The 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 (χ) 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 χ. 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 χ 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 FA > 0.6. The standard deviation of χ measured at high FA (0.0103 ppm) was nearly five times that at low FA (0.0022 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 FA < 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.
This magnetic resonance imaging (MRI) study demonstrates the anticorrelation between the fractional anisotropy (FA) and the reliability of quantitative susceptibility mapping (QSM) in the human brain at 7 T. QSM measures exhibit a large variability depending on the tissue spatial orientation in voxels with FA > 0.6, which usually correspond to major, highly myelinated fiber bundles. Hence, in these regions, QSM should be interpreted with care, but measures of χ have little variability elsewhere in the brain.
In the last 20 years, ultra-high field (UHF) magnetic resonance imaging (MRI) has become an outstanding research tool for the study of the human brain, with 90 of these scanners installed today, ...worldwide. The recent clearances from regulatory bodies in the USA and Europe to 7-T clinical systems have set the ground for a transition from pure research applications to research and clinical use of these systems. As today, UFH neuroimaging is demonstrating clinical value and, given the importance of this topic for both preclinical scientists and clinical neuroradiologists,
European Radiology Experimental
is launching a thematic series entitled “7-T neuro MRI: from research to clinic”, consisting of peer-reviewed articles, invited or spontaneously submitted, on topics selected by the guest editors, describing the state of the art of UHF MRI neuroimaging across different pathologies, as well as related clinical applications. In this editorial, we discuss some of the challenges related to the clinical use of 7-T scanners and the strengths and weaknesses of clinical imaging at UHF.
Background:
Brain magnetic resonance imaging (MRI) is the most effective surveillance tool for the detection of asymptomatic progressive multifocal leukoencephalopathy (PML). However, the optimal ...frequency for routine MRI surveillance is under-investigated.
Objective:
To understand whether, upon their first MRI appearance, PML lesions present a difference in volume when comparing patients who frequently underwent MRI surveillance (3/4 months) with those who were assessed at longer intervals (6/12 months) and to understand the impact of the volume of lesions on clinical outcome.
Methods:
The data of patients included in the Italian PML cohort were retrospectively analysed. Patients who had all the pre-diagnostic MRI scans available (n = 37) were included. The volume of PML lesion was calculated by manually outlining the PML lesion.
Results:
Compared with patients who underwent MRI examination at least every 4 months, patients who were assessed less frequently had a lesion of significantly higher volume (median: 2567 (883–3583) vs. 664 mm3 (392–963) p = 0.006) and suffered a higher rate of disability (median: 2.25 expanded disability status scale points (–2.5 to 8) vs. 0.5 (–1 to 2.5) p = 0.004).
Conclusion:
The positive clinical outcome of patients undergoing frequent MRI surveillance and the small volume of the PML lesion upon first appearance justify a frequent surveillance using MRI in patients at high risk of PML.
How conceptual knowledge is represented in the human brain remains to be determined. To address the differential role of low-level sensory-based and high-level abstract features in semantic ...processing, we combined behavioral studies of linguistic production and brain activity measures by functional magnetic resonance imaging in sighted and congenitally blind individuals while they performed a property-generation task with concrete nouns from eight categories, presented through visual and/or auditory modalities.
Patterns of neural activity within a large semantic cortical network that comprised parahippocampal, lateral occipital, temporo-parieto-occipital and inferior parietal cortices correlated with linguistic production and were independent both from the modality of stimulus presentation (either visual or auditory) and the (lack of) visual experience. In contrast, selected modality-dependent differences were observed only when the analysis was limited to the individual regions within the semantic cortical network.
We conclude that conceptual knowledge in the human brain relies on a distributed, modality-independent cortical representation that integrates the partial category and modality specific information retained at a regional level.
•Brain responses measured during multimodal semantic processing in sighted and blind.•Conceptual knowledge shows similar representations across modalities in both groups.•Regional representations still retain category- and sensory-based information.•Semantic information relies on a distributed, modality-independent representation.
Summary
Our inability to adequately treat many patients with refractory epilepsy caused by focal cortical dysplasia (FCD), surgical inaccessibility and failures are significant clinical drawbacks. ...The targeting of physiologic features of epileptogenesis in FCD and colocalizing functionality has enhanced completeness of surgical resection, the main determinant of outcome. Electroencephalography (EEG)–functional magnetic resonance imaging (fMRI) and magnetoencephalography are helpful in guiding electrode implantation and surgical treatment, and high‐frequency oscillations help defining the extent of the epileptogenic dysplasia. Ultra high‐field MRI has a role in understanding the laminar organization of the cortex, and fluorodeoxyglucose–positron emission tomography (FDG‐PET) is highly sensitive for detecting FCD in MRI‐negative cases. Multimodal imaging is clinically valuable, either by improving the rate of postoperative seizure freedom or by reducing postoperative deficits. However, there is no level 1 evidence that it improves outcomes. Proof for a specific effect of antiepileptic drugs (AEDs) in FCD is lacking. Pathogenic mutations recently described in mammalian target of rapamycin (mTOR) genes in FCD have yielded important insights into novel treatment options with mTOR inhibitors, which might represent an example of personalized treatment of epilepsy based on the known mechanisms of disease. The ketogenic diet (KD) has been demonstrated to be particularly effective in children with epilepsy caused by structural abnormalities, especially FCD. It attenuates epigenetic chromatin modifications, a master regulator for gene expression and functional adaptation of the cell, thereby modifying disease progression. This could imply lasting benefit of dietary manipulation. Neurostimulation techniques have produced variable clinical outcomes in FCD. In widespread dysplasias, vagus nerve stimulation (VNS) has achieved responder rates >50%; however, the efficacy of noninvasive cranial nerve stimulation modalities such as transcutaneous VNS (tVNS) and noninvasive (nVNS) requires further study. Although review of current strategies underscores the serious shortcomings of treatment‐resistant cases, initial evidence from novel approaches suggests that future success is possible.
Purpose
To obtain three‐dimensional (3D), quantitative and motion‐robust imaging with magnetic resonance fingerprinting (MRF).
Methods
Our acquisition is based on a 3D spiral projection k‐space ...scheme. We compared different orderings of trajectory interleaves in terms of rigid motion‐correction robustness. In all tested orderings, we considered the whole dataset as a sum of 56 segments of 7‐s duration, acquired sequentially with the same flip angle schedule. We performed a separate image reconstruction for each segment, producing whole‐brain navigators that were aligned to the first segment using normalized correlation. The estimated rigid motion was used to correct the k‐space data, and the aligned data were matched with the dictionary to obtain motion‐corrected maps.
Results
A significant improvement on the motion‐affected maps after motion correction is evident with the suppression of motion artifacts. Correlation with the motionless baseline improved by 20% on average for both T1 and T2 estimations after motion correction. In addition, the average motion‐induced quantification bias of 70 ms for T1 and 18 ms for T2 values was reduced to 12 ms and 6 ms, respectively, improving the reliability of quantitative estimations.
Conclusion
We established a method that allows correcting 3D rigid motion on a 7‐s timescale during the reconstruction of MRF data using self‐navigators, improving the image quality and the quantification robustness.
Objectives
The aim of this study was to evaluate the capability of sequences acquired on a 7-T MRI scanner, within times and anatomical coverage appropriate for clinical studies, to identify cortical ...lesions (CLs) in patients with Multiple Sclerosis (MS). Furthermore, we aimed to confirm the clinical significance of CL, testing the correlations between gray matter (GM) lesions and clinical scores.
Methods
A 7-T MRI protocol included 3D-T1-weighted and T2*-weighted sequences. Images were evaluated independently by three readers of different experience, and the number of CLs was recorded. Between-rater concordance was assessed calculating the intraclass correlation coefficient (ICC). Lin’s concordance correlation coefficient was used to compare CL detection between sequences, while partial correlations and multivariable regression models were used to study the relationship between CL and clinical data.
Results
Forty MS patients (M/F, 17/23; 44.7 ± 12.6 years) were enrolled in this study, and CLs were identified in 35/40 subjects (87.5%). CL detection rate on 3D-T1-weighted images was significantly correlated with the detection rate on T2*-weighted images (
r
= 0.99;
p
< 0.001), with high concordance between readers (ICC ≥ 0.995). CLs were significantly correlated with both motor and cognitive scores (all with
p
≤ 0.04).
Conclusions
CL can be identified over the whole brain at 7-T in MS using a 3D-T1-weighted volume, acquired in a clinically feasible time and with comparable performance to that achievable using the T2*-weighted sequence. Based on the central role of CL in the development of clinical disability, we suggest that 3D-T1-weighted volume may play a role in the evaluation of CL in MS undergoing MRI on ultra-high-field scanners.
Key Points
• Cortical lesions can be identified in a clinically feasible time with a 7-T protocol, which includes a 3D-T1-weighted volume.
• Cortical lesions correlated significantly with both motor and cognitive disability in MS patients.
• Given their correlation with clinical disability, evaluation of a cortical lesion on a 7-T clinical protocol could help in the management of MS patients.
•We evaluated iron deposition in N1 in HC and patients with early PD (ePD) and iRBD.•N1 aspect was pathological in T2*-w images in 45% of iRBD patients and in most ePD.•ePD N1 χ was higher than iRBD ...and HC χ but had no correlation with disease duration.•N1 χ in iRBD was similar to HC but increased with disease duration.•N1 χ may be a presymptomatic biomarker for neurodegeneration in prodromal PD.
Idiopathic rapid eye movement (REM) sleep behavior disorder (iRBD) is a prodromal stage of α-synucleinopathies, such as Parkinson's disease (PD), which are characterized by the loss of dopaminergic neurons in substantia nigra, associated with abnormal iron load. The assessment of presymptomatic biomarkers predicting the onset of neurodegenerative disorders is critical for monitoring early signs, screening patients for neuroprotective clinical trials and understanding the causal relationship between iron accumulation processes and disease development. Here, we used Quantitative Susceptibility Mapping (QSM) and 7T MRI to quantify iron deposition in Nigrosome 1 (N1) in early PD (ePD) patients, iRBD patients and healthy controls and investigated group differences and correlation with disease progression. We evaluated the radiological appearance of N1 and analyzed its iron content in 35 ePD, 30 iRBD patients and 14 healthy controls via T2*-weighted sequences and susceptibility (χ) maps. N1 regions of interest (ROIs) were manually drawn on control subjects and warped onto a study-specific template to obtain probabilistic N1 ROIs. For each subject the N1 with the highest mean χ was considered for statistical analysis. The appearance of N1 was rated pathological in 45% of iRBD patients. ePD patients showed increased N1 χ compared to iRBD patients and HC but no correlation with disease duration, indicating that iron load remains stable during the early stages of disease progression. Although no difference was reported in iron content between iRBD and HC, N1 χ in the iRBD group increases as the disease evolves. QSM can reveal temporal changes in N1 iron content and its quantification may represent a valuable presymptomatic biomarker to assess neurodegeneration in the prodromal stages of PD.
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Monogenic cerebral small vessel diseases are a topic of growing interest, as several genes responsible have been recently described, and new sequencing techniques such as Next-generation sequencing ...are available. Brain imaging is significant for the detection of these diseases. Since it is often performed at an initial stage, an MRI is a key to selecting patients for genetic testing and for interpreting nextgeneration sequencing reports. In addition, neuroimaging can be helpful in describing the underlying pathological mechanisms involved in cerebral small vessel disease. In this review, we aim to provide neurologists and stroke physicians with an up-to-date overview of the current neuroimaging knowledge on monogenic small vessel diseases.
Event-Related Potentials (ERPs) occurring independently from any stimulus are purely endogenous (emitted potentials) and their neural generators can be unequivocally linked with cognitive processes. ...In the present study, the subjects performed two similar visual counting tasks: a standard two-stimulus oddball, and an omitted-target oddball task, characterized by the physical absence of the target stimulus. Our investigation aimed at localizing the neural sources of the scalp-recorded endogenous/emitted ERPs. To optimize the source localization, the high temporal resolution of electrophysiology was combined with the fine spatial information provided by the simultaneous recording of functional magnetic resonance (fMRI). Both tasks identified two endogenous ERP components in the 300 to 520 ms interval. An earlier component, pP2, showed a bilateral generator in the anterior Insula. A later P3 component (P3b) was generated bilaterally in the temporal-parietal junction, the premotor and motor area and the anterior intraparietal sulcus (this latter one only in the standard oddball). Anticipatory slow waves (beginning 900 to 500 ms pre-stimulus), also of endogenous nature, were produced by the inferior and middle frontal gyrus and the supplementary and cingulate motor areas. Our protocol disentangled pre- from post-stimulus fMRI activations and provided original clues to the psychophysiological interpretation of emitted/endogenous ERPs.
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