Medical imaging is the process of creating pictures and images of parts of the body to assist doctors with examination and diagnosis. Images are created using painless techniques without the need to cut open the body. Medical imaging covers many disciplines and is used by most areas of the healthcare sector. In recent years, the development of computer technology, twinned with advances in 3D medical imaging systems, has meant a growing use of new and ever more advanced image reconstruction and display.
This article is written by Jackie Griffiths, and deals with x-ray, ultrasound, MRI and CT scans. The author is a freelance journalist who writes health, medical, biological, and pharmaceutical articles for national and international journals, newsletters and web sites.
Four main types of medical imaging are reviewed in this article: x-ray, ultrasound, magnetic image resonance (MRI) and CT scans. Each is used for different reasons and play pivotal roles in the early detection of diseases, diagnoses, and making the correct decision regarding treatment. There are many other, less common types of medical imaging, including nuclear medicine, fluoroscopy, mammography, digital vascular imaging, PET/CT (Positron Emission Tomography) etc. but these are not reviewed below.
An x-ray involves exposing a selected area of the body to ionizing radiation, which is absorbed by the body in varying degrees. Bones absorb radiation well and appear as clear, light-coloured structures, whereas soft tissue absorbs less well and appears as grey, indistinct patches. The x-ray machine is programmed to fire a short burst of radiation at the selected area of your body, which is placed on top of photographic film or a special image recording plate. This is where the shades of light and dark are recorded. A lead apron can be used to protect other parts of the body from exposure.
This kind of medical imaging is very quick – a matter of seconds – and completely painless. However, it takes a bit of time to position your body at exactly the right angle so the image won’t be blurred. It’s very important to get the positioning correct because if there isn’t enough information for a diagnosis, repeat x-rays may be needed. Images are either stored in digital format (and viewed on a computer screen) or stored as traditional film images.
An ultrasound uses high-frequency sound waves to construct an image of your body part. It is also quick and painless, but without the exposure to radiation that’s involved in an x-ray. This kind of medical imaging is almost always used for pregnant women to see their unborn child. Patients having an ultrasound will have conductive gel applied to the body part that needs to be scanned, and a probe will be gently moved over the surface of the skin. Cross-sectional images of the organs inside the body are created, interpreted by a computer, and shown on the screen as a moving image. Ultrasound medical imaging is performed either by a medical physician or sonographer, and can be particularly useful in helping doctors to diagnose thrombosis, stenoses in the arteries, tendon and nerve damage or degeneration, as well as its more familiar role in obstetrics.
Magnetic Resonance Imaging or MRI
This kind of medical imaging technique combines a large, powerful magnet with radio waves to produce highly detailed images of the soft tissues of your body. The scan is painless but can take up to an hour, and if you suffer from claustrophobia you may need to be sedated. It’s important to lie very still to prevent blurring. The MRI scan can also be quite noisy, although patients are often provided with headphones through which they can listen to a radio or CD to help muffle the noise. Once you’ve been moved into position inside the scanner, the radiographer will go into another room although they’ll be able to talk to you through the headphones to warn you when each session starts, and roughly how long it will take. After the scan is finished, you can get up and go home straight away.
CT scans or CAT scans
CT medical imaging involves taking a series of x-rays of your body and using a computer to process the images into an axial or cross-sectional three-dimension picture. During the scan, you will lie on a bed or table which will be moved under a doughnut-shaped machine. Sometimes you may have had a contrast dye injected into your body to help the tissues and vessels show up more precisely. The pictures created from a CT scan are viewed on a computer screen, and the entire process can take from a few minutes up to half an hour.