Medical imaging techniques include x-ray imaging, radiography, CAT scans, ultrasound and MRI. Typically these techniques produce images at the level of tissue or organs.
Light can be used to study a wide range of biological material, such as organs, tissue, cells and cellular components. Imaging at the molecular and cellular level is necessary for the future development of novel methods for early detection or diagnosis of a range of clinical conditions.
Optical imaging techniques make use of differences in transmitted, reflected or emitted light caused by variations in the properties of the sample being studied. For example the sample could be a cell, tissue or an organ.
Lasers are often used as an intense and convenient light source for optical imaging. A number of techniques are used to enhance contrast.
A commonly used imaging technique is microscopy.
Microscopy
A microscope is an instrument that is used to produce a magnified image of an object, making it possible to see objects that are too small to see just with the naked eye.
This explains the term microscopic: something too small to see with the naked eye that can only be viewed using microscope.
Microscopy is the technique of using a microscope to view a sample or objects. Optical or light microscopy involves the use of visible light that is transmitted or reflected from the sample through one or more lenses to give a magnified image of the sample.
There are a number of microscopic techniques including:
- Bright-field microscopy
- Dark-field microscopy
- Phase contrast microscopy
- Fluorescence microscopy
A simple microscope is just a single magnifying lens such as that found in a hand-held magnifying glass.
Magnification
A diagram of a convex lens is shown below.
The lens is shaped so that light rays at the centre are not significantly refracted but light rays at the edge are significantly refracted.
A parallel beam of light is focused down to a spot by a convex lens. The focal length (f) is the distance from the centre of the lens to the spot.
The compound microscope
An improvement on the simple microscope is the compound microscope, which consists of a combination of lenses which together provide a much greater degree of magnification.
Further information
Visit Nikon's MicroscopyU website to learn about different types of microscopy.
Visit the Nobel Prize website to learn more about microscopes and their inventors.
Optical coherence tomography
Optical coherence tomography (OCT) is a reflection imaging technique that is similar to ultrasound, except it is light rather than sound that is used to gain an image. Light travels around 1 million times faster than sound! The imaging depths are usually around 2mm (smaller depths than ultrasound) but OCT can provide image resolutions of a few millionths of a metre (much higher resolution than ultrasound).
OCT has clinical applications in areas such as ophthalmology and dentistry.
Further information
View an article about OCT on optics.org
Visit the FUN OCT website for more information on OCT including tutorials
Learn about cutting-edge research into OCT at Cardiff University