Imaging Flashcards
What are X-rays
Electromagnetic packet of energy short wavelength
What imaging uses radiation ?
X-rays
Barium
CT
What imaging’s don’t use radiation?
Ultrasound
MRI
Describe how X-rays work
Inner shell is of electrons is very important. Uses PACS (picture archiving communication system). Electrons are emitted from the cathode with a high velocity and crash into the anode releasing X-rays. Attenuation is the process by which X-rays loose there power as they travel through matter, this increases as the density increases i.e. X-rays pass straight through air but cannot pass through tooth. Dense material i.e. tooth will appear white on the image. X-ray images are produced by a three layer film, silver halide between two luminescent screens. X-rays clump together on silver hide and generate light.
What is ultrasound?
Sound pulses of high frequency
Where are ultrasounds used?
Used in image guidance biopsy’s.
Where are barium imaging used?
Used in barium swalling and meal examinations.
Causes bowel disturbances and colonic perforation at enema
What is the contrast agent in barium examination?
Contract agent i.e. Barium sulphate radio-opaque.
Describe how barium studies work
Used to outline the GI tract, Barium absorbs more X-rays that surrounding tissue and so appears white. In X-rays more dense tissue appears white.
What are CT?
Rotating X-rays
What are CTs used for?
Used for imaging trauma, cancer, staging cancer, monitoring treatment, guidance in procedures, bony detail. They are the mainstay for cancer imaging
What is the contrast used on CT?
Contract agent i.e. iodinated Contrast (given orally or in IV but IV harms kidneys)
Describe how CTs work
As X-rays (A group of photons) pass through the tissue it losses photons (some are absorbed, the denser the tissue the more X-rays or photons that are absorbed) , the number of photons that has been lost can be detected by a scanner. It uses pixels and voxels. Hounsfield unit of water is zero and then all other structures (i.e. bone or blood or fat) are given values relative to that.
What is MRI?
Magnetic fields and radiofrequency pulses
What is MRI used for?
Used for imaging the brain spinal cord, bony details, soft tissue. Pass makers cannot be imaged. MRIs are taken before a biopsy for prostate cancer but not for kidney
What contrast is used in MRI?
Contract agent i.e. gadolinium DTPA
How do MRI work ?
Strong magnetic field aligns protons in one direction, then radiofrequency pulses displace proton and the image is created by the movement of protons to ordinal position. Different tissue will have a different return time due to varying weight. Heavier will return first.
What unit is radiation measured in?
A sievert
What happens when ionising radiation hits healthy cells?
Cell damage
How can exposure to radiation be minimised?
Firstly, is by keeping your distance, as the distance from a radiation source doubles, the exposure rate decreases by a factor of four. Minimising the time of contact also helps to protect you. Wearing or use of a shield will also help protect you
What are the ALARA principles?
as low as reasonably achievable
What is screening?
Used to diagnose conditions at early stages
What makes a disease suitable for screening?
Disease that are suitable for screening have to be important health problem, have a latent stage of disease, there must be a test or examination for the condition, and treatment, facilities for diagnosis and treatment. Test should detect disease at an early stage where treatment can alter outcome Test should cause no harm. Test should have high sensitivity and specificity. Benefit to the individual and the population should outweigh the cost.
What cancer screening programs are there in the UK?
Breast cancer
Bowel
Cervix
lung in development.
