The Optimization And Application Of Pseudo-continuous Arterial Spin Labeling To Whole Brain High-resolution Imaging

As one of brain perfusion techniques,quantification of cerebral blood flow(CBF)is important for understanding and diagnosis of neurovascular and neutodegenerative diseases.Arterial spin labeling(ASL)is currently the only method to measure CBF non-invasively without any exogenous contrast agents.However there exist error sources and uncertainties in ASL including tissue T1 effect,transit time effect,low SNR,low spatial and temporal resolution,so the roubustness must be improved.Although the SNR can be increased greatly by 3D GRASE pCASL sequence developed in recent years,and the resolution can be improved by multi-shot readout approach,the parameters and the sampling strategy remain to be optimized.Temporal lobe epilepsy with hippocampus sclerosis(TLE-HS)has strong relationship with interictal low perfusion of hippocampus.The CBF laterality of TLE-HS was obtained previously without considering the tissue T1 effect.But the T1 of sclerous hippocampus is increased actually,which will impact the laterality.Many diseases correlate with aberrant white matter perfusion.But its accurate measurements using ASL were hindered by low SNR and transit time effect.Two main tasks have been performed in this thesis to address the above problems.(1)The impact of tissue T1 to CBF asymmetric index(AI)is studied with simulation and experiment.21 patients were scanned using a multi-shot high resolution 3D GRASE pCASL sequence.Three common models including Buxton,ParkesI and ParkesS models were choosed and compared.It is found that the median AI changed from-2.56 up to-6.96 and the diagnose rate changed from 61.9%up to 81.0%after using tissue T1 mapping.The CBF laterality is improved to make better distinction between patients and healthy,and improve the accuracy of diagnosis.The correlation with severity scale was improved,making the CBF laterality can be used as a reference parameter of seizure severity scale.(2)The issue of low SNR and transit time effect in white matter was overcomed by multi-post labeling delay(PLD)strategy,which was optimized further to enhance the reliability of CBF estimation by maximizing the effective SNR.The verification experiments have been performed in two healthy subjects using a 3D GRASE pCASL sequence whose SNR is highest so far.It has been found that the correlation coefficient values and the percentage of voxels with significant p-values were all increased with the improved method.