introduction to imaging MW % + Flashcards
What is an x-ray?
An electromagnetic packets of energy with a wavelength between 0.1 and 10 nm.
Recall in general terms the principles of xray generation and image capture.
- All x-ray machines contain X-ray tube envolped by a vacuum with a cathode emitter and an anode target.
- The cathode emitter is -ve charged, so emits -ve charged electrons and the electrons travel to the anode as it the opposite charge.
- As the electrons hit the anode, energy is released in the form of photons which are then converted into X-ray beams.
- These x-ray beams go through the patients body and an image is produced.
What is attenuation?
- The process by which radiation loses power as it travels through matter and interacts with it.
- Increases with Z (atomic number)
- Increases with density
- Increases with thickness
What happens when X-Ray interacts with Matter?
Explain why different anatomical structures have different appearances on x-ray imaging?
- Different stuctures within the body have different attenuation.
- Fats have a lower attenuation coefficient compared to bones which have high attenuation coefficient.
- So depending on how much radiation is absorbed, the image produced will be different.
What is Digital Radiography?
- Same xray tube generation
- Digital acquisition
- Networking of images
- Picture Archiving and Communication System
How does Ultrasound work?
- Transmitts a high frequency sound pulses
- Sound waves travel through the body until they hit a boundary between tissues.
- There some of the waves are reflected back and the rest travel again until they hit another boundary
- The reflected waves are picked up by the probe and the machines calculates them and produces a 2D image
What is Barium and why is it used in Barium studies?
- A radio-opaque contrast agent used for outlining the gastro-intestinal tract
- The high atomic number of barium absorbs more x-ray photons than surrounding tissues
What are the complications of Barium use?
- Bowel disturbance (very common)
- Colonic perforation at enema –Very rare (<1:25,000)
What is computed technology?
- Rotating x-ray tube
- Multiple beams
- Single axis of rotation
- Often give Iodinated Contrast
- IV contrast can lead to kidney failure
What is the point of using iodinated contrast media?
- It enhances the visibility of some structures within the body.
What are Radiation types?
Describe the scientific basis of the hazards of ionising radiation?
- Ionising radiation is a wave which has sufficient energy to knock electrons out of atoms/molecules leaving them as negatively or postively charged.
- This disrupts the chemical bonds within the tissues in the body,therefore it has health consequences.
Attenuation coefficients (comparision)
- Air< Fat< Muscle< Bone< Contrast Agents/Metal implants
Barium in clinical investigation
- Swallow and meal - oesophagus, stomach and duodenum
- Small bowel study - small bowel
- Enema - large bowel
When is computed Tomography used?
•Extensive applications throughout the body
–Trauma
–Cancer staging and response to treatment
–Guidance for procedures
- Great for defining bony detail
- Exposure to radiation
Minimising Exposure
- As the distance from a radiation source doubles, the exposure rate decreases by a factor of four
- Use Shield to protect staff and patients
- Minimise the time exposed to radiation
