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 degrees (x) RF pulse, followed by a nonselective composite locking pulse of 135 degrees (y) - n[360 degrees (y)]-135 degrees (y) and by a 90 degrees (-x) pulse. A spoiler gradient is then applied. A rapid imaging stage, which yields a T(1)rho-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.