The frame rate is the number of images displayed per second. One frame represents one complete sweep of the ultrasound beam and contains many pulse-listen cycles. The frame rates decrease with an increased dwell time.

Contrast microbubbles can be destroyed by intense ultrasound and the scattered signal level can increase abruptly for a short time during microbubble destruction, resulting in an acoustical flash (sudden increase in echogenicity).
Intermittent imaging with high acoustic output utilizes the properties of contrast microbubbles to improve blood-to-tissue image contrast by imaging intermittently at very low frame rates.
The frame rate is usually reduced to about one frame per second, or it is synchronized with cardiac cycles so that enough contrast microbubbles can flow into the imaging site where most microbubbles have been destroyed by the previous acoustic pulse. Because bubbles are destroyed by ultrasound, controlling the delay time between frames produces images whose contrast emphasizes regions with rapid blood flow rate or regions with high or low blood volume.

From ALOKA Co., Ltd.;
'Veterinary portable ultrasound system:
The SSC-210 Vet is a price performance breakthrough in diagnostic imaging. The variable frame rate, up to 30 frames/sec., combined with dynamic focusing produces highly detailed images that can be optimized and frozen at the touch of a button. The push key controlled, linear distance calipers permit fast, accurate measurement of any structure within the two-dimensional image. The built-in digital scan converter let you output the image directly to a video recording system.'

From ALOKA Co., Ltd.;
'The ProSound SSD-4000 utilizes the most advanced acoustic technologies available today, and its multidisciplinary technology architecture enables it to offer great versatility and flexibility over a wide range of clinical applications.
With its new-generation, front-end technology including a 12-bit A/D converter, the ProSound SSD-4000 offers superior contrast resolution−especially when compared to 10-bit systems.'

A bolus is a rapid infusion of high dose contrast agent. Dynamic and accumulation phase imaging can be performed after bolus injection. Since the transit time of the bolus is only a short time, images with high frame rate show the wash in and wash out of the contrast material. The injection rate and the total injected volume modifies the bolus peak profile. Substantial changes in the concentrations during signal acquisition induce artifacts. Furthermore, the hemodynamic parameters (cardiac output, blood pressure) influence the bolus profile. However, the characteristics of ultrasound contrast agents are favorable with a continuous perfusion.

See also Negative Bolus.