T1 Out of Phase (OOP) images in Abdominal imaging

• Sequence used to identify regions of fatty infiltration and help identify adenomas.
• aka chemical shift imaging
• Relies of differences in the precessional frequency of Hydrogen in fat and water molecules.
• Gradient echo image with TE set to a time where fat and water spins are 180 degrees out of phase causing fat and water signal components within a voxel to destructively interfere and reduce the brightness of the pixel.
• Degree of signal change depends on the ration of fat/water. All fat or all water, no signal drop (compared to in-phase image) 50/50 causes total signal loss
• OOP images identified by dark bands at fat water interfaces
• Select the shortest OOP TE to get best T1 contrast and largest number of slices
• Exact TE depends on filed strength