What it assesses
With a probe placed on the temple and at the base of the neck, transcranial colour Doppler measures blood flow in the main arteries inside the skull (middle, anterior and posterior cerebral arteries, vertebral and basilar arteries). It can detect intracranial stenosis, collateral circulation and the effects on brain blood flow of narrowing of the neck arteries.
The microbubble test (bubble test)
A small amount of saline agitated with air, which forms tiny microbubbles, is injected into a vein in the arm. Normally the microbubbles are filtered by the lungs and do not reach the brain. If there is an abnormal connection between the venous and arterial circulation (right-to-left shunt), in most cases a patent foramen ovale of the heart, the microbubbles pass into the arteries and are recorded as characteristic signals in the middle cerebral artery.
The test is performed at rest and during the Valsalva manoeuvre, a brief strain against a closed glottis that increases pressure in the right side of the heart and reveals a shunt that might not appear at rest. The number of signals recorded shows whether a shunt is present and allows its size to be graded.
When it is indicated
- after a stroke or TIA without an obvious cause, particularly in young adults;
- to detect and grade a patent foramen ovale or other right-to-left shunts;
- when intracranial artery stenosis is suspected, or to complete the assessment of carotid stenosis;
- in selected cases, on specialist advice, for example in divers or in some forms of migraine with aura.
How it is performed
You lie down; the probes are placed on the temples, sometimes held by a special headset to keep them in position during the recordings. For the microbubble test a small cannula is placed in an arm vein and several injections are given, at rest and during the Valsalva manoeuvre, which is explained and practised before the test. Overall the test takes about 20 minutes. No fasting or preparation is needed and you can return to your normal activities straight away.
Safety and limitations
The test uses no radiation and no iodinated contrast; the microbubbles are made from saline and a minimal amount of air, and the test is generally well tolerated. In some people the temporal bone is too thick for ultrasound to pass through (insufficient acoustic window): in these cases the test may not be feasible and other methods are used.
The bubble test is very sensitive in detecting a shunt but does not show where it is located: if the result is positive, the assessment is completed with echocardiography, and any treatment decisions are taken together with the cardiologist.
Where
Assessments and consultations in Milan, Osio Sotto (Bergamo) and Pistoia. To find out where the test is available and to book, see MioDottore or write to studio@drbonacchi.it.
The information on this page is for general information only and does not replace a medical visit. For sudden or severe symptoms call 112 or go to the Emergency Department.