E1255. Principles of Doppler Ultrasound: a comprehensive approach with clinical correlation
  1. Gisela Andrade; Hospital Prof. Doutor Fernando Fonseca
  2. Ana Nassauer Mónica; Hospital Prof. Doutor Fernando Fonseca
Ultrasound is known as a highly operator-dependent imaging technique. However, Doppler Ultrasound is even more dependent and particularly vulnerable to errors. This happens because the formation of the Doppler signal and its accurate display relies on the user’s understanding of physics concepts, machine parameters and artifacts. This work intends to review these basic concepts and to integrate them in the clinical setting.

Educational Goals / Teaching Points
To review fundamental concepts behind the formation of the Doppler signal, its processing, display and artifacts in Doppler Ultrasound. To highlight the importance of each concept in the clinical setting.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Doppler Ultrasound is based on the Doppler effect in sound waves. A change in a wave frequency happens when its source is moving relative to an observer and this is called the Doppler effect. The movement of blood in tissues relative to a fixed transducer allows the application of this principle in the assessment of arterial and venous systems. Many Doppler techniques measure this frequency change to produce and display a signal and each one has its advantages, limitations and artifacts. Furthermore, each technique has its own parameters that should be recognized and optimized by the user, with evident clinical implications. For example, pulse repetition frequency (PRF), defined as the number of pulses emitted in one second, is an important parameter of pulsed-wave Doppler; failure to set a high PRF in high-velocity blood flow results in an inaccurate measurement of the maximum velocity; this may cause an underestimation of arterial stenosis.

An understanding of Doppler basic concepts and its implications in clinical practice is fundamental for the correct interpretation of results and avoidance of diagnostic pitfalls.