Pretty Porous

MRI and contrast agent perfusion in brain tissue

Magnetic resonance imaging (MRI) is an immensely important and versatile imaging technique used for medical imaging. The technique is based on the nuclear magnetic resonance of hydrogen atoms to radio frequency signals in strong magnetic fields. MRI avoids damaging radiation (e.g. X-rays) and is usually considered non-invasive. MRI of the brain is, for example, used in the diagnosis and therapy monitoring of brain tumors, in the analysis of neurodegenerative diseases such as Alzheimer’s or Parkinson’s disease, and diseases of the central nervous system, such as multiple sclerosis. In a variant of MRI called perfusion MRI, a contrast agent is injected into the blood stream and a sequence of MR images is taken to observe the fate of this contrast agent.

Why is it important that the brain is a porous medium?
Like most biological soft tissues, brain tissue consists of a mixture of cells, fibres, and fluid within the cells and the interstitial space (pore space). Cells are supplied by blood vessels with oxygen and nutrients. The blood vessels also consist of cells and blood is a mixture of fluid and various cells. This complex tissue architecture complicates the interpretation of the MRI images.

How can computer simulations help?
Computer models are the basis for the image post-processing done for perfusion MRI data. The model simulates both contrast agent perfusion and the resulting MRI signal and compares the result with the data. Hereby, certain properties of the brain tissue can be inferred. For example, the blood volume fraction can be estimated—an important biomarker for tumors, but equally important to assess the possible damage after a stroke. Simple simulations only take seconds and thus immediately provide important additional informations to medical doctors for decision making.

At the University of Stuttgart, researchers develop novel simulation techniques with the goal of extracting further information from MRI data. Using computer simulations, they try to better understand how contrast agent spreads in brain tissue and how different properties of the tissue influence MRT data.

Credits: University of Stuttgart / Timo Koch