How Magnetic Particle Imaging Works

In this chapter, the basic concepts of MPI are introduced. In order to get MPI to work, two basic ingredients are needed: First, one has to find a way to get the particles to emit some kind of characteristic signal that reveals their existence. To end up at a quantitative method, this signal should also carry information about the amount of magnetic material, i.e., the particle concentration. How this signal encoding is done in MPI is explained in Sect. 2.3. As a second component, one needs a way to determine where the signal comes from in relation to the object under examination. This usually is called spatial encoding and is achieved by making the emitted characteristic particle signal spatially dependent. In Sect. 2.4, the basic principle of spatial encoding is introduced. As it turns out, the simplest method for spatial encoding is rather slow and cannot fulfill the real-time requirements that potential applications have. Therefore, the subject of Sect. 2.5 is a way to improve the MPI performance with respect to acquisition time. Still, this performance upgrade is only capable of imaging small volumes of few centimeters in length. To circumvent this size limitation, in Sect. 2.6 a way to handle large imaging volumes is introduced. Finally in Sect. 2.7, limitations of MPI in spatial resolution and sensitivity are discussed.