The degree that a transducer is finely tuned to specific narrow frequency range. For example: A low Q-value means wide bandwidth and high Q-value means narrow bandwidth.

See also Pulse Inversion Doppler, Narrow Bandwidth, Dead Zone, Ultrasound Phantom.

A phantom is used to control the imaging performance of ultrasound transducers. The spatial resolution, dead zone, linear fidelity, depth of penetration and image uniformity is important for the image quality. For the axial and lateral resolution, the standard definition is the resolution of objects parallel and perpendicular to the path of the sound beam. Ultrasound pictures created by scans of specially designed ultrasound phantoms can quantify the imaging quality and transducer performance.
Phantoms contain one or more materials that simulate a tissue in its interaction with ultrasound. Several phantoms are available specifically for quality control. Transducer characterization consists of a standard pulse echo analysis and insertion loss measurement for each probe. The quality variation from the baseline should be tracked over a period.