Black Boundary Artifact

The Black Boundary Artifact is an artificially created black line located at fat-water interfaces such as muscle-fat interfaces. This results in a sharp delineation of the muscle-fat boundary that is sometimes visually appealing but not an anatomical structure. The following is a coronal image through the upper body with an echo time of 7ms. A black line is seen surrounding the muscles of the shoulder girdle as well as around the liver.

This artifact can occur for a couple of reasons. The most common reason I have found is a result of selecting an echo time (TE) in which the fat and water spins (located in the same pixel at an interface) are out of phase, cancelling each other. At 1.5 T, the 3.5 PPM difference in frequency between water and saturated fat results in cancellation of spins at 4.5 ms multiples, starting at about 2.3 ms; for example at 6.8ms, 11.3ms, and 15.9 ms. To avoid this artifact, TE's close to 4.5ms, 9ms, 13.6ms,... should be chosen.