Applications of X-ray in medicine

1.1.1 Diagnostic imaging
X-rays have been used to produce medical images ever since their discovery by Rontgen in 1895. In United Kingdom, for example, it has been estimated that there are 644 medical and dental radiographic examinations per 1000 population per year, so that the technique is of major importance in medical imaging. This variation of transmitted radiation. This referred to as the primary radiological image. Since the eye is insensitive to X-rays, this image is converted to a visible image by a fluorescent screen or film. The beam that emerges from the patient contains primary and scattered radiation. For beams with energies up to 150 kV used in diagnosis, and for thickness of tissue involved in patient examination, the scatter component is considerably greater than the primary. Since only the primary beam contains useful information about the object being examined, it is desirable to reduce the scattered radiation reaching the screen or film by means of t grid placed. This grid allows only that radiation which comes from the direction of the source to reach the imaging system. The beam that finally reaches the film or screen contains both useful information and noise. The imaging system can never increase the information but may well lose some of it, resulting in deterioration of image quality. Images produced by Fat, Soft tissue, and bone can be distinguished from one another in an X-ray image because they attenuate X-rays in different ways.

1.1.2 X-ray therapy

Low-Energy X-ray Units
The practice of radiation therapy began almost immediately following Roentgen’ discovery of X-¬rays.

•Grenz-ray Units
Grenz rays are defined as those produced at potentials of less than 20 kV. They are extremely no penetrating and consequently have little value in radiation therapy.

• Contact Therapy Units
Contact therapy units operate at potentials of 40 to 50 kV and produce X-rays with half-value layers of 1 or 2mm. The tube is designed so that the surface to be irradiated is placed in contact with the housing, only approximately 2cm from the target. These units are suitable only for treatment of surface lesions. An advantage of such units is that their design facilitates their use in operating rooms. Cons act therapy machines have been used for intraoperative therapy because exposed tissues can be irradiated to high doses, while sparing deeper tissues.

• Superficial Therapy Units
X-ray machines operating in the range of 50 to 150 kV are described as superficial therapy machines. Aluminum filters of up to 5 or 6mm are added to increase the penetrating quality of the beam. Glass
or stainless-steel cones are used to collimate the beam, and the surface to be treated is placed in contact with the end of the cone.

• Qrthovoltage Therapy Units
As higher-voltage equipment became available X-ray machines operating in the range of 200 to 350 kV were developed. For many years, these units provided the most penetrating beams available to radiation therapists, and consequently called deep therapy machines. Because their energies are intermediate between those provided by superficial units and so-called super voltage units, they are also called orthovoltage units. Orthovoltage units are typically equipped with adjustable collimators and a light localizer, which aids in placement of the patient for treatment. Relatively short treatment distances, such as 50cm, are ordinarily used.

High-Energy X-ray Units
• Megavoltage X-ray Machines
Several types of X-ray machines operating at more than 1000 kV have been developed, including Van de Graaff generators, betatrons, and linear accelerators. Of the three, only linear accelerators are now in widespread use because they combine the advantages of high dose rates, compact design, and high reliability.

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