Study On Hemodynamics Of Epileptic Rats Based On Photoacoustic Imaging

Epilepsy is a common chronic brain disease that seriously endangers physical and mental health of human beings.At present,there are more than 40 million epileptic patients in the world,and the annual growth reaches up to 5%.When epileptic seizure occurs,abnormal discharges of brain neurons can be observed.The excitatory activity of neurons will increase the metabolism level of neurons,which consume more nutrients that provided by blood;as a result,functional and structural states of blood vessels may change.Electroencephalogram(EEG)is a conventional tool for recording the weak electrical-signal as emitted by brain neurons.EEG can reveal the state of nerve cells of the brain and it provides basic evidence for clinical diagnosis of epilepsy.However,limitation still exists.EEG lacks the capability for picking up the hemodynamic information of blood vessels around nerve cells.Conventional imaging methods can provide structural information of blood vessels;however,high-resolution is hard to be realized.As a result,novel imaging modality which can simultaneously provide hemodynamic information and high-resolution is attractive.Photoacoustic imaging(PAI)is a biomedical imaging technology based on photoacoustic effect.PAI combines both merits of optical imaging and ultrasonic imaging,which include high optical contrast and high resolution;as a result,it has very broad application in biomedical engineering,e.g.monitoring hemodynamics.In this paper,we have incorporated PAI technology and EEG acquisition technology to study the neural vascular coupling mechanism,which may thus reveal the biological hemodynamics in epileptic rats.A novel optical resolution PAI system is employed for the experimental set-up,and 4-aminopyridine was injected into the cerebral cortex by microinjection to establish the focal model of local epilepsy in rats.Then,the photoacoustic and EEG signals of rats in epileptic state were collected synchronously.After image reconstruction and signal-processing,such as eliminating sine distortion and dislocation correction,two-dimensional photoacoustic image is obtained.The hemodynamic changes of rats in epileptic state,in terms of variation of photoacoustic amplitude and vascular diameter of blood vessels,are extracted.Finally,we find the correlation characteristics between the two technologies,which can reflect the changes of neurovascular and the interaction in the process of epileptic attackthrough establishing neurovascular coupling with EEG.Results show that the amplitude of EEG signal is positively correlated with the photoacoustic amplitude and diameter of blood vessels,which is consistent with the physiological results.We attribute the reason to the acceleration of blood flow that associated with discharges of brain neurons.In summary,this study combines EEG and PAI for studying the hemodynamic changes of rats in epileptic seizure,which could provide reference for the related research.As is also highlighted that multi-scale information can be simultaneously obtained in this proposed study.