| 51. |
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| 52. |
- Olsson, Hampus, et al.
(författare)
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Magnetization transfer (MT) of human brain at 7T in the context of a 3D multi-parameter mapping protocol
- 2019
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Ingår i: Magnetization transfer (MT) of human brain at 7T in the context of a 3D multi-parameter mapping protocol. - 1545-4428. ; 27
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Konferensbidrag (refereegranskat)abstract
- 3D multi-gradient echo MRI can be used to estimate T1, T2*, PD and the magnetization transfer (MT), which is increasingly used for multi-parametricmapping (MPM) of human brain. The increased polarization at 7T compared to lower B0 allows for increased spatial resolution or reduced scantimes. However, SAR restrictions imposed on the MT pulse and B1 inhomogeneity pose challenges. In this work, we propose a protocol for MPM ofhuman brain at 7T with special attention paid to eliminating bias when mapping MT saturation while obtaining sub-millimeter isotropic spatial resolution inunder 12 minutes with acceptable SNR.
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| 53. |
- Olsson, Hampus, et al.
(författare)
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Radiofrequency bias correction of magnetization prepared rapid gradient echo MRI at 7.0 Tesla using an external reference in a sequential protocol
- 2021
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Ingår i: Tomography : a journal for imaging research. - 2379-1381. ; 7:3, s. 434-451
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Tidskriftsartikel (refereegranskat)abstract
- At field strengths of 7 T and above, T1-weighted imaging of human brain suffers increasingly from radiofrequency (RF) B1 inhomogeneities. The well-known MP2RAGE (magnetization prepared two rapid acquisition gradient echoes) sequence provides a solution but may not be readily available for all MR systems. Here, we describe the implementation and evaluation of a sequential protocol to obtain normalized magnetization prepared rapid gradient echo (MPRAGE) images at 0.7,0.8, or 0.9-mm isotropic spatial resolution. Optimization focused on the reference gradient-recalled echo (GRE) that was used for normalization of the MPRAGE. A good compromise between white-gray matter contrast and the signal-to-noise ratio (SNR) was reached at a flip angle of 3° and total scan time was reduced by increasing the reference voxel size by a factor of 8 relative to the MPRAGE resolution. The average intra-subject coefficient-of-variation (CV) in segmented white matter (WM) was 7.9 ±3.3% after normalization, compared to 20 ±8.4% before. The corresponding inter-subject average CV in WM as 7.6 ±7.6% and 13 ±7.8%. Maps of T1 derived from forward signal modelling showed no obvious bias after correction by a separately acquired flip angle map. To conclude, a non-interleaved acquisition for normalization of MPRAGE offers a simple alternative to MP2RAGE to obtain semi-quantitative purely T1-weighted images. These images can be converted to T1 maps, analogously to the established MP2RAGE approach. Scan time can be reduced by increasing the reference voxel size which has only a miniscule effect on image quality.
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| 54. |
- Olsson, Hampus, et al.
(författare)
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Reducing bias in dual flip angle T1-mapping in human brain at 7T
- 2020
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 84:3, s. 1347-1358
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To address the systematic bias in whole-brain dual flip angle (DFA) T1-mapping at 7T by optimizing the flip angle pair and carefully selecting RF pulse shape and duration. Theory and Methods: Spoiled gradient echoes can be used to estimate whole-brain maps of T1. This can be accomplished by using only two acquisitions with different flip angles, i.e., a DFA-based approach. Although DFA-based T1-mapping is seemingly straightforward to implement, it is sensitive to bias caused by incomplete spoiling and incidental magnetization transfer (MT) effects. Further bias is introduced by the increased B0 and B1+ inhomogeneities at 7T. Experiments were performed to determine the optimal flip angle pair and appropriate RF pulse shape and duration. Obtained T1 estimates were validated using inversion recovery prepared EPI and compared to literature values. A multi-echo readout was used to increase SNR, enabling quantification of R2* and susceptibility, X. Results: Incomplete spoiling was observed above a local flip angle of approximately 20 degrees. An asymmetric gauss-filtered sinc pulse with a constant duration of 700 us showed a sufficiently flat frequency response profile to avoid incomplete excitation in areas with high B0 offsets. A pulse duration of 700 us minimized effects from incidental MT. Conclusion: When performing DFA-based T1-mapping one should (i) limit the higher flip angle to avoid incomplete spoiling, (ii) use a RF pulse shape insensitive to B0 inhomogeneities and (iii) apply a constant RF pulse duration, balanced to minimize incidental MT.
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| 55. |
- Palmqvist, Sebastian, et al.
(författare)
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Detailed comparison of amyloid PET and CSF biomarkers for identifying early Alzheimer disease
- 2015
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Ingår i: Neurology. - : Lippincott Williams & Wilkins. - 1526-632X .- 0028-3878. ; 85:14, s. 1240-1249
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Tidskriftsartikel (refereegranskat)abstract
- Objective:To compare the diagnostic accuracy of CSF biomarkers and amyloid PET for diagnosing early-stage Alzheimer disease (AD).Methods:From the prospective, longitudinal BioFINDER study, we included 122 healthy elderly and 34 patients with mild cognitive impairment who developed AD dementia within 3 years (MCI-AD). -Amyloid (A) deposition in 9 brain regions was examined with [F-18]-flutemetamol PET. CSF was analyzed with INNOTEST and EUROIMMUN ELISAs. The results were replicated in 146 controls and 64 patients with MCI-AD from the Alzheimer's Disease Neuroimaging Initiative study.Results:The best CSF measures for identifying MCI-AD were A42/total tau (t-tau) and A42/hyperphosphorylated tau (p-tau) (area under the curve [AUC] 0.93-0.94). The best PET measures performed similarly (AUC 0.92-0.93; anterior cingulate, posterior cingulate/precuneus, and global neocortical uptake). CSF A42/t-tau and A42/p-tau performed better than CSF A42 and A42/40 (AUC difference 0.03-0.12, p < 0.05). Using nonoptimized cutoffs, CSF A42/t-tau had the highest accuracy of all CSF/PET biomarkers (sensitivity 97%, specificity 83%). The combination of CSF and PET was not better than using either biomarker separately.Conclusions:Amyloid PET and CSF biomarkers can identify early AD with high accuracy. There were no differences between the best CSF and PET measures and no improvement when combining them. Regional PET measures were not better than assessing the global A deposition. The results were replicated in an independent cohort using another CSF assay and PET tracer. The choice between CSF and amyloid PET biomarkers for identifying early AD can be based on availability, costs, and doctor/patient preferences since both have equally high diagnostic accuracy.Classification of evidence:This study provides Class III evidence that amyloid PET and CSF biomarkers identify early-stage AD equally accurately.
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| 56. |
- Rumetshofer, Theodor, et al.
(författare)
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Tract-based white matter hyperintensity patterns in patients with systemic lupus erythematosus using an unsupervised machine learning approach
- 2022
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 12, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- Currently, little is known about the spatial distribution of white matter hyperintensities (WMH) in the brain of patients with Systemic Lupus erythematosus (SLE). Previous lesion markers, such as number and volume, ignore the strategic location of WMH. The goal of this work was to develop a fully-automated method to identify predominant patterns of WMH across WM tracts based on cluster analysis. A total of 221 SLE patients with and without neuropsychiatric symptoms from two different sites were included in this study. WMH segmentations and lesion locations were acquired automatically. Cluster analysis was performed on the WMH distribution in 20 WM tracts. Our pipeline identified five distinct clusters with predominant involvement of the forceps major, forceps minor, as well as right and left anterior thalamic radiations and the right inferior fronto-occipital fasciculus. The patterns of the affected WM tracts were consistent over the SLE subtypes and sites. Our approach revealed distinct and robust tract-based WMH patterns within SLE patients. This method could provide a basis, to link the location of WMH with clinical symptoms. Furthermore, it could be used for other diseases characterized by presence of WMH to investigate both the clinical relevance of WMH and underlying pathomechanism in the brain.
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| 57. |
- Rydelius, Anna, et al.
(författare)
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Diffusion tensor imaging in glioblastoma patients treated with volumetric modulated arc radiotherapy : a longitudinal study
- 2022
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Ingår i: Acta oncologica (Stockholm, Sweden). - 1651-226X. ; 61:6, s. 680-687
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Chemo- and radiotherapy (RT) is standard treatment for patients with high-grade glioma, but may cause side-effects on the patient's cognitive function.AIM: Use of diffusion tensor imaging (DTI) to investigate the longitudinal changes in normal-appearing brain tissue in glioblastoma patients undergoing modern arc-based RT with volumetric modulated arc therapy (VMAT) or helical tomotherapy.MATERIALS AND METHODS: The study included 27 patients newly diagnosed with glioblastoma and planned for VMAT or tomotherapy. All subjects underwent magnetic resonance imaging at the start of RT and at week 3, 6, 15, and 26. Fourteen subjects were additionally imaged at week 52. The DTI data were co-registered to the dose distribution maps. Longitudinal changes in fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) were assessed in the corpus callosum, the centrum semiovale, the hippocampus, and the amygdala.RESULTS: Significant longitudinal changes in FA, MD, and RD were mainly found in the corpus callosum. In the other examined brain structures, only sparse and transient changes were seen. No consistent correlations were found between biodose, age, or gender and changes in DTI parameters.CONCLUSION: Longitudinal changes in MD, FA, and RD were observed but only in a limited number of brain structures and the changes were smaller than expected from literature. The results suggest that modern, arc-based RT may have less negative effect on normal-appearing parts of the brain tissue up to 12 months after radiotherapy.
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| 58. |
- Rydelius, Anna, et al.
(författare)
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Longitudinal study of cognitive function in glioma patients treated with modern radiotherapy techniques and standard chemotherapy
- 2020
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Ingår i: Acta Oncologica. - 0284-186X. ; 59:9, s. 1091-1097
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Tidskriftsartikel (refereegranskat)abstract
- Introduction: Cognitive function is an important outcome measure in patients with brain tumor, providing information about the patient’s clinical situation, treatment effects and possible progressive disease. The aim of this longitudinal study was to evaluate effects of the currently used radiation and chemotherapy treatment on cognitive function and to investigate associations between cognitive function at baseline and progression as well as overall survival. Methods: 32 patients newly diagnosed with malignant glioma were evaluated at baseline with CNS Vital Signs (CNS-VS), a computerized standardized neuropsychological test battery, prior to arc-based radiotherapy and concomitant chemotherapy with Temozolomide. CNS-VS measures the cognitive functions known to be affected in patients with brain tumor, covering nine cognitive domains. Follow-up cognitive evaluations were performed in 26 patients after 3.5 months and in 13 patients 1 year after treatment start. Results: Overall cognitive scores were lower in the studied patient cohort at baseline compared to standardized domain scores. At 3.5 months follow-up cognitive functioning was slightly decreased, but only in 1/9 cognitive domains–visual memory–where significant changes were found compared to baseline test results. Similarly, at 12 months follow-up no significant changes in cognitive test results were seen compared to baseline examination, except for a decrease in the visual memory domain. In relation to early progression, the most significant cognitive deficits were dysfunctional visual memory and low executive functioning at baseline. Low executive function at baseline correlated most significantly with shorter overall survival. Conclusion: The present study suggests that the currently used arc-based radiotherapy and chemotherapy might affect cognitive function less negatively than previously described during treatment and in the first year after treatment in malignant glioma patients. In general, a high cognitive test score at baseline was associated with longer time to progression and with longer survival.
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| 59. |
- Santillo, Alexander Frizell, et al.
(författare)
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Diffusion Tensor Tractography versus Volumetric Imaging in the Diagnosis of Behavioral Variant Frontotemporal Dementia
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:7, s. e66932-
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Tidskriftsartikel (refereegranskat)abstract
- MRI diffusion tensor imaging (DTI) studies of white matter integrity in behavioral variant frontotemporal dementia have consistently shown involvement of frontal and temporal white matter, corresponding to regional loss of cortical volume. Volumetric imaging has a suboptimal sensitivity as a diagnostic tool and thus we wanted to explore if DTI is a better method to discriminate patients and controls than volumetric imaging. We examined the anterior cingulum bundle in 14 patients with behavioral variant frontotemporal dementia and 22 healthy controls using deterministic manual diffusion tensor tractography, and compared DTI parameters with two measures of cortical atrophy, VBM and cortical thickness, of the anterior cingulate cortex (ACC). Statistically significant changes between patients and controls were detected in all DTI parameters, with large effect sizes. ROC-AUC was for the best DTI parameters: 0.92 (fractional anisotropy) to 0.97 (radial diffusivity), 0.82 for the best cortical parameter, VBM of the ACC. Results from the AUC were confirmed with binary logistic regression analysis including demographic variables, but only for fractional anisotropy and mean diffusivity. Ability to classify patient/nonpatient status was significantly better for mean diffusivity vs. VBM (p = 0.031), and borderline significant for fractional anisotropy vs. VBM (p = 0.062). The results indicate that DTI could offer advantages in comparison with the assessment of cortical volume in differentiating patients with behavioral variant frontotemporal dementia and controls.
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| 60. |
- Santillo, Alexander Frizell, et al.
(författare)
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Grey and white matter clinico-anatomical correlates of disinhibition in neurodegenerative disease
- 2016
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:10
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Tidskriftsartikel (refereegranskat)abstract
- Disinhibition is an important symptom in neurodegenerative diseases. However, the clinico- anatomical underpinnings remain controversial. We explored the anatomical correlates of disinhibition in neurodegenerative disease using the perspective of grey and white matter imaging. Disinhibition was assessed with a neuropsychological test and a caregiver information- based clinical rating scale in 21 patients with prefrontal syndromes due to behavioural variant frontotemporal dementia (n = 12) or progressive supranuclear palsy (n = 9), and healthy controls (n = 25). Cortical thickness was assessed using the Freesurfer software on 3T MRI data. The integrity of selected white matter tracts was determined by the fractional anisotropy (FA) from Diffusion Tensor Imaging. Disinhibition correlated with the cortical thickness of the right parahippocampal gyrus, right orbitofrontal cortex and right insula and the FA of the right uncinate fasciculus and right anterior cingulum. Notably, no relationship was seen with the thickness of ventromedial prefrontal cortex. Our results support an associative model of inhibitory control, distributed in a medial temporal lobe-insularorbitofrontal network, connected by the intercommunicating white matter tracts. This reconciles some of the divergences among previous studies, but also questions the current conceptualisation of the prefrontal syndrome and the central role attributed to the ventromedial prefrontal cortex in inhibitory control.
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