Radiography

Radiography is a sophisticated imaging technique used to view the internal structure of an object. It utilizes ionizing radiation, such as X-rays or gamma rays, and sometimes non-ionizing radiation. This technology is vital for both medical and industrial applications. In medicine, it is used for diagnosis and therapy. In industry, it allows for non-destructive testing of manufactured parts.

The basic mechanism of conventional radiography involves a specific sequence of events. First, an X-ray generator produces a beam of X-rays. This beam is then projected toward the object being studied. As the rays hit the object, they undergo attenuation. Attenuation is when the object absorbs some of the radiation. This absorption depends on the density and structural composition of the object. For example, calcium-rich bones absorb more X-rays than soft carbon-based tissues. The rays that are not absorbed pass through the object. A detector, such as photographic film or a digital detector, captures these remaining rays. This process creates a two-dimensional image known as projectional radiography.

There are several distinct types of radiographic techniques. Projectional radiography is the most common method for viewing bones or lungs. Computed tomography, or CT scanning, is a much more complex version. In a CT scan, an X-ray source and detectors rotate around the subject. The subject moves through a conical beam. Many different beams cross any single point from many directions. A computer then collects this information to create detailed images. These images can be viewed on three planes: axial, coronal, and sagittal. They can even be processed into three-dimensional images.

Another method is fluoroscopy, a term created by Thomas Edison. Fluoroscopy provides moving images rather than still photographs. This is useful for watching moving tissue or guiding medical interventions like pacemaker insertion. A specific type is angiography, which uses fluoroscopy to view the cardiovascular system. To see blood vessels clearly, doctors inject a high-density contrast agent like iodine into the bloodstream. This makes the vessels stand out against the less dense liquid blood.

There is also Dual energy X-ray absorptiometry, often called DEXA. This is used primarily to measure bone density to test for osteoporosis. It is not used for finding fractures because the image quality is lower. Instead, it uses two narrow beams scanned at 90 degrees from each other. It can also measure total body fat, though this is less common. The radiation dose in a DEXA scan is much lower than in standard projectional radiography.

The history of radiography began with a major discovery in 1895. On 8 November 1895, German physics professor Wilhelm Conrad Röntgen discovered X-rays. He was investigating cathode rays using a Crookes tube and a fluorescent screen. He noticed a faint green glow on a screen located one metre away. He realized invisible rays were passing through an opaque black cardboard shield. He called them "X" rays because the nature of the radiation was unknown.

Röntgen later captured the first radiograph of a human body part: his wife's hand.

Early medical use developed very rapidly after this discovery. In January 1896, John Hall-Edwards performed the first clinical X-ray to find a needle in a hand. In the United States, Frank Austin found that the Pulyui tube was uniquely effective for producing X-rays. This was due to an oblique mica target inside the tube. Later, Marie Curie advocated for the use of radiography to treat wounded soldiers during World War I. Today, the field has grown into the specialized medical discipline of radiology. Radiographers perform many tasks, including ultrasound and magnetic resonance imaging, while radiologists analyze the resulting images.