Page 55 - Libro 2

PART 2 • CEREBROVASCULAR
4
The Extracranial Duplex Ultrasound Examination
Kari A. Campbell and R. Eugene Zierler
OBJECTIVES
List the essential components of a carotid duplex ultrasound examination
Describe the normal waveform characteristics of the extracranial carotid vessels
Define the common diagnostic criteria used to evaluate the extracranial carotid vessels
Describe common pathology observed during a carotid duplex ultrasound examination
KEY TERMS
carotid artery | carotid duplex | extracranial cerebrovascular disease | spectral analysis | stroke | vertebral artery
GLOSSARY
bruit an abnormal “blowing” or “swishing” sound heard with a stethoscope while auscultating over an artery such as the carotid; the sound results from vibrations that are transmitted through the tissues when blood flows through a stenotic artery; although the presence of a bruit is a sign of arte- rial disease, the absence of a bruit is less diagnostic because all stenoses are not associated with bruits
carotid bulb a slight dilation involving variable portions of the distal common and proximal inter- nal carotid arteries, often including the origin of the external carotid artery; this is where the barorecep- tors assisting in reflex blood pressure control are located; the carotid bulb tends to be most promi- nent in normal young individuals
Doppler angle most commonly defined as the angle between the line of the Doppler ultrasound beam and the arterial wall (also referred to as the “angle of insonation”); this is a key variable in the Doppler equation used to calculate flow velocity
spectral analysis spectral analysis is a signal processing technique that displays the complete frequency and amplitude content of the Doppler flow signal; the spectral information is usually pre- sented as waveforms with frequency (converted to a velocity scale) on the vertical axis, time on the horizontal axis, and amplitude indicated by a gray scale
spectral broadening an increase in the “width” of the spectral waveform (frequency band) or “filling-in” of the normal clear area under the systolic peak; this represents turbulent blood flow associated with arterial lesions
transient ischemic attack (TIA) an episode of stroke-like neurologic symptoms that typically lasts for a few minutes to several hours and then resolves completely; this is caused by temporary interruption of the blood supply to the brain in the distribution of a cerebral artery
35