FIGURE 2.
Illustration of the image processing in patients with ICP <20 mm Hg (Left) and ICP ≥20 mm Hg (Right). Upper, transorbital ultrasound images, zoomed in on the optic nerve sheath complex. Cardiovascular pulsation causes a motion dLeft on the left side of the ONS and a motion dRight on the right side. The rectangles show the regions used for tracking the motion. Middle, transverse pulsatile displacements as a function of time (vertical axis) after extraction of the motion component corresponding to the fundamental heart rate frequency. Note that the curves are strongly zoomed in compared with the images in the upper row (the squares are 25 pixels wide; pulsation is approximately 0.1 pixel). Lower, the same curves superimposed, with transverse pulsatile displacement along the vertical axis and time along the horizontal axis. Note that the displacements are more symmetric on each side of the optic nerve for the patient with ICP ≥20 mm Hg in comparison with the patient with ICP <20 mm Hg. This is consistent with the idea that raised ICP makes the ONS stiffer, which could be observed as more equal transverse motion on each side of the ONS (ie, less deformation). ICP, intracranial pressure; ONS, optic nerve sheath. Color version available online only.