Interests

Early detection and development of cerebral ischemia with definition of different parts of ischemic tissue using the MRI-techniques of Diffusion Weighted Imaging (DWI) and Perfusion Imaging (PI).

• Perfusion Imaging - Bolus Tracking: Quantification of cerebral blood flow.
• Pathophysiological classification of stroke subtypes.
• Therapy monitoring: influences of interventions, e.g. thrombolysis, blood pressure.
• Functional recovery after stroke using a somatosensoric stimulus in fMRI-BOLD sequences.

TIAs before ischemic stroke: preconditioning in the human brain?

It has been reported that TIAs prior to ischemic stroke in the same vascular territory are associated with milder initial clinical deficits and better functional outcome in stroke (Weih et al. 1999, Moncayo et al. 2000). One potential explanation is that prior TIAs indicate patients with generally smaller perfusion deficits, another would be ”ischemic preconditioning”, i.e. an acquired resistance to an ischemic challenge which is a well established concept in animal models.

The hypothesis of this study is that TIAs can induce ischemic tolerance in the human brain. If patients with prior TIAs had less perfusion restriction at their subsequent stroke, initial perfusion deficit should be smaller. Same perfusion restriction but smaller infarcts would indicate a better protection of brain tissue by cellular mechanisms induced by prior TIA.

Susanne Wegener and Markus Weih

Thalamic stroke

This project intends to address various aspects of sensorimotor reorganisation and of clinical and morphological aspects in patients with thalamic sensory stroke.

First, we want to characterise the influence of different types of selective or combined deafferentation (cutaneous/proprioceptive) on changes of cortical sensory and motor "maps" (fMRI and somatosensory cortex) and on motor cortical excitability (Transcranial magnetic stimulation) in human subjects. Secondly, we intend to study the interaction between sensory and motor cortex via indirect sensory inputs to the motor cortex in cases of partial deafferentation. For this purpose we chose the model of patients with anatomically well defined circumscribed thalamic lesions.

The location and extent of the lesion within the thalmus will be defined by high-resolution MRI superimposed on a digitised stereotactic atlas of the thalamus. Clinically detectable functional consequences of the lesion will be assessed by a detailed examination.

We expect that the study will elucidate the role of partial deafferentation and interaction between the sensory and the motor cortex in generating phenomena of cortical reorganisation in the sensorimotor cortex.

Jan Jungehuelsing, Birol Taskin, and Kerstin Irlbacher

Diffusion Tensor Imaging

Diffusion Tensor Imaging is an advancement of the simple diffusion weighted imaging (DWI), a technique which has already proven to be very valuable for early diagnosis of cerebral infarcts. In contrast to the latter, DTI measures the decrease of MRT-signals caused by molecular motion in more than one direction (in general 6), making it possible to determine the diffusion tensor (a mathematical array describing the quantity of diffusion – the so-called diffusion coefficient – in all the three spatial dimensions).

Susanne Wegener and Alexander Hopt