Types of Radiologic Imaging
What are the different ways that radiology is produced?
Radiological procedures can be grouped by the means in which their images are produced –– the types of energies used on the body and how these energies are received, recorded, and analysed:
- transmission imaging
To produce images with X-rays, computed tomography (CT) scans, and fluoroscopy, radiologists transmit a beams of high-energy photons through the body structure that they are studying. This type of energy passes readily through more diffuse areas such as blood and other fluid and fat, producing darker areas in the image. Denser areas such as muscle and connective tissue absorb and deflect more of the energy, producing lighter areas in the resulting image. The energy does not pass through solid structures such as bone, which appear white on the image.
- reflection imaging
Radiologists use the phenomenon of reflection to produce images by recording energies that bounce back from structures to which they are directed. Primarily, this area of radiology refers to use of sound waves that, when aimed at the body, echo back to a receiver to differing degrees according to the type of tissue they strike. In ultrasound, high-frequency sounds bounce off of different types of structures in differing amounts and at differing speeds, depending on the density of the tissue and other factors. Processors in the equipment analyse the returning ultrasound to produce visual images of the body part.
- emission imaging
In emission imaging, the scanning equipment detects particle energies emitted from a body source or detect magnetic energy stimulated in an area of the body. In nuclear medicine, specialists instill radioactively labelled substances that selectively accumulate in certain body areas or types of tissues, and then they record the emissions from these substances to determine where they are concentrated. In magnetic resonsance (MR) imaging, the equipment creates strong magnetic fields around the body, which changes the orientation of certain molecules. When the magnetic field is pulsed off, the energy released by these molecules can be detected and processed to reveal an image of the types of tissue present.