Improved multi inversion time arterial spin labeling MRI of the brain

Abstract

Arterial spin labeling magnetic resonance imaging (ASL MRI) measures cere bral blood flow (CBF) quantitively without using any contrast agent or radiation.The calculation of labelled blood arrival time to tissue and arterial vessels provides hemody namic information, which may be useful in understanding neurodegenerative disorders. Separate pseudo-continuous ASL (pCASL) MR can be done at multiple inversion times (TI) to avoid inaccurate CBF estimation due to uncertainties in arrival times, which is time consuming and limits the number of averages. ASL MRI using Look-Locker (LL) readout and the time-encoded pCASL MRI (te-pCASL) using Hadamard matrix are two approaches for acquiring ASL data at multiple TIs. ASL-MRI with LL readout requires a complex model to accurately estimate CBF. On the other hand, te-pCASL MRI has a shine-through effect, which might cause errors in CBF estimation. In the first part of this thesis, the brain perfusion deficits in Parkinson’s disease with mild cognitive impairment (PD-MCI) were investigated using ASL MRI with LL readout. PD-MCI patients displayed a posterior hypoperfusion pattern, which classified these patients with over 90% accuracy in comparison to healthy controls. Moreover, geneti cally risky PD with microtubule-associated protein tau gene (MAPT) H1/H1 haplotype had visual hypoperfusion as compared with non-risky PD. In the second part of the thesis, the possible reasons of shine-through effect in te-pCASL MRI were assessed using simulations and in-vivo data. Based on the theoretical model, pCASL and te pCASL MRI resulted in the same ASL signals. On the other hand, our experimental results showed that the use of selective background suppression inversion pulses could lead to the appearance of the shine-through effect.|Keywords : Arterial spin labeling, Parkinson’s disease, mild cognitive impairment, te-pCASL, Look-Locker readout, Parkinson’s disease, shine-through effect.