| 1. |
- Nilsson, Markus, et al.
(författare)
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Evaluating the accuracy and precision of a two-compartment Kärger model using Monte Carlo simulations.
- 2010
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Ingår i: Journal of Magnetic Resonance. - : Elsevier BV. - 1096-0856 .- 1090-7807. ; 206:1, s. 59-67
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Tidskriftsartikel (refereegranskat)abstract
- Specific parameters of the neuronal tissue microstructure, such as axonal diameters, membrane permeability and intracellular water fractions are assessable using diffusion MRI. These parameters are commonly estimated using analytical models, which may introduce bias in the estimated parameters due to the approximations made when deriving the models. As an alternative to using analytical models, a database of signal curves generated by fast Monte Carlo simulations can be employed. Simulated diffusion MRI measurements were generated and evaluated using the two-compartment Kärger model as well as the simulation model based on a database containing signal curves from approximately 60000 simulations performed with different combinations of microstructural parameters. A protocol based on a pulsed gradient spin echo sequence with diffusion times of 30 and 60ms and with gradient amplitudes obtainable with a clinical MRI scanner was employed for the investigations. When using the analytical model, a major negative bias (up to approximately 25%) in the estimated intracellular volume fraction was observed for short exchange times, while almost no bias was seen for the simulation model. In general, the simulation model improved the accuracy of the estimated parameters as compared to the analytical model, except for the exchange time parameter.
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| 2. |
- Nilsson, Markus, et al.
(författare)
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Noninvasive mapping of water diffusional exchange in the human brain using filter-exchange imaging.
- 2013
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Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 69:6, s. 1572-1580
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Tidskriftsartikel (refereegranskat)abstract
- We present the first in vivo application of the filter-exchange imaging protocol for diffusion MRI. The protocol allows noninvasive mapping of the rate of water exchange between microenvironments with different self-diffusivities, such as the intracellular and extracellular spaces in tissue. Since diffusional water exchange across the cell membrane is a fundamental process in human physiology and pathophysiology, clinically feasible and noninvasive imaging of the water exchange rate would offer new means to diagnose disease and monitor treatment response in conditions such as cancer and edema. The in vivo use of filter-exchange imaging was demonstrated by studying the brain of five healthy volunteers and one intracranial tumor (meningioma). Apparent exchange rates in white matter range from 0.8 ± 0.08 s(-1) in the internal capsule, to 1.6 ± 0.11 s(-1) for frontal white matter, indicating that low values are associated with high myelination. Solid tumor displayed values of up to 2.9 ± 0.8 s(-1) . In white matter, the apparent exchange rate values suggest intra-axonal exchange times in the order of seconds, confirming the slow exchange assumption in the analysis of diffusion MRI data. We propose that filter-exchange imaging could be used clinically to map the water exchange rate in pathologies. Filter-exchange imaging may also be valuable for evaluating novel therapies targeting the function of aquaporins. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
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| 3. |
- Sjöbeck, Martin, et al.
(författare)
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Alzheimer's disease (AD) and executive dysfunction. A case-control study on the significance of frontal white matter changes detected by diffusion tensor imaging (DTI).
- 2010
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Ingår i: Archives of Gerontology and Geriatrics. - : Elsevier BV. - 1872-6976 .- 0167-4943. ; 50, s. 260-266
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Tidskriftsartikel (refereegranskat)abstract
- White matter (WM) changes are frequently seen on structural imaging in AD but the clinical relevance of these changes is uncertain. Frontal WM pathology is often observed upon neuropathological examination in AD. Since frontal cortical/sub-cortical pathology is known to relate to executive dysfunction, the aim was to elucidate if frontal WM changes in AD correlated with executive dysfunction. In all, 15 AD patients and 15 age-matched control cases were investigated in the study, which covered conventional magnetic resonance imaging (MRI), DTI, neuropsychiatric and neuropsychological examinations. Reduced performance on neuropsychological testing of executive function correlated significantly with an increasing degree of frontal WM changes detected by DTI in the AD group, while no such correlation was observed for the controls. Conventional semi-quantitative MRI assessment did not correlate with results on neuropsychological testing of executive function in any of the groups. The structural correlate to certain dimensions of executive dysfunction in AD patients could be related to changes in the deep frontal WM. DTI appears to be more sensitive in the detection of clinically significant WM alterations than conventional semi-quantitative MRI.
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