Physics, Techniques and Procedures

Frame rate

in ultrasound imaging, the number of complete scans carried out per second by the instrument. A real-time B mode image is produced by sweeping the ultrasound beam across the field of view while transmitting pulses and detecting echoes along closely positioned scan lines. The time spent at each scan line before sweeping to the next one is determined by the maximum depth of the field of view; echoes from the deepest structures must return to the transducer before the beam can move on to the next scan line position. The time required to complete a whole scan or frame also depends upon the number of scan lines (which is related to spatial resolution). High frame rates are possible when imaging is restricted to shallow depths and when the number of scan lines are few. A flicker-free display requires at least 16 frames per second. Adding colour flow data to a B-mode image reduces the frame rate significantly, because more time must be spent at each scan line to acquire the Doppler flow information (see colour Doppler sonography).

HJS