ASRT Digital Imaging Module 1 Flashcards
Primary Beam consists of photons of __________ energies. With different abilities to ____________.
- varying
2. penetrate tissue in a patient
The tissues in the human body have varying abilities to _______ or _______ x-ray photons.
attenuate or absorb
The beam containing useful and diagnostic information is the _____________.
remnant beam
In film imaging, the chemical interactions are between the _____________ and the _____________.
- processing solutions
2. emulsion/recording layer (of the film)
Digital images allow us to see structures that would have required ______________ with film technology.
additional imaging
Film screen is always considered __________.
analog
Analog IR has 3 components.
- cassette
- intensifying screen
- film
In analog, the _______ is the recording device.
film
the _____________________ turn x-rays into light, which in turn makes up the latent image.
intensifying screens
Film digitizers are ______ efficient in measuring slight changes in film opacity.
very
The ______________________ changes the continuous signal into a discrete signal.
ADC (analog-to-digital converter)
The process of assigning numeric values to a signal is _______________.
quantization
The number of gray levels in a bit depends on its ____________.
bit depth
formula for calculating bit depth
2^x = # of shades of gray
bit depth for ADC used in diagnostic imaging is _________
12-32
The ability to distinguish objects adjacent to each other is measured with _________________.
line pairs per millimeter
higher resolution = individual lines are ____________
separate and distinct
How is pixel size is measured?
from side to side of a single pixel
How is pixel pitch measured?
from the center of one pixel to the center of an adjacent pixel
A typical matrix size for a digital radiograph is _______ x _______ with a bit depth of ____.
3000 x 3000; bit depth of 12
A typical matrix size for CT is _____ x _____ with a bit depth of ___.
512 x 512; bit depth of 16
2 types of Photostimulable Phosphor plate systems
cassette-less and cassette-based
2 types of Flat-Panel Receptors
scintillator based and nonscintillator based
Define scintillation (in radiography) and its process
the ability of a material to absorb x-ray energy and produce light; the light is then converted to electrons which create an image
3 important parameters used to assess performance of receptors
- absorption efficiency
- conversion efficiency
- detective quantum efficiency (DQE)
What does Absorption Efficiency measure?
the percent of energy that strikes a receptor that is actually absorbed
What does Conversion Efficiency measure?
the percent of energy absorbed by the receptor that is converted to usable output
What is Detective Quantum Efficiency?
DQE is a product of absorption and conversion efficiencies
What are the two types of phosphor types for PSP?
- Turbid (randomly distributed)
2. Needle (columnar)
Needles have less __________ ___________ when compared to columnar. This helps improve ________ ________.
- light divergence
2. spatial resolution
How long can a latent image remain on a PSP detector?
several hours (roughly 8)
PSP latent image can lose ___% of its energy in ___ hours.
25% in 8 hours
What holds the electrons elevated in the higher energy state?
conductive band
Where do the electrons go while in the resting state?
valence band
T/F: The reader’s laser light releases all electrons from the F-Trap.
False, some are left behind
As the plate travels thru the reader, how is the laser light set up?
it is pointed towards an optic scanner
Newer plate readers are line-scan devices which have ______ _______ in a row.
several lasers
The newest type of PSP reader is the ___________.
dual-sided
Step-by-step process of signal conversion (starting with light emitted from electrons in F-trap)
- photodetector captures light from PSP plate
- converts light intensities to electronic signal
- signal sent to ADC
- signal undergoes sampling and quantization
Photoconductive material used for (1) scintillator-based and (2) non-scintillator-based
- Amorphous Silicon (aSi)
2. Amorphous Selenium (aSe)
TFT
Thin-Film Transistors; complex circuit device that collects electrons
DELs
detector elements of TFT array; a DEL collects electrons that represent the exposure level
Fill Factor
used to assess the quality of the FPD; a ratio of the radiation-sensitive area to the non-. 80% Fill Factor means 80% of the detector area is devoted to sensing radiation
Fill Factor affects a detector’s ______ and _______.
- spacial resolution
2. signal-to-noise ratio
Noise affects the observer’s ability to perceive ______ ______ within an image.
structural details
Indirect TFT systems are cassette based. The cassette’s scintillator system is made of _________ or ________.
Cesium Iodide or Gadolinium OxiSolfate
T/F: CCD requires a scintillator.
true; can be CsI or GdOS
3 Advantages of CCD receptors
- wide range of exposure settings
- respond to lower light levels from scintillator
- produces images quickly and instantly refreshes for the next image (good for fluoro)
4 steps for CCD image capture
- scintillator converts x-rays to light
- light photons reflect off mirror to focusing lens which get directed to CCD
- CCD converts light signal to electrical signal
- electrical signal is sent to ADC
In a CMOS detector, the light from the scintillator is directed to the CMOS by a ______________.
fiber-optic cable
If a detector has a higher spatial frequency, it represent a _________ number of viewable objects on an image
larger
Spatial Resolution is measured in _________ per _____
Line Pairs per mm
The _________ determines the line pairs per mm we can see.
size of the pixels
Better recorded detail (resulting from higher sampling frequency) is ideal for __________ exams.
extremity
For ____________ detector, the size of the detector determines spatial resolution.
flat-panel detector
- DEL size of 200 microns = spatial resolution of _____
2. 100 microns =
- 2.5 Lp/mm
2. 5 Lp/mm
T/F:
PSP w/200 micron pixels = FPD w/DEL of 200
however, PSP w/100 does not equal FPD w/100
true
Nyquist Frequency/Theorem
determines level of spatial resolution for IR
Analog receptors produce acceptable images between ___% underexposed to ___% overexposed.
30% under, 50% over
Digital receptors produce acceptable images between ___% underexposed to ___% overexposed.
50% under, 100% over
The only visual cue a tech has to indicate underexposure is _____ _____.
quantum noise (50%+ underexposed)
For a digital image overexposed, ________ ________ is decreased.
image contrast (100%+ overexposed)
