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kVp is the component that controls the QUALITY of the x-ray beam produced. It is also what controls the CONTRAST or GRAY SCALE in the produced x-ray film. Now let's talk about film density and film contrast. The mAs have a linear relationship to film density; kVP has an exponential relationship. show relatively low contrast [long gray scale], because many densities between kVp. HIGH kVp will result in images with WIDE latitude. Different films have.
The mAs also mean mA x time seconds. We can arrive at specific mAs value with various combinations of mA and s.
Effect of mAs and kVp on resolution and on image contrast.
For example, to get mAs, we can use the following: The mAs control the number of electrons produced at the cathode, and subsequently the number of x-rays produced at the anode. The mAs control the quantitative character of the exposure factors.
The mAs have a direct and linear relationship to intensity. If we double the mAs, we will double the beam intensity, providing all other factors remain the same. The beam intensity directly affects the film density, therefore, mAs have a direct and linear effect on the film density.
The film density relates to the total darkness or lightness of the film. The kVp or kilovoltage peak is the other factor we can control to obtain an x-ray.
A volt is defined as a unit of electrical force needed to move one ampere through a resistance of one ohm. Kilo means 1, so kilovoltage refers to a thousands volts. The "p" stands for peak, therefore, kVp means kilovoltage peak. Peak denotes the highest voltage attained in a given electrical alternating current.
The kVp is the factor which controls the energy of the electrons as they move across the tube, or the speed of the electrons. It follows that higher energy electrons produce higher energy x-rays.
Contrast | Radiography Blog
Scientifically speaking, high energy photons or x-rays mean short wavelength photons. The shorter the wavelength, the higher the energy, for the wavelength and the easier it becomes to pass through matter.
This is referred to as penetration. The greater the kVp, the greater the penetration. By controlling the energy of the x-ray beam, kVp controls the quality of the beam.
Unfortunately, kVp is not as easy to work with clinically as far as controlling the beam intensity. While both mAs and kVp directly affect beam intensity, kVp has a direct and exponential relationship.What does KVP do to contrast
If we wanted to double the intensity using kVp, we would not double the kVp but increase it by an amount determined by an equation in which beam intensity varies approximately according to the 2. You'll need a chart to figure it out, so it is much easier to use mAs to change the density since it has a linear relationship. Now let's talk about film density and film contrast. First, let's discuss film density.
For this discussion, we are going to define film density as blackness of the film. The blacker the film, the more density it has.
- Peak kilovoltage
Both kVp and mAs have a direct affect on film density. The mAs have a linear relationship to film density; kVP has an exponential relationship.
Peak kilovoltage - Wikipedia
It is hard to predict accurately and easily how much change the kVp will affect the change in density. The applied voltage kV accelerates these electrons toward an anode target, ultimately producing x-rays when the electrons are stopped in the anode. Thus, the kVp corresponds to the highest kinetic energy of the electrons striking the target, and is proportional to the maximum energy of the resulting X-ray emission spectrum.
One standard way to measure pulsating DC is its peak amplitudehence kVp. Most modern X-ray generators apply a constant potential across the x-ray tube; in such systems, the kVp and the steady-state kV are identical. Each body part contains a certain type of cellular composition which requires an x-ray beam with a certain kVp to penetrate it.
The body part is said to have "subject contrast" that is, different cellular make up: So the subject contrast is said to be higher in the chest than in the abdomen. In order to image the body so that the maximum information will result, higher subject contrast areas require a higher kVp so as to result in a low radiographic contrast image, and vice versa.
As the energy which is proportional to the peak voltage of the stream of electrons in the x-ray tube increases, the x-ray photons created from those electrons are more likely to penetrate the cells of the body and reach the image receptor film or plateresulting in increased film density compared to lower energy beams that may be absorbed in the body on their way to the image receptor. However, scattered x-rays also contribute to increased film density: Scatter adds unwanted density that is, density that does not bring pertinent information to the image receptor.