Ultrasound in the management of ischemic stroke

Ultrasound is increasingly being used in the diagnosis, management and treatment of ischemic stroke. Linear array probes with frequencies of 5 to 10 MHz are used for extracranial studies, and sector or small hand-held 2 MHz probes for transcranial studies. Ultrasound is non-invasive, safe, painless, portable, quick, inexpensive, repeatable and accurate, but it requires adequate training; accreditation for physicians and laboratories are available. The extracranial arteries imaged include the common, internal and external carotid, vertebral, subclavian arteries bilaterally, and the brachiocephalic trunk. For transcranial studies, the ophthalmic artery, carotid siphon, terminal internal carotid, and proximal anterior, middle, posterior, basilar and intracranial vertebral arteries are evaluated. Brightness-(B)mode, intensity/power mode, colour-coded and Doppler mode are used; more recently, motion-(M)mode is also employed. Velocity parameters measured include the Peak Systolic, End-Diastolic and Mean velocities; resistivity parameters include the Gosling's Pulsatility Index and Pourcelot's Resistance Index. For safety, the Thermal Index cannot exceed 6, Mechanical Index 1.9, Spatial Peak Temporal Average Intensity 720 mW/cm2. Ultrasound is used to evaluate extracranial and intracranial arterial stenosis, collateral flow as a result of severe stenosis/ occlusion, pulsatile neck masses, subclavian steal, carotid dissection, Takayasu disease, right-to-left shunting, embolisation, intra-operative monitoring during carotid endarterectomy or CABG and post-surgery/stent assessment of stenosis, as well as cerebrovascular reserve to predict stroke risk. It is also used therapeutically to enhance thrombolysis (sonothrombolysis). Neurosonology provides an invaluable tool for the clinician in the management and prevention of ischemic stroke.