Transcranial doppler

Transcranial doppler also known as transcranial color-coded duplex sonography, is a non-invasive, painless ultrasound technique that uses high-frequency sound waves to measure both the direction and velocity of the blood flow in the major cerebral arteries of the brain ¹. Some may refer to the imaging modality as transcranial color-coded duplex sonography (TCCS) and the non-imaging based continuous wave doppler modality as transcranial doppler (TCD). Transcranial doppler test examines and records the speed of the blood flow in arteries known as the Circle of Willis, which are located at the base of the brain, to facilitate the diagnosis of a wide range of conditions affecting the brain following:

• Subarachnoid hemorrhage (SAH)
• Transient Ischemic Attack (TIA)
• Sickle Cell Anemia
• Embolism
• Cerebrovascular Accident (CVA)
• Cerebral Circulatory Arrest

While most different forms of ultrasonography make images of the tissue state studied, the transcranial doppler makes audible sounds that can be heard, recorded and examined. Advantages of transcranial doppler over its “conventional” predecessor include an ability to identify structural perturbations, including the presence of masses and/or midline shift, and the presence of sonoanatomical landmarks to guide placement of a pulsed wave doppler gate ².

Transcranial doppler ultrasound provides rapid, noninvasive, real-time measures of cerebrovascular function. Transcranial doppler can be used to measure flow velocity in the basal arteries of the brain to assess relative changes in flow, diagnose focal vascular stenosis, or to detect embolic signals within these arteries. Transcranial doppler can also be used to assess the physiologic health of a particular vascular territory by measuring blood flow responses to changes in blood pressure (cerebral autoregulation), changes in end-tidal CO2 (cerebral vasoreactivity), or cognitive and motor activation (neurovascular coupling or functional hyperemia). Transcranial doppler has established utility in the clinical diagnosis of a number of cerebrovascular disorders such as acute ischemic stroke, vasospasm, subarachnoid hemorrhage, sickle cell disease, as well as other conditions such as brain death.

Transcranial doppler ultrasound indications

General indications for the use of transcranial doppler ultrasonography includes:

• clinical suspicion of cerebral vasculopathy
• evaluation for complications of subarachnoid hemorrhage
• cerebral microemboli
• positional vertigo
• intracranial aneurysms
• intra/peri-operative evaluation of cerebral perfusion
• confirmation of cerebral circulatory arrest
• presence or absence of midline shift
• dural venous sinus patency assessment
• sickle cell disease ³
  • risk stratification
  • cerebral infarction ⁴

Indications for transcranial doppler more specific to pediatric age groups, especially pertaining to neonates, include:

• prematurity
• low APGAR scores
• both scores, at one and five minutes, under 7
• dysmorphic features
• seizures
• macrocephaly
• suspicion for intraventricular hemorrhage
• craniosynostosis evaluation

Sonographic examination of the orbit will be also be discussed, as the measurement of the optic nerve sheath diameter (OSND) and spectral waveform analysis of the ophthalmic artery are essential parts of a complete transcranial Doppler examination. Sonography of the eye has a wide array of applications in point-of-care ultrasonography; indications for its use alone, distinct from the other elements of a transcranial doppler exam, include ⁵:

• trauma to the head, eye, or orbital structures
• acute alteration of vision
• altered mental status
• headache.

Transcranial doppler procedure

Transcranial doppler is performed by a technologist trained in the specific type of neurovascular ultrasound. The patient will be awake and lying on a bed during the test. A small device called a transducer is connected to a laptop computer, which provides the technologist with data about the blood flow.

One or more transducers will be placed directly on the patient’s skin, with a small amount of gel facilitating the ultrasound. The technologist will apply the gel and transducer to the patient’s temples, base of the skull at the back of the neck area or on closed eyelids. The gel can be easily washed off after the test.

The technologist will change the transducer’s position to direct the ultrasound waves toward the blood vessels being examined. The patient will be able to hear the noise of blood flowing through the arteries from the ultrasound. A transcranial doppler can take between 30 minutes to 1 hour to complete.

References

1. Purkayastha S, Sorond F. Transcranial Doppler ultrasound: technique and application. Semin Neurol. 2012;32(4):411–420. doi:10.1055/s-0032-1331812 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3902805
2. Blanco P, Blaivas M. Applications of Transcranial Color-Coded Sonography in the Emergency Department. (2017) Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 36 (6): 1251-1266. doi:10.7863/ultra.16.04050
3. Pawlak MA, Krejza J, Rudzinski W, Kwiatkowski JL, Ichord R, Jawad AF, Tomaszewski M, Melhem ER. Sickle cell disease: ratio of blood flow velocity of intracranial to extracranial cerebral arteries–initial experience. (2009) Radiology. 251 (2): 525-34. doi:10.1148/radiol.2512071180
4. Siegel MJ, Luker GD, Glauser TA, DeBaun MR. Cerebral infarction in sickle cell disease: transcranial Doppler US versus neurologic examination. (1995) Radiology. 197 (1): 191-4. doi:10.1148/radiology.197.1.7568822
5. O. John Ma, James Mateer, Robert F. Reardon, Scott A. Joing. Ma and Mateer’s Emergency Ultrasound, Third Edition. (2013) ISBN: 9780071793155