Fig 2.

First, warped images of the late arterial phase were obtained by using nonrigid registration (SyN–cross-correlation) adjusted to the arterial phase images. The subtracted spinal CTA by using nonrigid registration was then obtained by subtracting warped images that were multiplied by 1.1 from the arterial phase images. R-CTA and conventional spinal CTA were analyzed with digital subtraction angiography results as a reference standard, and the difference in diagnostic performance was assessed.