APPLIED RADIOLOGICAL ANATOMY

Detailed explanation-1: -The examiner should be able to differentiate the internal carotid artery (ICA) from the external carotid artery (ECA). The ICA is located posterior and lateral to the ECA. The ICA is slightly larger than the ECA. The ECA has branches such as the lingual artery, but the ICA does not.

Detailed explanation-2: -There is a distinct difference in the spectral Doppler pattern between the external and internal carotid artery. The external carotid artery supplies a “high” resistance vascular bed”, while the internal carotid artery supplies the brain which has a low resistance vascular bed.

Detailed explanation-3: -Since some disease states may alter the usual diastolic patterns, vigorous tapping on the ipsilateral superficial temporal artery (a branch of the ECA) is customarily used to produce undulation of the Doppler waveform, thus confirming a waveform was obtained in the ECA.

Detailed explanation-4: -The ICA has a typical low-resistance waveform that reflects the low resistance of the cerebral circulation. Normal velocities range from 60 to 90 cm/s. The ECA has a higher resistance pattern because it supplies the soft tissues of the face and neck.