Alternating current continuously changes in magnitude and direction. Commonly the current changes at a frequency of 50 - 60 Hz.

(ACR) Professional society of radiologists and medical physicists.

Amersham Health, now GE Healthcare was the imaging diagnostics and therapy business of Amersham plc. The imaging business produced contrast agents that are injected into the body to improve pictures obtained through medical imaging scans.

(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 µN (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.

The amplitude is the signal height.