Radiology is defined as a field of medical science in which different radiations ( X-Rays, gamma rays, sound waves etc) are used to create images of the body and to diagnose and treat the diseases.
Various imaging modalities are used in the field of radiology.
They are as follows:
- Plain Radiography
- Computed Tomography (CT)
- Magnetic Resonance Imaging (MRI)
In radiology, plain radiography is the most initial technique used to create an image. It uses X-Rays. X-Rays are produced when fast moving electrons strike the metal object. The kinetic energy of these electrons is converted into R-Rays.
X-Ray imaging system has three main components.
- The X-Ray tube.
- The operating console
- The high voltage generator.
It is now being replaced by Computed Radiography (CR) and Digital Radiography (DR).
Fluoroscopy provides real-time dynamic viewing of body structures. During fluoroscopy, the radiologist administers contrast media to the patient to highlight the structural anatomy. Then the internal structures are viewed in real time. When required a spot film can be taken.
It is an imaging technique for the breast. In mammography, only soft tissues like muscle and fat are imaged. Mammography has proved to be an accurate and simple method of detecting breast cancer.
Mammographic examinations are of two types.
- Screening mammography
- Diagnostic mammography
It refers to sound waves of high frequency (> 20kHz) that are inaudible to humans.
Ultrasound is not electromagnetic radiations thus are safe for obstetrical imaging. Ultrasounds undergo reflection and refraction at the interface between two different media.
Ultrasound waves are produced by a transducer that converts the electrical signals into an ultrasound beam. The transducer consists of piezoceramic disc or rectangular plate. The plate is made of compressed microcrystalline lead zirconate titanate (PZT) or of the plastic polyvinylidene difluoride (PVDF). The two flat faces are made electrically conducting with a very thin coating of silver.
Computed Tomography (CT):
Computed tomography was introduced in the early 1970s and is a revolution in the field of radiology. Tomography means slice view of the patient. The term sectional imaging is now preferred. CT generates images in transaxial sections.
CT provides cross-sectional imaging and 3D reconstruction.
CT uses more radiation than plain radiography but CT is better in anatomy visualization and contrast.
Magnetic Resonance Imaging (MRI):
MRI uses radiowaves and magnetic field to create the image. Although the nuclei of all atoms contain protons but only the nuclei with an odd number of proton possess the property of nuclear magnetic resonance.
Hydrogen has a single proton thus a large magnetic moment. It is abundant in the body, in water, and in fat, so provides best MRI signals.
The patient is placed in a magnet and a radiowaves is sent through the body. The transmitter is turned off and the patient re-emits radiowaves, which are received and used for reconstruction of the image.