| 131. |
- Szczepankiewicz, Filip, et al.
(författare)
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The link between diffusion MRI and tumor heterogeneity : Mapping cell eccentricity and density by diffusional variance decomposition (DIVIDE)
- 2016
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Ingår i: NeuroImage. - : Elsevier BV. - 1053-8119. ; 142, s. 522-532
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Tidskriftsartikel (refereegranskat)abstract
- The structural heterogeneity of tumor tissue can be probed by diffusion MRI (dMRI) in terms of the variance of apparent diffusivities within a voxel. However, the link between the diffusional variance and the tissue heterogeneity is not well-established. To investigate this link we test the hypothesis that diffusional variance, caused by microscopic anisotropy and isotropic heterogeneity, is associated with variable cell eccentricity and cell density in brain tumors. We performed dMRI using a novel encoding scheme for diffusional variance decomposition (DIVIDE) in 7 meningiomas and 8 gliomas prior to surgery. The diffusional variance was quantified from dMRI in terms of the total mean kurtosis (MKT), and DIVIDE was used to decompose MKT into components caused by microscopic anisotropy (MKA) and isotropic heterogeneity (MKI). Diffusion anisotropy was evaluated in terms of the fractional anisotropy (FA) and microscopic fractional anisotropy (μFA). Quantitative microscopy was performed on the excised tumor tissue, where structural anisotropy and cell density were quantified by structure tensor analysis and cell nuclei segmentation, respectively. In order to validate the DIVIDE parameters they were correlated to the corresponding parameters derived from microscopy. We found an excellent agreement between the DIVIDE parameters and corresponding microscopy parameters; MKA correlated with cell eccentricity (r = 0.95, p < 10− 7) and MKI with the cell density variance (r = 0.83, p < 10− 3). The diffusion anisotropy correlated with structure tensor anisotropy on the voxel-scale (FA, r = 0.80, p < 10− 3) and microscopic scale (μFA, r = 0.93, p < 10− 6). A multiple regression analysis showed that the conventional MKT parameter reflects both variable cell eccentricity and cell density, and therefore lacks specificity in terms of microstructure characteristics. However, specificity was obtained by decomposing the two contributions; MKA was associated only to cell eccentricity, and MKI only to cell density variance. The variance in meningiomas was caused primarily by microscopic anisotropy (mean ± s.d.) MKA = 1.11 ± 0.33 vs MKI = 0.44 ± 0.20 (p < 10− 3), whereas in the gliomas, it was mostly caused by isotropic heterogeneity MKI = 0.57 ± 0.30 vs MKA = 0.26 ± 0.11 (p < 0.05). In conclusion, DIVIDE allows non-invasive mapping of parameters that reflect variable cell eccentricity and density. These results constitute convincing evidence that a link exists between specific aspects of tissue heterogeneity and parameters from dMRI. Decomposing effects of microscopic anisotropy and isotropic heterogeneity facilitates an improved interpretation of tumor heterogeneity as well as diffusion anisotropy on both the microscopic and macroscopic scale.
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| 132. |
- Szczepankiewicz, Filip, et al.
(författare)
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Variability in diffusion kurtosis imaging: Impact on study design, statistical power and interpretation.
- 2013
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Ingår i: NeuroImage. - : Elsevier BV. - 1095-9572 .- 1053-8119. ; 76:1, s. 145-154
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion kurtosis imaging (DKI) is an emerging technique with the potential to quantify properties of tissue microstructure that may not be observable using diffusion tensor imaging (DTI). In order to help design DKI studies and improve interpretation of DKI results, we employed statistical power analysis to characterize three aspects of variability in four DKI parameters; the mean diffusivity, fractional anisotropy, mean kurtosis, and radial kurtosis. First, we quantified the variability in terms of the group size required to obtain a statistical power of 0.9. Second, we investigated the relative contribution of imaging and post-processing noise to the total variance, in order to estimate the benefits of longer scan times versus the inclusion of more subjects. Third, we evaluated the potential benefit of including additional covariates such as the size of the structure when testing for differences in group means. The analysis was performed in three major white matter structures of the brain: the superior cingulum, the corticospinal tract, and the mid-sagittal corpus callosum, extracted using diffusion tensor tractography and DKI data acquired in a healthy cohort. The results showed heterogeneous variability across and within the white matter structures. Thus, the statistical power varies depending on parameter and location, which is important to consider if a pathogenesis pattern is inferred from DKI data. In the data presented, inter-subject differences contributed more than imaging noise to the total variability, making it more efficient to include more subjects rather than extending the scan-time per subject. Finally, strong correlations between DKI parameters and the structure size were found for the cingulum and corpus callosum. Structure size should thus be considered when quantifying DKI parameters, either to control for its potentially confounding effect, or as a means of reducing unexplained variance.
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| 133. |
- Söderström, Pelle, et al.
(författare)
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Anticipating morphological and syntactic structures : investigating the pre-activation negativity
- 2017
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Konferensbidrag (refereegranskat)abstract
- It is known that listeners can predict upcoming words based on constraining contexts (e.g. DeLong et al., 2005). In a recent study, we proposed a left frontal brain potential, the pre-activation negativity, PrAN (Söderström et al., 2016), thought to reflect pre-activation of expected word continuations. Time-locked to word-initial fragments, PrAN’s amplitude was found to increase in a 136-280 ms time window as the number of possible continuations decreased, suggesting that PrAN increased with increased predictive certainty about a word’s ending. In the present study, we tested whether a similar effect could be found for pre-activation of expected syntactic structures. In Swedish, intonation is used to signal whether an unfolding embedded clause is a main or subordinate clause. Specifically, a clause-initial word with a low boundary tone cues only subordinate clause structure. Conversely, a corresponding high tone signals that any kind of embedded main clause structure may follow, i.e. it cues a more open set of structures. Test participants listened to complex sentences and judged the word order of the verb (V) and negation (NEG) after the boundary tone as quickly as possible (NEG–V word order occurs in subordinate clauses and V–NEG in main clauses). ERPs were time-locked to the tone-bearing syllable. A repeated-measures ANOVA showed a negativity in left anterior electrodes at 136-280 ms for low initial boundary tones, which cue only subordinate clauses. We propose that this effect is a PrAN, but that it here reflects pre-activation of syntactic structures rather than possible word endings.
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| 134. |
- Söderström, Pelle, et al.
(författare)
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Rapid syntactic pre-activation in Broca’s area : Concurrent electrophysiological and haemodynamic recordings
- 2018
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993. ; 1697, s. 76-82
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Tidskriftsartikel (refereegranskat)abstract
- Listeners are constantly trying to predict what the speaker will say next. We concurrently measured the electrophysiological and haemodynamic correlates of syntactic pre-activation, investigating when and where the brain processes speech melody cues to upcoming word order structure. Pre-activation of syntactic structure was reflected in a left-lateralised pre-activation negativity (PrAN), which was subserved by Broca’s area in the left inferior frontal gyrus, as well as the contiguous left anterior insula.
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| 135. |
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| 136. |
- Thordstein, Magnus, et al.
(författare)
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Transfer of cortical motor representation after a perinatal cerebral insult.
- 2011
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Ingår i: Pediatric neurology. - : Elsevier BV. - 1873-5150 .- 0887-8994. ; 44:2, s. 131-4
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Tidskriftsartikel (refereegranskat)abstract
- In a 16-year-old boy with hemiplegia and severe, intractable epilepsy after a neonatal cerebral ischemic insult, cortical motor control was only equivocally assessed by functional magnetic resonance imaging. Therefore, high-precision navigated transcranial magnetic stimulation was performed, which demonstrated that cortical control of muscles on the paretic side was selectively affected. Leg muscle control was located in the contralateral hemisphere, as expected in healthy individuals, whereas forearm muscles were controlled from both hemispheres, and hand muscles were controlled only from the hemisphere ipsilateral to the paresis.
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| 137. |
- Torisson, Gustav, et al.
(författare)
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Medial temporal lobe atrophy is underreported and may have important clinical correlates in medical inpatients.
- 2015
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Ingår i: BMC Geriatrics. - : Springer Science and Business Media LLC. - 1471-2318. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- The diagnostic workup in dementia includes brain imaging with reading focussed on signs of cerebrovascular and neurodegenerative disease. We hypothesised that these findings may be underreported in hospital patients, where imaging is often performed to rule out obvious pathology such as haemorrhage. In this study, we review cranial computed tomography (CT) in medical inpatients for white matter changes and atrophy. Our aim was to determine the clinical relevance of such findings and to what extent they were underreported.
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| 138. |
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| 139. |
- van Westen, Danielle, et al.
(författare)
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Bilder av hjärnan arbete.
- 2008
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Ingår i: Läkartidningen. - 0023-7205. ; 105:47, s. 3438-3442
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Tidskriftsartikel (refereegranskat)
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| 140. |
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