Ch 10 Radiographic Quality Flashcards
What is radiographic quality?
The exactness of representation of the anatomic part of interest in the finished radiograph
What are the (3) types of radiographic quality factors?
- Film factors (not allot of control over)
- Geometric factors (little bit of control over)
- Subject factors (no control over)
What quality factor do we have no control over?
Subject matter
What are the film factors?
Characteristic Curve
- Speed
- Latitude
- Density
- Contrast
Processing:
- Time
- Temperature
What are the Geometric Factors?
- Distortion
- Magnification
- Blur
What are the Subject Factors?
Contrast Thickness Density Atomic # Motion
Quality is the same for everyone? T/F
False
What is the criteria for evaluating quality?
- Spatial resolution
- Contrast resolution
- Artifacts
- Noise
What is spatial resolution?
Everything is in it’s appropriate place
What is contrast resolution?
Scales of gray
Spatial resolution is the ability to image objects that have ____ subject contrast.
High
Contrast resolution is the ability to detract or distinguish objects that have _____ subject contrast.
Similar
Which modality best demonstrates spatial resolution?
Diagnostic
What is noise?
The undesirable fluctuation of the OD of the image
Which modality best demonstrates contrast resolution?
CT, MRI
How do we get noise on an image?
- Film graininess
- Structure mottle- phosphor intensity screen
- Quantum mottle-
- Scatter Radiation-impact OD
What is Quantum Mottle?
Freckled appearance
What is the quality rule?
Fast image receptors have high noise and low spatial & contrast resolution
What is another name for the D max?
Shoulder
What is the Characteristic curve?
The graphic relationship between optical density and radiation exposure
What are the two pieces needed to contract a characteristic curve?
Sensitometer
Densitometer
What is the highest portion of the Characteristic curve?
Shoulder (D max)
What is the lowest portion of the Characteristic curve?
Toe
What is another name for the Characteristic curve?
H & D curve
What is the most useful part of the characteristic curve?
Straight line portion
Is D max useful?
- No, it’s black
- Densest part
- Burnt out
Is the Toe useful?
No, too white
- Washed out
- Loss of density
Where do you find your grays on the Characteristic curve?
In the straight line portion
What is the portion below the toe called?
Base + Fog (B+F)
What is B+F?
- What is inherent in the film and hasn’t been exposed
- Anything outside the range of exposure
In B+F, what is Base?
What the manufacturer put in the film
In B+F, what is F?
Fog in the dark room
What is optical density?
Measurement of light incident on a processed film and the level of light transmitted through the film
What chemical produces the black?
Hydroqonone
What chemical produces the shades of gray?
Phenedone
Base + Fog= ?
Optical Density
Base + Fog should not exceed…
0.3
B + F (below toe) falls ______ the exposure range.
Outside
What is the OD range of the unexposed and processed radiographic films?
0.1- 0.3
Hydroqonone and phenedone work _______ to produce the blacks and grays.
Synergistically
Optical density is looking at what’s _____ and what passes through
Inherent
B+F is the _______ and processed part of the processed radiographic film.
Unexposed
What is the base density?
0.1
What is the Fog density?
Doesn’t exceed 0.2
What is the useful range of optical density?
0.25- 2.5 LRE
What are some reasons you might get an OD greater than 0.3?
- Aging of the film
- Processor temp
- Chemical fumes
- Light
- Radiation
What does LRE stand for?
Log Relative Exposure
What are the OD ranges dependent on?
- Viewbox illumination
- Viewing conditions
- Shape of characteristic curve
Optical density is measured ________.
Log rhythmically
What are the (2) types of Radiographic Contrast?
- Image receptor contrast
2. Subject contrast
What is Image Receptor Contrast?
Inherent in the film and influenced by processing
Things we cannot control
What is Subject Contrast?
That which attenuates through our patient and the kVp we performed the image with
(other than kVp we cannot control)
How do we have any control over radiographic contrast, when it’s determined by things we have no control over?
By adapting
For the same film type a change in _____ will affect contrast only when above or below the straight line portion.
Density
Contrast is defined by the slope of the ______ _____ portion.
Straight line
When density impacts _____ it is above or below the straight line portion
Contrast
Contrast that is defined by the slope of the straight line portion is also know as…
Average gradient
When changing technique at the D max…
Cut mAs in half
When changing technique at the toe you…
Double mAs
What is the Average Gradient?
The slope of the straight line drawn between two points on the characteristic curve at 0.25 and 2.0 above B+ F
What is the useful range of average gradient?
0.25- 2.0
The B+ F should not exceed…
0.3
What are the average gradient constants?
- 25
2. 0
What is the B+ F range?
0.1- 0.3
When connecting (2) points on an H & D curve, the line is called the…
- Average Gradient
- Straight line portion
- Useful portion
What is the formula to determine Average Gradient?
AG= OD2 - OD1
_________
LRE 2 – LRE 1
The speed point on a film is defined as:
B + F+1
How do you chart a speed point?
As an open circle
When looking at a speed chart, the faster film is usually on the ____.
Left
- It has a shorter scale of contrast
- Goes from white to black faster
Speed point is ___ point above B + F.
1
What is speed?
How fast a film develops
