Ch. 4 Flashcards
What is the relationship between the display field of view (FOV) and pixel size for a fixed matrix size?
Direct
A combination of rows and columns (array) of pixels is called a
Matrix
The size of a pixel is measured in:
Microns (very small)
Digital image quality is improved with, which of the following?
- larger size matrix and larger pixel depth
- larger size matrix and smaller pixel size
- larger pixel depth and smaller sizes of pixels
All options are correct
If the matrix size is increased for a fixed field of view (FOV) the pixel size is _____
decreased
If the matrix size is increased for a given FOV: spatial resolution is ____
spatial resolution is increased
If the FOV is 500 mm and the matrix size is 1024, what is the pixel size?
Equation - FOV/matrix size = pixel size
0.49 mm
The number of bits that determines the amount of precision in digitizing the analog signal and the number of gray shades that can be displayed in the image is the:
bit depth
A larger bit depth increases what:
increases the number of shades of gray and increases contrast resolution
The pixel bit depth determines the image’s:
contrast resolution
A 10-bit pixel depth can display how many shades of gray?
1024
A system that can digitize and display a greater number of shades of gray will have _______ contrast resolution
increased
The greater the pixel bit depth:
the more precise digitization of the analog signal and a greater number of shades of gray will be displayed
The number of pixels per unit area is called the:
pixel density
The pixel spacing or distance measured from the center of a pixel to an adjacent pixel is called the:
pixel pitch
What two things results in improved spatial resolution?
Increased _____ and decreased _____
increased pixel density and decreased pixel pitch
Increasing the number of line pairs per millimeter resolved in the imaging system results in:
increased spatial resolution
The measure of the imaging system’s ability to display the contrast of anatomic objects varying in size is the:
modulation transfer function (MTF)
- An MTF of -_____ means a maximum difference in brightness levels.
1.0. or 100%
What term refers to the range of exposures that should be used to produce a diagnostic image?
exposure latitude
What dose monitoring value measures the exposure in air and estimated absorbed dose?
KAP
The measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image is the:
detective quantum efficiency (DGE)
The higher the DQE of a system, the radiation exposure required to produce a quality image is:
decreased
Which of the following is true concerning computed radiography imaging plates?
- The CR cassette houses the imaging plate and the tradition exiting the patient interacts with the imaging plate
- The CR cassette house the IP and the photon intensities are absorbed by the phosphor
- The radition exiting the patient interacts with the image plate and the photon intensities are absorbed by the phosphor
ALL options are correct
What is a term generally used to describe the emission of light from a substance as the result of stimulation by radiation?
Luminescence
The CR phosphor layer is composed of:
barium flourohalide with europium
The emission of light when stimulated by a high-intensity laser beam is:
photostimulable luminescence (PSL)
The CR latent image consists of:
electrons trapped in the phosphor layer or F trap, F center
- This material is composed of barium flourohalide and makes up the primary component of the CR
Photostimulable phosphor (PSP)
Which of the following is not a component of the CR IP:
- Thin film transistor layer
- Support layer
- Phosphor Layer
- Protective Layer
Thin film transistor layer
With CR, when the x-ray photons are absorbed by the phosphor, the _____ atoms become ionized.
europium
With CR, trapped electrons are:
proportional to the exit exposure intensity and released during the readout stage
Which of the following is not part of a CR reader unit?
Capacitor
The _______ collects, amplifies, and converts visible light to an electrical signal.
PMT
In the CR reader unit, the IP is scanned with a:
helium-neon laser beam (red in color)
What is the sequence of events, from beginning to end, of what happens in the CR reader unit?
Stored energy is released as visible light
PMT converts light energy to electrical signal
Analog electrical signal is sampled and digitized
(This was on someone’s registry!)
With CR, a higher sampling frequency results in:
Increased ___ ___ and smaller ___ ___
increased pixel density and smaller sampling pitch
With CR, a larger sampling pitch results in:
Increased ___ ___ & decreased ___ ___
increased pixel size and decreased pixel resolution
- How often the analog signal is reproduced in its discrete form is:
sampling frequency
With a fixed matrix CR reader system, changing to a larger IP, for the same FOV, will result in:
larger pixels
The distance between the analog points being sampled is the:
sampling pitch
- Pixel bit depth is determined by the:
ADC
- Immediately before leaving the CR reader unit, the IP is exposed to:
intense white light
What type of image receptor converts the exit radiation into electrical charges and stores them before readout and digitization?
DR
DR imaging systems briefly store the electrical charge in the:
TFT
The ____ array is divided into square detector elements
TFT
- The percentage of x-rays that have reached the detector and have been captured is the
fill factor (we want this to be high)
- Which of the following is not a component of a flat-panel detector?
- Phosphor layer
- Glass Substance
- X ray converter
- TFT array
Phosphor layer
The indirect conversion detector uses
a scintillator and a photodetector
An example of a scintillator used in an indirect conversion detector is:
gadolinium oxysulfide and cesium iodide (gd2o2s) - these convert x-ray into light
What is true about the indirect conversion DR systems?
x-rays are converted to light and then converted to electrical charges
What is the sequence of events for the production of a DR image using direct conversion detectors?
exit radiation is converted to electrical charge, charge is stored briefly in TFT array, electronic signal goes to ADC
The ability of the detector to accurately capture the variety of photon intensities in the remnant radiation is
dynamic range
The measurement of the efficiency of an image receptor in converting the x-ray exposure it receives to a quality radiographic image is the
detective quantum efficiency
The higher the DQE of a system, the radiation exposure required to produce a quality image is:
Decreased
Overexposing a digital image receptor may result in:
high SNR and increased patient exposure
A method of describing the strength of the radiation exposure compared with the amount of noise apparent in the digital image is the:
signal-to-noise ratio
A high SNR means that the:
signal strength is high
_________ the SNR increases the visibility of anatomic details
Increasing
A method of describing the contrast resolution compared with the amount of noise apparent in a digital image is the:
contrast to noise ratio (CNR)
T/F
Once the data is in digital format, there is no difference between image processing and display between the CR and DR
T
_________ the CNR increases the visibility of anatomic details.
Increasing
T/F
There is no light produced with CR when radiation interacts with the IP
F
T/F
The quality of the CR latent image will remain the same for up to 6 hours after exposure
F
T/F
Both CR and DR are electronic detectors that combine image capture and image readout
F- only DR
T/F
The DR system does not require a separate reader unit
T
T/F
With an FPD, electrical charges from each DEL are read out separately.
T
T/F
Exit radiation is converted to visible light with the direct conversion detector.
F (if it said indirect it would be true)
T/F
Small anatomic objects have higher spatial frequency.
T
T/F:
Because digital imaging has a large dynamic range, significantly lower than necessary x-ray exposure will still result in a quality image.
F
T/F
An image with high SNR will have decreased detail visibility
F (increased detail visibility)
T/F
Bit depth is determined by the matrix size
F
T/F
The spatial resolution of flat-panel receptors is generally superior to that of CR
T
T/F
The DQE is higher for DR when compared to CR.
T
What are the 2 types of digital radiographic imaging systems?
computed radiography (CR) and direct radiography (DR)
What is the formula that shows the relationship among pixel size, FOV, and matrix size?
Pixel size = FOV/Matrix size
Bit depth is measured how?
2^n
Defined by the unit of line pairs per millimeter (lp/mm)
spatial frequency
define contrast resolution:
The ability of the image receptor to distinguish between objects having similar subject contrast
Define Pixel Pitch:
The distance measured from the center of a pixel to an adjacent pixel
a method of describing the strength of the radiation exposure compared with the amount of noise apparent in the digital image is the:
signal-to-noise ratio
a method of describing the contrast resolution compared with the amount of noise apparent in a digital image it the
contrast-to-noise ratio
The main difference between Computed Radiography and Direct Radiography is…
CR is a two-step process, DR is a one-step process
The greater amount of pixels in an image matrix, the ____ their size.
Smaller
The acquired image data (released energy) are extracted from the ____, and converted to digital data, and computer-processed from image display.
Digital Receptor
Within how long should you process an exposed IP, and why?
Within 1 hour because the latent image dissipates overtime (CR Fading)
- CR fading occurs because some of the signal (energy released) captured in the IP is lost
