With the help of X-rays and scanners, images of the body parts are obtained to detect defects and abnormalities. The various imaging techniques are X-ray radiography, angiography, computed tomography, magnetic resonance imaging (MRI), positron emission tomography (PET), and sonography.
X-rays were discovered by Wilhem Roentgen in 1895. They have a remarkable property to penetrate materials which do not transmit visible light. Modern sophisticated apparatus can produce films with exposures taken within 0.1 of a second of less. It is employed for diagnosing diseases of the heart, lungs and bones.
It is radiographic visualizations of blood vessels of a region/organ after injecting a radio opaque/ contrast agent or a fluoroscopic chemical. It is of many types depending upon organ studied like coronary angiography, cerebral angiography, pulmonary angiography etc. in angiography image intensifiers are used to provide real image.
It was developed by Godfrey Hounsfield in 1972. He introduced a new method of forming images from X-rays and introduced it into clinical use. It is also known as computerized axial tomography.
It is a special type of radiograph technique which combines X-ray imaging with computer techniques to produce and visualize clear 2 or 3 dimensional cross-sectioned image of deep internal organs that could never be attained by conventional X-ray method.
The MRI study was described independently but almost simultaneously by Bloch and Purcell in 1946, its medical use was first reported by Raymond Damadian. It is based on the principle that when hydrogen atoms of water molecules are subjected to a very strong magnetic field and radio waves, hydrogen atoms release protons and protons carrying an electric charge.
It was developed by Louis Sokoloff in 1985. It is a diagonostic technique based on detection of positrons emitted by radio-isotopes such as C11, N13, O15 and F18 generated by cyclotron.
These radio-isotopes are incorporated into biochemical molecules such as glucose, amino-acids, carbon dioxide (CO2), and ammonia (NH3).
PET has been used for measurement of regional cerebral blood volume, blood flow, and metabolic rates for glucose and O2 in humans. Using these techniques, scientists have recently located the color processing centers in the visual cortex of human beings. It is also used to study epilepsy, schizophrenia, Parkinson's disease and drug addiction.
It is a non invasive technique which uses ultrasound for producing images of internal body parts. Ultrasound refers to sound waves above the human hearing range i.e. above 20,000 Hz or 20 kiloHz. In sonography in audible high frequency sound waves in range of 1-15 million Hz are used.
The waves of ultrasound are produced through a physical phenomen called piezoelectric effect which is based on the principle that when an electric potential is applied to certain crystals of lead zirconate, titantate housed in a transducer, they become exicited and start vibrating. These vibrations are source of ultrasound.
It is useful in diagnosing the diseases of kidney stones, gall bladder stones, liver cirrhosis, obstructions in intestine, uterus etc. it is especially useful in obstetrics. It also reveals pregnancy and foetal abnormalities like anencephaly and spina bifida and conditions liable to cause difficulty in labour. It is also useful to study heart functioning by studying echocardiography.
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