1,720,993 research outputs found
The impact of white matter fiber orientation in single-acquisition quantitative susceptibility mapping
No full textThe aim of this work was to assess the impact of tissue structural orientation on quantitative susceptibility mapping (QSM) reliability, and to provide a criterion to identify voxels in which measures of magnetic susceptibility (Ï) are most affected by spatial orientation effects. Four healthy volunteers underwent 7-T magnetic resonance imaging (MRI). Multi-echo, gradient-echo sequences were used to obtain quantitative maps of frequency shift (FS) and Ï. Information from diffusion tensor imaging (DTI) was used to investigate the relationship between tissue orientation and FS measures and QSM. After sorting voxels on the basis of their fractional anisotropy (FA), the variations in FS and Ï values over tissue orientation were measured. Using a K-means clustering algorithm, voxels were separated into two groups depending on the variability of measures within each FA interval. The consistency of FS and QSM values, observed at low FA, was disrupted for FAÂ >Â 0.6. The standard deviation of Ï measured at high FA (0.0103Â ppm) was nearly five times that at low FA (0.0022Â ppm). This result was consistent through data across different head positions and for different brain regions considered separately, which confirmed that such behavior does not depend on structures with different bulk susceptibility oriented along particular angles. The reliability of single-orientation QSM anticorrelates with local FA. QSM provides replicable values with little variability in brain regions with FAÂ <Â 0.6, but QSM should be interpreted cautiously in major and coherent fiber bundles, which are strongly affected by structural anisotropy and magnetic susceptibility anisotropy
The motor band sign differentiates hereditary spastic paraplegia from the others upper motor neuron syndromes
No full textDetection of pathological contrast enhancement with synthetic brain imaging from quantitative multiparametric MRI
No full textBackground and PurposeWe aimed to test whether synthetic T1-weighted imaging derived from a post-contrast Quantitative Transient-state Imaging (QTI) acquisition enabled revealing pathological contrast enhancement in intracranial lesions.MethodsThe analysis included 141 patients who underwent a 3 Tesla-MRI brain exam with intravenous contrast media administration, with the post-contrast acquisition protocol comprising a three-dimensional fast spoiled gradient echo (FSPGR) sequence and a QTI acquisition. Synthetic T1-weighted images were generated from QTI-derived quantitative maps of relaxation times and proton density. Two neuroradiologists assessed synthetic and conventional post-contrast T1-weighted images for the presence and pattern of pathological contrast enhancement in intracranial lesions. Enhancement volumes were quantitatively compared.ResultsUsing conventional imaging as a reference, synthetic T1-weighted imaging was 93% sensitive in revealing the presence of contrast enhancing lesions. The agreement for the presence/absence of contrast enhancement was almost perfect both between readers (k = 1 for both conventional and synthetic imaging) and between sequences (k = 0.98 for both readers). In 91% of lesions, synthetic T1-weighted imaging showed the same pattern of contrast enhancement visible in conventional imaging. Differences in enhancement pattern in the remaining lesions can be due to the lower spatial resolution and the longer acquisition delay from contrast media administration of QTI compared to FSPGR. Overall, enhancement volumes appeared larger in synthetic imaging.ConclusionsQTI-derived post-contrast synthetic T1-weighted imaging captures pathological contrast enhancement in most intracranial enhancing lesions. Further comparative studies employing quantitative imaging with higher spatial resolution is needed to support our data and explore possible future applications in clinical trials
Studying Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis with 7-T magnetic resonance
Get PDFAbstract Ultra-high-field (UHF) magnetic resonance (MR) scanners, that is, equipment operating at static magnetic field of 7 tesla (7 T) and above, enable the acquisition of data with greatly improved signal-to-noise ratio with respect to conventional MR systems (e.g., scanners operating at 1.5 T and 3 T). The change in tissue relaxation times at UHF offers the opportunity to improve tissue contrast and depict features that were previously inaccessible. These potential advantages come, however, at a cost: in the majority of UHF-MR clinical protocols, potential drawbacks may include signal inhomogeneity, geometrical distortions, artifacts introduced by patient respiration, cardiac cycle, and motion. This article reviews the 7 T MR literature reporting the recent studies on the most widespread neurodegenerative diseases: Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis
Present and future of ultra-high field mri in neurodegenerative disorders
No full textPurpose of Review With a high signal-to-noise ratio, unparalleled spatial resolution, and improved contrasts, ultra-high field MR (≥ 7 T) has great potential in depicting the normal radiological anatomy of smaller structures in the brain and can also provide more information about morphological, quantitative, and metabolic changes associated with a wide range of brain disorders. By focusing attention on specific brain regions believed to be associated with early pathological change, or by more closely inspecting recognized foci of brain pathology, ultra-high field MR can improve the accuracy and sensitivity of neuroimaging. This article reviews recent studies at ultra-high field about Alzheimer’s disease (AD), Parkinson’s disease (PD), and amyotrophic lateral sclerosis (ALS). Recent Findings The research on AD has mainly focused on detecting the thinning of hippocampal layers and the susceptibility effect supposed to be related to beta-amyloid deposition. In patients with PD, atypical parkinsonisms and subjects at risk of developing motor symptoms of Parkinson’s disease, the main aim was to detect changes in the substantia nigra, probably related to increased iron deposition. In patients with ALS, both brain and spinal cord were investigated, with the aim of finding changes in the primary motor cortex and corticospinal tract which reflect neurodegeneration and neuroinflammation. Summary Ultra-high field MR was shown to be useful for detecting subtle brain changes in patients with AD, and possible new diagnostic biomarkers in patients with PD and ALS were discovered. The ability of 7 T MR to provide prognostic biomarkers in subjects at risk for developing synucleinopathies is currently under evaluation
Occurrence of IgG oligoclonal bands in upper motor neuron disease: just by chance?
No full textIntroduction: Several mechanisms have been proposed to explain the pathogenesis of motor neuron disease (MND), including neuroinflammatory processes. Although results from routine cerebrospinal fluid (CSF) analysis are usually unremarkable, several studies have shown that oligoclonal bands (OCBs), indicating intrathecal synthesis of IgG, can be detected in 0.5–2 % of all MND cases. Case-reports: Here we report two cases of pure upper MND presenting with CSF OCBs. The first case is a 63 yrs-old woman that showed slowly progressive spastic paraparesis, dysarthria and swallowing disorders. Brain MRI showed unspecific little white matter lesions, spine MRI showed no lesion. DNA analysis for hereditary spastic paraparesis and for spinocerebellar diseases was negative. Needle elecromyography was normal, as was cerebral PET-FDG scan. CSF showed one OCB. The second case is a 69 yrs-old man that soon after a flu episode developed transitory thoracic dysesthesia and a progressive spastic paraparesis. Conventional brain and spine MRI were negative. The motor evoked potential showed pyramidal pattern. EMG was normal. Paraneoplastic markers and Hu, Yo, Ri antibodies were negative. At CSF two OCBs were detected. 7 Tesla MRI showed signal hypointensity and thinning of the primary motor cortex. There was no evidence of autoimmune, infectious or inflammatory diseases of the CNS in both cases. Paraproteinemia, lymphoma or any other systemic inflammatory or infectious conditions were also excluded. The first case did not improve with corticosteroid therapy, while the second responded only partially. The response to the intravenous Ig therapy was poor in both cases. Discussion: Intrathecal synthesis of OCBs is suggestive of a local humoral immune response, and is a common feature of multiple sclerosis and other chronic inflammatory or infectious diseases of the CNS, but is rarely detected in neurodegenerative diseases such as MND. This finding has been previously explained either by a former infection of the CNS, a concurrent paraproteinemia, a sign for a systemic infection, but also as an unspecific alteration. A recent study describes the occurrence of OCBs in ALS patients harboring TARDBP and ANG mutations, speculating the involvement of these genes on blood–brain barrier integrity. While it is not clear if there are differences in CSF profile between distinct motor neuron diseases (ALS, pure lower or pure upper MND, and hereditary spastic paraplegia), in TARDBP and ANG patients with OCBs there are evidences of a prevalent upper motor neuron involvement with unspecific white matter lesions and worst prognosis
Time-of-flight MRA of intracranial vessels at 7 T
No full textBackground: Three-dimensional time-of-flight magnetic resonance angiography (TOF-MRA) is a largely adopted non-invasive technique for assessing cerebrovascular diseases. We aimed to optimize the 7-T TOF-MRA acquisition protocol, confirm that it outperforms conventional 3-T TOF-MRA, and compare 7-T TOF-MRA with digital subtraction angiography (DSA) in patients with different vascular pathologies. Methods: Seven-tesla TOF-MRA sequences with different spatial resolutions acquired in four healthy subjects were compared with 3-T TOF-MRA for signal-to-noise and contrast-to-noise ratios as well as using a qualitative scale for vessel visibility and the quantitative Canny algorithm. Four patients with cerebrovascular disease (primary arteritis of the central nervous system, saccular aneurism, arteriovenous malformation, and dural arteriovenous fistula) underwent optimized 7-T TOF-MRA and DSA as reference. Images were compared visually and using the complex-wavelet structural similarity index. Results: Contrast-to-noise ratio was higher at 7 T (4.5 ± 0.8 (mean ± standard deviation)) than at 3 T (2.7 ± 0.9). The mean quality score for all intracranial vessels was higher at 7 T (2.89) than at 3 T (2.28). Angiogram quality demonstrated a better vessel border detection at 7 T than at 3 T (44,166 versus 28,720 pixels). Of 32 parameters used for diagnosing cerebrovascular diseases on DSA, 27 (84%) were detected on 7-T TOF-MRA; the similarity index ranged from 0.52 (dural arteriovenous fistula) to 0.90 (saccular aneurysm). Conclusions: Seven-tesla TOF-MRA outperformed conventional 3-T TOF-MRA in evaluating intracranial vessels and exhibited an excellent image quality when compared to DSA. Seven-tesla TOF-MRA might improve the non-invasive diagnostic approach to several cerebrovascular diseases. Relevance statement: An optimized TOF-MRA sequence at 7 T outperforms 3-T TOF-MRA, opening perspectives to its clinical use for noninvasive diagnosis of paradigmatic pathologies of intracranial vessels. Key points: • An optimized 7-T TOF-MRA protocol was selected for comparison with clinical 3-T TOF-MRA for assessing intracranial vessels. • Seven-tesla TOF-MRA outperformed 3-T TOF-MRA in both quantitative and qualitative evaluation. • Seven-tesla TOF-MRA is comparable to DSA for the diagnosis and characterization of intracranial vascular pathologies. Graphical Abstract: (Figure presented.
Distribution Indices of Magnetic Susceptibility Values in the Primary Motor Cortex Enable to Classify Patients with Amyotrophic Lateral Sclerosis
Get PDFQuantitative Susceptibility Mapping (QSM) can measure iron concentration increase in the primary motor cortex (M1) of patients with Amyotrophic Lateral Sclerosis (ALS). However, such alteration is confined to only specific regions interested by upper motor neuron pathology; therefore, mean QSM values in the entire M1 have limited diagnostic accuracy in discriminating between ALS patients and control subjects. This study investigates the diagnostic accuracy of a broader set of M1 QSM distribution indices in classifying ALS patients and controls. Mean, standard deviation, skewness and kurtosis of M1 QSM values were used either individually or as combined predictors in support vector machines. The classification performance was compared to that obtained by the radiological assessment of T2* signal hypo-intensity of M1 in susceptibility-weighted MRI. The least informative index for the classification of ALS patients and controls was the subject’s mean QSM value in M1. The highest diagnostic performance was obtained when all the distribution indices of positive QSM values in M1 were considered, which yielded a diagnostic accuracy of 0.90, with sensitivity = 0.89 and specificity = 1. The radiological assessment of M1 yielded a diagnostic accuracy of 0.79, with sensitivity = 0.76 and specificity = 0.90. The joint evaluation of QSM distribution indices could support the clinical examination in ALS diagnosis and patient monitoring
Hippocampal subfields at ultra high field MRI: An overview of segmentation and measurement methods
Get PDFThe hippocampus is one of the most interesting and studied brain regions because of its involvement in memory functions and its vulnerability in pathological conditions, such as neurodegenerative processes. In the recent years, the increasing availability of Magnetic Resonance Imaging (MRI) scanners that operate at ultra-high field (UHF), that is, with static magnetic field strength ≥7T, has opened new research perspectives. Compared to conventional high-field scanners, these systems can provide new contrasts, increased signal-to-noise ratio and higher spatial resolution, thus they may improve the visualization of very small structures of the brain, such as the hippocampal subfields. Studying the morphometry of the hippocampus is crucial in neuroimaging research because changes in volume and thickness of hippocampal subregions may be relevant in the early assessment of pathological cognitive decline and Alzheimer's Disease (AD). The present review provides an overview of the manual, semi-automated and fully automated methods that allow the assessment of hippocampal subfield morphometry at UHF MRI, focusing on the different hippocampal segmentation produced. © 2017 Wiley Periodicals, Inc
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