What are TR and TE time parameters and how do they relate to magnetic resonance imaging (MRI)?
MRI functions by submitting the tissue to a strong magnetic field and then disturbing that magnetization in tissue by using radiofrequency (RF) pulses. The return of an RF signal from the tissue is then detected and used to construct an image. TR is the time of repetition parameter or the time between 90° RF pulses. TE is the time to echo or the time between 90° pulse and the time when the signal from the tissue is recorded. Modulation of TR and TE parameters determines how much T1 and T2 weighting any given image displays ( Table 8.3 ). TR and TE also determine how long a sequence takes to acquire (from seconds to minutes) and how much heating of the tissue occurs.