An image in which the signal from two spectral components (such as fat and water) is 180°
out of phase and leads to destructive
interference in a
voxel.
Since fat precesses slower than water, based on their
chemical shift, their signals will
decay and
precess in the transverse plane at different frequencies. When the
phase of the TE becomes opposed (180°), their combined signal intensities subtract with each other in the same
voxel, producing a signal void or dark band at the fat/water interface of the tissues being examined.
Opposed
phase gradient echo imaging for the abdomen is a lipid-type tissue sensitive sequence particularly for the
liver and adrenal glands, which puts a
signal intensity around abnormal water-based tissues or lesions that are fatty.
Due to the increased sensitivity of opposed
phase, the tissue visualization increases the lesion-to-liver
contrast and exhibits more
signal intensity loss in tissues containing small amounts of lipids compared to a
spin echo T1 with
fat suppression.
Using an opposed
phase gradient echo also provides the ability to differentiate various pathologies in the
brain, including lipids, methaemoglobin, protein, calcifications and melanin.
See also
Out of Phase, and
Dixon.
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