Types of Imaging investigation
- X – Rays
- Mammograms
- Bone Scan
- Ultrasound Scan
- Computerised Tomography (CT) Scan
- Spiral Computerised Tomography (CT) Scan
- Contrast
- Magnetic Resonance Imaging (MRI) Scan
- Positron Emission Tomography (PET) Scan
X-rays
X-rays use beams of ionising radiation to expose photographic film. Placing the human body between the beam and the film leaves an image of the body on the film. When radiation penetrates tissue easily black areas are seen, for example air in the lungs on a chest x-ray. Bones appear white because they are hardest to penetrate.
The process of taking x-rays has now been digitalised using PACS (Picture Archiving and Communication Systems) although traditional x-rays are still used. X-rays are a good way of looking at bones and air inside the human body but they do not show up soft tissues very well. The one exception to this is mammograms – x-rays of the breast tissue. X-rays of the chest are still commonly used, the lungs and lung abnormalities show up well and chest x-rays are quick, easy and safe.
Chest x-ray image courtesy of National Institute of Health.
Mammograms
These are also x-rays but of the soft tissue of the breast. Abnormalities of the breast show up well because of the contrast between fat which is black and fibrous connective tissue which is white.
Mammogram image showing a round opacity in the breast (arrow) this is a breast cancer. Image courtesy of National Institute of Health
Bone Scan
A bone scan may also be called a radionuclide scan or a scintigram. A bone scan involves injecting a person with a tiny amount of a radioactive substance, which collects in bones. This substance collects in high concentration where there is most activity or turnover of bone cells, bones are normally uniformly fairly inactive when scanned like this but areas where there are secondary tumours will have very high activity and show up as ‘hot spots’ on the scan. The actual scan simply involves a photograph of the whole body using a special camera which detects radioactivity
Ultrasound Scan
Ultrasound scans use high frequency sound waves; these are emitted by a probe. The echoes that bounce back from structures in the body are shown on a screen. The structures can be much more clearly seen when moving the probe over the body and watching the image on the screen. Still pictures as seen below are much less informative. Can be used to take an accurate biopsy.
Ultrasound scan of normal prostate gland courtesy of Wellcome Photo Library.
Computerised Tomography (CT) Scan
Computerised tomography - CT scan uses multiple x-rays (ionising radiation) to create a slice by slice image of the body. The slices (scans) are viewed as if you are looking up through the feet of the person to see the cross section. Therefore, a right sided organ such as the liver appears on the left of the image. These can be used to take an accurate biopsy.
CT scan of the chest showing both lungs and the heart lying between them (white area). More details of the structure of lung can be seen on this scan.
Image courtesy of Wellcome Photo Library
Spiral Computerised Tomography (CT) Scan
This is a new way of taking CT images through multiple planes. Scans are quicker and more detailed even enabling 3D computer graphic reconstruction of internal organs and bones to look for abnormalities. They can be used to take an accurate biopsy.
Contrast
Contrast – is a substance, which shows up more clearly in the blood or organ on scanning. Contrast can be injected into veins to show up blood vessels or organs on scanning. It can also be drunk to show the outline of the gut better.
Magnetic Resonance Imaging (MRI) Scan
MRI - images are similar to CT images except they show up the details of soft tissue better. MRI scans do not use X-rays but use a strong pulsed magnetic force to polarise cells - line up the (electrons) and measure the energy given off by the electrons when they bounce back into their normal orbits in-between pulses.
MRI of the spine. Vertebral bodies should be square and smooth looking, but are irregular and squashed, they have been invaded by metastatic cancer and are crumbling. Image courtesy of Wellcome Photo Library
Positron Emission Tomography (PET) Scan
PET scanners use ionising radiation and contrast to produce 3D coloured images of the body. These scanners are very expensive and are rarely used in the UK. The contrast consists of a radioactive form of glucose, which tends to concentrate in areas of the body, which are very active – active cells like tumour cells use a lot of glucose. This can be very useful; sometimes chemotherapy treatment works well but leaves a mass of scar tissue where the original tumour was. This can be seen for example on a CT scan – it shows a lump of tissue but does not tell us what it is doing, is it scar tissue or a growing tumour? The PET scan shows areas of high cell activity and the lump of tissue will light up if the tissue is metabolising glucose at a fast rate. The PET scan does not show anatomy or structure of the body very well but a combination of CT scan for structure and PET scan for function of the same area will show what tissue is there and what its doing.
