Radiographic Quality Flashcards
The exactness of representation of the anatomic part of interest in the finished radiograph
Radiographic quality
Factors of film (characteristic curve)
density, contrast, speed, latitude, processing, time, temperature
Geometric factors
distortion, magnification, blur
subject factors (contrast)
thickness, density, atomic #, motion
Evaluation criteria for quality
spatial resolution, contrast resolution, noise, artifacts
ability to image objects that have high subject contrast
spatial resolution
ability to detect or distinguish objects that have similar subject contrast
contrast resolution
The undesirable fluctuation of the OD of the image
Noise
Kinds of noise
- film graininess
- structure mottle
- quantum mottle
- scatter radiation
a result of insufficient mAs in which an uneven distribution of x-ray within the beam leave a blotchy or freckled appearance on the finished radiograph
Quantum mottle
high mAs, low KVP and slower screen result in a __________ of quantum mottle and a smoother more even image appearance.
reduction
Radiographic Quality Rules
- Fast image receptors have high noise and low spatial & contrast resolution
- High spatial & contrast resolution require low noise and slow image receptor
- Low noise accompanies slow image receptors with high spatial & contrast resolution
The measurement of light incident on a processed film (Io)and the level of light transmitted through the film (It)
Optical density
Base + fog =___
OD
Base + fog
unexposed and processed radiographic films have an OD of 0.1 - 0.3
Base Density number-
0.1
Fog density number-
does not exceed 0.2
Useful range of OD
0.25-2.5 LRE
Useful range of OD are dependent Upon:
Viewbox illumination, viewing conditions, shape of characteristic curve
Inherent in the film and influenced by processing
Image receptor contrast
determined by size, shape, and x-ray attenuating characteristics of the subject and the energy of the beam (kvp)
Subject contrast
Contrast is defined by the slope of the ______ _________.
straight line portion (average gradient )
For the same film type a change in ________ will affect contrast only when above of below the straight line portion
density
The slope of the straight line drawn between two points on the characteristic curve at 0.25 and 2.0 above B+F
Average Gradient
Average gradient formula
AG= OD₂ -OD₁/ LRE₂-LRE₁
Speed
the speed point on a film is defined as OD 1.0+ B+F
Film speed is affected by:
Immersion time, Temperature, chemical activity
The longer the film is exposed to the chemicals the ________ the characteristic curve becomes indicating that contrast has been effected by an increase in density
straighter
Image receptor speed formula
Speed= 1/ exposure in R to produce OD 1.0+B+F1)
Receptor and speed formula
New image receptor speed/ old image receptor speed= Old mAs/ new mAs
Latitude and contrast are _______ proportional
inversely
The range of exposures that will produce densities within the diagnostic range
Latitude
Latitude
The Range of exposures that will produce diagnostically acceptable OD ranges.
Latitude formula
Latitude= Eh -Eᵢ Eh= high exposure point OD 2.5 Ei= low exposure point OD 2.25
A narrow latitude film requires
greater exposure accuracy and produce short gray scales
A film that has a wider latitude permits considerable variation in the exposure while still exhibiting densities within the diagnostic range produce ___ ____ ______ .
long grey scales
All images appear larger radiographically than their actual size
Magnification
__________ amount of magnification should be maintained
Smallest
Magnification is dependent on _________ conditions of the exam
geometric
magnification factor formulas
MF= image size/object size=SID/SOD
Two factors affect image magnification
SID, OID
The presentation of unequal magnification of different portions of the same object
Distortion
Distortion is dependent upon
- thickness of object/part
- position
- shape of the object
Object thickness
the thicker the object the more distortion present on the final radiograph
Object unsharpness
- main problem is trying to image a 3-D object on a 2-D film
- human body is not straight edges and sharp angles
____ X-ray beam width will produce a sharper image
smaller
Fine detail = __________
small focal spot
General Radiography uses ____________ focal spot
large
Penumbra
fuzzy border, obscures true border
The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image ____________.
sharpness
Most exam are done at ______iinches
40
the closer the object to the film, the _____ the detail.
sharper
OID goes down, penumbra goes down, sharpness goes ___
up
OID goes up, penumbra goes up, sharpness goes _____
down
Objects not on the central axis appear ______.
distortion
If the object plane and the image plane are not _____, image distortion will occur
parallel
Misrepresentation on the radiograph of the actual relationships present among objects or parts
spatial distortion
the misrepresentation by unequal magnification of the actual shape of the structure being examined
shape distortion
Two kinds of shape distortion
Foreshortening and elongation
Foreshortening
the image size is reduced as the angle of inclination along the central axis increases
-occurs only when the part is improperly aligned
Elongation
the image size is lengthened as the inclination is increased
- occurs when the tube or the image receptor are improperly aligned. tube angle results in elongation never foreshortening
the farther the part of interest is from the central ray of the image receptor with _______ the distortion
greater
Focal spot blur is _________ on the cathode side of the tube
greater
Focal spot blur occurs because
the focal spot is not a point, but rather a rectangular source (0.1-1.5mm)
most important factor in determining spatial resolution
focal spot blur
To minimize focal spot blur:
use small focal spots, decrease OID (position part and receptor as close as possible), increase SID to maximum allowed for exam
Subject contrast is dependent upon
patient thickness, density, atomic # of the tissue, shape
- kvp must be controlled based on the evaluation of these factors
