A fractal based model of diffusion MRI in cortical grey matter

Diffusion Weighted Magnetic Resonance (DWMR) Imaging is an important tool in diagnostic neuroimaging, but the biophysical basis of the DWMR signal from biological tissue is not entirely understood. Testable, theoretical models relating the DWMR signal to the tissue, therefore, are crucial. This work presents a toy version of such a model of water DWMR signals in brain grey matter. The model is based on biophysical characteristics and all model parameters are directly interpretable as biophysical properties such as diffusion coefficients and membrane permeability allowing comparison to known values. In the model, a computer generated Diffusion Limited Aggregation (DLA) cluster is used to describe the collected membrane morphology of the cells in cortical grey matter. Using credible values for all model parameters model output is compared to experimental DWMR data from normal human grey matter and it is found that this model does reproduce the observed signal. The model is then used for simulating the effect on the DWMR signal of cellular events known to occur in ischemia. These simulations show that a combination of effects is necessary to reproduce the signal changes observed in ischemic tissue and demonstrate that the model has potential for interpreting DWMR signal origins and tissue changes in ischemia. Further studies are required to validate these results and compare them with other modeling approaches. With such models, it is anticipated that sensitivity and specificity of DWMR in tissues can be improved, leading to better understanding of the origins of MR signals in biological tissues, and improved diagnostic capability

Tillid i og til pædagogiske sammenhænge

’Tillid’ i pædagogiske sammenhænge forstås overvejende som noget, der handler om personlige og interpersonelle forhold, fx om barnet har tilstrækkelig selvtillid, og om der eksisterer tillidsfulde relationer mellem børn og pædagoger, elever og lærere, pædagoger/lærere og forældre. Artiklen foreslår at inddrage et systemniveau udover de niveauer, der fokuserer alene på de nære og interpersonelle forhold. ’Tillid’ vedrører ikke alene aspekter i pædagogiske sammenhænge, men også til pædagogiske sammenhænge, dvs. til pædagogikkens muligheder eller til det, man kan kalde ’det pædagogiske projekt’. Repræsentanter for de pædagogiske professioner befinder sig i en paradoksal position, når de skal skabe konkret tillid inden for et system, der i stigende grad kræver forholdemåder, der indirekte medvirker til at skabe mistillid.