MRI pulse sequences Flashcards
Conventional Spin echo
Slice select gradient: Always on when a rf-pulse is given.
Phase encoding gradient: Sometime between the excitation pulse (the pulse that brings longitudinal magnetization into the transverse plane) and TE. It is usually drawn different from the other gradients (with multiple lines or solid) as it is the only gradient that keeps changing with each repetition to encode the different lines in k-space.
Frequency encoding gradient: Is on during readout (also called readout gradient for that reason) at TE, it is often drawn as a bilobed gradient. TE is often labeled or can be deduced by the 180 degree refocusing pulse, which is given at 1/2 TE. Also notice how the signal comes back at TE due to the effects of the refocusing pulse, also indicating at which point in the diagram TE is.
Dual echo spin echo sequence
Slice select gradient: Always on when a rf-pulse is given.
Phase encoding gradient: Sometime between the excitation pulse (the pulse that brings longitudinal magnetization into the transverse plane) and TE. It is usually drawn different from the other gradients (with multiple lines or solid) as it is the only gradient that keeps changing with each repetition to encode the different lines in k-space.
Frequency encoding gradient: Is on during readout (also called readout gradient for that reason) at TE, it is often drawn as a bilobed gradient. TE is often labeled or can be deduced by the 180 degree refocusing pulse, which is given at 1/2 TE. Also notice how the signal comes back at TE due to the effects of the refocusing pulse, also indicating at which point in the diagram TE is.
A fast spin echo sequence would have a phase encoding gradient before each echo, since each echo encodes a different line in k-space.
when does the slice select gradient get turned on
during an exciting pulse (90 or 180 degree pulses)
