What happens to scan time if TR is increased in a spin echo pulse sequence?

In a spin echo pulse sequence, the repetition time (TR) is the time between successive excitations of the same slice. When the TR is increased, it allows more time for relaxation processes (T1 recovery) to occur between the excitations. This extended relaxation time often results in an increase in scan time because the imaging acquisition is based on the TR; longer TRs mean that fewer slices can be excited within a given period, thus prolonging the overall scan duration.

As more time is allocated for each TR, it also provides the potential for improved image quality because it allows the tissues more time to relax, leading to better contrast based on T1 characteristics. However, the immediate impact is a direct correlation between longer TR and an increase in total scan time, making the correct answer indicative of this relationship.