Basic Principles and Physics of Duplex and Color Doppler Imaging. In: Mostbeck GH, editor. Duplex and Color Doppler Imaging of the Venous System. Berlin: Springer Berlin Heidelberg; 2004. pp. 1-18. [DOI: 10.1007/978-3-642-18589-2_1]

[Principles of Doppler sonography]

The techniques of medical Doppler are spectral Doppler (contiuous-wave (CW) and pulse-wave (PW) Doppler) and color flow imaging (Color Doppler and Power Doppler). All are based on the fact that the frequency of an echo from a moving reflecting particle will be altered by a characteristic frequency shift determined by its velocity in relation to the source/detector. The CW Doppler will only detect flow within a pre-defined depth and will not be guided by an image, whereas the PW Doppler is carried out with B-mode guidance (Duplex doppler). The so derived curves permit to assess the temporal distribution of flow velocities and directions and flow disturbances as well. In the case of color flow imaging, a part of the interrogated tissue section is mapped for Doppler signals and then color-coded, resulting in a dynamic color map of flow, where the colors encode characteristic flow parameters (e. g. mean flow velocity plus direction). This article describes the technical and physical basics of medical Doppler techniques.

Ultraschallkontrastmittel — physikalische Grundlagen

The concept of ultrasound contrast agents (UCA) is based on the inherent physical and acoustical properties of gas-filled microbubbles within an ultrasonic (US) field. Depending on the magnitude of the incident US wave different scattering behavior occurs. While it is linear for low acoustic pressures, increasing it leads to the occurrence of nonlinear effects, such as emission of harmonics. High pressure results in destruction of the bubbles producing a highly nonlinear echo signal. Using these specific acoustic signatures opens new perspectives for the development of bubble-specific imaging techniques such as harmonic or intermittent imaging. This review deals with the physical properties of the gas-filled microbubbles, their behavior within an ultrasonic field, and the use of the bubbles' acoustic signatures for contrast-specific imaging. Novel applications such as tissue-specific microbubbles, targeted imaging, and therapeutic applications using the bubbles as vehicles for drug or gene delivery are discussed as well as acoustically induced bioeffects and considerations for the safe use of UCA from an acoustic standpoint.