Development of Arterial Spin Labeling Techniques forQuantitative Perfusion Measurements at 3 Tesla

Microvascular perfusion is an important parameter of high clinical value as it provides important information on tissue viability and function. In contrast to dynamic contrastenhanced magnetic resonance imaging (DCE-MRI), arterial spin labeling (ASL) is a method to assess quantitative perfusion values non-invasively by MRI. The main goal of this work was the development of a 3D ASL technique that allows the quantitative perfusion measurement within a whole volume. Further, the diagnostic signifcance of ASL was tested by applying it in dedicated renal disease models. ASL yielded significantly (P < 0.01) different values in healthy kidneys ((500+-91) ml/100g/min) compared to kidneys with acute kidney injury ((287+-83) ml/100/min) as well as for acutely rejected transplanted kidneys compared to chronically rejected grafts. A comparison to DCE-MRI showed no signifcant differences. While literature reports on 3D ASL sequences show a prevalence for spin-echo based data acquisitions, the presented sequence employs a 3D balanced steady-state free precession (bSSFP) readout that has the ability to overcome some of the drawbacks of spin-echo based 3D sequences. The developed 3D ASL technique includes several features, each of which has been optimized separately. Special emphasis was put on design, simulation, and implementation of a slice-selective adiabatic inversion pulse. In an initial measurement, the whole-brain perfusion of a healthy volunteer was assessed with an isotropic resolution of 3mm. Mean perfusion values were f_GM = (51+-17) ml/100g/min and f_WM = (24+-8) ml/100/min for gray and white matter, respectively, which are in very good agreement with findings from the "gold-standard" method of 15O-positron emission tomography. The diagnostic value of ASL in combination with the possibility to assess absolute perfusion values in a whole volume makes it a promising technique for future clinical diagnosis.