Pulse Sequences and Image Contrast

Abstract

The MR signal intensity at a particular location is represented by the image pixel intensity. In Chaps. 8 and 9 it was shown that the strength of the MR signal relative to the background noise (SNR) depends on a number of instrumental factors including the magnetic field strength, the choice of receiver coil and system electronics, as well as image acquisition parameters including the field of view, image acquisition matrix size and slice thickness (defining the voxel volume), the number of signal samples, and the receiver bandwidth. It also depends on the sequence of rf and gradient pulses used to generate the MR signal echo, commonly referred to as the pulse sequence. The two main types of pulse sequences are gradient echo and spin echo pulse sequences. The choice of pulse sequence and its imaging parameters, including the timing parameters, repetition time, TR and echo time, and TE, determine the intrinsic strength of the MR signal from a particular tissue according to its proton density value and relaxation properties.