Improvements in neurovascular magnetic resonance angiography [electronic resource]
Keywords: Electrical Engineering.

Magnetic Resonance Angiography (MRA) is a technique to image the lumen of blood vessel with Magnetic Resonance Imaging (MRI). This work focuses on improvements in 3D and 4D non-contrast-enhanced magnetic resonance angiography. In the first part of this thesis, the feasibility of an optical motion correction system to prospectively correct patient motion for 3D Time-of-Flight (TOF) magnetic resonance angiography was investigated. Experiments were performed on five subjects with and without parallel imaging (SENSE R = 2) on a 1.5 T system. Two human readers assessed the data and were in good agreement (kappa: 0.77). The results presented in this chapter indicate that the optical motion correction system greatly reduced motion artifacts when motion was present and did not impair the image quality in the absence of motion. Statistical analysis showed no significant difference between the SENSE and the non-accelerated acquisitions. In conclusion, optical motion correction has the potential to greatly improve 3D TOF angiograms regardless of whether it is used with or without SENSE. TOF MRA is a static imaging technique and does not provide hemodynamic information, which is important for the evaluation of stenotic vessels or Arteriovenous Malformations (AVM)s. Therefore, in the second part of this thesis, a pulsed-Continuous Arterial Spin Labeling (PCASL) based angiographic method called Time-Resolved Angiography using InfLow Subtraction (TRAILS) is introduced. It allows the acquisition of time-resolved whole-head angiographic datasets in healthy volunteers in a clinical feasible scan time of under five minutes on a 3T MRI unit. Using this novel method, in conjunction with a sliding window reconstruction, a temporal resolution of 7.2 ms with a temporal footprint of 432 ms was achieved. Excellent vessel visibility compared to a TOF acquisition was demonstrated. Normal variations of the vascular system including the Circle of Willis (CoW) were identified using TRAILS. Signal intensities were picked in various vascular segments to visualize the blood transit time. The results showed that TRAILS could be used to acquire hemodynamic information in healthy volunteers. In the third chapter of this thesis, an extension to TRAILS, eXtended Time Resolved Angiography using InfLow Subtraction (X--TRAILS), is introduced to accommodate patients who exhibit extremely slow blood flow patterns and consequently longer blood transit times. X--TRAILS uses variable repetition times to reduce RF exposure during the readout without increasing the temporal footprint. A feasibility study on patients that suffer from vascular diseases (e.g. AVMs, Moya-Moya) has been performed. Initial results with X--TRAILS on patients provided hemodynamic in- formation of the intravascular system with measured blood arrival times of 4.1 seconds. Additionally, Bloch simulations indicate that X--TRAILS can produce acceptable angiograms even when blood transit times are up to 6 seconds, but a validation study on patient groups who have such long blood transit times needs to be performed.