Inside Out

Medical imaging is a discipline where highly technical medical equipment is used to produce visual images of the skeleton, body parts, tissues and organs. This is key in diagnosing, treating and monitoring illness. Medical imaging involves a multidisciplinary team which includes consultant radiologists, radiographers, medical physicists and support staff . It plays an important role in healthcare and public health screening and encompasses both radiology and nuclear medicine. Radiology looks at anatomy and physiology using computerised tomography (CT), X-Ray and magnetic resonance Imaging (MRI) scans. Nuclear medicine looks at the function and metabolism of the body using positron emission tomography (PET) scans. is article explains how a few of the scans used in medical imaging work and what they are used for in medicine.



Positron Emission Tomography works by detecting gamma ray radiation given off by a substance called a radio tracer. PET produces very detailed 3D images, however if combined with CT, it can produce even more detailed images. PET scans are usually used with x-ray and MRI. Fluorodeoxyglucose, similar to glucose, is a common radiotracer used in PET scans. The radio tracer collects at different levels in the body and these differences can inform doctors how well a certain part of the body is working, e.g. how the glucose is taken up and used by the cells. PET scans are a very useful tool in oncology as they are able to show whether a tumour, and in particular neuroendocrine tumours (NETS) which are difficult to diagnose using conventional imaging are present; as well as the stage of thetumour. They can also be used to diagnose epilepsy and Alzheimer’s. PET scans are very advantageous as they show how well an individual’s body is functioning at a cellular level.

‘Neurotransmitter in limbic areas of a human brain, PET’ by Dr Jim Myers, Imperial College London. Credit: Dr Jim Myers, Imperial College London. CC BY-NC

Computerised Tomography uses X-Ray radiation and computers to produce detailed images. During a CT scan several X-Rays are taken and the images are put together using the computer. CT can produce very detailed images of organs, blood vessels and bones. The CT scanner takes pictures at a series different angles giving cross sectional images of the body. A contrast is sometimes given using intravenous infusion during the procedure to enable a better image to be produced. CT scans are useful to diagnose damaged bones and internal organs and to monitor the size of tumours.

‘CT scan; brain metastases from unknown primary’ . Credit: Wellcome Collection. CC BY

During an X-Ray, X-Ray radiation passes through the body where the energy is adsorbed at different rates. The radiation finds it difficult to pass through dense areas of the body such as bones and cartilage, therefore these areas appear lighter. However X-Ray radiation finds it easier to pass through less dense areas such as internal organs. These areas of the body appear darker on the image. A detector picks up the x-rays after they have passed through the body and this results in an image. X-Rays are particularly useful for diagnosing broken bones, warn cartilage, pneumonia and lung cancer.

‘Pulmonary TB: plain chest x-ray ‘ . Credit: Wellcome Collection. CC BY



Magnetic Resonance Imaging uses magnetism and radio waves to create a cross sectional image of the body. It is able to look at body from all angles. An MRI scan will show soft tissue in the body so it is particularly useful when looking at the brain, breasts, heart and blood vessels. It can however be used to look at most parts of the body.

‘MRI scan; brain cancer (glioma)’ . Credit: Wellcome Collection. CC BY


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