Recently I was answering questions online and found so many young people in their 20s diagnosed with cerebral insufficiency by the local hospital, I was very curious as to what they were basing their diagnosis on. Upon further examination, the TCD suggested slowed blood flow in the anterior or middle cerebral artery and the diagnosis: cerebral insufficiency of blood supply. That’s hilarious. The full name of the TCD test is transcranial color ultrasound Doppler. This test is a new technique that uses the Doppler effect of ultrasound to study the hemodynamics in the large intracranial vessels. It was gradually carried out in China after 1988 because of its non-invasive nature, its easy operation and good reproducibility, and its importance in evaluating cerebrovascular disorders and in differential diagnosis. Because of the different levels of technology, the diagnosis of the vascular condition with the help of TCD is not consistent from hospital to hospital. However, with the gradual accumulation of experience and the development and improvement of technology, the application of transcranial Doppler ultrasound will occupy a more important position. It is mainly based on blood flow velocity, pulse index (PI) and audio signal and spectrogram waveform to reflect the local blood flow status of cerebral vessels. Therefore, it is not enough to judge the stenosis by the flow velocity alone, and it is not enough to diagnose the insufficiency of cerebral blood supply, but it is necessary to compare the left and right, the front and back of a vessel, and the pulse index and spectrum to jointly decide whether there is stenosis of cerebral vessels and whether there is insufficiency of cerebral blood supply. Therefore, standardized TCD training is very important. For patients, they should not easily believe in the TCD test when the doctor says that there is cerebral insufficiency, but go to a standardized hospital to avoid putting a heavy burden on themselves.