MRI (Magnetic Resonance Imaging) Introduction

Abstract

The organization of the MR gamuts is heavily based on the appearance of lesions on T1- and T2-weighted images. For those readers less familiar with magnetic resonance imaging, let me add that a T1-weighted spin echo image is one with a short repetition time (TR) and a short echo delay time (TE) (which are both operator-selectable imaging parameters). (“Short” in the context of TR is less than 500 msec and “short” in the context of TE is ideally less than 20 msec — for a high-field system — or 30 msec for a low or mid field system.) T1-weighted gradient echo images are acquired with flip angles larger than 45° and echo delay times generally less than 10 msec. If the repetition times are less than 200 msec, then either RF or gradient spoiling should be used. Such T1-weighted gradient echo techniques are known as FLASH (Siemens), SPGR (for spoiled GRASS, GE), or RF-Spoiled FAST (Picker).