fMRI of a patient with secondary glioblastoma (brain tumor). Functional localization was measured before surgery by means of a motor task (hand opening and closing). On the left, the uncorrected scan, on the right the result after dynamic image correction. Image courtesy of Quelle: MUW/ High Field MR Centre of Excellence
May 3, 2018 — With the support of the Austrian Science Fund FWF, researchers from Vienna have developed methods to improve functional magnetic resonance imaging (MRI) with the new generation of highly sensitive 7 Tesla (7T) scanners. These devices can create precise maps of the brain before surgery to help surgeons avoid damaging vital areas.
If one is about to cut into a human brain, it is better to have an exact map in hand. The seat of the human mind is richly perfused with blood vessels. Densely packed in furrows and trenches, vital bodily and mental functions are embodied in wired groups of neurons in distinct functional areas. In order to produce a precise map of these areas, the brains of patients are scanned using functional magnetic resonance imaging (fMRI). Images of their brains are recorded at short intervals while they perform various tasks, and the brain activity is mapped in three dimensions. This process is designed to ensure that areas vital for motor function, language and memory remain unharmed when diseased tissue is removed during surgery. The man-machine interaction results in distortions in the images, however, which need to be corrected in order to achieve a perfect match between brain anatomy and brain function.
The MRI scanners currently in clinical use have a magnetic field of 3 Tesla, but the next generation of ultra-high-field scanners with a 7T field are already being tested. “7T scanners are capable of an even higher resolution and give more contrast. But they are also more susceptible to distortions which lead to imprecise functional imaging. Hence, we first need to solve the problems of 7T in order to fully reap its benefits”, said principal investigator Simon Robinson, describing the motivation for a research project at the Medical University of Vienna (MUW) that was funded by the Austrian Science Fund FWF. Austria’s only 7T scanner, one of 50 in the entire world, was installed at MUW’s High Field MR Centre in 2008.
The higher magnetic field strength provides faster images of the brain functions at a higher resolution. “In this way we are able to see, for instance, whether the language center has been displaced by a tumor. Unfortunately, the distortions of the magnetic field caused by bones, tissue and air are also stronger with 7T, which has implications for the mapping accuracy,” explained Robinson, from the Department for Biomedical Imaging and Image-guided Therapy. Without image correction, the functional areas would not be localized in the brain at the required level of precision.
The proximity of a number of clinics was essential to realizing the project goals, and internal and external project partners contributed expert input relating to physics, programming, clinical fMRI and neurology. For the development of a 7T image correction method, Robinson and his team worked with people suffering from either epilepsy or brain tumors. fMRI depends on the fact that some of the body’s own molecules (hemoglobin in the blood in this particular case) alter the brain’s magnetic field. Countless scans register small changes (e.g. in blood flow or oxygen consumption), thus identifying the areas in the patient’s brain which process cognitive or motor tasks.
During the five-year project, the team developed a dynamic image correction process that is an international standard for fMRI studies — for pre-surgery planning, but also for basic research in neuroscience. Before the functional measurements start, the contribution of the scanner to the measured signals is determined precisely. This correction factor is then deducted from the functional images during the image computation. 7T thus helps to create a precise 3-D map of individual brains, where functional brain areas are localised exactly within the anatomy of the brain.
Neurologists can then decide whether surgery is useful or even possible, and which parts of the brain need to be spared at all costs. In a follow-up project, the team intends to develop the method further in order to help determine the best possible location for deep brain stimulation probes in patients suffering from Parkinson’s disease.
For more information: www.fwf.ac.at