What does TR stand for in a spin echo pulse sequence?

In a spin echo pulse sequence, TR stands for Repetition Time. This is a critical parameter that dictates the amount of time between successive radiofrequency (RF) pulse applications. It is vital in determining the timing of image acquisition and affects the contrast of the MRI images.

Repetition Time directly influences how much longitudinal relaxation can occur before the next RF pulse is applied, impacting the signal intensity and the overall image contrast. A longer TR allows for greater relaxation of the spins, which can enhance the signal from tissues with longer T1 relaxation times, leading to images that emphasize different tissue types.

Understanding TR is essential for optimizing MRI protocols, as it plays a significant role in achieving the desired imaging characteristics. While other terms such as Recovery Time, Realignment Time, and Radiation Time might exist in different contexts or be used in varying ways in radiology, they do not accurately define TR within the context of spin echo sequences.