What transducer configuration is typically used for TCD?

• A. 8-12 MHz phased array
• B. 2-2.5 MHz pulsed Doppler with spectrum analyzer
• C. 1-3 MHz continuous wave
• D. 5-7 MHz linear array

Answer: (B)

Transcranial Doppler relies on penetrating the skull with a low-frequency transducer and using pulsed Doppler with spectral analysis to measure velocities at specific intracranial depths. A transducer around 2 MHz is used because skull bone attenuates higher frequencies, allowing enough signal to reach the intracranial vessels. Pulsed Doppler provides depth resolution, so you can place the sample volume in a particular artery, such as the middle cerebral artery, and obtain a waveform. The spectrum analyzer then displays the velocity spectrum, letting you quantify peak and mean velocities. Higher-frequency or linear-array probes don’t penetrate the skull effectively for this purpose, and continuous-wave Doppler lacks depth discrimination, making it harder to localize the vessel. Therefore, the typical setup is a 2-2.5 MHz pulsed Doppler transducer with spectral analysis.