Characteristics 1
What are the two principal characteristics of digital imaging?
Spatial Resolution
Contrast Resolution
What is spatial resolution?
The ability to render small objects on the image
What is the capture element in Indirect DR?
Cesium Iodide
What is the capture element in Direct DR?
Amorphous Selenium
In a perfect imaging system, MTF would be equal to...
1
Line pairs per millimeter/centimeter
LP/mm or LP/cm
Spatial resolution is determined by...
Pixel size
Explain the process of Indirect DR
Exit beam -> capture element -> coupling element (turns x-ray into light) -> collection element
Explain the process of Direct DR
Exit beam -> capture/coupling element -> collection element
What kind of test is used to acquire data for MTF?
Bar pattern
As object size ______, spatial frequency _____ and spatial resolution ______.
decreases, increases, increases
How many shades of grey can a human see?
30
What does the amorphous selenium do?
Absorbs the exit beam and converts it into an electric signal
The ability of the CCD to detect and respond to very low levels of visible light is known as...
Sensitivity
Which imaging modality has the highest dynamic range?
Mammography
Describe the signal-to-noise ratio
The comparison of the useful signal of the image to noise
What is dynamic range?
The number of gray shades that an imaging system can reproduce.
What are some disadvantages of Indirect DR?
Lower DQE at higher energies; more dose to the patient
Amorphous selenium isn't optimal for general radiography
What does the Cesium Iodine do within the Indirect IR?
Takes the x-ray photons and converts them into light
What is DQE and what does it describe?
Detective Quantum Efficiency; the probability that an x-ray will interact with an IR by the thickness of the capture layer and the atomic composition
Digitial radiography images should only be repeat if there is a problem with...
Positioning
How is dynamic range identified in an imaging system?
The bit capacity or bit depth of each pixel
What are some advantages of Indirect DR?
Higher spatial resolution with an almost 100% fill factor
Less light interference due to selenium not emitting light when exposed to x-ray photons
With Indirect DR, what is the fill factor percentage?
80%
Which is better for patient doses? High DQE or Low DQE?
High DQE