Order of MR Imaging Encoding Steps

1. What is phase encoding steps in MRI?
2. How do we perform frequency encoding in MR imaging?
3. How is the number of phase encoding steps determined?

What is phase encoding steps in MRI?

The phase encoding gradient (GPE) intervenes for a limited time period. While it is applied, it modifies the spin resonance frequencies, inducing dephasing, which persists after the gradient is interrupted. This results in all the protons precessing in the same frequency but in different phases.

How do we perform frequency encoding in MR imaging?

Frequency-encoding of spatial position is accomplished through the use of supplemental magnetic field gradients. Gradients mildly distort the main magnetic field in a predictable pattern, causing the resonance frequency to vary as a function of position.

How is the number of phase encoding steps determined?

We need to repeat an entire MR sequence for each different phase-encoding gradient we need to measure, and we need to do one for each row of pixels in the image (i.e. if our image is 256 x 256, then we need to do 256 phase-encoding steps). Each phase-encoding step is stored as a different row in the K-space matrix.