Using X-rays in Medical Imaging
- X-rays have been highly developed to provide detailed images of soft tissue and even blood vessels
- When treating patients, the aims are to:
- Reduce the exposure to radiation as much as possible
- Improve the contrast of the image
Reducing Exposure
- X-rays are ionising, meaning they can cause damage to living tissue and can potentially lead to cancerous mutations
- Therefore, healthcare professionals must ensure patients receive the minimum dosage possible
- In order to do this, aluminium filters are used
- This is because many wavelengths of X-ray are emitted
- Longer wavelengths of X-ray are less penetrating, therefore, they are more likely to be absorbed by the body
- This means they do not contribute to the image and pose more of a health hazard
- The aluminium sheet absorbs these long wavelength X-rays making them safer
Contrast & Sharpness
- Contrast is defined as:
The difference in degree of blackening between structures
- Contrast allows a clear difference between tissues to be seen
- Image contrast can be improved by:
- Using the correct level of X-ray hardness: hard X-rays for bones, soft X-rays for tissue
- Using a contrast media
- Sharpness is defined as:
How well defined the edges of structures are
- Image sharpness can be improved by:
- Using a narrower X-ray beam
- Reducing X-ray scattering by using a collimator or lead grid
- Smaller pixel size
Contrast Media
- Contrast media is defined as:
A substance, such as barium or iodine, which is a good absorber of X-rays. A patient is given this so it can give a better contrast on an X-ray image
- These are sometimes used because:
- Some soft tissue organs do not show up on X-rays when the organ has a similar attenuation coefficient to other tissues in the same area
- Contrast media are good absorbers of X-rays as they have a large attenuation coefficient
- Hence when contrast media enter an organ, the image of the organ is enhanced when imaged using X-rays
- Barium and iodine are used depending on the organ being imaged
- Iodine is used as a contrast medium in liquids i.e. to observe blood flow - this is usually injected into the patient
- Barium sulphate is used as a contrast medium in the digestive system - this is usually ingested by mouth and is known as a barium meal
- The large attenuation coefficient of contrast materials is due to the large atomic number of these elements
- Barium has an atomic number of 56, while iodine has an atomic number of 53
