1
What are the two principal characteristics of digital imaging?
Contrast and Spatial resolution
Pixel brightness is affected by...
Quantity of photons and/or the quality of energy reaching the IR
What happens to spatial resolution when you have a large matrix size?
Increases due to smaller pixels being used
Which two factors affect image magnification?
SID and OID
How many shades of gray can a 16-bit system produce?
65,536
What is one of the main exposure factors affecting image contrast?
Bonus 100 points for the updated board answer.
kVp
Bonus answer: Look-up Tables
What is the ratio between the strongest and weakest signals a system can process or the number of shades of gray the computer system can produce overall?
Dynamic range
What describes how well an imaging system can transfer contrast at different spatial frequencies from the object being imaged to the image itself?
How can you minimize magnification?
Maximize SID and minimize OID
What is the formula for Detective Quantum Efficiency (DQE)?
DQE = (SNR2out)/(SNR2in)
What is the grainy or mottled texture on a digital image and is the major contributor of noise?
Quantum noise/Quantum mottle
What is the range of shades or grayscale values that can be displayed in the image on the monitor?
Window Width
What is the DQE of a perfect system?
1
What does mispositioning the body part, IR, or CR do?
It can cause foreshortening or elongation
If a heart measures 12.5 cm at its maximum width and its image on a chest radiograph measures 14.7 cm, what is the magnification factor?
1.176 cm
Image size/Object size
What can you do to increase the signal-to-noise ratio (SNR)?
Bonus 100 pts: What is the cost?
Increase mAs
Bonus: increased patient dose
What can happen if you use the small focal spot?
It will increase your spatial resolution
What is the formula for the Nyquist frequency?
1/2 x sampling frequency
or
Sampling frequency divided by 2
What is bit depth?
The number of gray shades that a pixel can represent
A renal calculus measures 1.2 cm on the radiograph. The SID is 100 cm, and the SOD is estimated at 92 cm. What is the size of the calculus?
1.1 cm
SID/SOD
How does subject contrast differ from image contrast?
Subject contrast = tissue density differences in the body being imaged
Image contrast = the image's overall contrast
What formula calculates pixel size?
Pixel size = FOV / matrix size
What happens when sampling frequency is below the Nyquist rate?
Details are missed, leading to aliasing artifacts like moire patterns.
If you increase bit depth, what happens to the file size?
It increases
A lateral view of the lumbar spine taken at 100 cm SID results in the image of a vertebral body with maximum and minimum dimensions of 6.4 and 4.2 cm, respectively. What is the object size if the vertebral body is 25 cm from the image receptor?
3.16 and 4.8 cm