Entry Slice Phenomenon

Entry slice phenomenon occurs when unsaturated spins in blood first enter into a slice or slices. It is characterized by bright signal in a blood vessel (artery or vein) at the first slice that the vessel enters. Usually the signal is seen on more than one slice, fading with distance. This artifact has been confused with thrombosis with disastrous results. The characteristic location and if necessary, the use of gradient echo flow techniques can be used to differentiate entry slice artifacts from occlusions.