Ischemic Stroke
Ischemic Stroke Multiparametric MR imaging analysis of ischemic stroke:The therapeutic effect of treatment in ischemic stroke relies not only on the recovery of blood flow, but also the amount of possibly non-impaired neurons in the human brain after stroke. Within 4.5 hours after the cerebrovascular accident is usually a critical and valuable period of time to give treatments. Therefore, defining the onset time of CVA, locating the lesion sites as well as evaluating the preserved brain tissues precisely are all important factors to consider before any intervention or thrombolytic drugs injection are given.
There have been many MR imaging related studies in ischemic penumbra, which proposed the ischemic penumbra could be referred as the location of possibly preserved neurons. Furthermore, its area and size may be regarded as a predictor for therapeutic efficacy of pharmalogical treatments. Generally, both diffusion tensor imaging (DTI) and perfusion-weighted imaging (PWI) are advanced MRI techniques essentially for evaluating ischemic penumbra, yet the contrast agent used in PWI is not suitable for patients with certain conditions.
The result of our research illustrated that the multiple parameters calculated from DTI could be treated as an effective indicator for assessing the region of ischemic penumbra and estimating the onset time of ischemic stroke. It had been tested and verified in a stroke model of rats. Currently the application of laboratory research findings under the advanced MRI method has already been linked to studies involving human participants. The high availability of DTI will provide clinicians a new opportunity for diagnosis and treatment of ischemic stroke.
Transneuronal degeneration (TND) is thought to be linked with cerebral vascular accident (CVA), which commonly lasts for several days to weeks from the acute stage of injury. It might occur in the intact brain regions involved in motor function such as the motor pathways or the striatonigral pathway in the extrapyramidal system, which causes the so-called post stroke movement disorders.
The long-term impairments in motor skills, memory function and consciousness disturbance result from TND are unpredictable, negatively impacting the arrangement of rehabilitation and the quality of life in patients with a poor outcome of disease progression. TIRC has created detailed images of the brain structure and function measured by advanced MR imaging techniques (e.g., diffusion tensor imaging, q-space imaging, resting-state functional MRI, cerebral perfusion MRI, susceptibility weighted imaging, and magnetic resonance spectroscopy).
The Functional Connectivity of Thalamic Networks after Acute Stroke:
The secondary trans-neuronal degeneration (TND) usually happens as a post-stroke symptom. The thalamus is generally recognized as a relay between cortical and subcortical networks. It plays an important role in processing sensory information (e.g., the ventral posterior thalamic nucleus and the ventral posterolateral thalamic nucleus), coordinating motor function (e.g., the ventral anterior nucleus and the ventral nucleus), and regulating states of consciousness.
The anterior nuclei of thalamus is associated with memory function. Despite blood supply for the thalamus largely comes from the basilar artery and the posterior communicating artery, other specified brain lesions will lead to the secondary TND of thalamus due to its connection with the cerebral cortex. There have been studies concerning the impairment of thalamus result from the secondary TND of infarction or ischemia in the territory supplied by the middle cerebral artery (MCA). However, the alternation of thalamic nucleus and the circuitries/functional connectivity between thalamus and the cerebral cortex have seldom been investigated.
Questions about the relation of TND and thalamic nucleus, the clinical symptoms found in the interaction between lesions of thalamic nucleus, and whether or not the apoptosis across a synapse could be prevented have all not been defined well yet. TIRC’s research groups aim to study, analyze and compare the stroke model of laboratory animals with the research of CVA patients. The goal of research will emphatically focus on the mechanism of the secondary TND in thalamus.
First of all, a parcellation scheme with respect to the specific localization of thalamic nucleus will be carried out using structural MRI. Secondly, based on the parcellation of thalamic nucleus, we may characterize the functional anatomy of thalamus by using advanced MR imaging techniques, such as diffusion tensor imaging, q-space imaging, resting-state functional MRI, cerebral perfusion MRI, susceptibility weighted imaging, and magnetic resonance spectroscopy.
Finally, in order to explore the pathological mechanism of TND following a cardiovascular accident, the research theme will focus on specific regions of the cerebral cortex. The photothrombotic stroke model of rats is applied to research of correlation between thalamocortical circuit and TND. Meanwhile, the MR imaging findings of TND in rats will link with the results of pathological data, which is ultimately applied to stroke-related clinical researches.
The research hypothesis is proposed that the pathological oscillation within thalamus induced by the secondary TND is specifically correlated with the atypical function of thalamocortical pathways. The longitudinal follow-up of TND induced change in the brain will be carried out, and the information analyzed from temporal characteristics of dynamic functional connectivity may be offered to better understand the effects of stroke, as well to give diagnosis and treatment more accurately. Finally, the goal of research is to enable more precise identification of biomarkers relying on medical imaging, and to enhance the ability of early detection of brain-related diseases with reliable biomarkers.
Applying brain compliance to investigate the pressure of cerebral venous:
Brain compliance was initially used to indicate the state of brain homeostasis, which could be affected by intracranial pressure and intracranial volume. The brain homeostasis is maintained normally relying on balance between the intracranial constituents that contains blood, cerebrospinal fluid (CSF), and brain tissue. When brain homeostasis or the state of volume equilibrium is not maintained, the intracranial pressure is elevated with decreased brain compliance. Thus, either the information about mediation of intracranial volume or the risk evaluation of intracranial hypertension can be obtained by measuring brain compliance accurately.
Motion-sensitive magnetic resonance imaging is a non-invasive technique used for monitoring volume arterial inflow, venous blood outflow and CSF during a cardiac cycle. On the other hand, the cine displacement-encoded MRI can be used to record the electric impulses sent by neurons in brain. We aim to explore the underlying mechanism and the correlation between volume arterial inflow, venous blood outflow, CSF and nerve impulse in brain during a cardiac cycle. We will obtain motion-sensitive magnetic resonance imaging from laboratory animals at 7T MRI and from human participants at 3T MRI. We will also propose an algorithm design to improve the estimation of brain compliance, which is expected to offer high value for clinical application in the future.
