Final Review Apparatus And Image Flashcards
The slope of the characteristic curve changes?
More slope = more contrast
Pros of vertical placement of the image plate during CR reading
- IP barely leaves cassette and is less likely to be damaged
- reduced occurrence of artifacts
What is image sampling?
The plate is scanned and the image location and size of signal is determined. A histogram is then generated
What is multiplanar reconstruction?
Allows you to change from an axial slice to a transverse slice, reconstructs image
How does window level work?
It increases/decreases the pixel values by the same factor to brighten or darken the image
Direct conversion parts, active layer material, and how it works
Amorphous selenium, and a TFT (thin film transistor)
Absorbs x-rays and coverts them into electrons, electrons are stored in TFT detectors
Amorphous selenium is sandwiched between two charged electrodes
How does density effect contrast?
If extremely overexposed or underexposed, the contrast will decrease
Synonyms for Detail
- recorded detail
- definition
- sharpness
- blur
- resolution
How does filtration affect scatter?
It takes away the low energy photons and increases the penetrability of the beam
Increased filtration = decreased contrast
4 factors that affect radiographic image quality?
- Photographic: OD and Contrast
- Geometric: detail and distortion
Why are imagers needed?
- Backup if PACS is unavailable
- Outside physicians
- Legal cases
- Teaching purposes
Advantages of a fixed kVp/variable mAs chart
- lower dose (higher kVp settings)
- adequate penetration of all anatomic parts
- consistent image contrast
- greater latitude with exposures
- measurement of part is not critical
What is a histogram?
A graph of all of the densities that the pixels captures
What are imaging plate artifacts? Examples?
- usually due to aging/wear
- ex. Cracks on the plate, appear as areas of radiolucency
- ex. Static
- ex. Backscatter
Factors that control detail
- Geometric unsharpness
- Motion unsharpness
- Image receptor unsharpness
Is a high SNR or low SNR better?
High
What is a review workstation?
- Most interactive part of PACS
- any computer that can be used to view a digital image
- received image from archive or modalities for viewing
- minor image manipulation
Radiographic contrast is the product of what?
Image receptor contrast and subject contrast
Why is the light filtered before it reaches the photodetector during CR reading?
So that none of the stimulation light swamps the emitted light signal
Purpose of the layers of film and what they’re made of
Film base: polyester or plastic, foundation of film that allows us to handle it
Emulsion: silver halide crystals suspended in gelatin, radiation and light sensitive layer
Adhesive layer: holds base and emulsion together
Supercoat/Overcoat: hard gelatin, protective layer to prevent damage to the emulsion layer beneath it
Is overexposure or underexposure ideal for the patient (EI numbers)
Underexposure
Radiographic contrast is a result of….?
Differential absorption
Line pairs consist of?
-Lead strip: line
-Air space: space
Together they are a line pair
How does phosphor size and thickness affect speed?
Greater size and thickness= higher speed
Network connections
- Wired
- Wireless
2 types of magnification?
- Magnifying glass function: a box placed over a section of anatomy shows a magnified version of that section
- Zoom: enlarges the entire image, need mouse to navigate because too large for screen
What is causal repeat rate? Formula?
Percentage of repeats from a specific cause # of repeats from a specific cause / total # of repeats x100
How to decrease focal spot blur
- use smallest focal spot possible
- largest SID
- smallest OID
What is health level seven (HL-7)
- universal standards used for most clinical and administrative data
- used for communication between HIS and RIS
2 types of spatial frequency filtering?
- High pass filtering: when frequencies are amplified, increases contrast and edge enhancement
- Low pass filtering: when frequencies are suppressed, smoothing, decrease contrast
Repeat rate maximums for different departments
General x-ray: less than 4-6%
Mammography: less than 5%
3 types of x-ray tube charts
- Radiographic rating chart
- Anode cooling chart
- Housing cooling chart
What is a CCD (charged couple device)
Is a photodetector and electronics embedded into a silicon chip
Converts light to an electric charge and stores it
Charge is released to the ADC (analog to digital converter)
Advantages to digital imaging
- wider range of exposure
- linear response
- greater density range
- easily manipulated with computer
- post processing
What is bit depth and what does it mean?
-the number of bits in a pixel
-the number of greys a pixel can produce
Ex. 8 bit = 2^8 = 256 greys
Configurations of RAID
- DAS: direct attached storage, couples to system with cable connections
- NAS: network attached storage, stand alone RAID arrays attached to network
- SAN: storage area network, high speed, special purpose network that link data storage devices with data servers
Exposure indicators represent?
The average gray shade values of the image
DQE
- Detective quantum efficiency
- % of x-rays absorbed by the screen
What has the greatest effect on geometric unsharpness?
OID
Formula to calculate magnification factor
MF = SID/SOD
MF= image size/object size
3 components of film
- Cassette
- Intensifying screen
- Film
Purpose of Anode Cooling Chart?
Shows maximum heat capacity for anode and how long it will take to completely cool
How direct conversion works
- Charge is applied from top surface of amorphous selenium layer
- Ionization from radiation causes selenium to release electrons
- Free electrons are collected at the bottom of the selenium layer
- Charged collected by a storage capacitor and read out line by line by the TFT to the computer
Define low subject contrast
Anatomy with similar tissue types (types that absorb the photons similarly)
Layers of film
- Film Base/base layer
- Emulsion
- Adhesive Layer
- Supercoat/Overcoat
Factors that limit detail
- phosphor size
- layer thickness
- concentration
- scanning of the screen and processing
2 types of luminescence
- Fluorescence: light it emitted only while being stimulated
- Phosphorescence: light is emitted even after stimulation
2 types of scintillator material and what does a scintillator do?
-Cesium Iodide (CsI)
-Gadolinium Oxysulfide (Gd2O2S)
Converts x-rays to light
Slope of the line is drawn between the point corresponding to OD 0.25-2 above the base and fog densities.
Add 0.25 and then add 2 to that and in between is your slope
How does fill factor affect resolution?
Higher fill factor (area of detector that is light sensitive) = higher resolution
How does magnification affect blur?
More magnification = more blur
If you have a technique chart do you still need to assess the patient and adjust technical factors accordingly?
Yes
Network classifications
- LAN: local area network, linked computers that are close together
- WAN: wide area network, computers that are far apart, connected by telephone lines, cables, or radio waves, internet
Layers of the intensifying screen
- Protective layer
- Phosphor layer
- Reflecting layer
- Base
Layers of intensifying screen
- Protective Coating
- Phosphor Layer
- Reflective Layer
- Base
What do array processors do?
Allow us to see the image instantaneously, puts all the info together into an image
What is an intensifying screen?
Device found in cassettes containing phosphors to convert x-rays into light which then exposes the film
Why are digitizers needed?
- teleradiology
- comparison
- duplication
- computer aided diagnosis
4 main types of artifacts
- Image plate artifacts
- Plate reader artifacts
- Image processing artifacts
- Printer artifacts
What is image stitching?
When 2 or more images or combined to create one image
Why do we need technique charts?
To provide a level of consistency among images and radiographers
Characteristics of a digital image
- spatial resolution
- contrast resolution
- noise
- dose efficiency (of the IR)
2 methods of image compression
- Lossy: reduced storage by eliminating information
- Lossless: exact replica of original
What is the fast scan mechanism?
When a laser is deflected across the image plate during reading
Advantages of digital
- Wide exposure latitude: detect a lot of greys
- Reduction in repeats
- Can compensate for over/under exposure
- Environmentally friendly
Film base plus fog
Base: colour added to the film base
Fog: any exposure during storage, contamination, storage
What is dynamic range?
The ability to respond to varying levels of exposure (how many greys the system can detect)
List and describe the role of the two types of contrast media
- Positive contrast agent: high atomic number, absorbs more photons, appears white
- Negative contrast agent: low atomic number, transmits more photons, appears black
When critiquing an image, techs must…
Magnify the image to check for noise or overexposure (burnout/saturation)
With an LCD monitor, what is response rate?
The amount of time for crystal to go from off state to on and vice versa
Why are beam shaping optics required during CR reading
To correct/even out the shape/intensity of the laser across the image plate
Why do we need LUTs?
Without it the images would look very low contrast because too many greys are able to be recorded.
Exposure indicators are affected by?
- technical factors
- histogram analysis errors
- patient positioning
- image processing algorithms
- SID
- collimation
- beam centering
- artifacts
What is offset correction?
Corrects image lag, determines the amount of signal inherent in the detector, creates a mask of residual signal
What is a matrix?
A display of the shades of grey of each pixel as numerical values
Advantages of repeat analysis
- improved department efficiency
- lower costs
- lower patient dose
Image receptor speeds affect what?
- Radiation sensitivity
- Density
- Dose
What does automatic rescaling do?
Produces an image with uniform density and contrast regardless of exposure-fixes under/over exposure to look good
In CRT monitors, what is the refresh rate?
How fast the monitor rewrites the screen “flicker” sometimes seen
What is fill factor?
% of the pixel face that is sensitive to x-rays
-Approx. 80% meaning 20% of the x-ray beam doesn’t contribute to the image
PACS fundamentals
- Image acquisition
- Display workstations
- Archiving
S numbers
Sensitivity numbers
How does electron beam scanning work in a CRT monitor?
Starts in upper left corner and scans across the glass from side to side, top to bottom
Purpose of layers of intensifying screens
- Protective Coating: protect active layer
- Phosphor: converts x rays into light
- Reflective Layer: reflects light toward film to enhance efficiency
- Base: mechanical support for active layer
Intensification Factor
Exposure without screen/ exposure with screen
Gives information about patient dose
Cons of intensifying screens
Recorded detail is reduced because of increased blur
How to minimize shape distortion
Proper alignment of:
- x-ray tube
- part
- IR
- Entry/exit point of CR
How does screen speed affect dose?
Higher speed= lower dose
Types of Networks
- Peer-to-peer: every computer is considered equal
- Client-Server based: server-facilitates communication between and delivers info to clients, clients-request information
CD/DVD burners
- less costly than printing films
- have DICOM viewer and minor enhancements are possible
We can minimize distortion with careful attention to?
- distances
- central ray
- patient position
- IR position
2 reasons image processing artifacts occur
- incorrect part position
- incorrect sampling
HU are calculated by
Heat Units = kVp x mA x time x modification factor
Common functions of workstations
- navigation
- image manipulation/enhancement
- image management
- advanced
What is image orientation?
The way the anatomy is oriented on the CR or detector
Types of distortion
Size: magnification
Shape: elongation, foreshortening
What is volume rendering technique?
Similar to MIP, but can assign colours to the different densities
Technologist workstation
- for reviewing images after acquisition
- Q/C station
- can make minor adjustments before sending
Total repeat rate formula
of repeats / total # of views x100
How does the data recognition program work?
Finds the collimation edges and eliminates scatter outside of the collimation
What is directly related to magnification?
OID
What is edge enhancement?
When fewer pixels are used for the averaging, the fewer pixels used, the greater the enhancement
Limitations of film
- Limited dynamic range
- Cost
- Time
- Film processors
- Permanent
- Can’t be stored electronically
What is the purpose of the intensifying screen?
Reduces patient dose because it converts x-rays to light (image will consist of not just x-rays but light)
Decreases resolution
Speed
Ability of an image receptor to respond to an x-ray exposure
Measure of sensitivity
On a characteristic curve, the slope is the contrast
.
What is photostimuable luminescence?
When the metastable electrons are stimulated by a laser and release visible light
Cesium Iodide vs. Gadolinium Oxysulfide
CsI: manufactured in thin crystal columns that direct light down to the TFT, higher spatial resolution due to less light spread
Gd2O2S: random, unstructured (turbid) crystal layer, light can escape through air pockets before reaching TFT, lower spatial resolution, good for rugged applications
SNR
Signal to noise ratio
Signal: meaningful pattern of information
Noise: chaotic pattern, no info- quantum noise, electronic noise
How does phosphor size affect detail?
Larger phosphor = less recorded detail
RAID
Redundant array of independent discs: several magnetic discs that are linked as an array
Purpose of europium in CR
To capture energy during interaction process-no latent image without it
Keep electrons in excited state as latent image
What is a network?
A group of 2 or more computers linked together
How does screen speed affect detail?
High speed= less detail
How does an LCD monitor work? What does it consist of?
- 2 pieces of polarized glass with a liquid crystal layer between the 2
- images are produces by shining/reflecting light through the crystal layer and a series of colour filters
Human errors that cause artifacts
- Collimation: can result in improper histogram
- Cassette use: cassette upside down
- Technical factors: over/under exposure
What does the TFT (thin film transisitor) do?
Light hits pixels and is converted to an electrical signal
TFT reacts like a switch to send electrical charge to image processor
How are values outside the set window width seen?
As either black or white. Anything inside the window width is grey
Screen speeds
Described efficiency of x-ray conversions to light
Calcium tungstate is used as a basis of comparison (100)
Different types of long term storage
- RAID
- Optical disc: MOD, DVD, ultra density optical
- Tape
- Magnetic disc
Changing speeds formula
RS1/ RS2 = mAs2/ mAs1
What is shuttering/masking?
Automatic shuttering is used to black out the white collimation borders eliminating veil glare
Purpose of cassette
The container for intensifying screen and film
Phosphor factors that affect the image (4)
- Material Composition: calcium tungstate vs rare earth
- Thickness of the layer: thicker layer increases DQE
- Concentration: more concentrated = higher screen speed
- Size of phosphor: larger = more light produced per x-ray interaction
What does image management consist of?
- Modification of demographic info
- query/retrieve function
- CD burning
- Printing
Network topologies
- Star: most common, devices connected to a central hub/switch
- Bus: all devices physically attached to and listen for communication on a single wire
- Ring: devices connected in a circle, info only travels one way
- Mesh: multiple pathways connect devices and network
What is gain calibration?
Corrects flaws in the detector, fills in white spots (dead pixels) with grey
EI_s
Exposure index sensitivity
Types of workstations
- Review workstations
- Radiologist workstation
- Technologist workstation
- Image management workstation
2 Primary factors that affect the resolution of all types of digital imaging systems?
- Geometric properties of the IR
- image processing system
PSP phosphor layer arrangements and what they are activated by
Turbid: random distribution of phosphor crystals
Structured: columnar phosphor crystals
Activated by barium flurorohalide or europium
Another name for high contrast is?
Short scale
What is maximal and minimal intensity projection?
Used for visualizing vessels and air filled structure, makes the, 3-D
Two types of technique charts
- Variable kVp/Fixed mAs: +2 kVp for every additional cm of part thickness, accurate measuring is critical, only effective for peds and small extremities
- Fixed kVp/ Variable mAs: selects optimal kVp and adjusts mAs for variations in part thickness, mAs x2 for every 4-5cm in part thickness
How does decreasing OID decrease blur?
Less room for diverging rays between patient and IR
On a histogram, values at the left are more black or white?
Left: black
Right: white
What is aspect ratio?
Ratio of the width of the monitor to the height of the monitor
What allows additional information to be added to the image?
Image annotation
What is recorded detail?
-degree of sharpness of structural lines on a radiograph
Refers to the amount of exposure received by the IR
Exposure indicators
Resolution is the combination of?
- Spatial resolution: ability to image small objects
- Contrast resolution: ability to distinguish between two objects with similar subject contrast
Factors that affect geometric unsharpness
- Focal spot size: ranges from 0.1-3.0mm
- Distance: SID and OID
What is repeat analysis and why is it useful?
Where rejected images are catalogued and classified with reasons for repeat
Provides info regarding equipment, performance, department procedures, and staff skill levels
Radiologist workstation
- has highest quality software and the best monitor
- requires little downtime
- has access to nearby RIS, connected to PACS
Digital radiography consists of what 2 things?
DR: direct radiography
CR: computed radiography
Primary parts of the CR system
- Cassette
- PSP plate (inside cassette)
- Cassette/CR Reader
- Computer work station
What does PACS do?
Allows the integration of many systems
Purpose of radiographic rating chart?
Provides info about which radiographic techniques are safe for the x-ray tube.
Different charts for focal spot, speed of anode rotation, target angle, and voltage rectification
What part is the basic picture element on a display?
Pixels
2 main types of imagers (printers)
- Wet imager: uses chemicals to process film, needs darkroom
- Dry laser imager: uses heat to process film, exposed with laser, quality slightly lower, takes up less space
What is the controlling factor of radiographic contrast?
kVp
What is DICOM
Set of standards for medical image interchange, allows images to be viewed and processed by many different types/brands of devices
Uncontrolled speed factors
- Phosphor composition
- Phosphor thickness
- Reflective layer (has or doesn’t have)
- Dye in phosphor layer
- Crystal size
- Crystal concentration
Distortion is directly related to?
Positioning
With a Q/C program in place, most repeats are due to?
Positioning errors
Is there more or less distortion with a thick object? With an irregular shaped object?
More distortion with both
How does window width affect contrast?
Wider window width = less contrast because more shades of grey
What are Look Up Tables?
Manipulates the histogram values to change density/contrast on an image based on an ideal image of that body part
Define radiographic contrast
The difference in OD between adjacent structures
How an image in acquired- CR
- PSP plate is exposed to x-rays, phosphor atoms are ionized
- electrons are excited into metastable state and form the latent image
- laser beam of light is directed at PSP
- metastable electrons return to ground state and emit visible light
- light is detected and measured by photodetector
- phosphor is flooded with intense light to erase any leftover latent image
What is shade surface display?
Used a range of pixel intensity values and everything below is removed, everything above with be assigned a colour and shown as a 3-D object
What is image lag?
Image taken before the detector has released all of the signal from the previous image, looks like a double exposure
-caused by images taken too quickly back to back, overexposure, area with little beam attenutation
Less blur on the anode side
.
Gradient on a characteristic curve
Slope of the tangent at any point on the curve
Toe gradient: more important than average because many clinical ODs appear in this region
Shoulder Gradient: more important in mammography
2 main types of film digitizers
- Laser film digitizer: “gold standard”, expensive, Q/C and maintenance critical
- CCD film digitizer: less expensive, slower
Parts of an indirect conversion detector
- Scintillator
- TFT or CCD (charged coupled device)
How to intensifying screens affect patient dose
Decrease because less mAs is required to obtain exposure (using light as well as x-rays)
Factors that affect scatter and how they affect contrast
- Grids: absorb scatter before it hits IR. Less scatter = increase contrast
- Collimation: more matter more scatter, less matter less scatter
- OID: increase OID means that more scatter will miss the IR = increase contrast
CE
- Conversion efficiency
- amount of light emitted for each x-ray absorbed
Controllable speed factors
- Radiation quality: high kVP = high IF
- Processing
- Temperature: higher IF @ lower temp
Levels of RAID
-expands to level 11
-most common: 0, 1, 3, 5
Most PACS use RAID 5
What is contrast media used to image?
Anatomy with low subject contrast
Quantum Mottle
Not enough radiation hits the IR
Appears splotchy, mottles, grainy
Decreases image detail
Need to increase mAs to correct it
Modification factors of types of generators
Single phase: 1.0
3 phase: 1.4
High frequency: 1.4
What is Moiré artifact?
- a plate reader artifact
- when grid lines run parallel with laser scan direction lines are seen on the image
How does increasing SID reduce blur?
Straighter rays hitting the anatomy
blur on the sides misses the IR
Most important factor for spatial resolution
Focal spot blur
High contrast objects that are smaller than the focal spot blue can’t be imaged
What is resolution?
-the ability of an imaging system to distinguish between two adjacent structures
Expressed in line pairs per millimeter (lp/mm)
What contains the pixels?
Photodetector
Amorphous silicon
Spectral Matching
Film sensitivity must be properly matched to the spectrum of light emitted by the screen (green to green, red to red)
Only direct transmission photons hitting the IR would result in high or low contrast?
Extremely high contrast because no scatter
What is the slow scan mechanism?
The image plate of the cassette is moved at a constant rate along the horizontal axis during reading
Only indirect transmission hitting the IR would result in what?
No image, only grey because of so much scatter
How does image receptor speed affect unsharpness on the image?
Faster IR = more unsharpness
What is window width sometimes called?
Grey scale expansion or compression
What does a CRT monitor consist of and how does it work?
- Cathode and anode in a vacuum tube
- works like an x-ray tube
3 types of computers found on a network
- Server: manages resources for other computers, data storage etc.
- Thick client: computer that can work independently from the network, can process and manage its own files
- Thin client: requires a server to complete its tasks, requests services and resources from server
2 types of detectors
- Direct conversion: immediate conversion into electrical signal
- Indirect conversion: x-rays converted to light and then light converted to electrical signal
What is dot pitch?
How close the dots are in the pixel, smaller dot pitch = higher resolution
PSP plate layers
- Protective layer
- Phosphor layer
- reflective layer
- conductive layer
- support layer
List some subject factors that affect radiographic contrast
- Anatomy
- Thickness
- Composition
Image management workstation
-used to look up exams or print copies
What do window level and width do?
Window level: adjusts brightness
Window width: adjusts contrast
What will happen to radiographic contrast if the kVp is increase?
Contrast will decrease because less absorption and more scatter
Nyquist Theorum: if too few pixels are sampled what happens?
There will be a loss of resolution on the image
Smallest element on a digital image?
Pixel
What does the Nyquist Theorum state?
When sampling a signal, the sampling frequency must be greater than twice the frequency of the input signal so you’ll have accurate reconstruction of the original image
What is the primary purpose of radiographic imaging?
To transfer the information from the x-ray beam to the eye
Factors that affect recorded detail for film/screen systems?
- phosphor size
- phosphor layer thickness
- phosphor concentration
- film screen contact
What is image acquisition with regards to PACS?
Images are acquired in a digital format and can be transferred by a computer network
What are artifacts?
Any undesirable density on the processed image
Latitude in Digital Imaging
The amount of error that can be made and still maintain and quality image
200% above ideal exposure
50% below ideal exposure
Latitude
- range of exposures that the image receptor can display
- wider latitude: lower contrast
- narrow latitude: higher contrast
How does pixel size affect detail?
Smaller pixel = greater detail
Two types of monitors
- CRT: cathode ray tube
- LCD: liquid crystal display
What is Aliasing?
An image produced that looks like two superimposed images just slightly misaligned
What is repeat rate affected by?
- Quality of equipment
- Staff skill level
- Patient type
- Data collection method
- Shift
- Radiologist
A computer consists of?
- input devices
- output devices
- processing devices
Shape distortion can occur from?
- inaccurate central ray alignment of the tube
- inaccurate alignment of the part- (foreshortening)
- Inaccurate alignment of the IR- (elongating)
2 categories of PACS archiving
- Image manager: contains master database of everything in archive, receipt, retrieval, and distribution of the images stored
- Image storage or archive server: physical storage of archive system, short/medium/long term
2 types of patient motion?
- Involuntary
- Voluntary
What is reject film?
- Scrap film
- anything that did not require a repeat on a patient (test images, Q/C etc)
Purpose of layers of a PSP plate
- Protective Layer: protect phosphor layer
- Phosphor layer: active layer traps electrons during exposure
- Reflective layer: reflects light released during reading phase
- Conductive layer: reduces/conducts away static electricity
- Support layer: sturdy material to give structure to plate
How do line pairs affect resolution?
More line pairs= high resolution=higher recorded detail
What is quantum mottle?
The image is formed mostly by light and not by x-rays. Not enough x-rays hit the IR and it looks grainy. Quantum noise is what we see
What are HIS, RIS, and EMR?
HIS: hospital info system, holds patient’s full medical info
RIS: radiology info system, holds all radiology specific info
EMR: electronic medical record, contains all of the patients records
The most detrimental effect on recorded detail?
Motion unsharpness: motion of anatomy, tube, or IR
Flat panel artifacts
- dead pixels
- incorrect gain calibration
Plate reader artifacts
- line patterns that appear randomly on the image (issue with electronics
- if multiple IPs are loaded into a cassette
- insufficient erasure
Types of film
- Direct exposure: non-screen film, single emulsion, requires more exposure
- Specialty film: for copies, already exposed to max OD
- Screen film: most widely used, single/double emulsion
Purpose of the housing cooling chart?
Max heat capacity for the housing and how long it will take to cool
