2.1
X-ray Imaging
X-ray imaging is a common diagnostic imaging technique. It uses X-rays - which are high-energy electromagnetic radiations that pass through the human body, to produce a negative-type image of internal body structures.
The resulting image is called a radiograph - shadows of the rays on a digital or film medium. Radiation dose and exposure time are monitored to avoid radiation induced sickness.
X-rays passing through the body are differentially absorbed depending on the tissue density. Dense structures like bones appear white, as the rays cannot pass through them; therefore, they are radiopaque. Soft tissues like muscles, and organs like the liver and stomach are less dense; since they allow more rays to pass through, they appear in shades of gray. Air that has the lowest radiopacity appears black.
X-ray imaging can detect bone fractures, dental problems, tumors, and certain infections.
However, this technique allows only two-dimensional image capture. Further, it poorly differentiates structures with the same densities, these require better imaging techniques like computed tomography or MRI.
German physicist Wilhelm Röntgen (1845–1923) was experimenting with electrical current when he discovered that a mysterious and invisible "ray" would pass through his flesh but leave an outline of his bones on a screen coated with a metal compound. In 1895, Röntgen made the first durable record of the internal parts of a living human: an "X-ray" image (as it came to be called) of his wife’s hand. Scientists worldwide quickly began their own experiments with X-rays, and by 1900, X-ray was widely used to detect various injuries and diseases. In 1901, Röntgen was awarded the first Nobel Prize for physics for his work in this field.
An X-ray is a form of high-energy electromagnetic radiation with a short wavelength capable of penetrating solids and ionizing gases. X-rays are emitted from an X-ray generator and directed toward a specially treated metallic plate placed behind the patient's body. As the beam of radiation passes through the patient, it forms shadows of tissues and structures inside the body on the X-ray plate. X-rays are slightly impeded by soft tissues, which show up as gray on the X-ray plate, whereas hard tissues, such as bone, essentially block the rays, producing a light-toned "shadow." Thus, X-rays are best used to visualize rigid body structures such as teeth and bones. A contrast medium, like a radiopaque barium solution, can be ingested to help visualize soft tissues of the upper digestive tract to show the contours of the stomach and intestine.
Like many other high-energy radiations, X-rays are capable of damaging cells and causing mutations that can lead to cancer. Despite their widespread use, this danger of excessive exposure to X-rays was not fully appreciated for many years. Today, the impact of radiation on patients and operators is attenuated by proper shielding and limiting exposure.
Refinements and enhancements of X-ray techniques have continued throughout the twentieth and twenty-first centuries. Although often supplanted by more sophisticated imaging techniques, the X-ray remains a standard in medical imaging, especially for viewing fractures and dentistry.
This text is adapted from Openstax, Anatomy and Physiology, Section 1.7: Medical Imaging
X-ray imaging is a common diagnostic imaging technique. It uses X-rays - which are high-energy electromagnetic radiations that pass through the human body, to produce a negative-type image of internal body structures.
The resulting image is called a radiograph - shadows of the rays on a digital or film medium. Radiation dose and exposure time are monitored to avoid radiation induced sickness.
X-rays passing through the body are differentially absorbed depending on the tissue density. Dense structures like bones appear white, as the rays cannot pass through them; therefore, they are radiopaque. Soft tissues like muscles, and organs like the liver and stomach are less dense; since they allow more rays to pass through, they appear in shades of gray. Air that has the lowest radiopacity appears black.
X-ray imaging can detect bone fractures, dental problems, tumors, and certain infections.
However, this technique allows only two-dimensional image capture. Further, it poorly differentiates structures with the same densities, these require better imaging techniques like computed tomography or MRI.
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