Hannes M. Wiesner

Alumni of the Department High-Field Magnetic Resonance

Main Focus

Increased oxygenation of blood is the base for signal increases in the BOLD signal in functional Brain Imaging (fMRI). I am interested in the question to what extent energy consumption measured by oxygen consumption is related to an increase in the neural activity in the brain during the processing of information (stimulation). Aerobic metabolism (i.e. oxidative phosphorylation from oxygen gas to water and carbon-dioxide) being the most efficient biochemical pathway of tissue respiration, could be used as a key indicator of the bioenergetics of neural networks.

In my project in the group 'physiological basis of fMRI signals' of Dr. Uludag the oxygen metabolism of brain tissue in rats is investigated at 16.4 Tesla by the use of 17-O MRI, fMRI and ASL. Using the strongest available field-strength of an MRI-magnet this size, the challenges in the imaging of the low abundant, of are adressed by: physiological stability, custom MRI sequences, novel heteronuclear 17O/1H RF-coils and further development in the quantification of the cerebral metabolic rate of oxygen (CMRO2).

Further literature can be found

Increases of neural activity result in changes of blood flow (CBF) in brain tissue, involving increases in glucose consumption as well as changes in the cerebral metabolic rate of oxygen consumption (CMRO2) and most prominently in a change of blood oxygenation (BOLD) which is the base of fMRI brain-imaging. The dynamics of CMRO2 are investigated by the use of 17-O in this project.

It is widely assumed that neural activity is accompanied by an increase of oxygen consumption, but measurements from positron emission tomography (PET) lack consistent confirmation of this effect due to limits of spatial resolution and reproducibility of the method. Therefore, the detailed coupling between oxygen metabolism, hemodynamics and neural activity is still debated, especially during prolonged activity and different types of stimuli. Using the stable isotope of oxygen 17-O, which is rare in natural abundance, it is possible to image oxygen metabolism with nuclear magnetic resonance. The approach is similar as in PET but more specifically focused in terms of resolution and specifically limited on the product of oxygen metabolism in mitochondria: metabolized water.

Measuring MR signals of 17-O at ultra high field strengths like 9.4 up to 16.4 Tesla, in animals and humans is especially advantageous as 17-O is hardly detectable at lower field strengths. With specific MR equipment and kinetic models developed in this project the imaging of oxygen metabolism is potentially expected to excel in spatial resolution, have higher functional specificity and presumably show higher reproducibility than alternative oxygen imaging methods. This opens up the possibility to correlate the coupling of CMRO2 with BOLD contrast and CBF, resulting in a better understanding of the underlying physiology of the BOLD signal.

For further literature related to this project visit:

Curriculum Vitae

Curriculum Vitae


2000-2003 & at Baden-Wuerttemberg Cooperative State University - Stuttgart (DHBW)

2004-2005 M.Sc. in Cognitive Science and Natural Language at , Thesis on Neural Computation under supervision of .

2006-present PhD student in the at the , MPI for Biological Cybernetics in the research group on fMRI & brain physiology of

2007-present Visiting research fellow at investigating cerebral oxygen metabolism for and .

Professional Experience

2003-2004 Software-Developer at
2006 Internship at in the group of .
2007 Independent Lecturer in 'Database Systems' at .

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