Radiation: Radiation is a type of energy which travels from a source and behave like wave as well as photons.
Ionizing radiation: the radiation which dissociate matter into ions. For example: X-rays, gamma rays, and beta rays etc.
X-rays are the electromagnetic radiation having short wave length.
X-ray physics
The X-ray tube is a vacuum tube that is used for converting electrical input into X-rays. X-rays are produced by accelerating electrons. These X-rays used in radiography.
There are two types of X-ray tube:
If the electrons are bombarded on the large area of the target or anode then it is called as large or broad focus. Filament is polished with thorium oxide to increase the production of electrons from the filament. Filament requires a current of 10 volt 10 ampere for the productivity of electrons. At the cathode terminal of X-ray tube a focusing cup is also present to focus the electrons towards the anode, this focusing cup is made up of the molybdenum and it is coated with the nickel so it acts as an electrode.
The filament will experience a heating cycle of 25°C to 2600°C. Therefore the filament is heated at a temperature of about 800°C in the absence of oxygen to provide dimensional stability for expanding and contracting during the heating cycle.
The anode is slightly angulated so that the X-rays can pass the window of the X-ray tube and dispersed in all directions. The anode angle in stationary tubes varies from 6°-20°, an oil circulation is used around the copper block for the transfer of heat from the anode terminal.
If the electrons are bombarded on the large area of the target or anode then it is called as large or broad focus. Filament is polished with thorium oxide to increase the production of electrons from the filament. Filament requires a current of 10 volt 10 ampere for the productivity of electrons. At the cathode terminal of X-ray tube a focusing cup is also present to focus the electrons towards the anode, this focusing cup is made up of the molybdenum and it is coated with the nickel so it acts as an electrode.
The filament will experience a heating cycle of 25°C to 2600°C. Therefore the filament is heated at a temperature of about 800°C in the absence of oxygen to provide dimensional stability for expanding and contracting during the heating cycle.
The stator is made up of metallic plates which are fitted together and it is in the form of a ring. Small depressions or cuts are present in which copper wires are wrapped to form the coils. These coils forms magnetic field, when electric current is supplied to them. The rotor and stator assembly is responsible for the movement of anode disc.
When the electric current is applied on the cathode terminal of the X-ray tube it produces or release electrons after heating. This current has fixed voltage which is of the order of 10 volt 10 ampere. A high voltage or potential difference is applied between the cathode and anode to provide acceleration to the electrons. This energy provides kinetic energy to the electrons and they strikes with the anode or target of the X-ray tube all the energy of the incident electrons are absorbed by the electrons or nucleus of the target material. After gaining this extra amount of energy the electrons of the target or anode reaches at the excited state and they releases extra amount of energy in the form of X-rays and heat. About 99% heats is formed at the target and only 1% X-rays are formed.
Types of radiation produced from the X-ray tube:
Each time a radiograph is to be produced a set of exposure factors has to be chosen to give the type of image required. To choice of these factors will depend on the region being examined, including its thickness, density, pathology etc.
Exposure factors to be selected:
Exposure factors chosen will different for different types of image acquisition, device and depend on whether a grid is being used.
This indicates the intensity or, put simply the amount of radiation being used. If the radiation has enough energy to penetrate the body, then it will be detected by image density or, again put the image blackening.
mAs = produce of the X-ray tube current and exposure time in seconds
mAs= mA x s mA is mili ampere & s is time
mA should be as high as possible with a short time to reduce the risk of movement un-sharpness. Highest mA and lowest time select automatically by X-ray generator. If insufficient mA is used, than a photographic film will be underexposed and lack photographic density. If mAs is too high it will result in an overexposed film excessive density and lack of contrast. mAs only effect quality of electrons and X-ray production.
This indicates how X-ray beam will penetrate the body. Range of Kvp is used in diagnostic radiography is normally between 50-120 Kvp. For soft tissues examined Kvp can be as low as 25 Kvp such as mammography. High Kvp such as those used in chest radiograph (120 Kvp). If Kvp increases X-rays produced have a high energy and more able to penetrate the body and it is detected by image acquisition device. Kvp is the most important factor in control of the contrast of radiographic image, therefore should be chosen carefully. Kvp should be such that the radiation has enough energy to penetrate the body part and reach the image acquisition device. Maximum contrast will achieve if the lowest Kvp is used. Kvp increases more radiation will be able to penetrate the dense body part compared with less dense part.
Greater the FFD lower the intensity of the radiation reaching the film for given Kvp & mAs. If FFD is increased mAs must be increased. While choosing the FFD the following factors are taken into consideration. X-ray tube must not too close to patient’s skin otherwise radiation damage could be caused. Short FFD could give unacceptable geometric un-sharpness. The FFD must not be excessive, otherwise the large increase in mAs required would wear high tube loading.
It is a device consists of a series of narrow lead strips closely spaced on their edges and separated by spacers of low density material. Grids are used to reduce the amount of the scattered radiation towards the image receptor. Grids increases contrast and remove different type of un-sharpness during exposure.
There are two types of grids:
Types of stationary grids:
Types of moving grids
Grid ratio: It is the ratio of the height of lead strips or transparent passage to the width of the transparent passage.
Grid frequency: It is defined as the number of lead strips per inch or centimeter.
Scattered radiation: It is the type of radiation that occurred when the useful X-ray that occurred when the useful X-ray beam interacts with the object and deviate from its original path due to attenuation coefficient of the objects. The radiation which deviates from its original path
Attenuation: It is the reduction in the intensity of an X-ray beam as it transverse matter by either absorption or deflection of photon from the beam.
Two terms used to express the characteristics of X-ray beam are quality and quantity.
Quality refers to number of photons in the beam and quality refers to their energies. Intensity of a beam is product of number and energy of photon, so it depends on both quantity and quality.
Macro radiography: The technique of producing an image by direct magnification and enables fine anatomical details than the real and accurate diagnosis.
Micro radiography: The imaging technique used to examine very small objects or details, often with the use of high voltage, very small focal spot size and an ultrafine film emulsion. It is also called as fluoroscopy.
Collimation: The process by which X-ray beam are lined up to minimize divergence or convergence. Ideally, a collimated beam is a bundle of parallel rays perfectly lined up align an optical line of sight between transmitter and receiver.
It refers to the lower field intensity towards the anode is comparison to the cathode due to lower X-ray emission from the target material at angles perpendicular to the electron beam.
Basic concept: The conversion of the electron beam into X-ray beam doesn’t simply occur at the surface of the target material but deep within it. Because the X-ray beam are produced deep in the target material they must Travers back out of it by they can proceed to the target field. More target materials needs to be transverse at emission angles that are perpendicular to the electron beam than at those more parallel to it. This increase in material leads to more desorption of the X-rays by the target material leads to more desorption of the X-ray by the target, resulting in fewer X-rays reaching the field at angles perpendicular to the electron beam, it also means that the X-ray emitted to angles closer to the incident beam and fewer are desorbed. The end result is that the field intensity towards the cathode is more than that towards the anode.
Factors:
Magnification: Magnified image can be produced by increasing the object to film distance (OFD) in which X-rays diverging from the point source will produce a directly magnified image.
Distortion: Misrepresentation of the true size and shape of an object is called as distortion. It results from unequal magnification of different parts of the same object.