Ch 20, 22-24 Flashcards
Image on film after exposure but before processing
Latent
Image put into developer
Manifest/visible
Takes latent image and makes it manifest
Developer
The step in film processing; silver is deposited at the latent image sites and an image becomes visible
Developing
The process of removing undeveloped silver halides to make the image permanent for viewing
Fixing
Rinse of chemicals
Washer
The process of using water to remove as much of the fixer and developer solutions as possible
Washing
Blow on either side of film to dry it off
Dryer
The process of film developing in which hot air is forced over both sides of the film as it exits the processor
Drying
Able to give off light; the ability of a material to emit light in response to excitation
Luminescence
Instantaneous emission, preferred; the ability of a material to emit light instantaneously in responses to excitation within one nanosecond
Fluorescence
Delayed emission, bad; the ability of a material to delay emission of light in response to excitation
Occurs when light is emitted for a period longer than necessary
Screens would continue to emit light and end up with an picture with two images on it
Phosphorescence
Not enough x-rays/lack of exposure/mAs; a lack of sufficient incoming data to process an image (noise)
Increase mAs to fix this
Insufficient amount of x-rays interacting with imaging plate fixed by increasing exposure (increase mAs or kV)
Grainy image, takes away from detail
Can be caused by person setting technical factors
Quantum mottle
Chemical used in film developing in the fixer solution to maintain an acidic pH to enhance the functioning of the clearing agent
Activator
The effect on a film when unexposed silver halides are reduced
Chemical fog
A part of the automatic processing system designed to stabilize temperatures, agitate solutions, mix the chemistry and filter the solution
Circulation system
Primary agent of the fixer
Clearing agent
Twice the time necessary for the milky appearance of the film to disappear
Clearing time
Final stage of film processing that removes the excess water, cools and dries the film and seals the film for viewing and storage
Dryer system
Specially designed crossover network to begin the film traveling from the feed tray down into the developer section
Entrance roller
Chemical used in film processing that controls the swelling of the gelatin to prevent scratches and abrasions to the emulsion during processing; in a fixer solution, must function in an acidic environment
Hardener
Chemical used in film processing to help decrease the oxidation of the reducing agents when they are combined with air; also used in fixer solution to aid in removal of silver from the emulsion
Preservative
Chemical used in film processing that provides electrons to the silver ions attached to the sensitivity specks of the silver halide crystals
Reducing agent
Replaces chemicals that are depleted through the chemical reactions of processing, oxidation and evaporation
Replenishment system
Chemical used in film processing added to the developer to restrict the reducing action to those crystals with sensitivity speck gates
Restrainer
Chemicals used in developing film suspended in water
Solvent
When two reducing agents are combined, forming a PQ developer, their reducing ability is the sum of their independent abilities
Superadditivity
Part of the automatic processing unit that maintains all three solutions at compatible temperatures
Temperature control system
Part of the automatic processing system designed to move a film through the developer, fixer, wash and dryer sections of the processor
Transport system
Delayed phosphorescent emission
Afterglow/screen lag
Material film is made from
Usually polyester, tough, stable, rigid and uniformly lucent
Usually contains a blue tint
Base
Ability of the phosphor to emit as much light per x-ray photon interaction as possible, related to the screen speed
Conversion efficiency
Most accurate factor that measures the speed or sensitivity of an intensifying screen; measurement of the amplification of the image that occurs due to the screen’s ability to convert x-ray photons to light
Intensification factor
Device used to amplify the incoming x-ray beam and reduce patient radiation dose
Intensifying screen
When the incident x-ray photons match the K-shell binding energy of the phosphor, there is an increase in characteristic production within the screen
K-shell absorption edge
Measurement of recorded detail, sharpness and resolution; the minimum size and space between objects that can be visualized on the final image
Line pairs per millimeter (lp/mm)
Measurement of recorded detail, sharpness and resolution; measures the resolving ability of a film/screen combination
Modulation transfer function
Layer of material used in an intensifying screen that is capable of absorbing the energy of an incident x-ray photon and then emitting light photons
Phosphor layer
Layer of material used in an intensifying screen applied to the top of the phosphor layer to protect it from abrasions and stains, usually thick plastic
Protective coat
Layer of material used in an intensifying screen to reflect light toward the film
Reflective layer
The most useful rating of intensifying screens expressed with par-screens and film being arbitrarily assigned a relative speed number of 100 as a control point
Relative speed
An indication of the precise wavelength of light emitted by the phosphor
Spectral emission
Measures the ability of a film/screen system to accurately measure the boundaries of an image
Line spread function (LSF)
Platforms that are used for medical purposes, such as patient care, and for biological applications and activities related to health care, including both preclinical research (studying disease or treatments in cells and animals) and clinical research (ex: testing new drugs on patients or analyzing health-care statistics)
Biomedical informatics (BMI)
Standard format for communicating imaging files around the world
Must protect patients’ healthcare data
Digital imaging and communication in medicine (DICOM)
An electronic version of an individual patient’s collection of medical documents
Electronic health-care (or health) record (EHR)
All patient medical documentation stored in electronic format
Electronic medical record (EMR)
Images that are visualized on film
Laser printers and dry processors
Print them out onto film
Hard copy
The electronic database used in the hospital to store, generate and retrieve information on patients
Hospital information system (HIS)
A body of ideas, devices and processes related to handling multiple types of information
Informatics
Computer system that can manage images in an electronic form
Picture archiving and communication system (PACS)
Database of images and patient records specific to imaging department
Radiology information system (RIS)
Images visualized on monitors, either flat panel technology or older cathode ray tubes
Flat screen computer monitors, many advantages
Soft copy
Binary digits
Bit
8-bit word
Byte
Type or indirect digital radiography; the radiographer must usually move the detector, that is most often housed in a cassette, between image acquisition and display
Photostimulable imaging plates (PSP, IP) and filmless cassette
Computed radiography (CR)
Measure of the sensitivity and accuracy by which the image receptor converts the incoming data to the output viewing device
How effective IR is at detecting x-rays and sending it on
1 = 100% or no loss of information
Most IRs 30-70% accurate (0.3-0.7)
Detective quantum efficiency (DQE)
Indicator as to whether the detector response of a specified image Kind agrees with Ktgt
Deviation index (DI)
Flat-panel detectors
Imaging systems that replace traditional film with a reusable detector
Manufactured in table/wall bucky or cassette
Digital radiography (DR)
Conversion of incoming x-ray photons to an electronic signal without scintillation
Use amorphous selenium and thin film transistor (TFT)
Direct conversion
Increase in contrast due to high-pass filtering
Edge enhancement (sharpening)
Descriptive term used for the plates used in both direct and indirect DR digital systems
Flat panel detector
The number of shades of gray; ranges from 8 bits to 32 bits which equals a range of 1-4 bytes of storage that would be required per pixel in the image matrix
12 produces 2^12 gray levels
Represents 4096 different shades of gray
Grayscale bit depth
Amplifies or deletes all but the high frequencies
Uses a Fourier transform algorithm to convert the image into the spatial frequency domain
High-pass filtering
Generated by dividing a scanned area into pixels and determining the signal intensity for each pixel, can be calculated for specific anatomy and procedures
Histogram
Two-part process involving a scintillator (which converts incoming x-ray photons to light) and a photodetector (which converts light into an electronic signal)
Converts x-ray protons to light, photodetector converts light into an electronic system
Use amorphous silicon and TFT
Indirect conversion
Data that are stored to substitute new values for each pixel during processing
Look-up table (LUT)
Amplifies or deletes all but the low frequencies
Intentionally blur image, thus reducing noise and the displayed brightness level of the pixels, decreases image detail
Low-pass filtering/smoothing
Square series of boxes laid out in rows and columns that gives form to the image
Made up of pixels and voxels
Matrix
Rigid sheet of several layers
Records and transmits image from x-ray beam
Typically inside a cassette, used in CR (filmless cassette)
More sensitive to scatter both before and after exposure than radiographic film
Photostimulable imaging plate
Picture elements, individual matrix boxes
Pixel
Physical distance between pixels generally measured from center to center
Inversely related to spatial resolution
Dependent on matrix size and image receptor size
Pixel pitch
Correction of an exposure that is outside the range from underexposure or overexposure by shifting the histogram to the correct area
Rescaling
Quantity of incoming information compared to the level of random background information
Signal-to-noise ratio
How clearly the image is seen (sharp, shades of gray, bone and heart outline visible, etc); dependent on matrix size
One of the geometric properties of image quality; the degree of geometric sharpness or accuracy of structural lines actually recorded in the image; also referred to as detail, definition, sharpness and recorded detail
In digital images, it can be expressed in terms of three dimensions of the image
Spatial resolution
A point processing operation that changes the contrast and brightness of the image on the monitor
Windowing
2 types of digital radiography systems
Computed (CR)
Digital (DR)
2 types of flat panel detectors
Direct conversion without scintillator
Indirect conversion with scintillator
Requires binary machine language
Two-symbol alphabet of 0 and 1
Digital image formation
Each pixel represents a 3D volume of tissue
Voxels
How big the cassette is
Field of view (FOV)
What unit is spatial resolution measured in?
Line pairs per millimeter (lp/mm)
How is the total number of pixels in a matrix calculated?
By multiplying the number of boxes in the row by the number of boxes in the column
2 spatial domains
Spatial (pixel) location
Frequency
Cycles per unit of length
Object size and contrast
Frequency
Algorithm applied to change an image from spatial location domain to the spatial frequency domain (x-ray uses spatial location)
Fourier transformation
3 image processing operations
Point processing
Local processing
Geometric processing
Happens between when you make exposure and before image pops up
Image processing operations
4 steps of grayscale processing
Creation of histogram
Analysis of histogram
Application of the look-up table
Windowing for contrast and brightness
Adjusting input image with output image
Point processing operations
Shape will correspond to the specific anatomy and technique used for an exam
Creation of histogram
Determines the values of interest (VOI) and exposure index
Analysis of histogram
Used to locate the minimum and maximum exposure values for the body part
Values of interest (VOI)
Proper one will provide the proper grayscale, regardless in kVp and mAs resulting in consistent images
Application of the look-up table (LUT)
Range of densities that will be displayed, narrow one will have few densities so the image will have high contrast
Window width (WW)
Small group of pixels
Kernel
Subtracts a low-pass filtered image from the original image, thus producing a new subtracted and sharper image
Unsharp masking/blurring
A kernel is applied repeatedly to each pixel in a matrix in order to weigh the values or to apply a coefficient across the matrix
Spatial location filtering/convolution
Calculations applied to small group of pixels that sharpens image
Local processing operations
4 types of local processing operations
High-pass filtering/edge enhancement
Low-pass filtering/smoothing
Unsharp masking or blurring
Spatial location filtering
Changing position or orientation of pixels
Allows rotation and magnification
Geometric processing operations
How detailed the image is
Want pixels small to see fine details & big matrix
Matrix size increases, pixel size decreases, spatial resolution increases
Gray scale bit depth increases, density resolution increases
Controlled by matrix size
Direct relationship between matrix and pixel size and spatial resolution (inverse/indirect between matrix and pixel size)
Resolution
Degrades quality of image
Noise
2 types of noise
Electronic
Quantum mottle
What’s there from a normal functioning system
System has to try to get this down to minimum
Has inverse relationship to contrast (increased noise decreases image contrast; increased image contrast tends to obscure or decrease noise)
Electronic noise
What is noise measured as?
Signal-to-noise (S/N) ratio
High S/N ratio = less noise
Provides information about exposure to image receptor
If you take image and there’s too much radiation being used, machine fixes it; have to have something to look at after exposure is made to tell you if that image is within acceptable ranges of radiation
No universal system: different manufacturers use different systems
Carestream (formally Kodak) CR indicator system
Directly proportional to the radiation striking the IP
Calculated by formula: EI = Log (exposure in mR) x 1000 + 2000
Exposure index
What are the acceptable ranges of exposure index for best image quality?
1800-2200 (usually 1400-1650)
Fuji, Konica and Philips CR systems
Inversely proportional to the exposure reaching the imaging plate; higher one indicates that the imaging plate (IP) was underexposed whereas a lower one indicates overexposure of IP
Calculated by formula: S = 200/(exposure in mR)
S number
Agfa exposure indicator
Compares the exposure level of an image to a baseline established for the department
Log median exposure LgM
What is the active layer in PSPs?
Phosphors
2 common PSP phosphors
Barium fluorohalide Bromides (most common) = BaFBr:Eu
Barium fluorohalide Iodides = BaFI:Eu
X-rays expose cassettes and latent image is stored in IP (can be used tabletop or with grid)
Rules of positioning remain the same
Wider latitude than film/screen (should avoid overexposure)
Image acquisition
Electron pattern stored in active layer of exposed IP
Fluorohalides absorb beam through photoelectric interactions
Liberated electrons have extra energy
Fluorohalides trap electrons to create holes at Europium sites
Latent image will lose approximately 25% of its energy in 8 hours so it is important to process cassette shortly after exposure
Latent image production
Energy transferred to photoelectrons
Several photoelectrons liberated
More electrons freed by photoelectrons
Fluorohalides absorb beam through photoelectric interactions
Fluorohalide crystals trap half of liberated electrons
Europium sites contain electron holes (actual latent image)
Hole formation
Red laser beam
Photostimulated luminescence
Electrons return to lower energy state
Emit blue-purple light
IP scanned by finely focused neon-helium laser beam in raster pattern
Light goes in all direction
Light captured by photomultiplier (PM) tubes or CCD array
PM tubes convert light to analog electronic signal
Analog electronic signal sent to analog to digital converter (ADC)
ADC sends digital data to computer for additional processing
IP erased via exposure to intense light
Plate throughput = 30-200 plates per hour
Throughput and spatial resolution can be improved by using dual-sided PSP
Self-contained units
PM tubes output signal
Reading CR data
Trapped electrons from europium area freed and get rid of excess energy in form of light
Photostimulated luminescence
House plates and reader within upright bucky or table
Self contained units
Determines number of density values
Affects density and contrast of system
Controlled by ADC
Pixel bit depth
What is sampling frequency expressed as?
Pixels/mm
2 things pixel pitch is dependent on
Matrix size
Image receptor size
3 things image file size is affected by
Pixel size
Matrix
Bit depth
Before image is processed Raw data located and prepared What anatomical part is selected Orientation of part on IP (parallel/straight with cassette) Number of projections on IP
Data manipulation/preprocessing
3 types of Fuji’s scanning detectors patterns (data manipulation)
Automatic
Semiautomatic
Fixed
Adjusts latitude and sensitivity for image
Automatic
Adjusts sensitivity, but not latitude for image
Semiautomatic
Does not adjust sensitivity or latitude for image
Fixed
Clinically irrelevant data not included in image display
Determined by VOI
Different for each body part
LUT has appropriate contrast for each body part
Data clipping (histogram analysis)
4 histogram analysis errors
Obtained image data does not match reference histogram
Computer cannot find collimated edges
Prosthetic devices
Abnormal areas of increased or decreased attenuation
Algorithm that detects edges of exposure versus non-exposure
Can sometimes be triggered by prosthetics or implants
Collimator edge identification
Overlapping exposures
Verified registration marks
Combine several images into one
Ex: leg length operation, doctor wants x-ray of whole leg; take separate images and machine puts them together
Image stitching
Use photoconductor
Directly convert x-rays into electronic signal
Amorphous selenium (active layer) with thin film transistor (TFT)
Amorphous selenium (a-Se)
Directly converts ionization from x-rays into electronic signal
Electronic signal received by thin film transistors (TFTs) and sent to computer
Direct detectors
Use scintillator Analog to digital convertors Need scintillator (emits light isotropically) or intensifying screen to convert x-rays to light Amorphous silicon flat panel (a-Si:H) Converts light to electronic signal TFTs send signal to computer
Indirect detectors
2 types of indirect detectors
Flat panel
Charge-coupled device (CCD)
In all directions
Isotropically
Array or matrix of pixel Detector Elements (DEL)
Collects electric charges
Switch for each DEL activated and signal sent to computer
Fill factor expressed as percentage
Flat panel TFTs
Photodetector typically used with screen scintillator
Requires optical coupling by lenses or fiber optics
Electric signal from this sent to computer
Charge-coupled device (CCD)
Similar to CR: exposure field recognition, iis and application of LUT
Difference is only exposed detector elements used for image data
DR image processing
May appear as a result of incomplete image plate erasure
Requires troubleshooting of both the CR plate preparation system and the display systems (laser imagers and/or display monitors)
Extreme overexposure may require two erasure cycles to completely remove the image
Phantom/ghost images
Permanent artifacts caused by damage to CR plates
Replacement of CR plates is expensive but is the only solution because these artifacts cannot be repaired
Scratches or tears
Usually caused by dust or other foreign material on the IP
CR plates can be cleaned but this must be done carefully according to the manufacturer’s recommendations to avoid permanant damage
Light spots
Due to dust on the light guide
White line along the length of travel
Reductions in resolution either overall or in specific areas of image
Result of dust accumulation in the CR or laser imaging unit components (polygonal mirror, light gate or other reflective surfaces
Cleaning of these units on a regular quality assurance schedule may avoid both image deterioration and early replacement of both CR and laser imaging equipment
Tend to be accompanied by contrast scale reductions but is difficult to assess because there are so many ways to modify image contrast and display monitors have inherent contrast deterioration over time
Dropout artifacts
Due to IPs being much more sensitive that film
Fogging from background radiation
Cover a wide range of image problems that correspond to the post-acquisition processing functions that are available on a specific CR system
To control these artifacts, manufacturers restrict access or provide preset values in order to provide a reasonable level of consistency between images for diagnostic comparisons
Algorithm artifacts
Caused by uneven transport of film material through a laser imaging system
Uneven scanning, distortion and overlapping shading
Laser film transport artifacts
Due to any of the following: improper collimation or technique, beam alignment, scatter and extreme density differences
Histogram analysis error
Histograms require that collimation edges be parallel to the sides of IP
Nonparallel collimation
Poor grid alignment may result in this, as the computer may not display the grid lines
Grid lines/poor image quality
Particular device to pursue informatics
Platforms
5 BMI platforms
Picture archiving and communications systems (PACS) Hospital information system (HIS) Radiology information system (RIS) Electronic medical record (EMR) Electronic healthcare record (EHR)
2 classes of DICOM information
Object
Service
Contains information about study and patient
Object
Describes what to do with object
Service
Medical information must be encrypted
Health Insurance Portability and Accountability Act (HIPAA) of 1996
Provides standards of interoperability between stakeholders
HL-7
Network infrastructure and file management (large impact on data distribution)
Images need to be distributed to radiologists and clinicians
Image distribution
What is storage like in a typical large radiology department?
150000 exams per year
3.2 terabytes of memory (3-5 years of storage, 10-16 terabytes)
Digital processing that produces changes in density/brightness
Window level
