%0 Generic
%A Mie, Moritz Bernhard
%D 2011
%F heidok:12151
%K Oxygenation , Brain , BOLD , MRI
%R 10.11588/heidok.00012151
%T Quantification of Brain Tissue Oxygenation : Comparison of Different Gradient Echo/Spin Echo MRI Techniques at 3 Tesla
%U https://archiv.ub.uni-heidelberg.de/volltextserver/12151/
%X In this work, an established tissue model was used to calculate the venous blood fraction (lambda), the irreversible relaxation rate (R2) and the reversible relaxation rate (R2') on the basis of a three-parameter fit of the MR signal (white matter: lambda = (1.9 ± 0.9)%, R2 = (14.9 ± 1.4)Hz, R2' = (2.3 ± 0.7)Hz; gray matter: lambda = (2.8±2.1)%,R2 = (11.6±3.2)Hz, R2' = (3.5±2.4)Hz). These parameters enable the quantification of the susceptibility difference (D_chi) between venous blood and surrounding tissue and, therewith, the oxygen extraction fraction (OEF, white matter: (42.9 ± 16.3)%; gray matter: (43.9 ± 14.4)%). The focus of this work was on the development of different methods to reduce the number of required fit parameters by separate measurements of the parameters to increase the fit accuracy. This was achieved with a separate calculation of the cerebral blood volume (CBV) by a dynamic susceptibility contrast (DSC) measurement. This value could be used as an input parameter of the signal equation resulting in a two-parameter fit. This method yielded OEF values of (37.5±4.6)% in healthy white matter and (27.8±4.3)% in tumorous brain tissue. Another approach was the determination of the other two other parameters (R2 and R2') in separate measurements (white matter: R2 = (14.4 ± 0.8)Hz, R2' = (7.3 ± 1.4)Hz; gray matter: R2 = (12.8 ± 1.8)Hz, R2' = (8.0 ± 2.2)Hz) and a subsequent correction and validation using different phantom measurements. This technique was finally employed for in vivo experiments. The separate fitting approach promises a high fit certainty and yielded OEF values of (22.0±3.4)% and (26.9±6.5)% for white and gray matter, respectively. In this work, another method for OEF calculation is described based on the separation of the signal components originating from the veins from the remaining signal. The subsequent measurement of the transverse relaxation rate - (13.1 - 18.9)Hz in the investigated regions - and a calibration of the oxygenation level enable the OEF calculation. Furthermore, susceptibility weighted imaging (SWI), a method with an imaging contrast depending on the oxygenation status of the veins, was transferred from brain to renal imaging. The implemented technique improved the average contrast-to-noise ratio by 33% compared to the standard SWI method. After the reconstruction of SWI images of the kidneys, the change of the contrast due to oxygenation variation was qualitatively observed. The presented methods yielded promising results for the determination of the OEF, which is an indicator for tissue viability. This determination might be used in radiotherapy for irradiation planning and therapy monitoring.