QUS: Quantitative Ultrasound
What is it?
The term ultrasound describes sound waves above the audible threshold, generally defined as 20 kHz. Sound waves are mechanical pressure waves in origin, which propagate through a material, the velocity and attenuation being strongly dependent upon the mechanical and structural properties of the medium.
The majority of clinical applications of ultrasound are related to the imaging of soft tissue structures using a pulse-echo technique; although for the assessment of highly attenuating materials such as cancellous bone, transmission techniques are often adopted, whereby two transducers are utilised, one acting as transmitter, the other as receiver.
The variable that we may alter in ultrasound procedures is the frequency, the choice of which is often a compromise between the quality of the image (spatial resolution) and the amount of signal detected (signal-to-noise ratio). As frequency increases, so does the spatial resolution, but also the attenuation.
A range of image analysis techniques may be utilised including A-Scan (simple 1D amplitude modulated time trace), B-Scan (2D brightness modulated image), M-Mode (Motion or Time-Position used to identify moving tissues) as well as Doppler analysis (measure tissue velocity and flow) which may be incorporated into a B-Scan image. 3D and 4D techniques have more recently become available which essentially are further developments of the B-scan. Quantitative analysis may be performed, particularly measurement of velocity and attenuation.