Ultrasonic investigation of blood flow

Ultrasound and the Doppler effect are used to measure blood velocity non-invasively in order to diagnose blood vessel disease. Intrusive lesions on arterial walls give rise to an alteration of the time-varying blood velocity waveform and local blood flow disturbance which are detected and measured using the envelope and width of the Doppler signal spectrogram respectively. Flow may also be imaged in colour superimposed on a grey-scale anatomical image allowing vessel narrowing and the accompanying flow disturbance to be visualized. Developments in three-dimensional imaging, angle tolerant velocity measurements and increased sensitivity using second harmonic backscatter from encapsulated-bubble contrast media ensure increasing use of this modality.