Intro Flashcards
Radiographs are _____ (good/bad) at contrast resolution.
bad
Why do we choose radiology as a modality?
idk we shouldn’t it sucks :(
jk jk
accurate representation of orientation and relationship b/t anatomic structures
correct reproduction of anatomy ± pathology
cheap, fast, ubiquitous, good at spatial resolution if adjacent
List the Roentgen signs and tell me why they’re important.
they are important bc they help you figure out if something is abnormal or not, and why it is abnormal
size, shape, number, position/location, density/opacity, structure, function
Suzy Says “No, Please Don’t Slap Freddy”
Why do we dislike radiographs?
poor detail due to limited contrast
radiation risk
bad at special resolution if overlapping
need >1 view! (2 views min., but depends on what you’re looking at)
error rates high, interpretation result of complex perceptual mechanisms, previous experience plays a large role, attitude impacts interpretation
tell me about the basic physics (yuck) of a radiograph/radiation
x-rays generated in X-ray tube, cloud of electrons formed at the cathode in the tube. electrons travel across tube until they get to anode at the focal spot. electrons lose their energy when they hit anode, and photons (x-rays) are produced, radiating in a cone shape from focal spot.
what is the focal spot?
area of the anode which receives the beam of electrons from cathode. - apparent source of x-rays
what is the byproduct of x-ray production and how to mitigate this?
heat!!
mitigated by rotating anode or focal spot
x-rays radiate out in a cone shape from the focal spot and are directed towards the patient. how do we make sure the cone isn’t huge or going away from the patient?
collimation and shielding
the quality and quantity of x-rays detected are controlled by multiple factors. tell me about them.
generation - mA/mAs, kVp, distance, grids
absorption/subject factors - density, thickness
detector - DR vs CR vs plain film
what is kVp? what happens when you increase kVp?
kilovoltage peak. the speed of electron flow across the tube
increase kVp = increase speed when electrons hit target = greater penetration of x-rays = high PRESSURE hose –> able to penetrate thicker/denser material
What is mA/mAs? What happens when you increase mA or mAs?
Milliamperage or milliamere second. the amount of current flowing through the tube
increase mA = increase amount/volume of X-rays produced = high VOLUME hose –> increase amount of black on image (increase density)
2x mAs = _____x density/blackness of image
2x
increase kVp = ______ scatter = _____ contrast
increase scatter
decrease contrast
what does the “grid” do?
reduce scatter to increase contrast
only lets xrays through that are in line with focal spot (like a sieve)
what is contrast?
the number of shades of grey between black and white
high contrast = whites and blacks on image, less shades of grey, more difference between shades
low contrast = more shades of grey, less blacks and whites, less difference between shades - picture looks sort of hazy
which controls contrast, kVp or mAs?
kVp
what is latitude of a radiograph? what does high latitude mean vs low latitude?
range of material thickness that can be imaged.
high latitude = greater amount of different thickness tissues can be seen
low latitude = lower amount of different thickness tissues can be seen
what is the relationship between latitude and contrast?
low contrast = high latitude
high contrast = low latitude
(think about kVp. kVp and latitude are intertwined, and when kVp goes up, contrast goes down)
what are long-scale radiographs? describe the mAs and kVp for this case. what anatomy do we want a long-scale radiograph for and why?
radiographs that have low contrast and high latitude
low mAs & high kVp
thorax - imaging of soft tissues (more shades of grey!)
what are short-scale radiographs? describe the mAs and kVp for this case. what anatomy do we want a short-scale radiograph for and why?
radiographs that have high contrast and low latitude
high mAs & low kVp
MSK - better delineation of bone defects (don’t need to see soft tissue as well, but need to see the difference between black and white really well!)
what is the inverse square law in relationship to radiographs? why is this important?
intensity of x-ray beam is inversely proportional to the square of the distance – basically, lower distance = higher intensity
to achieve the same darkness/density:
- increase distance = increase mAs (in order to increase the intensity to account for the inverse square law)
- decrease distance = decrease mAs
tissues absorb xrays depending on _____. High _____ = more absorption = _____ image
atomic number
atomic number = more absorption = whiter image
list the 5* radiographic capacities from whitest to darkest (how they show up on image)
*there are technically 5, but 6 capacities
metal & contrast media = white
mineral (bone)
soft tissue <–> fluid
fat
air = black
what is summation?
as multiple tissue types are exposed, the sum total of their density is represented on radiograph
as density increases, xrays are absorbed to a greater degree –> lighter image
so like, if there are two soft tissue structures partly overlapping, the overlapping section will be lighter than the other parts, even though they are the same material. think about a Venn diagram with the middle part lighter than the outer parts.
what is a silhouette sign?
lack of ability to differentiate between similar adjacent tissue types
in order to see the outline of a tissue, it must be surrounded by a tissue of a different density
ex. liver is behind pancreas (don’t think about correct anatomy here, this is just an example of 2 things with the same density) - you just see a big blob on radiograph, you can’t differentiate between the two structures.
We want the subject _____ to the plate. Why?
adjacent
less penumbra formed (halo of unsharpness)
describe the concept of magnification in respect to radiographs.
the further the subject is from the plate (and closer to the focal spot), the bigger the subject is on the picture (but not actually bigger, just an artifact basically)
describe the concept of distortion in respect to radiographs.
if subject is not flat to plate (i.e. part is on plate, other part is closer to the focal spot, tilted), the part that is closer to the focal spot will be bigger and less sharp than the other part
bigger focal spot = ____ penumbra = ____ image (worse/better)
larger
worse
Motion is ____ for radiographs. it is exacerbated by _______.
bad
increased mAs (long exposure times)
What is plain film?
silver plated photographic film. xrays activate silver which stay on film after processing (dark). unexposed areas lose silver (light)
subject to processing errors
old skool way
how is digital radiography different from plain film?
detector plate replaces film, but generator remains the same
why is digital radiography good? why is digital radiography bad?
good:
- can decrease exposure (plates tend to be more sensitive)
- faster, more convenient processing
- fewer retakes needed
- much more detailed image produced
bad:
- very expensive!
- technically more complicated
- temp sensitive sometimes
- environmentally sensitive sometimes
- difficult to troubleshoot
tell me the difference between computed radiography (CR) and direct radiography (DR)
CR: generator and plates look the same, film is covered in hard plastic coated with phosphor that is stimulated by a laser, plate can be reused after processing
DR: generator the same, detector replaces film, xrays hit detector and it captures the distribution of xrays on the surface and sends signal directly to computer.
what is the Mach phenomenon?
optical illusion - false white or black lines that appear at sharp boundaries. be careful bc they can mimic lesions
what is the contrast background effect?
optical illusion - depending on the background colour, a shape may look like it has a different colour, when in reality it’s the same colour
