Transcranial Doppler Ultrasound: A Review of the Physical Principles and Major Applications in Critical Care

Abstract

Transcranial Doppler (TCD) is a noninvasive ultrasound (US) study used to measure cerebral blood flow velocity (CBF-V) in the major intracranial arteries. It involves use of low-frequency (≤2 MHz) US waves to insonate the basal cerebral arteries through relatively thin bone windows. TCD allows dynamic monitoring of CBF-V and vessel pulsatility, with a high temporal resolution. It is relatively inexpensive, repeatable, and portable. However, the performance of TCD is highly operator dependent and can be difficult, with approximately 10–20% of patients having inadequate transtemporal acoustic windows. Current applications of TCD include vasospasm in sickle cell disease, subarachnoid haemorrhage (SAH), and intra- and extracranial arterial stenosis and occlusion. TCD is also used in brain stem death, head injury, raised intracranial pressure (ICP), intraoperative monitoring, cerebral microembolism, and autoregulatory testing.

Patients with sickle cell disease are frequently excluded from the benefits of transcranial doppler screening for the risk of stroke despite extensive and compelling evidence

“…The cost-effectiveness, portability and repeatability of TCD make it an ideal neuroimaging technique, especially for patients with SCD who need regular monitoring for primary stroke prevention 2,5,6 . Patients with SCD are at risk for a spectrum of brain injuries such as subclinical infarction, acute ischemic stroke and hemorrhage due to the high level of circulating irreversibly-sickled red blood cells and their adherence to the vascular endothelium.…”

“…Despite its usefulness, TCD is highly operator-dependent, hence in many countries where TCD facilities are not widely available, the examination is unfortunately underutilized 2,3 . This descriptive cross-sectional study was conducted to examine the baseline characteristics and TCD results of children and adolescents with SCD who were screened in nine different medical centers in Brazil.…”

Assessment of Cerebrovascular Autoregulation Using Regional Cerebral Blood Flow in Surgically Managed Brain Trauma Patients

“…In certain situations, Mx may be the only valid option to directly assess the status of cerebrovascular autoregulation. However, TCD is technically demanding, dependent on both the operator and bone window availability, and yields intermittent information thus limiting its clinical utility [26]. Use of the Hemedex Ò rCBF monitor overcomes several of these limitations with the additional benefit of providing absolute perfusion measures.…”

Deep tissue imaging with acousto-optical tomography and spectral hole burning with slow light effect: a theoretical study

“…22 There have been transcranial US studies to stimulate the cortex using low-frequency US. [22][23][24] Therefore, transmitting US into the brain is possible. In this sense, AOT would have the advantage over PAT as AOT only requires US to be transmitted into the tissue and is not detected again.…”