MRI Glossary

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This is a glossary of terms for MRI - feel free to add any more.

- One data set of n Fourier lines where n = the number of phase encoded lines of the matrix. Two or more sets may be averaged to improve signal to noise ratio.

Amplitude - Maximum value - eg the peak of an echo.

Angular Magnetic Moment - Magnetic property which produces a magnetic field and causes alignment with external magnetic fields.

Bipolar Flow-Encoding Gradients - Gradients whose polarity is inverted ti encode velocities as charges of phase - a technique used in phase-contrast angiography. (1)

Bloch Equations - Equations which approximate the signal strength received as a result of various imaging sequences.

Cross Excitation - Radio Frequency (RF) interference between adjacent slices due to non rectangular RF pulse profiles. This may result in loss of signal and Repetition Time (TR) shortening.

Echo - Characteristic signal received during spin-echo sequence following refocusing with 180 degree pulse - shaped like two back to back Free Induction Decay (FIDs).

First Echo Image - Also known as a 'Proton Density' image generated with a long Repetition time (TR) and a short Echo Time (TE).

Flow Related Enhancement - Phenomenon of increased intensity in moving tissues relative to stationary tissue.

Fourier Transformation - Mathematical technique used to resolve the complex wave-form into phase and frequency components to allow spatial localization of the signal.

Free Induction Decay (FID) - Signal produced by rotating transverse magnetization following a 90 degree pulse. Decays at a rate governed by T2*.

Frequency Encoding - Method of spatially localizing an MR signal using a magnetic gradient to vary the frequency dependent on position.

Gauss - Unit of magnetic field strength. 1 Gauss = 1/10,000 Tesla. The earths magnetic field varies from about 0.3 to 0.7 Gauss. (Pacemaker line = 5 Gauss).

Gradient Echo Imaging - Method of producing an echo by reversing the direction of a magnetic gradient

Signal Averaging - An SNR-enhancing technique in which the same MRI signal is repeatedly acquired tow or more times and then combined and averaged. (1)


1. Bontrager, K. L., & Lampignano, J. P. (2005). Textbook of Radiographic Positioning and Related Anatomy 6th edition. Elsevier Mosby