Frank Träber

1H metabolite relaxation times at 3.0 tesla: Measurements of T1 and T2 values in normal brain and determination of regional differences in transverse relaxation

To measure 1H relaxation times of cerebral metabolites at 3 T and to investigate regional variations within the brain.

Dual-Source Parallel Radiofrequency Excitation Body MR Imaging Compared with Standard MR Imaging at 3.0 T: Initial Clinical Experience

PURPOSE To prospectively compare the image quality and homogeneity of magnetic resonance (MR) images obtained by using a dual-source parallel radiofrequency (RF) excitation body MR imaging system with parallel transmission and independent RF shimming with the image quality and homogeneity of single-source MR images obtained by using standard sequences for routine clinical use in patients at 3.0 T. MATERIALS AND METHODS After institutional review board approval and informed patient consent were obtained, a dual-source parallel RF excitation 3.0-T MR system with independent RF shimming and parallel transmission technology was used to examine 28 patients and was compared with a standard 3.0-T MR system with single RF transmission. The RF power was distributed to the independent ports of the system body coil by using two RF transmission sources with full software control, enabling independent control of the phase and amplitude of the RF waveforms. Axial T2-weighted fast spin-echo (SE) and diffusion-weighted (DW) liver images, axial T2-weighted fast SE pelvic images, and sagittal T1- and T2-weighted fast SE spinal images were obtained by using dual- and single-source RF excitation. Two radiologists independently evaluated the images for homogeneity and image quality. Statistical significance was calculated by using the nonparametric Wilcoxon signed rank test. Interobserver agreement was determined by using Cohen kappa and Kendall tau-b tests. RESULTS Image quality comparisons revealed significantly better results with dual-source rather than single-source RF excitation at T2-weighted liver MR imaging (P = .001, kappa = 1.00) and better results at DW liver imaging at a statistical trend level (P = .066, tau-b > 0.7). Owing to reduced local energy deposition, fewer acquisitions and shorter repetition times could be implemented with dual-source RF excitation pelvic and spinal MR imaging, with image acquisition accelerating by 18%, 33%, and 50% compared with the acquisitions with single-source RF excitation. Image quality did not differ significantly between the two MR techniques (P > .05, tau-b > 0.5). CONCLUSION Dual-source parallel RF excitation body MR imaging enables reduced dielectric shading, improved homogeneity of the RF magnetic induction field, and accelerated imaging at 3.0 T.

Improved in vivo detection of cortical lesions in multiple sclerosis using double inversion recovery MR imaging at 3 Tesla

ObjectiveTo investigate the impact of a higher magnetic field strength of 3 Tesla (T) on the detection rate of cortical lesions in multiple sclerosis (MS) patients, in particular using a dedicated double inversion recovery (DIR) pulse sequence.MethodsThirty-four patients with clinically isolated syndromes or definite MS were included. All patients underwent magnetic resonance imaging (MRI) at 1.5 T and 3 T, including T2-weighted turbo spin echo (TSE), fluid-attenuated inversion recovery (FLAIR) and DIR sequences. All images were analysed for focal lesions categorised according to their anatomical location.ResultsThe total number of detected lesions was higher at 3 T across all pulse sequences. We observed significantly higher numbers of lesions involving the cortex at 3 T using a DIR sequence. DIR at 3 T showed 192% more pure intracortical (p < 0.001) and 30% more mixed grey matter-white matter lesions (p = 0.008). No significant increase in cortical lesions could be detected on the FLAIR and T2-weighted images. Using the T2-weighted and FLAIR sequences, significantly more lesions could be detected at 3 T in the infratentorial, periventricular and juxtacortical white matter.ConclusionDIR brain MR imaging at 3 T substantially improves the sensitivity of the detection of cortical lesions compared with the standard magnetic field strength of 1.5 T.

Whole-Body High-Field-Strength (3.0-T) MR Imaging in Clinical Practice Part II. Technical Considerations and Clinical Applications

In the year 2002, magnetic field strength of more than 2 T was cleared for clinical patient care. Since then, an increasing number of magnetic resonance (MR) systems operating at a field strength of 3.0 T (and higher) have been installed worldwide. This article is the first of a two-part series on clinical high-field-strength MR imaging. Some basic physical effects of higher magnetic fields as they pertain to clinical MR imaging and spectroscopy are reviewed, from the perspective of a clinical radiologist, and strategies that are useful to avoid magnetic field-related difficulties and artifacts are discussed. Advantages and downsides, which can be expected for clinical MR, are presented and compared with the current level of evidence based on published data about MR of the brain and MR angiography. In the second part of the series, clinical applications regarding cardiac, breast, musculoskeletal, abdominopelvic, and pediatric MR and MR spectroscopy will be presented.

Diffusion-weighted whole-body MR imaging with background body signal suppression: a feasibility study at 3.0 Tesla

The purpose was to provide a diffusion-weighted whole-body magnetic resonance (MR) imaging sequence with background body signal suppression (DWIBS) at 3.0 Tesla. A diffusion-weighted spin-echo echo-planar imaging sequence was combined with the following methods of fat suppression: short TI inversion recovery (STIR), spectral attenuated inversion recovery (SPAIR), and spectral presaturation by inversion recovery (SPIR). Optimized sequences were implemented on a 3.0- and a 1.5-Tesla system and evaluated in three healthy volunteers and six patients with various lesions in the neck, chest, and abdomen on the basis of reconstructed maximum intensity projection images. In one patient with metastases of malignant melanoma, DWIBS was compared with 18F-fluorodeoxyglucose positron emission tomography (FDG-PET). Good fat suppression for all regions and diagnostic image quality in all cases could be obtained at 3.0 Tesla with the STIR method. In comparison with 1.5 Tesla, DWIBS images at 3.0 Tesla were judged to provide a better lesion-to-bone tissue contrast. However, larger susceptibility-induced image distortions and signal intensity losses, stronger blurring artifacts, and more pronounced motion artifacts degraded the image quality at 3.0 Tesla. A good correlation was found between the metastases as depicted by DWIBS and those as visualized by FDG-PET. DWIBS is feasible at 3.0 Tesla with diagnostic image quality.

Proton MR spectroscopy of the hippocampus at 3 T in patients with unipolar major depressive disorder: correlates and predictors of treatment response.

Various lines of research suggest that neurotrophic processes in the hippocampus are key mechanisms in major depressive disorder and are of relevance for response to antidepressive treatment. We performed proton magnetic resonance spectroscopy (1H-MRS) of the hippocampus at 3 T in 18 unmedicated subjects with unipolar major depressive episodes and in 10 age- and gender-matched healthy volunteers. Thirteen patients underwent a second examination after 8 wk treatment with either citalopram (n=7) or nortriptyline (n=6). Of these patients, 11 MRS datasets could be used for the assessment of treatment correlates. In the cross-sectional comparison, we observed a significant reduction of the metabolic ratios Glx/Cr (Glx=glutamine, glutamate and gamma-aminobutyric acid) and glutamine (Gln)/Cr in the patient group. The Gln/Glx ratio also showed a trend towards significant reduction. The individual effect of treatment correlated with an increase in the absolute concentrations of N-acetylaspartate (NAA) and of choline compounds (Cho). Low baseline NAA and Cho levels predicted positive treatment effects. There was no difference in any clinical or metabolic measure, either at baseline or at follow-up between the two treatment groups (citalopram, nortriptyline). Our data provide first evidence for a reduction of Gln in the hippocampus of subjects with major depression. Furthermore, we provide first evidence in patients with major depression for neurorestorative effects in the hippocampus by pharmacological treatment expressed by a correlation of NAA and Cho increases with treatment response. This accounts in particular for those patients with low NAA and Cho baseline levels.

Diagnostic imaging of patients in a memory clinic: comparison of MR imaging and 64-detector row CT.

PURPOSE To investigate the assessment of global cortical atrophy (GCA), medial temporal lobe atrophy (MTA), and white matter changes (WMCs) in patients screened at a memory clinic with a 64-detector row computed tomography (CT) brain protocol, in comparison with the reference standard, magnetic resonance (MR) imaging. MATERIALS AND METHODS The study protocol was approved by the local institutional review board. Written informed consent was obtained from all participants. Thirty patients (21 men, nine women; median age, 62 years) who presented to a memory clinic underwent 64-detector row CT and multisequence MR imaging of the brain on the same day. Three readers blinded to the clinical diagnosis assessed the resultant images. Images were presented in random order and scored for GCA, MTA, and WMC with published visual rating scales. Intermodality agreement between CT and MR imaging (intrareader agreement across both modalities), expressed by weighted kappa analysis, and interobserver agreement within each modality between readers (Kendall W test) were assessed. RESULTS Overall, excellent intraobserver agreement between CT and MR imaging was observed for GCA (mean kappa, 0.83) and MTA (mean kappa, 0.88 and 0.86 on the left and right sides of the brain, respectively). There was substantial overall agreement concerning WMC (mean kappa, 0.79). For all three tested scales, interobserver variability was low and comparable for CT and MR imaging. CONCLUSION Use of 64-detector row brain CT yields reliable information that is comparable with that obtained with MR imaging. Thus, multidetector row CT is a suitable diagnostic imaging tool in a memory clinic setting.

In-vivo proton MR-spectroscopy of the human brain: Assessment of N-acetylaspartate (NAA) reduction as a marker for neurodegeneration

Summary. Proton magnetic resonance spectroscopy (1H-MRS) is a non-invasive method to investigate changes in brain metabolite composition in different cerebral diseases.We performed proton spectroscopy in patients with dementia of the Alzheimers type (AD) and in patients with motor neuron disease (MND) with the aim to detect the specific metabolic pattern for these neurodegenerative disorders.In the MND group we found a significant reduction of NAA/tCr metabolite ratios in the motor cortex, which correlates with the disease severity and the clinical lateralization of neurological symptoms and further decreases in the time course of the disease. In AD patients a reduction of NAA/tCr was observed in the medial temporal lobe.Since NAA is exclusively expressed in neurons as shown by immunohistochemical studies, reduced NAA levels suggest neuronal loss or dysfunction in the observed regions.The observed regional metabolic alterations reflect the neuronal basis of the characteristic neurological symptoms in AD (dementia) and MND (muscular palsy) and mirrors the disease progress over time.

Proton magnetic resonance spectroscopy in subjects at risk for schizophrenia

We used proton magnetic resonance spectroscopy (1H MRS) to examine biochemical characteristics of the brain tissue in subjects at risk for schizophrenia. Nineteen participants fulfilling research criteria for an early (n=10) or a late (n=9) at-risk syndrome, 21 patients with full disease according to DSM IV and 31 healthy control subjects were included in the study. Single-voxel 1H MRS was performed in the left frontal lobe, the anterior cingulate gyrus and the left superior temporal lobe. Subjects were followed longitudinally to detect conversion to schizophrenia. We observed a significant reduction of the metabolic ratios NAA/Cr and NAA/Cho in the left frontal lobe and of NAA/Cr in the anterior cingulate gyrus in both at-risk groups and in the schizophrenic patients compared with healthy controls. Those at-risk subjects, who converted to schizophrenia within the observation period, had a higher Cho/Cr and a lower NAA/Cho ratio in the anterior cingulate gyrus compared with non-converters. NAA/Cr did not differ between converters and non-converters. Six at-risk subjects were taking antidepressants, two were taking antipsychotics. There was no difference in any metabolic ratio in any region between at-risk subjects with and without medication. We conclude that the reduction of the neuronal marker NAA in the left prefrontal lobe and the anterior cingulate gyrus may represent a vulnerability indicator for schizophrenia in at-risk subjects, while elevated Cho in the anterior cingulate gyrus may be a predictor for conversion from the prodromal state to the full disease.

Decreased frontal lobe ratio of N-acetyl aspartate to choline in familial schizophrenia : a proton magnetic resonance spectroscopy study

Neuropathological and neuroimaging studies suggest neuronal dysfunction in schizophrenia. N-acetyl aspartate (NAA) is a useful marker of neuronal dysfunction that can be measured with magnetic resonance spectroscopy (MRS). In the present study NAA, choline (Cho), phospho-creatine ((P)Cr), inositol containing compounds and glutamine/glutamate (Glx) were assessed in the left frontal lobe and basal ganglia of subjects with familial schizophrenia, family members with mixed psychiatric diagnoses, unaffected family members, and community controls. Concentrations of metabolites were analyzed and expressed as ratios. NAA/Cho, NAA/(P)Cr and Glx containing compounds showed a negative correlation with age in the frontal lobe. After covarying for age, subjects with schizophrenia had a significant reduction in the left frontal lobe NAA/Cho ratio compared with unaffected family members (P=0.018) as well as with community non-familial (P=0.037) controls. These MRS observations support the hypothesis of a disease-related neuronal deficit in the frontal lobe of schizophrenic patients, and relatively normal basal ganglia.