black boundary artifact
Black boundary artifact, also known as India ink artifact or type 2 chemical shift artifact, is an artificially-created black line located at fat-water interfaces such as those between muscle and fat. This results in a sharp delineation of the muscle-fat boundary lending the image an appearance as if someone has outlined these interfaces with ink that is sometimes visually appealing but not an anatomical structure.
This artifact occurs in gradient echo (GE) sequences as a result of selecting an echo time (TE) in which the fat and water spins (located in the same voxel at an interface) are out of phase, canceling each other. At 1.5 T, the 3.5 ppm difference in frequency between water and saturated fat results in cancelation of spins at 4.5 ms multiples, starting at about 2.3 ms; for example at 6.8 ms, 11.3 ms, and 15.9 ms. This artifact does not occur with spin echo (SE) sequences as the spins are rephased by the 180 refocusing gradient.
To avoid this artifact:
- choose TEs close to 4.5 ms, 9 ms, 13.6 ms
- fat suppression can be used
- use SE sequence instead of GE
Black boundary artifact has several other synonyms, including chemical shift artifact of the 2 kind, phase cancelation artifact, edging artifact, and black line artifact.
Aids in the diagnosis of benign conditions :
Aids in the identification of inflammation :