RAD 210 - Final Exam Review
What is the typical CR/DR latitude?
-50% to +400%
CR image receptor response ranges from _______ levels of gray
0 to 10,000
In film-screen, the IR response has an optical density range of _______ or _______ shades of gray
0 to 3; 1000
Each dexel contains?
1) A thin film transistor (TFT) 2) A charge collection electrode 3) A storage capacitor 4) A photo detector
Names examples of image noise from computer control defects?
1) Electronic noise 2) Inadequate sampling 3) Inadequate quantization
What are the 4 steps in creating a CR Image?
1) Exposure - excite electrons into a metastable state 2) Stimulation 3) Read 4) Erase
Name examples of image noise from optical components defects?
1) Laser intensity control 2) Scatter of stimulating beam 3) Light emitted by screen 4) Light collection
What are the 3 primary components of a CR system?
1) Photostimulable phosphor plate (PSP) - in the cassette 2) Plate Reader 3) Computer workstation
What are the layers of the CR-PSP?
1) Protective layer - clear plastic 2) Phosphor layer - made of barium fluorohalide & europium 3) Reflective layer - sends light in a forward direction 4) Conductive (antistatic) layer - reduces static 5) Support layer 6) Base layer - made of Aluminum w/ a bar code
What are the 3 steps to digitizing an analog image
1) Scanning 2) Sampling 3) Quantization
Name 2 examples of image noise in CR from mechanical defects?
1) Slow scan driver 2) Fast scan driver
Discuss the differences between 2 forms of indirect capture?
1) Use of a CCD, x-ray scintillation and optics 2) Use of scintillator, photodetectors, and a thin-film transistor (TFT)
CR has a wide exposure latitude that results in _______ shades of gray
10,000
Many CR systems operate at a ___ speed class which is only ½ the speed of rare earth ___ speed class for film-screen
200; 400
In CR, compression algorithms can reduce the size of the data in an image matrix by a factor of ___
30
In DR, at least ___% of the plate must be exposed. With small digits - use one large plate for multiple views
30
What is a typical film-screen latitude?
30% to 50%
The human eye can distinguish ___ shades of gray
32
DR spatial resolution is up to?
5 lp/mm
During the exposure, x-ray photons strike the PSP and this excites the electrons into a metastable state. ~ ___% of these electrons return to their ground state which results in the emission of light
50
kVp ranges for pediatrics that weigh less than 100 lbs is?
50-90
The CR processing cycle requires ~ ___ seconds
60
A pixel with a bit depth of 6 has a range of 2⁶ = ___ shades
64
_______ of the dexel face is sensitive to x-ray, the remaining _______ does not contribute to the formation of the image
80%; 20%
A PSP plate needs to be read within ___ hours or the resultant image will be compromised by losing ___% of its energy every ___ hours
8; 25; 8
For most digital imaging ___ bits ( ___⁸ = ___ ) would be sufficient while maintaining the ability to use post processing manipulation of the image
8; 2; 256
What is indirect capture?
A 2-step process: x-ray photons are converted to light and then, the light photons are converted into an electrical signal
What is a dexel?
A detector element arranged in rows and columns on the flat panel detector
What is a matrix?
A group of cell/numbers arranged in rows and columns that is stored in computer memory
What is a pixel?
A picture element of a matrix that contains information on its location and intensity
What is a charged-coupled-device (CCD)?
A solid-state silicon-base semiconductor device that converts visible light photons to electrons
What is flat-field correction?
A technique used to remove artifacts from 2D images that are caused by variations in the pixel to pixel sensitivity of the detector
What is fast scanning?
An oscillating mirror deflects a laser back and forth in a rastor pattern across the detector plate
What is quantization?
Assigning a value to each pixel to represent a discrete gray level > This number is what the computer can read and manipulate
kVp ranges for adults is?
Between 60 and 120
In DR, light energy is transmitted through the fiberoptic bundle to the _______ where it is converted into an _______ > sent to the computer for display
CCD; electronic signal
DR systems are mostly considered?
Cassetteless
During the erase phase, any remaining electrons can cause an artifact called _______ the next time the Image Plate (IP) is used
Ghosting
_______ kVp assures adequate penetration of the beam
Higher
What is quantum mottle?
In film/screen it indicates low mAs
What is an Analog to digital converter (ADC)?
It converts an analog signal to a digital signal for a computer to analyze
What is a Digital to analog converter (DAC)?
It converts the digital signal to an analog signal
What is Amorphous silicon?
It is a fluid form which is painted on the flat panel detectors (aka: photodetectors)
What is window width?
It is the adjustment used to change the radiation contrast
What is spatial resolution?
It is the minimum separation between 2 objects
What is pixel density?
It is the number pixels per unit area
What is pixel pitch?
It is the pixel spacing or distance from the center of a pixel to an adjacent pixel
What is the dynamic range?
It is the range of gray levels
What is quantum noise?
It is when few photons reach the IR to form the image; resulting a grainy appearance.
What does the PSP do?
It traps electron energy and fluoresces (emits light)
What is a cesium iodide CCD?
It uses a scintillator comprised of a cesium iodide phosphor, which absorbs x-ray energy and emits visible light
Spatial resolution is measured by what units?
Line pairs per millimeter (Lp/mm). (aka - spatial resolution)
FOV: -Increases -Decreases -Remains constant -Remains constant Matrix size: -? -? -? -? Pixel size: -? -? -? -? Spatial Resolution: -? -? -? -?
Matrix size: -Remains constant -Remains constant -Increases -Decreases Pixel size: -Remains constant -Remains constant -Decreases -Increases Spatial Resolution: -Decreases -Increases -Increases -Decreases
What is the pixel size formula?
Pixel size = FOV/Matrix
What is the major determining factor of spatial resolution?
Pixel size and pixel pitch
What is the spatial frequency formula (aka Image Resolution)?
SF =1/2 (P.S) PS - pixel size in mm
The primary cause of noise in any radiographic image (film-screen or digital) is?
Scatter radiation
Describe the process of the digital x-ray exposure?
TFT is closed > the exposure is collected and stored in the storage capacitor. After the exposure > TFT opens > allows flow of electric charge to the charge amplifier > it converts the electrical charge into a digital code which results in a gray scale value for each dexel. This process is completed row by row
What is contrast resolution?
The ability of the imaging system to distinguish between small objects that attenuate the x-ray beam similarly in digital imaging
What is brightness?
The amount of luminance or light emission of the display monitor
What is the manifest image?
The complete conversion of the analog stored digital data resulting in a visible image
What is sampling?
The function of detecting and measuring radiation that occurs at the imaging plate or detectors
What is Sampling?
The intensity of the radiation from each pixel is measured by a detector
What is the window level?
The location on a digital image number scale at which levels of grays are assigned
What is bit depth?
The number of bits that determines the precision with which the exit radiation is recorded; controls the pixel brightness or gray level that can be specified. It is an exponent of a base of 2
What is the fill factor?
The percentage of the dexel devoted to the semiconductor detection area
What is quantization?
The process in which the continuous range of values of an analog signal is sampled and divided into nonoverlapping subranges, and a discrete, unique value is assigned to each subrange
What is slow scanning?
The slow and precise movement of the IP in the CR reader
_______ occurs when there is insufficient exposure to the IP or IR which will cause _______ mottle or noise to be seen
Underexposure; quantum
What is the Indirect Capture Radiography (ICR)?
Use of a scintillator with Cesium Iodide to capture x-rays and transmit scintillation light to a collection element
In DCR (Direct Capture Radiography), the flat panel detectors or IR use a TFT and a photoconductor made of _______
amorphous-Selenium (a-Se)
In CR, the area between the images must be "_______" therefore it is recommended to use one field on a CR plate
blank white
During the read phase, the metastable electrons emit a shorter wavelength of _______ light. The latent image becomes visible
blue-green
CR is a _______ system
cassette-based
Silicon is a semiconductor in a _______ form
crystalline
On an image; the areas of _______ density are seen as _______ areas of brightness on the monitor
decreased; increased
X-ray photons interact with a-Se which converts to an _______. The + charge is stored in the capacitor where it is amplified and converted into a _______. The electrical charger is amplified and then sent to the ADC and finally to the computer. Here the images can be transferred electronically to the _______
electrical charge; digital code; Picture Archiving & Communication System (PACS)
A linear response displays a _______ range of radiographic densities
greater
CR and DR have _______ exposure latitude than film-screen imaging
greater
The higher the bit depth the _______ the resolution
greater
A _______ pixel value would signify a volume of tissue where the x-ray beam had _______ attenuation and would be displayed as an area of _______ brightness (increased density) on the monitor (e.g. lungs/soft tissues)
high; minimal; decreased
Manufacturers recommend _______ kVp settings for CR and DR and discourage using _______ kVp for extremities
higher; <60
Dexels with an 80% fill factor have a _______ contrast resolution or SNR and _______ spatial resolution
higher; better
Pixels with a _______ number have a _______ density than do pixels of a lower number
higher; greater
Bone has a _______ atomic #, therefore it will attenuate _______ of the beam and have fewer photons that will reach the IR
higher; more
An _______ in bit depth produces _______ shades of gray, which _______ contrast resolution
increase; more; increases
Dose Creep is a technique of using an _______ in mAs to avoid _______ but this will _______ patient dose
increase; underexposure; increase
As the window level is _______, the displayed image brightness (density) will _______
increased; increase
The size of the matrix is _______ proportional to the pixel size and _______ proportional to the spatial resolution
inversely; directly
In DR, the image receptor (IR)/image plate (IP) response is _______ vs the response of film-screen which is _______
linear; curvilinear
In digital imaging, the response of the IR is _______ compared to the _______ response of film-screen
linear; curvilinear
When using AEC for DR or CR, any _______ can cause premature termination of the exposure
off-centering
The primary cause of scatter radiation is _______ coupled with a _______
patient size; lack of appropriate collimation
When compared to film-screen, digital systems have _______ spatial resolution but _______ contrast resolution
poorer; better
During stimulation, an infrared laser beam scans the PSP in a _______ pattern and gives energy to the trapped electrons. These trapped electrons now are able to leave where they emit _______ light photons
raster; blue
In CR, the analog signal is digitized with attention to _______ and _______
sampling; quantization
The collection element consists of _______ sandwiches between the _______
silicon; TFTs
The larger the size of the matrix the _______ the pixels and the _______ the image sharpness (spatial resolution)
smaller; better
In DR, _______ are absorbed by the CSI phosphor which gives off _______
x-rays; scintillation light
Film-screen systems can display _______ shades of gray
~30