Transcranial Doppler: An Introduction for Primary Care Physicians
Journal of the American Board of Family Medicine
Transcranial Doppler (TCD) is a diagnostic tool that can be used at bedside to assess the cerebral vasculature noninvasively. It is inexpensive, safe, and reliable when compared with other techniques. It can be repeated multiple times and can be used for continuous monitoring if needed. Screening of children with sickle cell disease to assess and prevent ischemic strokes and monitoring for vasospasm after subarachnoid hemorrhage are well established, evidenced based utilizations of TCD. It is
... ons of TCD. It is useful for the evaluation of occlusive intracranial vascular lesions with many emerging indications in the management of ischemic stroke. TCD with micro-bubble enhancement has comparable sensitivity to transesophageal echocardiogram in detecting right-to-left atrial cardiac shunts. TCD is underused as a clinical tool despite well established indications. The pressure to contain increasing medical cost will likely result in increased utilization of this test in future. (J Am Board Fam Med 2007;20:65-71.) Christian Johann Doppler, a mathematician, physician, and astronomer, first described the Doppler principle in 1843. Its use in neurology was first reported in 1982, 1 and since then, its convenience and growing range of uses have made it an attractive tool to evaluate the cerebrovascular tree in patients with neurovascular disorders. Transcranial Doppler (TCD) is a noninvasive ultrasound device that allows real-time evaluation of the intracranial cerebral circulation. It is currently under-utilized in part due to the lack of awareness about the diagnostic usefulness of this test. In this article, we will review TCD testing as a procedure and discuss its clinical applications of special interest to the primary care physician. Examination and Doppler Instrument Ultrasound examination of a vessel by means of TCD is referred to as insonation. The TCD probe is placed over different "acoustic windows" that are specific areas of skull where there is a lack of boney covering or the cranial bone is thin (Figure 1 ). The transtemporal (temporal) window is used to insonate the middle cerebral artery (MCA), the anterior cerebral artery (ACA), the posterior cerebral artery (PCA), and the terminal portion of the internal carotid artery (TICA), before its bifurcation. The transorbital (orbital) window gives access to insonate the ophthalmic artery (OA) as well as the internal carotid artery at the siphon level. The transforaminal (occipital) window allows insonation of the distal vertebral arteries (VA) and the basilar artery (BA). Finally, the submandibular window allows insonation of the more distal portions of the extracranial internal carotid artery. TCD does not allow direct visualization of insonated vessels like carotid Doplex, rather it is an indirect evaluation by means of an ultrasonic beam of 2 MHz frequency that is produced from piezoelectric crystals that have been stimulated electrically. This beam bounces off the erythrocytes within the insonated artery. The reflected signal is received by the transducer and converted to an electric signal (Figure 2 ). This information is subtracted from the transmitted signal and then processed to obtain a waveform that allows accurate This article was externally peer reviewed.