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X-Rays
X-rays are a form of electromagnetic radiation, similar to visible light. X-rays were discovered by a German scientist named Roentgen in 1985. Unlike light, however, x-rays have higher energy and can pass through most substances including soft tissues of the body but not through bones and most metals.
Medical x-rays are used to generate images of tissues and structures inside the body. If x-rays traveling through the body also pass through an x-ray detector on the other side of the patient, an image will be formed that represents the “shadows” formed by the objects inside of the body.
Photographic film is is just one type of x-ray detector , but there are many other types of detectors that are used to produce digital images. The x-ray images that result from this process are called radiographs.
X-Ray Production
X- rays are produced by modified discharge tubes called X-ray tubes. The cathode is in the form of a filament which emits electrons on heating.
The anode is made of solid copper molybdenum and is called the target. A high potential difference between the anode and the cathode is maintained (10,000 v to 1,000,000 or more) by an external source. The filament is made up of tungsten and coiled to provide high resistance to the current.
The electrons produced are changed into x-rays on hitting the anode and getting stopped.
Only 0.2% of the energy is converted into x-rays.
Cooling oil is led in and out of the hollow of the anode to maintain low temperature. The lead shield absorbs stray x-rays.
To create a radiograph, a patient is positioned so that the part of the body being imaged is located between an x-ray source and an x-ray detector. When the machine is turned on, x-rays travel through the body and are absorbed in different amounts by different tissues, depending on the radiological density of the tissues they pass through. Radiological density is determined by both the density and the atomic number (the number of protons in an atom’s nucleus) of the material being imaged.
For example, our bones contain calcium, which has a higher atomic number than most other tissues. Because of this property, bones readily absorb x-rays and therefore produce high contrast on the x-ray detector. As a result, bony structures appear whiter than other tissues against the black background of a radiograph.
Conversely, x-rays travel more easily through less radiologically dense tissues, such as fat, muscle, and air-filled cavities such as the lungs. These structures are displayed in shades of gray on a radiograph.
X rays can be classified into two:
- Hard X-rays
These are x-rays on the lower end of their range (10-11 – 10-8 m) and have more penetrating power than normal x-rays.
They are capable of penetrating flesh but are absorbed by bones.
- Soft X-rays
They are on the upper end of the range and are less penetrative. They can only penetrate soft flesh and can be used to show malignant growth in tissues.
Properties of X-Rays
- i) They travel in straight lines
- ii) They undergo reflection and diffraction
iii) They are not affected by electric or magnetic fields since they are not charged particles.
- iv) They ionize gases causing them to conduct electricity
- v) They affect photographic films
- vi) They are highly penetrating, able to pass easily through thin sheets of paper, metal foils and body tissues
vii) They cause fluorescence in certain substances for example barium platinocynide.
Application of X-Rays
- In Medicine
Listed below are examples of examinations and procedures that use x-ray technology to either diagnose or treat disease:
- Diagnostic
X-ray radiography: Detects bone fractures, certain tumors and other abnormal masses, pneumonia, some types of injuries, calcifications, foreign objects, or dental problems.
- Mammography: A radiograph of the breast that is used for cancer detection and diagnosis. Tumors tend to appear as regular or irregular-shaped masses that are somewhat brighter than the background on the radiograph (i.e., whiter on a black background or blacker on a white background). Mammograms can also detect tiny bits of calcium, called microcalcifications, which show up as very bright specks on a mammogram. While usually benign, specific patterns of microcalcifications could indicate the presence of cancer. Learn more about mammography here.
- Computed Tomography (CT): Combines traditional x-ray technology with computer processing to generate a series of cross-sectional images of the body that can later be combined to form a three-dimensional x-ray image. CT images are more detailed than plain radiographs and give doctors the ability to view structures within the body from many different angles. Learn more about CT here.
- Fluoroscopy: Uses x-rays and a fluorescent screen to obtain real-time images of movement within the body or to view diagnostic processes, such as following the path of an injected or swallowed contrast agent. For example, fluoroscopy is used to view the movement of the beating heart, and, with the aid of radiographic contrast agents, to view blood flow to the heart muscle as well as through blood vessels and organs. This technology is also used with a radiographic contrast agent to guide an internally threaded catheter during cardiac angioplasty, which is a minimally invasive procedure for opening clogged arteries that supply blood to the heart.
- Radiation therapy in cancer treatment: X-rays and other types of high-energy radiation can be used to destroy cancerous tumors and cells by damaging their DNA. The radiation dose used for treating cancer is much higher than the radiation dose used for diagnostic imaging. Therapeutic radiation can come from a machine outside of the body or from a radioactive material that is placed in the body, inside or near tumor cells, or injected into the blood stream
- In other Non-medical fields
a). Industry – they are used to photograph and reveal hidden flaws i.e. cracks in metal casting and welded joints.
b). Science – since the spacing of atomic arrangement causes diffraction of x-rays then their structure can be studied through a process called X-ray crystallography.
c). Security – used in military and airport installations to detect dangerous metallic objects i.e. guns, explosives, grenades etc.
Dangers of X-rays and the precautions.
- They can destroy or damage living cells when over exposed.
- Excessive exposure of living cells can lead to genetic mutation.
- As a precautionary measure X-ray tubes are shielded by lead shields.