MR angiography using spin‐lock flow tagging

A method for MR angiography using an RF labeling technique is suggested. The method utilizes a slice‐selective spin‐lock pulse sequence for tagging the spins of inflowing blood. The pulse sequence begins with a spatially selective 90° x RF pulse, followed by a nonselective composite locking pulse of 135° y − n[360° y ]‐135° y and by a 90° ‐x pulse. A spoiler gradient is then applied. A rapid imaging stage, which yields a T 1 ρ‐weighted signal from the tagged spins, completes the sequence. Untagged spins are thoroughly dephased and consequently suppressed in the image. Thus, contrast is obtained without an injection of a contrast material or image subtraction. Furthermore, the flow of the tagged bolus can be visualized. The sequence was implemented on phantoms and on human volunteers using a 1.5T scanner. The results indicate the feasibility of the suggested sequence. Magn Reson Med 46:1041–1044, 2001. © 2001 Wiley‐Liss, Inc.