| 1. |
|
|
| 2. |
- Chakwizira, Arthur, et al.
(författare)
-
Non-parametric deconvolution using Bézier curves for quantification of cerebral perfusion in dynamic susceptibility contrast MRI
- 2022
-
Ingår i: Magnetic Resonance Materials in Physics, Biology, and Medicine. - : Springer Science and Business Media LLC. - 1352-8661. ; 35:5, s. 791-804
-
Tidskriftsartikel (refereegranskat)abstract
- Objective Deconvolution is an ill-posed inverse problem that tends to yield non-physiological residue functions R(t) indynamic susceptibility contrast magnetic resonance imaging (DSC-MRI). In this study, the use of Bézier curves is proposedfor obtaining physiologically reasonable residue functions in perfusion MRI.Materials and methods Cubic Bézier curves were employed, ensuring R(0)=1, bounded-input, bounded-output stability anda non-negative monotonically decreasing solution, resulting in 5 parameters to be optimized. Bézier deconvolution (BzD),implemented in a Bayesian framework, was tested by simulation under realistic conditions, including efects of arterial delayand dispersion. BzD was also applied to DSC-MRI data from a healthy volunteer.Results Bézier deconvolution showed robustness to diferent underlying residue function shapes. Accurate perfusion estimates were observed, except for boxcar residue functions at low signal-to-noise ratio. BzD involving corrections for delay,dispersion, and delay with dispersion generally returned accurate results, except for some degree of cerebral blood fow(CBF) overestimation at low levels of each efect. Maps of mean transit time and delay were markedly diferent betweenBzD and block-circulant singular value decomposition (oSVD) deconvolution.Discussion A novel DSC-MRI deconvolution method based on Bézier curves was implemented and evaluated. BzD produced physiologically plausible impulse response, without spurious oscillations, with generally less CBF underestimationthan oSVD.
|
|
| 3. |
- Dussex, Nicolas, et al.
(författare)
-
Moose genomes reveal past glacial demography and the origin of modern lineages
- 2020
-
Ingår i: BMC Genomics. - : Springer Science and Business Media LLC. - 1471-2164. ; 21:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Numerous megafauna species from northern latitudes went extinct during the Pleistocene/Holocene transition as a result of climate-induced habitat changes. However, several ungulate species managed to successfully track their habitats during this period to eventually flourish and recolonise the holarctic regions. So far, the genomic impacts of these climate fluctuations on ungulates from high latitudes have been little explored. Here, we assemble a de-novo genome for the European moose (Alces alces) and analyse it together with re-sequenced nuclear genomes and ancient and modern mitogenomes from across the moose range in Eurasia and North America.Results: We found that moose demographic history was greatly influenced by glacial cycles, with demographic responses to the Pleistocene/Holocene transition similar to other temperate ungulates. Our results further support that modern moose lineages trace their origin back to populations that inhabited distinct glacial refugia during the Last Glacial Maximum (LGM). Finally, we found that present day moose in Europe and North America show low to moderate inbreeding levels resulting from post-glacial bottlenecks and founder effects, but no evidence for recent inbreeding resulting from human-induced population declines.Conclusions: Taken together, our results highlight the dynamic recent evolutionary history of the moose and provide an important resource for further genomic studies.
|
|
| 4. |
|
|
