Chapter 10 Exam Flashcards
What represents the latent image in a PSP CR system?
a. Electrons trapped in conduction band
b. Ionized silver halide crystals
c. Scattered photons in the patient
d. Chemical reaction in the processor
a. Electrons trapped in conduction band
Which PACS storage option offers the fastest retrieval of data?
a. Offline
b. Nearline
c. Online
d. All are equal in retrieval speed
c. Online
Which of the following controls brightness of a digital system?
a. mAs
b. kVp
c. The display monitor
d. Room lighting
c. The display monitor
Rescaling a digital image adjusts the histogram to reflect which of the following?
a. kVp
b. mAs
c. LUT
d. VOI
d. VOI
Which of the following is used by both forms of indirect cassetteless systems?
a. Scintillator
b. CCD
c. Optics
d. TFT
a. Scintillator
Which of the following is used by both forms of indirect cassetteless systems?
a. Direct capture DR system
b. Indirect capture DR system
c. CR system
d. Cassette-based system
a. Direct capture DR system
Which component of the CR reader digitizes the signal?
a. Photodetector
b. ADC
c. Optics
d. Laser
b. ADC
The emission of light by a phosphor when exposed to a laser is known as _____
a. Phosphorescence
b. Sensitometry
c. Conversion efficiency
d. Photostimulable luminescence
d. Photostimulable luminescence
What is the phosphor for CR (PSP)?
Barium fluorohalide (turbid)
How do we get the CR image off of the cassette?
- The phosphor is ionized when exposed to x-rays, approx half the liberated electrons are trapped in the conduction band.
- The plate I then scanned in the reader, the energy is released and converted to an electronic signal becoming a manifest image
digital receptor’s response to exposure is linear and the range of exposures is very wide (dynamic range)
Linear response
Non-linear response
CR
Digital detectors are separated into small individual components termed:
detector elements (DELs)
the size of individual DELs is referred to as the
pixel pitch
the matrix size is the number of _____ in each direction on the detector
DELs
- At the time of processing the energy of the trapped electrons is released by exposure to a laser in this process
- Release of stored energy within a phosphor by stimulation with visible light, to produce a luminescent signal
Photostimulable luminescence
an automatic function of the system that occurs before the image is displayed, the human eye hasn’t seen it yet
Pre-processing
computer software operations that allow manual manipulation of the displayed image
Post-processing
- An integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor
- Can respond to a wide range of light intensities
Associated with indirect capture
Charged-coupled device (CCD)
- The direct method uses amorphous selenium photoconductor and a TFT array
- Before exposure an electric field is applied via the bias electrode across the surface of the amorphous selenium layer
- During exposure, x-rays are absorbed by the amorphous selenium and electric charges are created in proportion to received x-ray exposure
- The charges are stores in capacitors attached to TFTs where they are amplified and converted to digital code
Direct Digital Radiography (DDR)
What systems use cassettes and a processor?
Computed radiography (CR)
CR cassette layers top to bottom
Protective layer
Phosphor layer
Reflective layer
Conductive layer
Support layer
a thin layer of plastic to protect the phosphor layer
Protective layer
the heart of the plate and contains the phosphor, which is usually of the barium fluorohalide family and europium activated, may be turbid or structured
Phosphor layer
reduces and conducts away static electricity
Conductive layer
a sturdy material to give some rigidity to the plate
Support layer
random distribution of phosphor crystals within the active layer and can be used with both CR and DR systems
Turbid
columnar phosphor crystals within the active layer resembling needles standing on end and packed together
Structured
These devices are scintillators made up of crystalline silicon matrix. Each detectors element has its own amplifier, photodiode, and storage capacitor and is surrounded by transistors
Complete mentary metal oxide semiconductor (CMOS)
A material that absorbs x-ray energy and emits visible light in response
Scintillator
A process in which several CCD detectors abut to create on large detector
Tiling
sequence of events for Indirect DR
x-ray > phosphor (scintillator) > visible light > photodetector > TFT > digital signal
sequence of events for Direct DR
x-ray > electronic / digital signal
A liquid that can be painted onto a substrate (foundation or underlying layer), is the material that makes flat-panel detectors possible
Amorphous silicone
- Captures the remnant beam through a detector array and transfer it to a computer for almost immediate processing and viewing
- Involve the use of a scintillator that converts x-rays to light and then to an electronic signal
Indirect capture
Does not use a scintillator, it uses a photoconductor and TFT array, thereby avoiding the loss of resolution caused by indirect capture
Direct capture
- A graphic representation of a data set, this graph represents the number of digital pixel values versus the relative prevalence of those values in the image
- The x-axis represents the amount of exposure and the y-axis represents the incidence of pixels for each exposure level
Histogram
- The primary factor influencing contrast with digital systems
- Histograms of luminance values used as a reference to evaluate the input intensities and assign predetermined grayscale values-VOI, rescaling occurs at this stage
Look up table (LUT)
VOI
Values of interest in histogram
Displayed as a single numerical value, which is represented as a single brightness level on a computer monitor
Pixel
Refers to the range of exposure intensities an image receptor can accurately detect
Dynamic range
The range of exposure values to the receptor that produce an acceptable range of densities for diagnostic purposes and are consistent with exposure rates as low as reasonably achievable
Exposure latitude
The adjusting of the image by the computer program to present an image of predetermined image brightness
Rescaling
- A measure of exposure in air, followed by computation to estimate absorbed does to the patient, measured by a ____ meter embedded in the collimator
- This value depends on the exposure factors and field size and is expressed in centigray-meter squared (cGY-m2)
Dose Area Product (DAP)
System’s ability to preserve signal contrast
Modulation transfer function (MTF)
- The highest spatial frequency that a digital detector can record
- Determined by the sampling frequency of CR systems and the DEL spacing of DR systems
Nyquist Frequency
- Focuses on the display monitors and viewing equipment
- The AAPM published an online report, Report No. OR-03, to provide guidelines for proper performance of display devices intended for medical use, this report presents 26 test patterns
DR Quality Control
Overall visual appearance: this test looks at general image quality and for the presence of any artifacts
uses the TG18-QC test pattern
Resolution tests: assesses the system’s ability to display images of different parts of an image with high fidelity
TG18-QC and TG18-CX test patterns
Reflection: evaluates the ambient light contribution to the light reflected by the display monitor
TG18-AD test pattern
An electronic network for communication between the image acquisition modalities, display stations, and storage
PACS
A common language used by different systems for communication
DICOM
an expression of the radiation exposure level that is required to produce an optimal image
detective quantum efficiency (DQE)
represents the exposure at the detector relevant to the region being imaged and is defined by the signal-to-noise ratio (SNR)
exposure index (EI)
the target reference exposure obtained from a properly exposed image receptor
target exposure index (EIT)
a measure of deviation of the EI from projection-specific EIT values
deviation index (DI)
equal to one half the nyquist frequency
spatial resolution
detector’s ability to resolve small structures
limiting spatial resolution (LSR)
what are the two ways to effectively control scatter and radiation’s effect on the image?
collimation and grid use
electronic component that includes the readout, charge, collector
act as individual switches that allow the pixels to change state rapidly
thin film transistor (TFT)
what radiology method uses barium?
CR
what radiology method uses selenium?
direct digital
