the different epileptogenic brain lesions.

RESULTS

When taken alone, none of the MRI parameters was able to distinguish each disease from the others. Conventional MRI failed classifying two patients. When adding ADC to the linear discriminant analysis (LDA), one patient was still misclassified. Complete separation of the three groups was possible when combining conventional MRI, diffusion, and MRS either at long or short TE.

CONCLUSION

This study shows the added-value of multimodal MRI and MRS in the presurgical diagnosis of epileptogenic brain lesions in children.

Frequency of cognitive impairment dramatically increases during the first 5 years of multiple sclerosis

Previous studies have demonstrated that cognitive impairment is already present in patients suffering from a clinically isolated syndrome (CIS) suggestive of multiple sclerosis (MS). However, little is known about the course of cognitive impairment after the occurrence of a CIS. In order to characterise the early evolution of cognitive impairment, the authors assessed during a 5-year follow-up period a group of 24 CIS patients with high risk of developing MS. Longitudinal neuropsychological assessment was performed at two time points (baseline and year 5) in patients and controls (baseline and year 1). At year 5, 54% of patients showed cognitive impairment against 29% at baseline. Multiple regression models showed that patients with a higher T(2) lesion load at baseline had a higher cognitive impairment at year 5. This longitudinal study performed in CIS patients showed that the frequency of cognitive impairment increases dramatically during the first 5 years following a CIS and that the cognitive status at year 5 was predictable by conventional MRI parameters recorded at baseline.

Is brain maturation comparable in fetuses and premature neonates at term equivalent age?

BACKGROUND AND PURPOSE

Improved knowledge of brain maturation in fetuses and premature neonates is crucial for the early detection of pathologies and would help determine whether MR data from the premature brain might be used to evaluate fetal maturation. Using diffusion-weighted MR imaging and (1)H-MR spectroscopy, we compared cerebral microstructure and metabolism in normal in utero fetuses imaged near term and premature neonates imaged at term equivalent.

MATERIALS AND METHODS

Forty-eight subjects were investigated: 24 in utero fetuses (mean gestational age, 37 ± 1 weeks) and 24 premature neonates (mean postconceptional age, 37 ± 1 weeks). ADC values were measured in cerebellum, pons, white matter, brain stem, basal ganglia, and thalamus. MR spectroscopy was performed in deep white matter.

RESULTS

Mean ADC values from fetuses and premature neonates were comparable except for the pons and the parietal white matter. ADC values were lower in the pons of premature neonates, whereas greater values were found in their parietal white matter compared with fetuses. Proton MR spectroscopy showed higher levels of NAA/H(2)O, Glx/H(2)O, tCr/H(2)O, and mIns/H(2)O in premature neonates compared with fetuses.

CONCLUSIONS

Our study provides evidence of subtle anomalies in the parietal white matter of healthy premature neonates. In addition, the reduced ADC values in the pons together with the increased levels of NAA/H(2)O, tCr/H(2)O, and Glx/H(2)O in the centrum semiovale suggest a more advanced maturation in some white matter regions. Our results indicate that MR data from the premature brain are not appropriate for the assessment of the fetal brain maturation.

Multiparametric differentiation of posterior fossa tumors in children using diffusion-weighted imaging and short echo-time 1H-MR spectroscopy

PURPOSE

To assess the combined value of diffusion-weighted imaging (DWI) and proton magnetic resonance spectroscopy (1H-MRS) in differentiating medulloblastoma, ependymoma, pilocytic astrocytoma, and infiltrating glioma in a pediatric population.

MATERIALS AND METHODS

A total of 17 children with untreated posterior fossa tumors (seven medulloblastoma, four infiltrating glioma, two ependymoma, and four pilocytic astrocytoma), were investigated with conventional MRI, DWI, and MRS using a single-voxel technique. Within the nonnecrotic tumor core, apparent diffusion coefficient (ADC) values using a standardized region of interest (ROI) were retrieved. Quantification of water signal and analysis of metabolite signals from MRS measurements in the same tumorous area were reviewed using multivariant linear discriminant analysis.

RESULTS

Combination of ADC values and metabolites, which were normalized using water as an internal standard, allowed discrimination between the four tumor groups with a likelihood below 1 x 10(-9). Positive predictive value was 1 in all cases. Tumors could not be discriminated when using metabolite ratios or ADC values alone, nor could they be differentiated using creatine (Cr) as an internal reference even in combination with ADC values.

CONCLUSION

Linear discriminant analysis using DWI and MRS using water as internal reference, fully discriminates the four most frequent posterior fossa tumors in children.

Structure of WM bundles constituting the working memory system in early multiple sclerosis: a quantitative DTI tractography study

Working memory impairment is frequently observed in patients with early multiple sclerosis (MS). MRI and functional MRI studies have shown that working memory impairment is mostly due to diffuse white matter (WM) damage affecting the connectivity between distant cortical areas. However, working memory deficits in early MS patients can be either completely or partly masked by compensatory functional plasticity. It seems likely that concomitantly with the WM bundle injury resulting from pathological processes, the functional plasticity present in early MS patients may be accompanied by reactive structural WM plasticity. This structural plasticity may effectively compensate for connectivity disturbances and/or contribute to functional brain reorganization. The diffusion characteristics of WM bundles involved in working memory were assessed here by performing quantitative diffusion tensor imaging (DTI) tractography on 24 patients with early relapsing-remitting MS and 15 healthy control subjects. The DTI tractography findings showed that WM connections constituting the executive system of working memory were structurally impaired (the fractional anisotropy was lower than normal and the mean diffusivity, higher than normal). A significantly larger number of connections between the left and right thalami was concurrently observed in the MS patients than in the control subjects, which suggests that the WM is endowed with reactive structural plasticity.

Relationships between gray matter metabolic abnormalities and white matter inflammation in patients at the very early stage of MS : a MRSI study

Proton magnetic resonance spectroscopic imaging ((1)H-MRSI) was used to study metabolic abnormalities inside the gray matter (GM) during or distant to white matter (WM) inflammatory processes reflected by T(1) gadolinium-enhancing lesions in patients at the very early stage of multiple sclerosis (MS). The spectroscopic examination was performed in the axial plane using a home-designed acquisition-weighted, hamming shape, 2D-SE pulse sequence (TE = 135 ms; TR = 1,600 ms). Bilateral thalami and the medial occipital cortex were explored in 35 patients (15 with and 20 without T(1)-Gd enhancing lesions) with clinically isolated syndrome suggestive of MS and in 30 controls. The mean duration since the first presenting symptom was 9.1 (+/-6.7) months. The two groups of patients (with or without T(1) Gd-enhancing lesions) did not differ in terms of time elapsed since the first clinical onset and T(2) lesion load. The spatial contamination of surrounding WM tissues was obtained in each GM region by determining the tissue component in the ROI from GM and WM probability maps smoothed with the point spread function of the MRSI acquisition. Contribution of WM signal was important (60%) inside thalami while the region centered on the medial occipital cortex was well representative of GM metabolism (>70%). Comparisons of relative metabolite levels (ratios of each metabolite over the sum of all metabolites) between all patients and controls showed significant decrease in relative N-acetyl aspartate (NAA) levels, increase in relative choline-containing compounds (Cho) levels and no change in relative creatine/phosphocreatine levels inside the three ROIs. Decrease in relative NAA levels and increase in relative Cho levels were found in patients with inflammatory activity, while no metabolic alterations were present in patients without T(1) Gd-enhancing lesions. These results suggest that abnormalities in GM metabolism observed in patients at the very early stage of MS are mainly related to neuronal dysfunction occurring during acute inflammatory processes.

Diffusion-weighted imaging in normal fetal brain maturation

Diffusion-weighted imaging (DWI) provides information about tissue maturation not seen on conventional magnetic resonance imaging. The aim of this study is to analyze the evolution over time of the apparent diffusion coefficient (ADC) of normal fetal brain in utero. DWI was performed on 78 fetuses, ranging from 23 to 37 gestational weeks (GW). All children showed at follow-up a normal neurological evaluation. ADC values were obtained in the deep white matter (DWM) of the centrum semiovale, the frontal, parietal, occipital and temporal lobe, in the cerebellar hemisphere, the brainstem, the basal ganglia (BG) and the thalamus. Mean ADC values in supratentorial DWM areas (1.68 +/- 0.05 mm(2)/s) were higher compared with the cerebellar hemisphere (1.25 +/- 0.06 mm(2)/s) and lowest in the pons (1.11 +/- 0.05 mm(2)/s). Thalamus and BG showed intermediate values (1.25 +/- 0.04 mm(2)/s). Brainstem, cerebellar hemisphere and thalamus showed a linear negative correlation with gestational age. Supratentorial areas revealed an increase in ADC values, followed by a decrease after the 30th GW. This study provides a normative data set that allows insights in the normal fetal brain maturation in utero, which has not yet been observed in previous studies on premature babies.

Infratentorial pediatric brain tumors: the value of new imaging modalities

The correct assessment of the four most frequent infratentorial brain tumors in children (medulloblastoma, ependymoma, pilocytic astrocytoma and infiltrating glioma) has always been problematic. They are known to often resemble one another on conventional magnetic resonance (MR) imaging. We tested the hypothesis whether the combined strength of diffusion-weighted imaging (DWI) and proton MR spectroscopy (MRS) could help differentiate these tumors. Seventeen children with untreated posterior fossa tumors were investigated between January 2005 and January 2006 with conventional MR imaging and combined DWI and MR spectroscopy using a single-voxel technique at short and long echo time (TE) of 30 ms and 135 ms respectively. Apparent diffusion coefficient (ADC) values were retrieved after regions of interest were manually positioned within non necrotic tumor core. Water signal was quantified and metabolite signals were compared and analyzed using linear discriminant analysis. When a combination of ADC values and normalized metabolites was used, all tumors could be discriminated against one other. This could only be achieved when metabolites were normalized using water as an internal standard. They could not be discriminated when using metabolite ratios or ADC values alone, nor could they be differentiated using creatine (Cr) as an internal reference even in combination with ADC values. In conclusion, linear discriminant analysis and multiparametric combination of DWI and MRS, although not replacing histology, fully discriminates the four most frequent posterior fossa tumors in children, but metabolites have to be normalized using water and not Cr signal as an internal reference.

Assessment of normal fetal brain maturation in utero by proton magnetic resonance spectroscopy

Cerebral maturation in the normal human fetal brain was investigated by in utero localized proton MR spectroscopy ((1)H MRS). Fifty-eight subjects at 22-39 weeks of gestational age (GA) were explored. A combination of anterior body phased-array coils (four elements) and posterior spinal coils (two to three elements) was used. Four sequences were performed (point-resolved spectroscopy (PRESS) sequence with short and long TEs (30 and 135 ms), with and without water saturation). A significant reduction in myo-inositol (myo-Ins) and choline (Cho) levels, and an increase in N-acetylaspartate (NAA) and creatine (Cr) content were observed with progressing age. A new finding is the detection of NAA as early as 22 weeks of GA. This result is probably related to the fact that oligodendrocytes (whether mature or not) express NAA, as demonstrated by in vitro studies. Cho and myo-inositol were the predominant resonances from 22 to 30 weeks and decreased gradually, probably reflecting the variations in substrate needed for membrane synthesis and myelination. The normal MRS data for the second trimester of gestation (when fetal MRI is usually performed) reported here can help determine whether brain metabolism is altered or not, especially when subtle anatomic changes are observed on conventional images.

Structural and functional surrogates of cognitive impairment at the very early stage of multiple sclerosis

Following our previous reports based on parametric MRI methods (T(2)-weighted MRI, statistical mapping analysis of magnetization transfer ratio images and functional MRI) applied to a population of 18 patients with clinically isolated syndrome suggestive of multiple sclerosis, we have reviewed the possible structural and functional surrogates of MS that could explain the subtle cognitive impairment related to attention and working memory deficits evaluated with paced auditory serial addition test (PASAT). We propose that the brain substrates underlying cognitive impairment observed at the very early stage of MS are multifactorial. Several components could influence PASAT performances in patients: i) the extent of diffuse white matter damage, ii) the location of visible and non visible lesions, iii) the connectivity efficiency between distant brain functional areas involved in working memory processes and iv) the cortical reorganization. Nevertheless, individually, each of these parameters may have few influences on PASAT performance in patients. Using a multiregression model built with independent MR parameters, a very good evaluation of PASAT scores has been obtained in this limited number of patients explaining 90% of the variance. In conclusion, the different aspects of tissue and functional pathological brain underpinnings must be accounted to monitor accurately new therapeutic strategies for the treatment of early cognitive deficits related to MS.

MRS of normal and impaired fetal brain development

Cerebral maturation in the human fetal brain was investigated by in utero localized proton magnetic resonance spectroscopy (MRS). Spectra were acquired on a clinical MR system operating at 1.5 T. Body phased array coils (four coils) were used in combination with spinal coils (two coils). The size of the nominal volume of interest (VOI) was 4.5 cm(3) (20 mm x 15 mm x 15 mm). The MRS acquisitions were performed using a spin echo sequence at short and long echo times (TE = 30 ms and 135 ms) with a VOI located within the cerebral hemisphere at the level of the centrum semiovale. A significant reduction in myo-inositol and choline and an increase in N-acetylaspartate were observed with progressive age. The normal MR spectroscopy data reported here will help to determine whether brain metabolism is altered, especially when subtle anatomic changes are observed on conventional images. Some examples of impaired fetal brain development studied by MRS are illustrated.

Magnetic resonance study of the influence of tissue damage and cortical reorganization on PASAT performance at the earliest stage of multiple sclerosis

We sought to determine the influence of tissue damage and the potential impact of cortical reorganization on the performance to the Paced Auditory Serial Addition Test (PASAT) in patients at the earliest stage of multiple sclerosis (MS). Magnetization transfer ratio (MTR) imaging and functional magnetic resonance imaging (fMRI) experiments using PASAT as paradigm were carried out in 18 patients with clinically isolated syndrome suggestive of MS (CISSMS) compared to 18 controls. MTR histogram analyses showed structural abnormalities in patients involving the normal-appearing white matter (NAWM) but also the gray matter (GM). Mean PASAT scores were significantly lower in the group of patients taken as a whole, and were correlated with the mean NAWM MTR value. No correlation was observed between PASAT scores and GM MTR. However, in the subgroup of patients with normal PASAT performance (n = 9), fMRI showed larger activations in bilateral Brodmann area 45 (BA45) and right BA44 compared to that in controls (n = 18). In these areas with potentially compensatory reorganization, the whole group of patients (n = 18) showed significantly greater activation than controls (n = 18). Activation in the right BA45 was inversely correlated with the mean NAWM MTR and the peak position of GM MTR histograms of patients. This study indicates that even at the earliest stage of MS, cortical reorganization is present inside the executive system of working memory and could tend to limit the determinant functional impact of NAWM injury on the execution of the PASAT.

Voxel-based analysis of MTR images: a method to locate gray matter abnormalities in patients at the earliest stage of multiple sclerosis

PURPOSE

To determine whether voxel-based analysis of magnetization transfer ratio (MTR) maps can provide evidence of a coherent pattern of gray matter (GM) macroscopic and microscopic tissue damage in patients at the earliest stage of multiple sclerosis (MS).

MATERIALS AND METHODS

We acquired GM MTR maps in 18 patients with clinically isolated syndrome suggestive of MS (CISSMS), and 18 sex- and age-matched healthy controls. We evaluated the clinical status of the patients using the MS functional composite score and the expanded disability status scale. A two-sample t-test (P <0.0001, k=20, uncorrected for height threshold) was used to compare GM MTR maps from patients and controls on a voxel-by-voxel basis. We then extracted data from regions with t-values above the statistical threshold to verify the significance of differences using a nonparametric Mann-Whitney U-test.

RESULTS

A between-groups comparison of GM maps revealed large abnormalities in the basal ganglia, including the bilateral thalamus, bilateral lenticular nucleus, bilateral head of caudate, and protuberance, and smaller abnormalities in the right insula, right BA 4, and left BA 40. The MTR measured in the left caudate and right insula was inversely correlated with duration following the first clinical event.

CONCLUSION

These results suggest that although MS is a multifocal demyelinating disease that affects white matter (WM), a pattern of tissue damage is present inside the GM involving predominantly basal ganglia at the earliest stage of the disease.

Local tissue damage assessed with statistical mapping analysis of brain magnetization transfer ratio: relationship with functional status of patients in the earliest stage of multiple sclerosis

BACKGROUND AND PURPOSE

In the early stage of Multiple Sclerosis (MS), conventional MR imaging parameters such as T2 lesion load fail to explain the clinical status of patients. In the present work, we aimed to determine the ability of magnification transfer imaging to better reflect the relationship between local tissue damage and functional status of MS patients.

METHODS

We performed a comparative statistical mapping analysis on brain tissue magnetization transfer ratio (MTR) data measured in 18 patients with clinically isolated syndrome suggestive of MS (CISSMS) and 18 matched control subjects.

RESULTS

In the patients with CISSMS, a pattern of significant low MTR values was observed in the white matter, corpus callosum, bilateral occipitofrontal fascicles, right fornix, right parietal white matter, external capsule, right superior longitudinal fasciculus (SLF), right inferior longitudinal fasciculus, optica radiata, parietal white matter, right cingulum, gray matter, bilateral thalamus, bilateral caudate, right insula, and left Brodmann area (BA) 8. No correlation was found between local MTR decrease and Expanded Disability Status Scale score. Significant correlations between MTR and MS Functional Composite scores (Spearman rank test, P <.05) were observed in the left BA40, right SLF, right frontal white matter, splenium, and anterior corpus callosum. Local MTR values correlated with Paced Auditory Serial Addition Test scores in the left BA40, right BA4, right SLF, and splenium.

CONCLUSION

Statistical mapping analysis of brain MTR data provides valuable information on the relationship between the location of brain tissue damage and its functional impact in patients with MS, even in the earliest stage of the disease.

High cerebral scyllo-inositol: a new marker of brain metabolism disturbances induced by chronic alcoholism

Cerebral metabolic changes that concur to motor and/or cognitive disorders in actively drinking alcoholics are not well established. We tested the hypothesis that chronic alcoholics exhibit profound alterations in the cerebral metabolism of scyllo-inositol. Brain metabolism was explored in nine actively drinking and 11 recently detoxified chronic alcoholics by in vivo brain (1)H-MRS and in vitro(1)H-MRS of blood serum and cerebrospinal fluid. The cohort was composed of individuals with acute, subacute or chronic encephalopathy or without any clinical encephalopathy. Chronic alcoholism is associated with a hitherto unrecognized accumulation of brain scyllo-inositol. Our results suggest that scyllo-inositol is produced within the central nervous system and shows a diffuse but heterogenous distribution in brain where it can persist several weeks after detoxification. Its highest levels were observed in subjects with a clinically symptomatic alcohol-related encephalopathy. When detected, brain scyllo-inositol takes part in a metabolic encephalopathy since it is associated with reduced N-acetylaspartate and increased creatine. High levels of cerebral scyllo-inositol are correlated with altered glial and neuronal metabolism. Our findings suggest that the accumulation of scyllo-inositol may precede and take part in the development of symptomatic alcoholic metabolic encephalopathy.

Multimodal magnetic resonance imaging of the central nervous system

The physiological and biochemical properties of the diseased brain that can be explored with magnetic resonance imaging (MRI) are increasing. Progress in MR-based technology affords a large panel of MRI sequences that explore different phenomena and, thus, provide complementary informations. The diagnostic accuracy of MRI is improved by the combination of all MR modalities. However, this abundance of data requires an efficient multiparametric analysis to fully achieve the goal of the multimodal strategy. We will discuss the potential impact of this advanced MRI analysis in the clinical management and the therapeutical strategies of the most common brain pathologies (intracranial tumors, multiple sclerosis, stroke, epilepsy and dementia). This non-invasive approach is of utmost importance since it already improves the diagnosis and the therapeutic choice in the management of several central nervous system diseases.

Use of proton magnetic resonance spectroscopy of the brain to differentiate gliomatosis cerebri from low-grade glioma

OBJECT

Gliomatosis cerebri (GC), a rare entity characterized by a widespread infiltration of brain by tumor, lacks objective and quantitative diagnostic criteria. Single-voxel spectroscopy and chemical shift imaging (two-dimensional proton magnetic resonance [MR] spectroscopy) were performed using both short (20- or 22-msec) and long (135-msec) echo times in nine patients suffering from GC, nine patients with low-grade gliomas (LGGs), and 25 healthy volunteers to establish the precise metabolic pattern of this uncommon brain neoplasm.

METHODS

The gliomatosis infiltration was characterized by markedly elevated levels of creatine-phosphocreatine (Cr) and mvo-inositol (Ins), a reduced level of N-acetyl aspartate (NAA), and a moderately elevated level of choline-containing compounds (Cho). This pattern differs strikingly from LGGs, which are characterized by elevated levels of Cho and Ins, markedly reduced levels of NAA, and low-to-normal Cr concentrations. Although the distinction between GC and LGG, based on histological and MR imaging criteria, is a matter of debate, MR spectroscopy produces valuable information for the differentiation between these two entities and, hence, the choice of therapeutic strategy. It also provides new insight into the pathophysiology of GC because elevated Cr and Ins levels may be related to proliferation of glial elements or, more probably, activation of normal glia. Elevated levels of Cho reflect cellular proliferation and reduced NAA corresponds to reversible neuronal injury and/or focal invasion by the tumor process.

CONCLUSIONS

Owing to the unfavorable clinical outcome associated with GC compared with that associated with LGG, the findings of this study illustrate the diagnostic and prognostic value of proton MR spectroscopy in the characterization of infiltrating gliomas.

Objective and noninvasive metabolic characterization of donor hearts by phosphorous-31 magnetic resonance spectroscopy

OBJECTIVE

The authors performed a multi-institutional, prospective, blind study on hearts from local donors to validate the feasibility and accuracy of the metabolic evaluation of human hearts by phosphorus-31 ( P) magnetic resonance spectroscopy (MRS) before transplantation.

METHODS

Twenty-one hearts were separated into two groups according to a transplantation score (TS) on the basis of the current clinical and echocardiographic evaluation as follows: TS1 (n=7), grafts for United Network for Organ Sharing (UNOS) 1 patients only; and TS2 (n=14), grafts suitable for UNOS 2 patients. All hearts were cold preserved with Celsior and underwent ex situ P MRS to measure ratios of various high-energy phosphate metabolites and the intracellular pH (pHi).

RESULTS

The total duration of the MRS procedure was 32 min, thereby not unacceptably increasing the total ischemic time for the transplanted grafts. Phosphocreatine (PCr) and inorganic phosphate (Pi ) was significantly different between the two groups (0.95+/-0.29 for TS1 and 2.05+/-0.74 for TS2). The difference in pHi was also significant (7.44+/-0.13 for TS1 and 7.64+/-0.19 for TS2).

CONCLUSIONS

Determination of PCr-Pi and pHi as markers of ischemic injury before transplantation can be considered as an objective and accurate criterion for the decision to accept or refuse heart grafts for transplantation.

[Contribution of magnetic resonance spectrometry to the diagnosis of intracranial tumors]

Magnetic resonance spectroscopy (MRS) is a method enabling the analysis of the tissue metabolic content. It may offer a more accurate diagnosis of the intracranial tumors than conventional MRI sequences. MRS of normal brain parenchyma displays 4 main metabolites: N-acetyl aspartate (neuronal marker), creatine (cellular density marker), choline (membrane activity marker) and myoinositol (glial marker); pathological processes lead to variations of the level of these metabolites and/or the appearance of abnormal metabolites (lactate), following different patterns according to pathological process involved: glioma, meningioma, metastasis, bacterial or toxoplasmic abscess, radionecrosis. The potential clinical use of this method includes positive, differential and etiological diagnosis of tumors, determination of the level of malignancy of gliomas, screening for tumor recurrence following treatment. Our laboratory has been performing MR spectroscopic explorations of brain tumors for many years. Based on this experience, we show how MRS can be routinely performed in the clinical setting, what are its limitations and potential, and what kind of information can be supplied to the clinician.

Magnetic resonance spectroscopy study of glycine pathways in nonketotic hyperglycinemia

Nonketotic hyperglycinemia is a life-threatening disorder in neonates characterized by a deficiency of the glycine cleavage system. We report on four cases of the neonatal form of the disease, which were investigated by in vitro(1)H magnetic resonance spectroscopy of blood and cerebrospinal fluid, and in vivo(1)H magnetic resonance spectroscopy of brain. The existence of glycine disposal pathways leading to an increase in lactate in fluids and creatine in fluids and brain was demonstrated. This is the first observation of elevated creatine in brain in nonketotic hyperglycinemia. A recurrent decrease of glutamine and citrate was observed in cerebrospinal fluid, which might be related to abnormal glutamine metabolism in brain. Finally, the cerebral N-acetylaspartate to myo-inositol-glycine ratio was identified as a prognostic indicator of the disease.

Regional metabolite levels of the normal posterior fossa studied by proton chemical shift imaging

MR spectroscopy of the posterior fossa is pitted with numerous technical difficulties. It is, however, of great clinical interest in the study of the degenerative diseases and tumors of this area. We have developed a method to perform 2D CSI of this area, by using a sagittal slice and a careful positioning of outer volume saturation. We performed this acquisition in 30 healthy volunteers to determine the normal metabolic ratios in five voxels of this area (mesencephalon, pons, medulla oblongata, vermis, cerebellar white matter). The main technical difficulty was magnetic field inhomogeneity in the lower brainstem generated by dental alloys. However, 88% of the voxels were of sufficient quality to be analyzed. The statistically significant regional variations were a higher NAA/Cr ratio in the pons than in the medulla oblongata, higher Cho/Cr in the pons than in the mesencephalon and higher Cho/Cr in the cerebellar white matter than in the vermis. We conclude that 2D CSI of the brainstem, although technically delicate can be performed in most patients.

Magnetic resonance spectroscopy of serum and acute-phase proteins revisited: a multiparametric statistical analysis of metabolite variations in inflammatory, infectious and miscellaneous diseases

Proton MR spectra and biochemical assays have been recorded on the sera of 40 patients and ten controls in order to document the correlation between spectroscopic and biochemical variations in selected pathologies (cancer, inflammatory and infectious diseases, diabetes). N-acetyl proton resonances are essentially generated by the N-acetyl residues of the glucidic moieties borne by the most abundant acute-phase proteins (alpha1-acid glycoprotein, alpha1-antitrypsin and haptoglobin). These resonances are not correlated to immunoglobulins A, G and M levels. Principal component analysis shows that variations in spectroscopic and biochemical data are independent markers of the inflammatory status of patients but no additional sensitivity or specificity is obtained when the two sets of data are combined.

Experimental protocol for clinical analysis of cerebrospinal fluid by high resolution proton magnetic resonance spectroscopy

High resolution magnetic resonance spectroscopy (MRS) of cerebrospinal fluid (CSF) is a non-destructive analytical method which allows rapid and simultaneous detection of molecules involved in intermediary and oxidative metabolic pathways. We developed a protocol suitable for routine MRS analysis of lyophilized CSF samples. This procedure guarantees sample integrity, from CSF collection to spectrum acquisition. MRS analysis of blood serum was included in our protocol as a complementary method to CSF analysis. This protocol can contribute to establish MRS of CSF as a new analytical tool to better understand the metabolic processes involved in neurological diseases.

Further assignment of resonances in 1H NMR spectra of cerebrospinal fluid (CSF)

A number of previously unidentified 1H NMR signals detected in CSF spectra of patients with various neurological and metabolic diseases are assigned to metabolites, drugs and drug excipients. Two-dimensional 1H NMR spectroscopy (COSY and J-resolved) is employed to resolve resonances which are hidden by superimposed peaks in one-dimensional spectra. Assignments obtained by making use of 2-D techniques, and of a 1-D 1H NMR data base created for ca. 150 authentic compounds, enable us to clarify the nature of complex signal patterns found in crowded spectral regions of CSF such as the aliphatic methyl region at ca. 1.0 ppm.

Value of Doppler echocardiography in the detection of low-grade rejections after cardiac transplantation

Modifications of the diastolic parameters pressure half-time (PHT) and isovolumic relaxation time (IVRT), recorded using cardiac Doppler echocardiography (CDE), were studied in 23 heart transplant recipients and compared to the results of 345 endomyocardial biopsies (EMB) performed on the same day. Two different protocols, analyzing respectively (1) a decrease of 20% or more in IVRT and/or PHT with respect to the mean and (2) a decrease of 20% or more in IVRT and/ or PHT with respect to its preceding value, were used to evaluate the efficiency of CDE in diagnosing mild and moderate rejections. When a mild rejection was detected by EMB, a statistically significant decrease was found in the average CDE parameter values of the patient population. However, these variations were weak and did not differ from the spontaneous variations observed in each patient in the absence of rejection. Thus, it is not surprising that the sensitivity of CDE in the detection of mild rejections was very low (45%) using the most sensitive protocol (variations of the parameters from their preceding value). We conclude that CDE alone does not seem to be sufficient to perform the noninvasive diagnosis of low-grade rejections and must be complemented by other noninvasive methods.

Rapid evaluation of ethanol content and metabolism in human plasma using quantitative proton magnetic resonance spectroscopy

Proton magnetic resonance spectroscopy (MRS) was used to assay ethanol in plasma. Ethanol concentrations determined by MRS and conventional enzymatic methods are in excellent agreement. In addition to ethanol, acetone, acetate and beta-hydroxybutyrate can be quantified simultaneously in the same sample. Proton MRS of plasma offers a rapid evaluation of human ethanol metabolism and may be useful in screening for chronic alcoholism.

Analysis of plasma lipids by NMR spectroscopy: application to modifications induced by malignant tumors

Lipid extracts of plasma were studied by 31P and 1H NMR spectroscopy at 9.4 T. Signals recorded on lipid mixtures were assigned to different lipid classes using a data base built with two-dimensional 1H COSY spectra of seven standard lipids. Signals unique to glycerophospholipids, sphingolipids, and triacylglycerols were identified. 31P and 1H NMR spectroscopy was used to study qualitative and quantitative modifications induced in plasma by malignant tumors. The results show a significant increase in triglyceride/phospholipid ratio and a concomitant decrease of total phospholipids in patients with cancer. In order to check for the possible presence of particular lipids such as glycolipids in these patients, 1H COSY spectra were recorded on the intact plasma and on extracts of plasma lipids in patients with cancer and in healthy subjects. Only in one case of ovarian cancer, a cross-peak at 1.35 and 4.15 ppm, corresponding to fucose residue in glycolipids, was detected.

Graphic-aided study of metabolic modifications of plasma in cancer using proton magnetic resonance spectroscopy

Proton high-resolution MRS of human plasma allows the rapid detection, on the same spectrum, of many compounds originating from different metabolic pathways. In this paper, we illustrate the modifications of the plasma metabolic profiles recorded by proton NMR spectroscopy in different classes of cancers. These modifications can be easily monitored with graphic aids such as 'star plots' which define for each type of cancer a particular pattern describing the most altered metabolic pathways. By using 'star plots' three types of metabolic patterns have been distinguished: (i) the 'inflammatory' pattern characterized by an increase of glycosylated moieties of glycoproteins; (ii) a 'lipid modified' pattern, characterized by various modifications occurring mainly in the lipid moieties detected by MRS; and (iii) a pattern which is often observed in sarcomas and mainly characterized by an alteration in the N-acetyl glucosamine/N-acetyl neuraminic acid ratio. This study demonstrates the ability of proton MRS of plasma to rapidly detect the occurrence of metabolic modifications brought about by cancer evolution or therapy.

[Plasma glycosylated residues demonstrated by proton NMR spectroscopy. Value in the detection of heart graft rejection]

In conjunction with biopsy and Doppler studies, we analysed by high resolution proton NMR spectroscopy the blood plasma of 22 heart transplant recipients. There was a significant variation in the glycosylated residues of proteins with the development of acute cardiac rejection. A more extensive study is underway to assess the sensitivity and specificity of this approach for the early diagnosis of acute cardiac rejection.