Norm of Doppler Ultrasonographic Flow Studies (Carotid Doppler, Carotid Artery Echography, Carotid Artery Ultrasonography, Duplex Ultrasonography, Transcranial Doppler Ultrasonography)
Normal intracranial arterial flow velocity. Normal carotid artery anatomy or unimpeded blood flow of that portion of the circulation evaluated.
Usage of Doppler Ultrasonographic Flow Studies (Carotid Doppler, Carotid Artery Echography, Carotid Artery Ultrasonography, Duplex Ultrasonography, Transcranial Doppler Ultrasonography)
Transcranial Doppler ultrasonography is used to evaluate blood flow through the cerebral arteries. Diagnostic in intracranial aneurysms, arteriovenous malformations, and moyamoya syndrome. Allows assessment of blood supply in intracranial neoplasms. Used intraoperatively to monitor velocity in the middle portion of the cerebral artery during carotid endarterectomy. Used in the evaluation of collateral circulation stenosis, vasoconstriction as a result of insult, and cerebral dynamics after head injury and in establishing brain death in adults. Used to predict the risk of stroke in children with sickle cell anemia. Carotid Doppler ultrasonography, carotid artery ultrasonography, and carotid artery echography are used for detection or preoperative evaluation of atherosclerotic carotid artery disease and cerebrovascular disease. Duplex ultrasonography is used for evaluation of conditions such as renal artery stenosis and deep vein thrombosis, and postoperatively for evaluating carotid endarterectomy and cardiac function. When evaluating for deep vein thrombosis (DVT), the flow of the vessel is studied as the vessel is compressed. If the vessel cannot be completely compressed to eliminate flow, the test is very sensitive and specific for DVT in a symptomatic client.
Description of Doppler Ultrasonographic Flow Studies (Carotid Doppler, Carotid Artery Echography, Carotid Artery Ultrasonography, Duplex Ultrasonography, Transcranial Doppler Ultrasonography)
A noninvasive, hand-held mechanical ultrasonograph that uses a low-frequency (2–2.5 MHz) sector transducer through temporal, orbital, and suboccipital acoustic windows of the skull. Constant-frequency ultrasonic waves are transmitted into the vessel of interest by a transducer in the form of either fixed-wave or pulsed signals. Using the color and power technique of the Doppler signal instead of the frequency shift, it records the anatomy, flow direction, and mean blood flow velocity in real-time imaging. Doppler ultrasonography can display very small quantitative and qualitative volumes, allowing great morphologic detail. Inferences about the presence of obstruction to blood flow can be made with this procedure. When this technique is combined with a static image of the vessel provided by B-mode imaging ultrasonography, the procedure is referred to as “duplex Doppler ultrasonography.” When a color image is generated by changes in blood flow, the term “color Doppler” is applied.
Professional Considerations of Doppler Ultrasonographic Flow Studies (Carotid Doppler, Carotid Artery Echography, Carotid Artery Ultrasonography, Duplex Ultrasonography, Transcranial Doppler Ultrasonography)
Consent form is NOT required.
- Although portable ultrasonographic equipment is available, this test is frequently performed within the radiology suite.
- Occasionally clients are required to fast before abdominal ultrasonographic procedures. No other pretest preparation or medication is required.
- Remove any restrictive clothing to allow access to the portion of the client's body to be studied.
- The client is usually positioned recumbent with a small pillow supporting the head.
- See Client and Family Teaching.
- The test is generally performed in a darkened room either by a radiology technician or by a radiologist who is seated at the bedside.
- Acoustic jelly is applied to the skin on the area over the part of the circulatory system of interest.
- The ultrasound transducer is applied to the skin, and acoustic jelly and ultrasonographic recordings are made. The procedure is painless and usually brief (minutes).
- Ultrasonic waves are released from the transducer and reflected back to it. An image is then generated within the ultrasound apparatus where it is displayed on a viewing screen. The sound waves used during the test are not audible to the client.
- For transcranial Doppler ultrasonography, a time-averaged mean blood flow velocity of >200 cm/second is indicative of cerebral ischemia. Stenosis >60% diameter reduction is reported immediately.
- Wipe ultrasonic gel from the client's body.
- Although preliminary results of the procedure may be available in the radiology suite, the client should be informed that a physician interpretation is required before the test results are available.
Client and Family Teaching
- The test takes approximately 60 minutes, can be performed at the bedside, and is painless and safe.
- Results are usually available in 24 hours.
- Vascular (carotid) surgery may occur because of the test results, and this will require special educational and emotional support for the client and family.
Factors That Affect Results
- The accuracy of this test is highly dependent on the skill of the operator (technician or radiologist) and the interpreter of the results.
- The body habitus of the client and the technical condition of the equipment may affect the test results.
- Accurate transmission and reflection of ultrasonographic signals can be affected by the presence of calcium (bone or calcification deposits) or gas overlying the vessel of interest, and condition may preclude the achievement of accurate results.
- Intramural calcification may inhibit sound penetration, leading to false-positive results.
- Flow velocity is age dependent and decreases continuously from early childhood to adulthood.
- Detection of small aneurysms is limited by insonation angles and spatial resolution.
- Transcranial procedure:
- a. ICP, blood pressure and volume, hematocrit, and subarachnoid hemorrhage affect flow velocity in transcranial Doppler scanning.
- b. False-negative exams of vasospasm are associated with chronic high blood pressure, increased intracranial pressure, severe spasm of the carotid siphon, and distal vasospasm.
- c. Use of tobacco and caffeine can affect the results.
- d. In clients with occlusive cerebrovascular disease, false-positive and false-negative results have been reported when one is evaluating for cross flow through the anterior and posterior communicating arteries.
- In previous years carotid endarterectomy was almost always preceded by carotid arteriography; however, the high diagnostic accuracy of carotid ultrasonography (when performed by experienced operators) has eliminated this requirement in many cases.
- Most accurate for diagnosis of proximal DVT but less reliable in isolated calf vein thrombi.
- See also Ankle-brachial index.