Ouhsc Image Processing & Quality Test 2

Front 1

What are intensifying screens?

Back 1

Radiolucent plastic, coated w/ light-emitting phosphors that produce light when exposed to radiation

Front 2

Who invented intensifying screens?

Back 2

Thomas Edison

Front 3

What are intensifying screens used for?

Back 3

- Used to amplify the effects of incoming x-ray beam
- Requires less radiation (=less dose) to produce same film density

Front 4

What are the layers of the intensifying screen?

Back 4

Base, reflective layer, phosphor layer, protective coating

Front 5

Intensifying Screen - Base

Back 5

- must be flexible but rigid while being chemically inert
- radiolucent polyester plastic

Front 6

Intensifying Screen - Reflective Layer

Back 6

- forces light through base towards film
- reflects light toward the film

Front 7

Intensifying Screen - Phosphor Layer

Back 7

- active layer of screen
- absorbs incident x-ray photons & emits light photons

Front 8

Intensifying Screen - Protective Coating

Back 8

- a layer of radiolucent plastic that protects the phosphor layer
- right next to film

Front 9

What must phosphors have?

Back 9

1) High Atomic Number
2) High Conversion Efficiency
3) Appropriate Spectral Emission
4) Minimal Phosphorescence

Front 10

Phosphors - High Atomic Number

Back 10

- increases the probability of an incident x-ray photon interaction
- permits PE & Compton interactions

Front 11

Phosphors - High Conversion Efficiency

Back 11

- ability to accept the x-ray photon & then emit energy as light photons
- conversion efficiency should be 1 x 10^3 light photons per incident x-ray photon (w/ energy of 50 keV)

Front 12

The higher the conversion efficiency, the _______ (less/more) radiation required to produce an equal density.

Back 12

Less

Front 13

Phosphors - Appropriate Spectral Emission

Back 13

- indication of the precise wavelength of light emitted by the phosphor
- need to match the wavelength sensitivity of screen with same wavelength sensitivity of film

Front 14

Phosphors - Minimal Phosphorescence

Back 14

Luminescence -- ability of a material to emit light in response to excitation

Front 15

Fluorescence

Back 15

- INSTANTANEOUS emission
- occurs within the time it take an electron to complete one orbit of the affected shell (1 ns)

Front 16

Phosphorescence

Back 16

- DELAYED emission
- occurs when the light is emitted for a period longer than necessary for 1 orbit of the affected shell electron
- associated w/ "afterglow" or "screen lag"

Front 17

Ideal intensifying screens should....

Back 17

i. Possess fluorescence
ii. Have minimal phosphorescence
iii. Be replaced periodically (5-7 years)
iv. Be replaced simultaneously

Front 18

Roughly _________ photons per mm^2 must exit an object being examined in order to produce a radiographic image.

Back 18

50,000

Front 19

What was used in the past for screen phosphors?

Back 19

Calcium tungstate (5% conversion efficiency)

Front 20

What's used now for screen phosphors?

Back 20

Rare-earth
- conversion efficiency of 15-20%
- made of gadolinium & lanthanum (high atomic #s)

Front 21

What's an advantage of the rare-earth screen phosphors?

Back 21

Increased speed while maintaining resolution

Disadvanage: increased cost

Front 22

Resolution

Back 22

- the ability to accurately image an object
- controlled by size of phosphor crystals, the thickness of the phosphor layer, & concentration of the crystals

Front 23

(Direct/Inverse) ____________ relationship between crystal size & resolution.

Back 23

Inverse

Front 24

Increasing crystal density ______________ (increases/decreases) resolution & screen speed

Back 24

Increases

Front 25

Resolution is measured in....

Back 25

line pairs per millimeter lp/mm

Front 26

An increase in lp/mm would __________ (increase/decrease) spatial resolution

Back 26

Increase

Front 27

Naked eye can resolve _______ lp/mm

Back 27

10-20

Front 28

Film-Screen Contact

Back 28

Poor contact between radiographic film & the intensifying screen will reduce the resolution of the images

Front 29

Quantum Mottle

Back 29

- caused by insufficient quantity of photons striking the intensifying screen
- has grainy appearance

Front 30

Speed (sensitivity) of the intensifying screen is determine by...

Back 30

The same factors that control resolution

Front 31

Increasing crystal size ______________ (increases/decreases) speed

Back 31

Increases

Front 32

Intensification Factor

Back 32

- Most accurate factor that measures the speed or sensitivity of an intensifying screen
- measurement of how well can it take a photon & convert it to a light photon

Front 33

How is the intensification factor calculated?

Back 33

IF = Dn/Ds

Dn = nonscreen mR measurement (large0
Ds = screen mR measurement

Front 34

Descriptive Ratings

Back 34

High Speed = 200-1200
Par Speed (Universal/Medium Speed) = 100
Slow Speed (fine detail, high resolution) = 20-80

Front 35

K-Shell Absorption Edge

Back 35

Deals w/ the binding energy of the "K" shell of the phosphor of the intensifying screen

Tungsten = 70 keV K-shell binding energy
Gadolinium = 50 keV
Lanthanum = 39 keV

Causes erratic density production in response to minor adjustments in kVp settings

Front 36

Asymmetrical Screens

Back 36

- used in highly efficient intensifying screens

Front 37

The back of a film cassette may contain a sheet of lead foil that serves what purpose?

Back 37

Reduce the residual beam & absorb backscatter

Front 38

The appropriate film-screen combo for a specific clinical situation must be selected based on...

Back 38

The combined qualities of the film & the screen

Front 39

Blue-sensitive film _________ (will/will not) respond to most of the wavelengths emitted by the rare-earth phosphors.

Back 39

Will not

Front 40

Green-sensitive film is sensitive to...

Back 40

Entire range of phosphor emissions, including yellow-green wavelengths

Front 41

Speed is ___________ (directly/inversely) related to patient dose

Back 41

Directly

Front 42

Fine detail screen, _____ (slow/fast) speed, _______ (lots/little) of exposure

Back 42

Slow / Lots of

Front 43

The more latitude something has, the ________ (more/less) different amounts of exposure will get us an appropriate image.

Back 43

More

Front 44

Relative Speed

Back 44

- Combo of both film speed & screen speed
- changing either film or screen speed result in relative speed change

Front 45

Relative Speed Equation

Back 45

(mAs1/mAs2) = (RS2/RS1)

Front 46

Narrow Latitude (steep slope) = ______ [high/low] contrast

Back 46

High

Front 47

3 Parts to a Computer System

Back 47

Hardware, Software, Someone to Input Info

Front 48

Mainframe Computers

Back 48

- very large
- capable of multiple actions at once
- ex. the type of computer used to run a large hospital

Front 49

Minicomputers

Back 49

- not large server-based systems
- performs multiple, complex operations w/ high levels of input & output
- must be very fast
- ex. computers part of CT machines that construct a 3D image

Front 50

Microcomputers

Back 50

- personal computers
- tied back to either a minicomputer or a mainframe computer for communication w/ servers

Front 51

Input Hardware

Back 51

Keyboard, mouse, scanner, microphone, etc.

Front 52

Processing Hardware

Back 52

CPU, memory for computing each command, BUSes (ex. USB)

Front 53

Output Hardware

Back 53

Hard copy items (printers, voice synthesizers), computer screen, video display

Front 54

Storage Hardware

Back 54

Magnetic tapes/discs, optical discs, portable hard drive, flash memory

Front 55

Array Processors

Back 55

Bigger part of CPU that function w/ part of memory storage

Front 56

LAN

Back 56

Local Area Network

- based on functionality of the internet
- only serves to connect a finite number of computers to one another

Front 57

HIS

Back 57

Hospital Information Network

Front 58

RIS

Back 58

Radiology Information Network

Front 59

PACS

Back 59

Picture Archiving and Communication Systems

Front 60

DICOM

Back 60

Digital Imaging and Communications in Medicine

- how digital imaging is transferred
- includes both a file format & a standard network communications protocol

Front 61

Computed Radiography (CR)

Back 61

- use photostimulable storage phosphor IP known as a PSP/IP; held inside cassette or IR
- 2 step process: expose the plate, process the plate to acquire the image

Front 62

Direct Digital Radiography (DR)

Back 62

- without a scintillator
- x-rays are converted directly to an electrical signal
- selenium flat panal imaging system

Front 63

Indirect Digital Radiography

Back 63

- x-rays converted to light, then to an electrical signal
- amorphous silicon is usually paired w/ a thin film transistor (TFT) array

Front 64

Charged-Coupled Devices (CCD)

Back 64

Take incoming photons & emit light photons, which are then converted to an x-ray signal

Front 65

Binary Number System

Back 65

- base 2 system; only 0s and 1s (binary digits)
- bits are each a discrete unit

Front 66

What does an 8 bit "word" form?

Back 66

A "byte"

Represents each of the 26 letters of our alphabet

Front 67

Computer memory is often rated in terms of total ________

Back 67

Bytes

Front 68

Matrix

Back 68

Series of boxes in a grid laid out in rows & columns

Front 69

Pixel

Back 69

- Individual boxes in the matrix
- Location determined by its "address" using X-Y coordinate system

Front 70

Field of View (FOV)

Back 70

-Overall dimension of image matrix
- determined by the size of the detector
- if FOV remains the same, then as matrix size increases, the pixels get smaller, increasing spatial resolution

Front 71

Spatial Location

Back 71

- domain used in digital imaging (the before & after)
- representative x. y coordinates

Front 72

Spatial Frequency

Back 72

- used in MRI
- frequency refers to the number of times the signal changes per unit length
- small anatomical structures produce high frequencies, vis versa

Front 73

Fourier Transform (FT)

Back 73

Math algorithm that's applied to change an image from the spatial location domain to the spatial frequency domain (inverse FT can return it back)

Front 74

Analog

Back 74

A mechanism in which data is represented by continuously variable physical quantities (e.g. info entered into computers)

Front 75

What 2 processes must happen to see digital image?

Back 75

Analog-to-Digital Conversion (ADC) & Digital-to-Analog Conversion (DAC)

Front 76

Analog-to-Digital Conversion (ADC)

Back 76

- requires sampling, quantization, & coding
- represented as a sine wave illustrating continuous function (shows smooth transition)
- any time we see an image on the screen, we're seeing an analog image

Front 77

Scanning

Back 77

Image is divided into individual pixels within a matrix; light is transmitted through individual pixels

Front 78

Sampling

Back 78

Measures the brightness of each individual pixel (areas of high density have less light coming through them)

Front 79

Quantifying

Back 79

Assigning on an integer to represent the brightness of light transmitted through the image; grayscale

Front 80

How can you calculate image dimensions?

Back 80

MxNxk bits (M = matrix columns, N = rows)

Front 81

Nyquist Theorm

Back 81

-Each sine wave of an analog signal must be sampled at least twice per cycle
- more samples that are taken, more accurate the model based on the original (ADC accuracy)

Front 82

Accuracy and speed are __________ (directly/inversely) proportional

Back 82

Inversely

Front 83

Digital Imaging Processes (from most simple to most complex)

Back 83

Point Operations
Local Processing Operations
Global Operations
Geometric Operations

Front 84

Point Operations

Back 84

- least complicated, most frequently used
- takes grayscale data to output matrix pixels w/ little manipulation (affects appearance of pixel)

Front 85

Histogram

Back 85

- scale to determine nature of the output image based upon the number of shades of gray used
- if modified, brightness/contrast will change

Front 86

Wide histogram implies...

Back 86

More contrast (vis versa is true)

Front 87

If the values of the histogram are on the lower end, how will the image appear?

Back 87

Dark (vis versa is true)

Front 88

Look-Up Tables (LUT)

Back 88

Process that takes a structure that's low contrast & converts it so that the difference btw. contrasting tissues is increased

Front 89

Local Processing Operations)

Back 89

- manipulation of data from an individual pixel base on comparison of value of the pixels immediately surrounding it
- if a pixel is very different than the others, it may be manipulated to fit in better

Front 90

Spatial Location Filtering - Convolution

Back 90

Done by taking a weighted avg. of the surrounding pixels; can be used to help smooth areas or help define lines or enhance edges

Front 91

High spatial frequency will show ________ (small/large) changes in gray in either the horizontal or vertical directoins

Back 91

Large

Front 92

High-Pass Filtering

Back 92

- edge enhancement or sharpness in a spatial domain that's blurred
- used in high contrast regions (skeleton)
- problem --> increased noise

Front 93

Low-Pass Filtering

Back 93

- output image is smoothed, intended to reduce the noise
- image detail is compromised (blurred edges)

Front 94

Global Operations

Back 94

- all pixels from input image used to change value of a pixel in output image
- popular method is to use FT in filtering images in the frequency domain rather than the spatial domain location
- can process images for edge enhancement, image sharpness, & image restoration

Front 95

Geometric Operations

Back 95

Involve changes to the image in relation to size, orientation, or position (e.g. rotating or resizing the image)

Front 96

PSL

Back 96

Photostimulable Luminescence Radiography

Front 97

SPR

Back 97

Storage Phosphor Radiograph

Front 98

DLR

Back 98

Digital Luminescence Radiography

Front 99

DSP

Back 99

Digital Storage Phosphor Radiography

Front 100

PSP

Back 100

Photostimulable Phosphor IP

Front 101

History of CR/DR - 1600s

Back 101

Discovery of the Bolognese stone of Italy

Front 102

History of CR/DR - 1800s

Back 102

Becquerel worked on the notion of de-excitation of atoms by optical means

Front 103

History of CR/DR - 1983

Back 103

Fuji produced first commercial CR imaging system for use in diagnostic radiology (FCR-101)

Front 104

Physics of CR Image Formation

Back 104

IP contains PSP layered on base to provide support; PSP must be scanned by laser of specific wavelength in order to render the latent image visible

Front 105

Time for luminescence must be shorter than...

Back 105

1 µsec

Front 106

Latent Image Formation

Back 106

- x-ray photons hit the PSP IP
- europium atoms are ionized by radiation & electrons move from valence band to conduction band (higher energy state)
- electrons in conduction band are free to travel to "F center"

Front 107

The number of trapped electrons is ______________ (proportional/not proportional) to the absorbed radiation

Back 107

Proportional

Front 108

Photostimualted Excitation

Back 108

Process in which a laser beam scans a PSP IP inside a CR reader to render the latent image visible

Front 109

Why must the laser lights be capable of being absorbed by F centers?

Back 109

- causes trapped electrons to move up to the conduction band, where they are free to return to valence band

Front 110

Photostimulable Luminescence (PSL)

Back 110

The transition of the electrons from a higher energy to a lower one, which results in an emission of bluish-purple light

Front 111

Layers of CR IP

Back 111

Protective Layer
CR Phosphor Layer
Electroconductive Layer
Support Layer
Light Shield Layer
Protective layer

Front 112

Standard Resolution CR IP

Back 112

- thicker phosphor layers
- may absorb more radiation
- faster speed

Front 113

High Resolution CR IP

Back 113

- thinner phosphor layer
- provide sharper images
- slower speed
- similar to emulsion layers of film/intensifying screen phosphor layers

Front 114

Cassettes

Back 114

- made of aluminum or aluminum honeycomb panel
- front of cassette is radiolucent
- lead backing on back prevents backscatter radiation

Front 115

CR Image Processing Imaging Cycle

Back 115

"Ready-to-use" IP is exposed; energy stored on IP; exposed IP processed in CR reader to render latent image visible; laser light erase it

Front 116

Cassette-Based CR Reader Types

Back 116

- IP has to physically be taken into CR reader for scanning & erasing
- it all involves transport of IP, which can result in damage

Front 117

Cassette-Less CR Reader Types

Back 117

- incorporate single fixed IP encased in special housing that's part of the stationary unit
- no contact w/ the IP in the unit when it's read

Front 118

Components of a Scanner

Back 118

Laser source, IP transport system, light channeling guide, photodetector, & ADC

Front 119

Laser Source

Back 119

- stimulates trapped electrons
- stimulation of IP causes it to emit light at a much different wavelength than the laser

Front 120

Point Scanner

Back 120

Scan in a method called the raster pattern (like reading a book, from left to right)

Front 121

Line Scanner

Back 121

- much faster than point scanner b/c they cover more area in the same amount of time by scanning line by line

Front 122

Pixel Pitch

Back 122

Physical distance between pixels

Front 123

IP Transport System

Back 123

Removes IP from cassette & transports for exposure to laser, erasure, & re-insertion into cassette

Front 124

Light Channeling Guide

Back 124

Emitted light is optically filtered & collected by light channeling guide (light collection optics)

Front 125

Photodetector

Back 125

After light is captured by channeling guide, it's sent to photodetector which converts PSL into an electrical analog signal

Front 126

ADC

Back 126

PSL is converted to electrical analog signal, is amplified, & is digitized by the ADC ("signal conditioning")

Front 127

"Slow Scan" Direction

Back 127

Direction in which the IP travels

Front 128

"Fast Scan" Direction

Back 128

Laser beam movement across the IP

Front 129

Dual-Side Reading

Back 129

- newer technology where 2 sets of photodetectors are used to capture PSL from front & back side of IP
- more signal obtained, improved signal to noise ratio, improved image quality

Front 130

What are pre-processing operations?

Back 130

Used to identify, correct, & scale raw image data when IP is scanned in reader before image is displayed for viewing

"acquisition processing"

Front 131

Exposure Field Recognition

Back 131

Purpose is to identify the appropriate raw data values to be used for image grayscale rendition; provide an indication of average radiation exposure to IP

Front 132

What are the steps of exposure field recognition?

Back 132

1) Collimated edges detected, anatomical structures are detected by specific algorithms
2) Histogram of info on IP is created ("measured/scanned")
3) Grayscale rendition of image occurs

Front 133

Incorrect exposure values result in...

Back 133

Under/Over exposure, can be used as a quality control tool to facilitate optimization of radiation protection

Front 134

What does Fuji use to represent the quality control?

Back 134

"S" Number (sensitivity number)
S - 200 / exposure to IP (mR)

Sweet Spot = 200

Front 135

S number is __________ (directly/inversely) proportional to exposure

Back 135

Inversely

Front 136

What does AGFA use to represent the quality control?

Back 136

LGM or log of median value
LGM = 2.2 + log (exposure in mR)

Front 137

Each increment of 0.3 LGM corresponds to...

Back 137

Doubling or halving of the exposure level

Front 138

What does Kodak use to represent the quality control?

Back 138

Exposure Index (EI)

Sweet spot = 2000

Front 139

Exposure Index is __________ (directly/inversely) proportional to exposure

Back 139

Directly

Front 140

Acceptable Range for the 3 Types

Back 140

Fuji = 150-300
LGM = 2.05-2.35
Kodak = 1850-2150
Incident Exposure = 0.67-1.33

Front 141

Algorithms

Back 141

Contrast enhancement (optimize image contrast), spatial frequency (edge enhancement [decreasing grayscale]), multi-scale, multi-frequency enhancement, dual-energy, & disease-specific processing

Front 142

Image Quality Detectors - Spatial Resolution

Back 142

- related to size of pixels in image matrix
- smaller the pixel size, greater the spatial resolution

Pixel Size = FOV / Matrix Size

Front 143

Image Quality Detectors - Density Resolution

Back 143

- linked to bit depth
- greater the bit depth, the better the density resolution

Front 144

Image Quality Detectors - Noise

Back 144

- electronic noise (system noise)
- quantum noise (determined by # of x-ray photons interacting w/ the detector to create an image)

Front 145

Detective Quantum Efficiency (DQE)

Back 145

- measure of the efficiency & fidelity with which the detector can perform this task
- takes into consideration SNR, system noise

Front 146

What allows imaging plates to capture more data during acquisition?

Back 146

The linear exposure range, which is largely dynamic

Front 147

What do over- & under- exposure describe?

Back 147

Actual exposure (mR) to the IR

Front 148

Overexposure implies _______ (dark/light) images

Back 148

Dark

Low contrast b/c of extra scatter

(vis versa also true)

Front 149

Dynamic range of screen/film is....

Back 149

From the straight-line portion of H&D curve

Front 150

Dynamic range of digital is...

Back 150

A linear response (has more than 50x in dynamic range)

Front 151

What does the speed of the receptor determine w/ screen-film?

Back 151

The appropriate level of receptor exposure required to achieve the optimal image density

Front 152

What does the speed of the receptor determine w/ digital systems?

Back 152

The speed class at which the system operated

Front 153

If digital exposure is <50% of the optimal signal level...

Back 153

Quantum Mottle may be objectionable to the viewer (too few photons)

Front 154

If digital exposure is >100% of the optimal signal level...

Back 154

ALARA is violated; extra scatter generated will decrease contrast (200% more radiation)

Front 155

What 3 things are required for high image clarity?

Back 155

1) Selection of correct technical factors
2) Correctly positioned anatomical part
3) Precise alignment of the beam, the part, the IR

Front 156

How can one reduce patient exposure by 12-15%?

Back 156

Performing routine radiography at 48" rather than typical 40"

Front 157

How does grid cutoff show up on digital images?

Back 157

Flattening of the luminance from plate & loss of contrast

Front 158

What 2 factors have a significant role in determining amount of scatter radiation generated?

Back 158

Beam size & Water content of patient

Front 159

Lack of collimation generates ________ (more/less) scatter, reducing contrast

Back 159

More

Front 160

When is there an increased risk of grid cutoff?

Back 160

On portables, due to poor central ray & grid/IR alignment

Front 161

Moiré Artifacts (aliasing)

Back 161

- lines seen as artifacts on CR images
- reduce risk by selecting appropriate grid frequency that isn't near scanning frequency of IP

Front 162

What determines image contrast on digital image?

Back 162

Processing algorithm (instead of kVp)

Can use 10-20 more kVp for digital systems to limit patient dose

Front 163

What happens when the acquired data width is reduced in digital imaging?

Back 163

More of the anatomy may be visualized for a single image display setting

Front 164

kVp for a non-grid exam should never exceed...

Back 164

80

Because of increased sensitivity to scattered radiation

Front 165

The actual exposure latitude of the typical digital system is about _________ (double/half) that of the typical screen/film system

Back 165

Double

Front 166

Exposure levels < 50% below optimal level will...

Back 166

Produce excessive mottle

Front 167

Exposure levels >100% above optimal level will...

Back 167

Produce excessive scatter that degrades the image quality

Front 168

Most common reason for histogram analysis errors is....

Back 168

Exposure field recognition failure

Front 169

What's a way to avoid exposure field recognition error?

Back 169

Acquire 1 image on the smallest plate available (some companies don't utilize highest detail until smallest plate is employed)

Front 170

What's undercutting?

Back 170

Occurs when intense raw radiation degrades the structure visibility along the margin of the structure

To reduce this, collimate

Front 171

What increases geometric blur?

Back 171

Short SID, long OID, large focal spot

Front 172

Max spatial resolution is equal to...

Back 172

Nyquist frequency (1/2x pixel pitch, mm)