Regular transfusion therapy can prevent stroke in children with sickle cell disease (SCD). Thus, identifying patients most likely to experience a stroke is an important aspect of care. The increased risk of stroke in children with SCD is due primarily to the progressive occlusion of large intracranial arteries.1
Transcranial Doppler (TCD) ultrasonography is a non-invasive diagnostic tool that allows for indirect real-time evaluation of intracranial cerebral circulation.1,2 It is used to measure abnormal blood flow velocity in large intracranial arteries, which can help to predict stroke risk in children (Table).3-5
|TAMMV, cm/s||Stroke risk|
TAMMV = time-averaged mean of the maximum velocity.
TCD ultrasonography is safe, inexpensive, and reliable compared with other techniques. It can be repeated multiple times and can be used for continuous monitoring if needed.
TCD ultrasonography uses an ultrasonic beam (2 MHz frequency) produced from piezo-electric crystals that have been stimulated electrically.1,2 The ultrasonic beam bounces off erythrocytes within an artery. The reflected signal is received by a transducer and converted to an electric signal. This information is subtracted from the transmitted signal and processed to obtain a waveform (Figure).
Figure. Typical TCD ultrasonography recording from the middle cerebral artery (MCA).6
The velocity scale is shown on the left.
Reproduced from McCarville MB, et al. AJR. 2004;183:1117-22 Â© American Roentgen Ray Society.
The waveform allows accurate determination of blood flow velocities, flow direction, and addition of calculated parameters, such as pulsatility index (PI). PI is a reliable marker of resistance distal to the site being evaluated. The calculated blood flow velocities can be used to predict stroke risk.3
The predictive value of TCD ultrasonography correlates well with findings from magnetic resonance angiography (MRA), which is often used to study blood flow in children with SCD.
Imaging TCD ultrasonography adds further information, allowing visualization of arteries and angle-corrected blood velocity measurement.7
Regular screening with TCD ultrasonography is recommended in the USA and UK for patients aged > 2 years.8-10
For further information about TCD:
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