Cerebrovascular Testing Explanation:
Diagnostic Transcranial Doppler (TCD):
Diagnostic transcranial Doppler is used for a combination of multiple patient situations with both imaging and non-imaging technology. TCD gives the ability to access in real-time the basal segments of the Circle of Willis.
It allows the assessment of intracranial stenosis and collateralization after extracranial stenosis/occlusion. This provides valuable information to determine the aggressiveness of the patient care plan be it non-surgical or surgical. 1
TCD is used extensively in treatment management of inpatients who experience a subarachnoid hemorrhagic or intracranial hemorrhagic. A patient with this ailment always presents with some form of cerebral vasospasmic response. TCD is traditionally preformed daily on these patient to assess the vasospasmic response. Daily use of TCD in these patients allows the patient to be safely monitored at their current facility without the need to transport to a facility with neurointervention. 5 If the patient has a significant vasospasmic response, the process is a slow curve that usually takes 36 to 72 hours giving the attending physician ample time to transport. 2
Diagnostic transcranial Doppler is also used in the assessment of Sickle Cell Disease. The disease malformation causes increased velocities throughout the circulatory system with usually affect the brain in the form of a stroke. TCD is valuable in assessing the cerebral circulation to provide information to indicate the need for transfusions in these patients. 1
Embolic Detection Monitoring (EMB):
Embolic detection monitoring allows for real-time assessment of active emboli in the cerebral circulation using non-imaging transcranial Doppler. It will track the cerebral embolization rate from an ulcerated plaque, systemic hypercoagulability or cardiac source providing information to provide the best medicinal or surgical treatment for the patient. 1
Right-to- Left Atrial/Pulmonary Shunt Evaluation with Transcranial Doppler (PFO-TCD):
Right-to- left atrial/pulmonary shunt evaluation with transcranial Doppler is the most sensitive non-invasive method for evaluation of a PFO. It has a documented sensitivity rate of 99%. 3 This non-imaging technique provides a 15% better positive predictive rate than transthoracic echocardiography and a 5% better positive predictive rate than transesophageal echocardiography for the presence of a PFO. 4 This technique also gives the ability to grade the conductance of the shunt to access the true risk factor the PFO may cause for the patient. A documented high conductance grade with two documented prior strokes are the CMS guidelines to justify closure of a patent’s PFO. 4
Vasomotor Reactivity Testing
Vasomotor reactivity testing uses non-imaging transcranial Doppler to check a patient’s cerebral circulation autonomic reserve. After a patient has a significant extracranial or intracranial stenosis the patient activates the cerebral autonomic reserve process to attempt to rebalance the cerebral circulation. Using simple breath-holding to increase the patient’s CO2 level, transcranial Doppler can evaluate the remaining autonomic reserve in the patient’s cerebral circulation to determine the best treatment options, be it surgical or medicinal. 1
Head-Turn Syncope/Positional Evaluation
Head-turn syncope/positional testing uses non-imaging transcranial Doppler to evaluate the posterior circulation of brain to access a compromised circulation by extrinsic arterial compression or positional changes. This is used traditionally in patients with vertebral artery disease but has proved to be a valuable tool to evaluate patients with decreases cardiac output, intracranial hypertension and in-patients with positional issues. 1
Cerebral Circulatory Arrest Evaluation
Non-imaging transcranial Doppler is used as a confirmatory test to document reverberating flow in patients which indicates brain death due to cerebral circulatory arrest. TCD can also be used as a screening tool to determine the timing for other confirmatory tests such as nuclear brain scanning or angiography. It is of particular value in patients with high barbiturate levels when clinical examination and electro-encephalography are unreliable. 1
- Alexandrov AV, Joseph M: Transcranial Doppler; An Overview of its Clinical Applications. The Internet Journal of Emergency and Intensive Care Medicine 2000; Vol4 N1: http://www.ispub.com/journals/IJEICM/Vol4N1/tcd.htm;
Published January 1, 2000.
- Newell DW, Winn HR: Transcranial Doppler in cerebral vasospasm. Neurosurg Clin N Am. 1990 Apr: 1(2): 319-28
- Spencer MP, et al. Journal of Neuroimaging 2004; 14:342-349
- Ozdemir AO, et al. Journal of Neurologic Science. 2008; 275:121-127
- Nakae R, Yokota H, Yoshida D, Teramoto A: Transcranial Doppler Ultrasound for Diagnosis of Cerebral Aneurysmal
Subarachnoid Hemorrhage: Mean Blood Flow Velocity Ratio of the Ipsilateral and Contralateral Middle Cerebral
Arteries. Neurosurgery. 2011; 69:876-883.