Ipsilateral describes a structure on the same side; for example in a sonogram of the left internal carotid artery, the ipsilateral common carotid artery would be the left common carotid artery.

The transorbital window allow to insonate ophthalmic artery and ipsilateral carotid siphon through the eye. It is also possible to use the transorbital entrance to scan the middle and anterior cerebral arteries, if it is impossible through the transtemporal window.
The patient is asked to remove any contact lenses prior to examination and is instructed to close the eyes. The power output of the Doppler instrument has to be decreased to 10-20% to reduce the ultrasonic exposure of the eye.

See also Transcranial Doppler, Ultrasound Safety.