Basics of Imaging Flashcards
What type of studies are mammograms and fluroscopic?
X-ray based
How is a standard X-ray generated?
Via heating of Tungsten to fire off photons. More dense areas will by light because fewer photons got thru. Many photons = black
What color does air appear on CT? Fat? Water?
Air = completely black
Fat = slightly more black than water (less dense)
Water = neutral
Muscle / tissue = slightly more white than water
Why are X-rays dangerous?
They break molecular bonds, and specifically water bonds to produce H and OH free radicals
What percentage of photons emitted from a Tungsten filament are actually used for imaging?
15%
85% are emitted away
How many equivalents of background radiation are used for a thorax CT?
About 6 months of background radiation
How much equivalent radiation does a flight from USA to China give?
One single view chest X-ray
What is the most common cancer linked to radiation and when does it occur?
Leukemia - usually 15 years after exposure longterm. Exposure effects are cumulative
What are the two most radiosensitive organs?
- Thyroid
2. Reproductive organs
What is MRI measuring?
Protons in water will align to the lowest energy state in a magnetic field. When a radiofrequency pulse is applied, MRI measures the time it takes for a proton to return to resting state, and the energy that was released to do this
Measures the energy as it relates to surrounding tissue (absorbed via fat, soft tissue, or other fluid)
What is MRI best for? How does the strength of the magnet change this?
Best for evaluating soft tissues, since energy released is very much based on surrounding soft tissues.
Higher magnet strength = greater resolution
3T magnet is the standard today
How does fluid appear in T1 weighted sequences and what are they used for?
Fluid appears black. Used for studying anatomy + when we are using a contrast (which will appear a different color)
How does fluid appear in T2 weight sequences and what is it used for?
Fluid is white
Sensitive to pathological processes like vascular abnormalities.
Eyes will be white in this scan (filled with water)
What is a gradient echo and what is it used for?
A type of T2-weight image
CSF will appear white, but its parameters are turned up so high than black dots are seen in blood due to iron (FE)
Used for detection of microhemorrhages
What type of image is Diffusion Weighted Imaging and why is the CSF black?
It’s a T2 weighted image
CSF is black because it is diffusing freely. The parameters are turned up so only fluid trapped in cellular swelling in stroke can be seen (osmolytes build up in brain cells)
