Introductory Magnetic Resonance Imaging Physics

This chapter introduces the key conceptual underpinnings of magnetic resonance imaging (MRI) with an intuitive description of the underlying physics. The behavior of proton magnetization within an externally applied magnetic field is described, as is the use of radiofrequency magnetic field pulses to manipulate magnetization and create detectable signal. Determinants of image contrast are explored by describing the growth and disappearance of longitudinal and transverse magnetization due to the effects of the inherent tissue T1 and T2 relaxation rates during the repetition time and echo time. Spatial localization by magnetic field gradients is explained, including a conceptual description of k-space and Fourier transformation. These elements of signal creation, image contrast creation, and spatial localization are brought together as building blocks of the basic MRI pulse sequence. Other commonly used techniques are introduced, including diffusion weighted and susceptbility weighted imaging, motion compensation methods, and parallel imaging.