Spin Gymnastics 1 & 2
Frank Korosec1

1University of Wisconsin - Madison, United States


This educational lecture will provide a general overview of the basic physics of MRI. A broad range of topics will be covered, including magnetization and signal generation, relaxation of magnetization, the spin echo phenomenon, spatial encoding of signal, and a very brief introduction to the concept of k-space. Several of the topics will be introduced in this lecture and will be further elucidated by other presenters in this course.

Magnetization and the MR Signal

This educational lecture will begin by describing the concepts of magnetization, alignment of nuclear magnetic moments, formation of bulk magnetization, precession, the Larmor equation, the rotating frame of reference, tipping the magnetization from the longitudinal axis to the transverse plane, and signal generation and detection.


After signal generation and detection are described, the principles of T1 and T2 relaxation will be explained. This will include a description of spin dephasing, spin-spin interactions, signal decay, spin-lattice interactions, spin flips, regrowth of longitudinal magnetization, T1 and T2 relaxation properties of various states of matter (liquids, solids, and viscous tissues), effects of field strength on T1 and T2 relaxation, and other principles related to T1 and T2 relaxation.

Spin Echo

Principles of the spin echo phenomenon also will be described, including spin dephasing, spin rephrasing (refocusing spins with a 180-degree radiofrequency pulse), and the spin echo radiofrequency (RF) timing sequence. The timing sequence parameters known as TE (echo time) and TR (repetition time) will be defined, and their effects on T1, T2, and proton density weighting of the MR signal will be described.

Spatial Encoding of the MR Signal

The basic concepts of spatial encoding of the MR signal to produce images will be described. This will include explanations of the concepts of slice selection (tipping spins in a specific slice by applying a radiofrequency pulse containing a range of frequencies while simultaneously applying a slice selection gradient), frequency encoding (encoding position using different frequencies during signal readout), and phase encoding (encoding position using different phases). The concept of pulse sequence timing diagrams also will be introduced.


The lecture will finish with a very brief introduction to k-space. The relationship between imaging gradients and k-space will be described. Some common artifacts that arise from the misrepresentation of k-space will be explained.


No acknowledgement found.


No reference found.
Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)