Radiology techniques

What is an X-ray?

An X-ray is a picture of the internal structures of the body produced by exposure to a controlled source of X-rays and generally recorded on a digital sensor and shown on a computer screen.

What is ultrasound?

Ultrasound uses high frequency sound waves (too high for the human ear to detect), emitted by an ultrasound probe to image the body. These travel through the body and are reflected by various layers of tissue. The probe then detects these reflected waves which are relayed onto a screen allowing the pictures to be interpreted. Ultrasound is now the method of choice for monitoring the foetus during pregnancy and in diagnosis of numerous conditions involving organs such as the liver, kidney, heart and blood vessels.

What is a CT scan?

Computed tomography (CT) is another X-ray technique using a scanner that takes a series of pictures across the body allowing the radiologist to view the images in two dimensional or three dimensional forms. CT scans of the whole body can be performed in a few seconds and often require the use of contrast (X-ray dye) to improve image quality.

Download our leaflet about having a CT scan.

What is an MRI?

An MRI (magnetic resonance imaging) scan provides an image similar to a CT scan but uses magnetism and radio waves to build up a series of cross sectional images. MRI pictures provide additional information on the characteristics of tissues and organs that is often not available from other techniques. For this reason MRI has potential to reduce the number of certain diagnostic procedures. MRI does not use X-rays and the magnetic fields are not known to be harmful. However, it takes longer to obtain the pictures than a conventional X-ray machine or CT. Some patients cannot have an MRI scan, for example those with pacemakers or who have had other interventions.

Download our leaflet about having an MRI scan.

What is a DEXA scan?

A DEXA scan is a special type of X-ray that measures bone mineral density. DEXA stands for ‘dual energy X-ray absorptiometry’. This type of scan is also often known as DXA, or ‘dual X-ray absorptiometry’. It's also sometimes referred to as a bone density scan or a bone densitometry scan.

DEXA scans are often used to diagnose osteoporosis (when the bones become weak and fragile and are more likely to break). They can also be used to assess the risk of osteoporosis developing in women aged over 50 and in men over 60. As well as being quick and painless, a DEXA scan is more effective than normal X-rays in identifying low bone mineral density.

What is nuclear medicine or isotope scanning?

Radioisotopes give out a very small amount of radiation that can be detected by a specially designed sensitive type of camera. When a radioisotope is linked with certain chemicals it can, harmlessly, trace the workings of the human body. These tests allow radiologists to find alterations in the normal functioning of the body organs, for examples the heart or kidneys, or show early indications of infections or cancer.

The dose of radiation given is very small, but following some tests we do advise that contact with children or breastfeeding mothers should be avoided for a short time. This is particularly the case when radioisotopes have been given in higher doses in order to treat some conditions, for example an overactive thyroid gland or some types of cancer. Suitable advice will always be given by the radiologist before a patient leaves the hospital.

What is fluoroscopy?

Fluoroscopy is a technique where a series of low dose X-rays are used to create a moving picture of the body, enabling the doctor to perform real-time imaging of organs and image guided interventional procedures. Common fluoroscopic procedures techniques look at blood vessels (angiography, venography) or show the outline of body structures (barium x-rays).

What is a PET scan?

A PET (positron emission tomography) scan is a diagnostic imaging technique in which patients are given a special radioactive substance that emits positrons which in turn give rise to gamma rays that are detected by a gamma camera. This is used to image conditions where tissues are known to be more metabolically active, for example tumours or inflammatory conditions.

What is a mammography?

The technique of using X-rays of the breast to detect irregularities or early signs of cancer.