Signal Intensity Gradient in Cerebral Arteries

"In time-of-flight (TOF) MRA, The signal intensities at the iso-point (Φa; signal intensity at position A \[Xa\] along the arterial contour line) and at the inner point (Φb; signal intensity at position B \[Xb\]) were calculated by using a trilinear interpolation algorithm based on the positions and signal intensities in the eight neighboring voxels. The signal intensities of TOF-MRA were normalized to eliminate the offset and scale effects across the MRA datasets of participants. For each iso-point (position A), the SIG was calculated from the difference in signal intensities between points A and B as follows:~Scalar SIG, SI/mm = (Φb - Φa) / │Xb - Xa│ (1)~Vector SIG, SI/mm = (Φb - Φa) n / │Xb - Xa│ (2)"