The FEER method was the first clinically useful
flow quantification method using
phase effects, from which all
spin phase related
flow quantification techniques currently in use are derived.
In this sequence a
gradient echo is measured after a
gradient with
flow compensation. The measured signal
phase should be zero for all pixels. A deviation from
gradient symmetry by shifting the
gradient ramp slightly away from the symmetry condition will impart a defined
phase shift to the
magnetization vectors associated with spins from pixels with
flow.
Slight stable variations in the
magnetic field across the imaging volume will prevent the
phase angle from being uniformly zero throughout the volume in the flow-compensated image.
The first image (acquired without
gradient shift) serves as reference, defining the values of all
pixel phase angles in the
flow (motion) compensated sequence.
Ensuing images with
gradient phase shifts imparted in each of the 3 spatial axes will then permit measurement of the 3 components of the
velocity vector v = (vx, vy, vz) by calculating the respective phases px, py and pz by simply subtracting the
pixel phases measured in the compensated image from the 3 images with a well defined
velocity sensitization.
The determination of all 3 components of the
velocity vector requires the measurement of 4 images.
The
phase quantification requires an imaging time four times longer than the simple measurement of a
phase image and associated
magnitude image.
If only one arbitrary
flow direction is of interest, it suffices to acquire the reference image plus one image
velocity sensitized in the arbitrary direction of interest.
See also
Flow Quantification.
•
] and 1 definition [
], (+ 5 Boolean[
] results
Further Reading:
Random Page
top
