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Principles of Magnetic Resonance Imaging Physics
Technical Aspects
The principles of magnetization and physics allow us to create images via magnetic resonance imaging (MRI) noninvasively. In this chapter, an overview is provided on how images are created, illustrating the concepts of protons, radiofrequency (RF) excitation, T1 and T2 relaxation, image acquisition, spatial encoding, and Fourier transform analysis and k-space.
Magnetization and Protons
The nucleus of choice for imaging is hydrogen because the human body consists of an abundance of water as well as hydrogen. Every water molecule contains two hydrogen atoms, and lipids or proteins frequently contain numerous hydrogen atoms. Hydrogen atoms, also referred to as protons, precess at the Larmor frequency ( Figure 9-1 ). The Larmor frequency can be calculated from the gyromagnetic ratio and also the magnetic field strength of the magnet. All the spins comprise the net magnetization as aligned to B0. The Larmor frequency is the frequency at which the RF excitation pulse must be to alter magnetization to generate a signal and, subsequently, images.
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