Clinical radiology I Flashcards
(40 cards)
Bad radiographs should never be..
interpreted. They are not diagnostic.
The nearer the cassette/film is to the object, the…
sharper the outline will be.
Distance causes magnification: blurring, distortion.
The nearer the object is to the source of radiation, the greater will be the degree of magnification.
Standard distance from the source of the radiation is
100cm.
Distance between xray subject and cassette/film?
near as possible to the cassette/film so as to avoid size distortion.
Why aren’t whole body xrays of animals favored?
Decreased image quality - thorax and abdomen should be captured with different parameters so detail isn’t lost.
What parameters denote the following:
Amount of radiation?
Voltage of radiation source?
Amount of radiation = mAs
mAs controls the quantity of X-rays produced. Increasing mAs results in more X-rays reaching the image receptor (e.g., film or digital sensor). This increases the overall density or darkness of the image.
voltage of radiation source = kV
kV controls the energy of the X-rays.
Increasing kV reduces the contrast between different tissues in the image. Higher energy X-rays are more likely to pass through tissues without being absorbed, resulting in an image with more gray shades (lower contrast).
mAs does what for your images?
kV does what for your images?
mAs = general lightness/brightness. If the picture too light, increase mAs (so that the beams will penetrate better).
kV = permeability of beams, contrast.
Increasing kV reduces the contrast between different tissues in the image. Higher energy X-rays are more likely to pass through tissues without being absorbed, resulting in an image with more gray shades (lower contrast).
Standard xray orientation?
head to the left, tail to the right
Right or left?
Check the diaphragmatic crus: are they parallel or do they form a V?
on the right side they’re parallel
Right or left?
Check the diaphragmatic crus: are they parallel or do they form a V?
on the left side, they form a V.
Cat or dog?
Cat
Body of vertebra longer, oblong
Dogs: The vertebrae tend to be more robust, especially in larger breeds.
Cats: their vertebrae are more uniform and slender.
Cat or dog?
Dog
Body of vertebra shorter, square-like
Dogs: The vertebrae tend to be more robust, especially in larger breeds.
Cats: their vertebrae are more uniform and slender.
Interpreting size in xrays.
Size can be affected by technical method or position of animal.
When measuring strictly from the picture, magnification and distortion can occur.
Always better to compare with some other organ in the same picture.
Interpreting shape in xrays.
Shape in xrays is two-dimensional so always take 2 projections.
Overlapping of shadows can create optical illusions = artefacts.
Subjective contours – overlapping outlines create false object.
Radiopaque =
Radiolucent =
Radiopaque = materials with good contrast, most radiation beams will be absorbed (or stopped) by them.
Radiolucent = very small absorption of radiation beams meaning they pass through e.g. gas and air.
5 different densities in xrays:
Gas – respiratory tract, GIT
Fat
Soft tissue/fluid – including blood, body fluids, muscle, parenchymal organs
Bone
Metal
Note: The shadows of structures with similar density will look the same on radiographs (fluid vs soft tissue)!
Bone tumors: primary tumors are usually found in what part of bones?
And metastases?
primary tumors in metaphyseal area, metastases usually in diaphyseal area.
But not a strict rule!
Explain Mach bands/lines.
Light or dark line artefacts that appear on the border between objects with different optical densities.
May be helpful – can create more contrast.
NB Can mimic fractures.
Classical site where they’re found - tibia and fibula overlapping
Background effect in xrays.
Depending on the color of the background, objects may appear as different colors/densities. This is an optical illusion and just how our eye interpret colors.
Image depiction: contrast agent injected into bladder with urinary stones. stones seem to “change” color based on the background color.
Uberschwinger/rebound artefact
Is a digital illusion
This artifact is characterized by the appearance of a bright halo or edge around high-density objects, such as metal implants, screws, or other dense materials.
May be misinterpreted as inflammation or lytic change
describe the artefacts pointed at
white arrows point at white lines that are artefacts from skin folds and appear denser than they truly are.
black arrows = cassette artefact
Purpose of contrast agents
To visualize structures that are poorly visible or not visible at all on plain radiographs – agents create necessary contrast.
Can be used to specify location, size, shape, internal architecture.
Positive contrast – radiopaque (bright)
Negative contrast – radiolucent, usually air (dark)
Combined – both positive and negative contrast agent can be used at the same time for even better contrast.
describe negative contrast
= using room air injected (bladder, GIT, joints).
Organ location, size, wall thickness.
Will show marked wall thickening and large luminal filling defects (masses, foreign bodies).
Little information about the mucosal surface.
Smaller filling defects may be overexposed.
Small tears in the wall may be missed.
describe positive contrast
= mainly barium and iodine preparations.
Provides little more information than negative contrast studies.
Are the best to detect a small defect in the wall of the organ – even small leakage is detectable.
