Time spatial labeling inversion pulse cerebral MR angiography without subtraction by use of dual inversion recovery background suppression.

Time-spatial labeling inversion pulse (time-SLIP), which is a technique of nonenhanced magnetic resonance angiography (MRA) based on arterial spin labeling (ASL), is used in various situations. Although subtraction between the images obtained with and without ASL is usually employed in cerebral time-SLIP MRA, to reduce the imaging time, dual inversion recovery (IR) has been applied for suppression of the background signals in this study. Appropriate timings for the 1st IR, 2nd IR, and the interval of data acquisition were investigated using computer simulation and a phantom experiment. With a short interval of data acquisition, the visibility of the simulated vessel was inadequate because replacement of the suppressed flow was insufficient. With a long interval of data acquisition, the contrast between the vessel and background was reduced. The reasons for this appeared to be the following: the longitudinal magnetization of the replaced flow is reduced because of the prolonged 2nd inversion time, causing a mismatch of the null point between the calculated and the actual values to become prominent. As a result, 3-4 s seemed to be an appropriate interval for data acquisition. Sufficient angiographic information could be obtained by use of dual IR background suppression in a volunteer study. With this technique, cerebral time-SLIP MRA can be performed in half of the imaging time required with the conventional subtraction technique.