(A or amp) The SI base unit of electric current.
Definition: Two parallel conductors, infinitely long and having negligible cross section should be placed 1 meter apart in a perfect vacuum. One ampere is the current that creates between them a force of 0.2 microNewton per meter of length.
One ampere represents a current flow of 1 coulomb of charge per second.
One ampere of current results from a potential distribution of 1 volt per ohm of resistance, or from a power production rate of 1 watt per volt of potential.
The unit is known informally as the amp, but A is its official symbol and is named for the French physicist André-Marie Ampère.

See also System International.

Apodization is a method for reducing side lobes (lateral array elements) in some arrays. It gradually decreases the vibration of the transducer surface with distance from its center by improving the directivity. It is usually accomplished by using more power to excite the innermost elements.

From Bracco Research SA, Geneva, Switzerland,
BR14 is a new experimental ultrasound contrast agent, consisting of bubbles containing a high molecular weight filling gas enclosed by a flexible phospholipid monolayer shell a few nanometers thick.
This agent shows significant non-linear scattering and agent modification even at low insonation pressures, the detection pulses used did not destroy the contrast bubbles. The results obtained with HPD before the release burst show that the BR14 bubbles are efficient scatterers that can be modified and, thus, detected by low power insonation.

The backscatter energy is the portion of the incident acoustic power scattered back toward the transducer.

The width of the main beam lobe of the transducer is described in degrees. The beam width is usually defined as the width between the half power point and the -3dB point.