(f)MRIToolkit 2019

Introduction

In this tutorial we will go through the standard processing pipeline for quantitative susceptibility mapping (QSM), a novel contrast mechanism that can provide local tissue magnetic properties, which is very useful to measure, for example, iron concentration in the brain.

Briefly, there are two main types of magnetic property (a.k.a magnetic susceptibility) we can measure with MR:

• Paramagnetism: substances with paramagnetic property generate a secondary magnetic field that can enhance the existing magnetic field generated by the MRI scanner. A typical example is iron molecules;
• Diamagnetism: substances with diamagnetic property generate a secondary magnetic field that can reduce the existing magnetic field strength. Examples included myelin and calcification.

Because of the secondary magnetic field generated by (both paramagnetic and diamagnetic) tissues, the overall magnetic field experienced by the water protons (which is the main source of MRI signal) will no longer be the same across the whole brain. The strength of this magnetic field inhomogeneity will depend on the local magnetic susceptibility sources: stronger source can create a stronger inhomogeneity effect. As a result, the water protons will resonate in different frequencies across the whole brain. Measuring the frequency shift can, therefore, compute the magnetic susceptibility of brain tissues and reveal their cellular environment.

You follow the exercises to know more about some QSM knowledge and processing techniques:
Exercise 1
Exercise 2
Exercise 3
Exercise 4