LITERATURE REVIEW

An experiment to investigate the effect of KVp & mAs on the image quality and lesion visibility in chest x-ray (kilovoltage=KVp) and (milliampere=mAs)

An experiment to investigate the effect of KVp & mAs on the image quality and lesion visibility in chest x-ray (kilovoltage=KVp) and (milliampere=mAs)

KV / KVp Potential difference between film and anode

By adjusting the voltage, the energy of X-ray beam can be controlled. The energy here is referred to the penetration power. The penetration power will be based on the how high the voltage is set. The control level is known as kilo voltage potential (KVp) and the label for control is in (thousand electron volts (KeV). If it is confusing, the reader should simply remember that in order to control the potential difference between anode and cathode a control is present. The energy will be high if the voltage setting is high (Christensen, 1977, pp. 128). A beam with more penetrating power will have relatively low contrast radiograph as compared to the one with less penetration power. Hence, the density of the tissues would have less affect in attenuation of that beam when the beam is more energetic. The generator waveform will have an effect on the effective KV unless the potential is constant.

mA Tube Current

Another control used to control the x-ray output is the milliamperage (mA) control. This control helps in controlling the amount of current allowed to flow through the cathode side of the tube contained in the filament (International Commission Radiological Protection, 1990, pp. 60). If through the filament, more current is passed, there would be more electrons which would be present in the 'space charge'. As the high voltage circuit is energised, these high numbers of electrons would accelerate and as a result a greater flux would be produced. The mA circuit shows linear effect. Simply by doubling the mA, the number of photons in the tube can be doubled too. The blackness of the film is affected by increasing or decreasing the number of photons produced. But altering the number of photons will not have an affect on the film contrast.

S Time

The tertiary control for the x-ray tube is exposure timer. Exposure timer is pooled with mA control and is symbolized by “S” (Prokop, 2003, pp. 148). This symbol indicates the exposure time in seconds. If an exposure of 10 milliampere per second can be gained by both using 1 second exposure and 10 milliampere current or using 0.5 second exposure with 20 miiliampere current. Hence the combination of the exposure timer and milliampere control results in milliampere seconds (mAs). If the film's blackness is to be reduced by half, the mAs should be reduced by half. Therefore, it can be concluded that the combination of the factors and film blackness are affected in a linear way.

The X-Ray beam

There are two properties of an x-ray beam that requires detailed understanding. These include Beam quality and beam intensity.

Firstly, a beam with higher ability of penetration through an object ...