Figure 1:

SI versus frame number for two voxels at time-resolved MR angiography. SIs increase in response to arrival and transit of contrast material. TOA is determined for each voxel by first identifying maximal measured SIs (M1 and M2for Voxel 1 and Voxel 2, respectively), next calculating 0.30 of maximal values (0.3 M1, 0.3 M2), and finally interpolating between the frame numbers whose respective SIs straddle these 0.30 values. In this example, for voxel 1, TOA is determined to be 5.5 frame intervals after time origin. For voxel 2, TOA is 11.6 frame intervals. From knowledge that frame interval is 5.4 seconds, absolute TOA values for voxels 1 and 2 are 29.7 and 62.6 seconds, respectively. a.u = Arbitrary unit.