How Scans Help Diagnose Disease

Modern Imaging Methods Can Reveal Much About Our Health

In around just a hundred years, imaging of the body has gone from the simple X-ray to sophisticated scanning methods that give sharp images of any kind of body tissue.

Although to us X-rays might seem a bit primitive, when they arrived on the medical scene they represented a huge advance in doctors’ ability to diagnose illness. Until then they relied upon the case history and physical examination to determine the nature of a disease. Although limited, X-rays could at least provide an image of dense tissue such as bone and some tumors, something that previously was only available during risky surgery or at a post-mortem examination – which of course is a bit late.

X-rays are still useful and in their modern evolved forms such as CT scans, extremely so. In addition to X-rays, scanning techniques based on different principles have been developed so that the range of scans available to doctors is wide. Here are some common methods of imaging.

X-rays

X-rays are high energy beams of radiation that can penetrate all but very dense material. The densest material in the body is bone and medical X-rays don’t penetrate this to the degree that they do the softer tissues. So although the ghostly shapes of organs can show up on an X-ray, the bones come through most clearly. Some tumors will show on X-ray. The main advantage of X-rays is that they are cheap, the main disadvantage is their potentially harmful effects, especially to rapidly growing cells.

CT Scans

These are really highly sophisticated X-rays. They use the same type of radiation but at varying strengths so that the soft tissues are picked out. Beams are directed into the tissues to pick out varying levels of tissue density. All this information is processed by a computer which produces pictures of ‘slices’ of the body. Most body tissues can be imaged this way. Safety concerns are the same as for X-rays. CT scanning may take up to about 30 minutes to complete.

MRI Scans

These are based on an entirely different principle to X-rays. They work because all the tissues of the body contain water – some a great deal like blood and some rather less like bone. When hydrogen atoms in this water are placed in a magnetic field – as in an MRI scanner – they will align in a particular direction, a bit like iron filings would. During a scan radio pulses are sent through the body to knock the hydrogen atoms out of alignment; surprisingly you don’t feel this and neither is it harmful. When the hydrogen atoms realign themselves they emit energy which is then detected by the scanner. A computer collects this information, which shows the amount and distribution of water in the tissues, and constructs detailed images of the body’s organs. Because MRI scans do not use beams of high energy radiation they are less risky than X-rays.

Ultrasound Scans

These use beams of sound waves which are directed at internal organs and analyzed when they are bounced back. Very safe and cheap to do, they are used to determine the condition of the internal organs and blood vessels. They do not give such clear information as CT and MRI scans but are useful for picking out major anomalies. Often used to detect clots in blood vessels and to monitor the progress of the growing fetus.