Small animal or laboratory animal research is a cornerstone of modern biomedical advancement. Research using small animals enables researchers to understand complex biological mechanisms, to understand human and animal disease progression, and to develop new drugs to cure or alleviate many human and animal maladies. Small animal research is important in many areas of biomedical research including neurobiology, developmental biology, cardiovascular research and cancer biology. High-frequency ultrasound and high-frequency Doppler ultrasound can be used to image small animals for biomedical research.
Typically, when producing images of an animal using high-frequency Doppler ultrasound, the animal's breathing motion causes artifacts and inaccuracies in the image. For Doppler measurement of the velocity of blood flowing in a vessel, movement of the vessel due to the animal's breathing motion contributes to erroneous measured velocities. When an image is constructed using an ultrasound technique exploiting the total power in the Doppler signal to produce color-coded real-time images of blood flow (“Power Doppler”) over a two-dimensional surface, a motion artifact is displayed as large stripes in the image. Researchers have therefore been limited to producing images of only those parts of the small animal's anatomy not affected by breathing motion. Thus, breathing motion artifacts and inaccuracies hinder beneficial small animal research.
Acquisition of 3D volumes also suffers from respiration artifacts. 3D volumes typically consist of between approximately 2 and 500 individual image frames acquired with a spacing of between approximately 0.01 millimeter (mm) to 1.0 mm. When a number of slices have been acquired they are compiled to render a 3D volume. Each position consists of an independently acquired frame which may consist of a “Power Doppler” frame, a B-Mode frame, or combination of the two. Respiration artifacts cause unwanted motion which reduces the accuracy of the rendered volume.