Magnetic Resonance Vessel Wall Imaging For Early And Accurate Diagnosis Of Cerebrovascular Disease

Cerebrovascular disease is a leading cause of morbidity,mortality and disability in China.It has become a serious burden of medical expenditure for society and family and arises from different intra-and extracranial wall pathologies,such as atherosclerosis,vasculitis,and dissection.Atherosclerotic plaque rupture and causing blood clot is the major cause of cerebrovascular disease.Accurate characterization of these pathologies may help elucidate stroke etiology and allow for therapeutic intervention before severe cerebrovascular events occur.However,the existing technology can not provide the pathological information related to plaque and other vessel wall lesions.Magnetic resonance(MR)vessel wall imaging is the unique new frontier technique for noninvasively and panoramically imaging intracranial vessel wall and plaques and can provide accurate diagnosis information for intracranial artery plaques.Based on the special anatomical basis of intracranial artery,it is necessary to meet the following technical conditions to achieve clinically useful MR vessel wall imaging of intracranial arteries.(1)0.5mm or less high spatial resolution with sufficient image signal-to-noise ratio(SNR).(2)Simultaneous suppression of the arterial blood flow and cerebrospinal fluid(CSF)signal for obtaining good contrast of vessel wall and the surrounding tissues.(3)Three dimensional isotropic acquisition of the whole brain or head and neck.The study aims to address the several challenges such as insufficient SNR,limited spatial resolution,and incomplete suppression of CSF,which preventing the use of MR vessel wall imaging in diagnostic applications.In this study,New imaging principle and algorithm are studied in order to improve the image SNR.New CSF signal suppression method is studied to improve the tissue contrast.On the basis of the above study,multi-contrast MR vessel wall imaging techniques are further studied to comprehensively recognize atherosclerotic plaque composition and its stability.and Finally,the clinical application value of the proposed method in the accurate diagnosis of intra-and extracranial vessel wall lesions in patients with ischemic stroke is verified through reliability study and preliminary clinical application research.The study was approved by the local institutional review board.All subjects were recruited with written informed consent.The main contributions of this thesis are summarized as follows.1.The variable-flip-angle of the SPACE(Sampling Perfection with Application-optimized Contrasts by using different flip angle Evolutions)imaging sequence is the basis of determining the SNR of the image.In this thesis,based on the existing inverse solution of the variable-flip-angle according to “prescribed signal evolution”,a new imaging algorithm for calculating the optimal variable-flip-angle is proposed by iteratively searching for an optimized solution with applying the constraint condition for the variable-flip-angle change mode.A Simulation and human experiment results show that this algorithm can effectively improve the SNR of the image.The isotropic spatial resolution of 0.5mm with suffient image SNR and good tissue contrast is achieved using the new image algorithm and self-developed high-performance 32-channel head-neck joint coil.2.The suppression of blood flow and CSF signal is the key to obtain fine arterial vessel wall images and for multi-contrast plaque imaging.We propose black blood imaging technique DANTE(Delay Alternating with Nutation for Tailored Excitation)as the preparation pulse of SPACE sequence to addresse the difficulty of SPACE in simultaneously suppress the signals of intracranial and carotid arterial blood with very different flow rates and CSF with very slow flow rates.The interaction of DANTE and SPACE on the sensibility of moving signals is first studied for optimizing DANTE module,and then a whole brain and head-neck combined vessel wall imaging methods with DANTE preparation are developed.The results show that the CSF signal was effectively suppressed and plaque-mimicking flow artifacts at the bifurcation of carotid artery were eliminated,which improve the tissue contrast of vessel wall images.On this basis,a three-inversion-pulse based signal restore scheme was used after T1-weighted DANTE-SPACE echo chain to further suppress the CSF signal with slower flow velocity in the M2 segment of middle cerebral artery.The results show that the reversion-pulse significantly increases the contrast between the vessel wall and the CSF,espectial in M2 segment of middle cerebral artery,and also improves the T1-weighted contrast of the vessel wall images,which facilitates the identification and quantitative analysis of the plaque.3.Based on the above studies,T1-weighted whole-brain and head-neck joint MR vessel wall imaging based on the new imaging algorithm and DANTE and inversion-pulses is achieved with an isotropic spatial resolution of 0.5 mm in 8 minutes.DANTE module is also combined with multi-contrast vessel wall imaging(T2-weighted SPACE and heavy T1-weighted MPRAGE sequences)to improve the identification ability of atherosclerotic plaque composition and stability.4.The reliability of T1-weighted SPACE and clinical value of multi-contrast MR vessel wall imaging in accurate diagnosis of intra-and extracranial artery disease in patients with ischemic stroke are experimentally verified in volunteers and clinical cerebral atherosclerosis patients.The results show that both T1 weighted whole brain and head-neck combined MR vessel wall imaging exhibit excellent reproducibility and inter-method agreement(with the clinical reference standard 2D TSE)for vaessel wall and plaque morphologic measurements.Preliminary clinical application results show that the multi-contrast MR vessel wall imaging can not only identify intra-and extracranial artery plaques and evaluate its stability,but also diagnose other vessel wall lesions including arterial dissection,vasculitis,etc.