GI imaging Flashcards
Who invented X-rays?
Wilhelm Roentgen
What determines the absorption of X-ray beams?
Thickness of tissue
Density of tissue
Atomic number
How much affect does the atomic number of the substance have?
The 4th power
Which absorbs more X-rays, fluids or fat?
Fluids
How do you improve X-ray sensitivity?
Add contrast
Use a more sensitive method (CT)
What is a barium enema?
Retrograde introduction of barium into the system
What is an endoscopic retrograde cholangio-pancreatography?
Insert an endoscope down the GIT until you reach the major duodenal papilla then squirt contrast fluid up it
What is a percutaneous transhepatic cholangiography?
Procedure where a needle is inserted, goes through the liver and into the bile duct where contrast is injected
Which compound do you use for intravenous/intra-arterial contrast?
Iodine (53)
How long after intravascular contrast administration will it be seen in the kidneys?
30 minutes
What happens when contrast is tagged with a bilirubin like compound?
It is metabolised in the liver
What is a houndsfield unit used for?
CTs
What is radioisotope imaging?
Intravenous administration of tagged molecules that target a certain organs and emit gamma rays, these are recorded using a camera
What is the frequency and wavelength of ultrasounds?
High frequency
Short wavelengths
Why is gel required in ultrasounds?
Exclude air
How do ultrasounds create an image?
Beams of sound are reflected by tissue and sensed
What is shadowing in ultrasounds?
Where a substance completely reflects the sound
What is the doppler effect used for?
Measuring blood flow - RBCs reflect sound
What is the principle of MRI’s?
Sends pulses of strong magnetic field and measures the resulting differences in radiowaves that return. Works due to the spin of H molecules
What percentage of blood is supplied to the liver via the portal veins?
75% (25% from hepatic arteries)
