Recorded Detail Ch. 28 Flashcards
Detail is AKA
Recorded detail, spacial resolution
How many geometric properties of image quality?
2
Geometric properties control…
detail itself
What is the degree of geometric sharpness or accuracy of the structural lines actually recorded in the image?
recorded detail
What is one of the easiest prime technical factors to evaluate & adjust?
recorded detail
What is lp/mm?
the point at which the viewer can discern the closest pair of lines from each other
How is recorded detail determined?
primarily by matrix size, pixel size and grayscale bit depth
High resolution is …
a shorter wavelength signal (higher frequency) represents pairs of lines that can be visualized very close together
What would be easier to see the spacial resolution..a small or large body part?
small
When fine detail is lacking the image will look
blurred
What order should resolution problems be approached?
- eliminate motion
- reduce OID
- Reduce FSS
- Reduce intensifying screen phosphor size and concentration
- Increase SID
What is the most important factor in establishing the level of resolution desired for recorded detail?
the geometry of the beam (divergence of the beam)
What happens to resolution when OID is decreased, increased?
Improves, degrades
What happens to resolution when SID is decreased, increased?
degrades, improves
Why is the lateral C-spine done at 72”?
B/c you cannot reduce OID so you must increase SID to get better detail/less magnification.
What is FSS controlled by?
the line focus principle
What is the umbra?
the distinctly sharp area of a shadow or region of complete shadow
What is the penumbra?
the imperfect, unsharp shadow surrounding the umbra
Penumbra is also referred to as..
the edge gradient
What controls penumbra?
FSS
What causes penumbra?
the fact that the source of the xray photons is not a point source.
As FSS decreases, penumbra…
also decreases & increases resolution
Other than increased FSS, decreased SID and increased OID, what could cause increased penumbra?
attenuation or absorption unsharpness
What is better for detail in F/S…fast or slow film speed?
slow!
What are the primary factors affecting the recorded detail of digital imaging systems?
the detector geometric properties and image processing system
What is the #1 cause of decreased detail?
Motion
What is the best way of controlling voluntary motion?
communication
What is the best way to control involuntary motion?
Decrease exposure time
How does the xray machine cause motion?
movement of the reciprocating grid, if the suspension system is not balanced - both can vibrate
What is SOD?
source to object distance
How do you calculate SOD?
SID-OID=SOD
How do you calculate FSS?
OID/SOD
How do you calculate penumbra?
FSS x OID / SOD
smaller pixels =
sharper image
What is the Focal spot?
the exact point on the target or target track on the anode where xrays are produces
Why are kidneys imaged AP?
B/c the kidneys are retroperitoneal
What are picture elements of certain densities?
pixels
Overexposure and underexposure reduces
detail
