The vascular properties of the BOLD signal

The work presented in this thesis is intended to contribute towards the understanding of the cerebral vascular behaviour in response to changes in neuronal activation. The blood oxygenation-level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal provides an indirect measure of neuronal activation, arising from a combination of metabolic and vascular (blood flow and blood volume) changes local to the activation. Therefore the BOLD signal is dependent on local vascular properties as well as on the neuronal activation, leading to a variability of the BOLD signal, based on the underlying vascular structure. It has become an important goal to improve understanding of the mechanisms underlying the BOLD signal in order to separate out this vascular variability from the underlying correspondence with the neuronal activation. The effect of field strength on the temporal characteristics of the BOLD haemodynamic response function is investigated. An earlier BOLD response onset has been measured with increasing static magnetic field strength, consistent with an earlier microvascular (compared with macrovascular) signal response. This result can be used to improve haemodynamic models of the BOLD signal. Hypercapnia, a vasodilator, has been used both to assess the relationship between transverse relaxation and blood oxygenation at 3 and 7 Tesla and to identify vascular heterogeneity between two equivalent brain regions. A tight, linear relationship was found between the level of hypercapnia and transverse relaxation at both 3 and 7 Tesla, whilst the change in transverse relaxation due to hypercapnia increased 2.1 ± 0.5 fold from 3 to 7 Tesla, indicating an approximately linear relationship across field strength. In a separate experiment, a vascular asymmetry was found between the left and right precentral gyri using hypercapnia. This result highlights the need to account for the vascular contribution to the BOLD signal before using this BOLD signal to make comparisons of neuronal activity across brain regions. Finally, an improved model for calibrated BOLD has been proposed and implemented, which requires fewer assumptions than existing approaches. This uses the BOLD response to some task, repeated both at normoxia and hyperoxia. To assess the validity of this model, the effects of paramagnetic oxygen molecules are considered, both dissolved in blood plasma and in airspaces adjacent to the brain. These effects were found to be small, except for in the frontal cortex

Single shot partial dual echo (SPADE) EPI—an efficient acquisition scheme for reducing susceptibility artefacts in fMRI

SPADE is a new acquisition scheme for fMRI based on dual echo EPI. As in previous work, additional spin echo EPI images are used to recover signal in regions that are affected by susceptibility related sensitivity loss in gradient echo EPI. However, with SPADE the additional spin echo images are only acquired for the affected slices, which reduces the acquisition time and enhances the time normalised signal-to-noise ratio. We demonstrate the feasibility of this approach and discuss potential applications of the SPADE technique in fMRI. We conclude that SPADE provides an efficient acquisition scheme for fMRI applications where whole brain coverage and sensitivity is required

Central Nervous System Tumors

Though the treatment of central nervous system (CNS) tumors has been challenging, new advances have helped us better understand the molecular and genetic makeup of many tumor types, and new chemotherapies and immunotherapies have extended survival in patients with aggressive primary CNS tumors. This book discusses pediatric and adult tumors of the CNS, the classification schemes used to categorize them, advances in surgical techniques, and several important genetic alterations found in these tumors. We hope this book contributes to the reader’s understanding of these tumors and provides the most up-to-date and cutting-edge discoveries in this exciting field

Medical-Data-Models.org:A collection of freely available forms (September 2016)

MDM-Portal (Medical Data-Models) is a meta-data repository for creating, analysing, sharing and reusing medical forms, developed by the Institute of Medical Informatics, University of Muenster in Germany. Electronic forms for documentation of patient data are an integral part within the workflow of physicians. A huge amount of data is collected either through routine documentation forms (EHRs) for electronic health records or as case report forms (CRFs) for clinical trials. This raises major scientific challenges for health care, since different health information systems are not necessarily compatible with each other and thus information exchange of structured data is hampered. Software vendors provide a variety of individual documentation forms according to their standard contracts, which function as isolated applications. Furthermore, free availability of those forms is rarely the case. Currently less than 5 % of medical forms are freely accessible. Based on this lack of transparency harmonization of data models in health care is extremely cumbersome, thus work and know-how of completed clinical trials and routine documentation in hospitals are hard to be re-used. The MDM-Portal serves as an infrastructure for academic (non-commercial) medical research to contribute a solution to this problem. It already contains more than 4,000 system-independent forms (CDISC ODM Format, www.cdisc.org, Operational Data Model) with more than 380,000 dataelements. This enables researchers to view, discuss, download and export forms in most common technical formats such as PDF, CSV, Excel, SQL, SPSS, R, etc. A growing user community will lead to a growing database of medical forms. In this matter, we would like to encourage all medical researchers to register and add forms and discuss existing forms