Generators, cine pulse systems, and x-ray tubes for coronary cineangiography
A modern x-ray generator consists of a 3-phase transformer, a 12-pulse rectifying circuit, and an electronic contactor on the high-tension side. The generated tube potential (kV) is monitored and automatically maintained at an exact preset value. The tube potential is free from ripple and the cine pulses are essentially square waves. Full operating potential can be reached in less than 0.2 msec. The repetition rate of the contactor is at least 200 pulses/sec.
The practical working range is 50 to 120 kV and tube currents higher than 800 mamp are not needed. Thus, the power requirements are never more than 100 kW.
Due to the image intensifier lag, exposure times shorter than 1.5 msec should be avoided. Exposure times shorter than 2 msec are in fact not needed to avoid motion blur in coronary cineangiography. Exposure times longer than 10 msec are not accepted by cine cameras at a frame rate of 50 fr/sec or more. The Arritechno camera will not permit more than 6.3 msec exposures at 60 fr/sec due to its 149° shutter-open phase. A suitable exposure time is about 3.2 msec and this can be used up to a maximum of 120 fr/sec.
The most common generator programming in the past 20 years was based on constant tube potential (kV) and variable tube current (mamp) during exposure. This is a slow reacting system and is no longer recommended due to underutilization of the x-ray loadability. (The tube load may vary from 25% to 100% . . .