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8/22/2012
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Section I: Chapter 1 1
RADT 3463 - COMPUTERIZED IMAGING RADT 3463 - COMPUTERIZED IMAGING
RADT 3463 Computerized Imaging 1
Section I: Chapter 1 2
SECTION I - CHAPTER 1
DIGITAL RADIOGRAPHY:
AN OVERVIEW OF THE TEXT
RADT 3463 COMPUTERIZED IMAGING
2 RADT 3463 Computerized Imaging
Exam Content Specifications
Section I: Chapter 1 RADT 3463 Computerized Imaging 3
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Exam Content Specifications
Section I: Chapter 1 RADT 3463 Computerized Imaging 4
Film/Screen Radiography
• Film/screen cassettes
• X-rays strike the
intensifying screens –
expose film (latent image)
• Film is chemically
processed
• Latent image becomes
manifest image
Filmless Imaging /
Digital Imaging
• Any image acquisition process
– that produces an electronic image
– that can be viewed and manipulated on a computer
Section I: Chapter 1 5 RADT 3463 Computerized Imaging
VS
DIGITAL RADIOGRAPHY: A DEFINITION
• Uses computers to
process data collection
from patients
• Electronic detectors
replace x-ray film cassette
and it becomes filmless
radiography
Section I: Chapter 1 6 RADT 3463 Computerized Imaging
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DIGITAL RADIOGRAPHY: A DEFINITION
• Detectors measure x-ray
attenuation data from
the patient
• The data is then
converted into electronic
(analog) signals
• The analog signals are
converted into digital
data for computer
processing
Section I: Chapter 1 7 RADT 3463 Computerized Imaging
DIGITAL RADIOGRAPHY: A DEFINITION
• Computer processing
converts digital data
into a digital image
• The digital image is
then converted to an
analog image so it
can be viewed on a
computer monitor
• The displayed image can be manipulated
(annotated, enhanced, etc.) using digital image
processing techniques (post-processing)
Section I: Chapter 1 RADT 3463 Computerized Imaging 8
WHAT?
Section I: Chapter 1 RADT 3463 Computerized Imaging 9
STOP REWIND SIMPLIFY
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• Waveform = analog
– radiation, visible light, sound
• Electricity = electrical pulses
– (+/-) Is electricity analog?
• Digital = binary language (0, 1)
– the language of computers
Section I: Chapter 1 RADT 3463 Computerized Imaging 10
Why?
Section I: Chapter 1 RADT 3463 Computerized Imaging 11
System components and steps to digital image production
Section I: Chapter 1 RADT 3463 Computerized Imaging 12
PUT IT ALL TOGETHER!
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FILM-BASED RADIOGRAPHY:
A BRIEF REVIEW
• Basic steps in the Production of a
Radiograph
• The Film Characteristic Curve
• Limitations of Film-Screen Radiography
Section I: Chapter 1 RADT 3463 Computerized Imaging 13
BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH
• X-rays penetrate the patient and form a latent
image on the film.
• Chemical processing converts latent image in a
visible image.
• Image is displayed a view box. Section I: Chapter 1 RADT 3463 Computerized Imaging 14
BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH
Density results from the
amount of exposure and
anatomic attenuation in
an images
• Higher mAs = more
dense (overexposed)
• Lower mAs = less
dense
(underexposed).
Section I: Chapter 1 RADT 3463 Computerized Imaging 15
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BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH
Contrast is the differences in image densities.
• Higher kVp = Long scale = more gray shades – Low contrast
• Lower kVp = Short scale = fewer gray shades – High contrast
Section I: Chapter 1 RADT 3463 Computerized Imaging 16
BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH
X-ray film through
chemical processing
converts the
transmitted radiation
by the various types
of tissues (tissue
contrast) into film contrast.
Section I: Chapter 1 RADT 3463 Computerized Imaging 17
BASIC STEPS IN THE PRODUCTION OF A RADIOGRAPH
Optical Density (OD)
• The measurement of the
amount of light transmitted
through the film
• Describes the degree of
film blackening as a result
of radiation exposure
• Can be measured by a densitometer.
Section I: Chapter 1 RADT 3463 Computerized Imaging 18
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THE FILM CHARACTERISTIC CURVE
• Characteristic Curve or
the Hurter-Driffield (H
and D) curve describes
film contrast.
• The curve is a plot of the
OD to the logarithm of
the relative exposure
(radiation exposure) to make the radiograph.
Section I: Chapter 1 RADT 3463 Computerized Imaging 19
THE FILM CHARACTERISTIC CURVE
• The curve indicates the
degree of contrast
(different densities) that a
film can display using a
range of exposures.
• The curve has three main
segments:
• Toe
• Slope (straight-line
portion) • Shoulder.
Section I: Chapter 1 RADT 3463 Computerized Imaging 20
THE FILM CHARACTERISTIC CURVE
• Toe = underexposure • OD = ~0.12-0.20
• Slope = acceptable
exposure = useful
range of exposures • OD = 0.3-2.2
• Shoulder =
overexposure • OD = >3.2
• Base plus fog =no
exposure is used • OD = 0.1 to 0.2
Section I: Chapter 1 RADT 3463 Computerized Imaging 21
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THE FILM CHARACTERISTIC CURVE
• Four other factors that can be described using
the characteristic curve:
• Film Speed
• Average Gradient
• Film Gamma
• Film Latitude
Let’s talk briefly about each………
Section I: Chapter 1 RADT 3463 Computerized Imaging 22
THE FILM CHARACTERISTIC CURVE
Film Speed
• Sensitivity of film to radiation
• Fast film ( higher speed) = less exposure
• Slow film (lower speed) = more exposure
• Bonus: Which one would you use for high detail imaging?
Section I: Chapter 1 RADT 3463 Computerized Imaging 23
THE FILM CHARACTERISTIC CURVE
Average Gradient
• slope of the straight-line
region of a sensitometric
curve
• Long scale contrast when
film has average gradient
of 3.0
• Short scale contrast when
film has average gradient of 2.7)
Section I: Chapter 1 RADT 3463 Computerized Imaging 24
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THE FILM CHARACTERISTIC CURVE
Film Gamma
• Calculated from points
surrounding optical
density of 1.0 of
sensitometry curve
• Used for information
about contrast by type of film
Section I: Chapter 1 RADT 3463 Computerized Imaging 25
THE FILM CHARACTERISTIC CURVE
Film Latitude
• Wide exposure
latitude = ability to use
a wide range of
exposures
• Narrow exposure
latitude means it
respond to small range of exposures.
Section I: Chapter 1 RADT 3463 Computerized Imaging 26
LIMITATIONS OF FILM-SCREEN RADIOGRAPHY
• Problem: poor quality radiograph if the initial
radiation exposure was not accurate.
• Too high an exposure = overexposed radiograph
• Too low an exposure = underexposed radiograph
• Solution: Repeat radiograph to obtain one of
acceptable quality for interpretation
• Drawbacks: Repeating radiographs increases
radiation exposure to the patient
Section I: Chapter 1 RADT 3463 Computerized Imaging 27
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LIMITATIONS OF FILM-SCREEN RADIOGRAPHY
Limitation 1: Film based imaging is limited to its
contrast resolution
• Film-screen cannot show differences in tissue
contrast less than 10%.
• Spatial resolution for film-screen radiography
(5-15 line pairs/mm) is higher than other
imaging modalities. (more on this later)
Section I: Chapter 1 RADT 3463 Computerized Imaging 28
Contrast Resolution mm at 0.5% difference
Radiography 10
Nuclear Medicine 20
Sonography 10
Computed Tomography 4
Magnetic Resonance Imaging 1
LIMITATIONS OF FILM-SCREEN RADIOGRAPHY
Limitation 2: The film’s optical range and contrast
are fixed and limited and cannot be manipulated to
enhance image quality.
• Exposure technique factors and integrity of
chemical processing determine optical range
and contrast.
• To change displayed images, a repeat
radiograph increases patient’s radiation dose.
Section I: Chapter 1 RADT 3463 Computerized Imaging 29
LIMITATIONS OF FILM-SCREEN RADIOGRAPHY
Limitation 3: To archive, radiographs are usually
stored in envelopes and files in a large room.
• Manual handling is required for archiving and
retrieving each patient’s radiography examination.
Section I: Chapter 1 RADT 3463 Computerized Imaging 30
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A DIGITAL RADIOGRAPHIC IMAGING SYSTEM:
MAJOR COMPONENTS
Data Acquisition
Computer Data
Processing
Image Display and
Post Processing
Image Storage
Image and Data
Communications
Image and
Informational
Management
Section I: Chapter 1 RADT 3463 Computerized Imaging 31
DATA ACQUISITION
Section I: Chapter 1 RADT 3463 Computerized Imaging 32
COMPUTER DATA PROCESSING
Section I: Chapter 1 RADT 3463 Computerized Imaging 33
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IMAGE DISPLAY AND POST PROCESSING
• To view a digital
image, it must be
converted into an
analog signal
• This occurs in the
digital-to-analog
converter (DAC).
• The image can now be
viewed in multiple
ways at the viewers
discretion
Section I: Chapter 1 RADT 3463 Computerized Imaging 34
IMAGE DISPLAY AND POST PROCESSING
Using post-processing, the
displayed image can be
manipulated to:
• Reduce noise
• Enhance image
sharpness
• Change contrast
• Stitch images together to
form one image
• Gray scale mapping
• Annotate
Section I: Chapter 1 RADT 3463 Computerized Imaging 35
IMAGE STORAGE
Image are archived and stored for retrospective
analysis and for
medico-legal purposes.
Old Standard of Optical
• CD
• DVD
• Permanent Hard
Drive
New Plug and Play
Entries
• Flash Memory /
• Memory Cards)
• USB Jump drive
• Portable hard drives
Section I: Chapter 1 RADT 3463 Computerized Imaging 36
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IMAGE STORAGE
• Long term storage of digital images needs to rely
on large capacity servers such as a RAID
(redundant array of independent disks) system.
• Short-term archival systems are deleted after a period of time defined by the institution.
Section I: Chapter 1 RADT 3463 Computerized Imaging 37
DIGITAL FILE SIZE
MEDICAL IMAGE IMAGE SIZE EXAMINATION SIZE
Nuclear Medicine 0.25 MB 5 MB
Diagnostic Sonography 0.25 MB 8 MB
Magnetic Resonance Imaging 0.25 MB 12 MB
Computed tomography 0.5 MB 20 MB
Digital Radiography 5 MB 20 MB
Digital Mammography 10 MB 60 MB
IMAGE AND DATA COMMUNICATIONS
Images need to be transmitted from the acquisition
phase to the display/viewing and storage phase.
• HIS - Hospital Information System are now being
integrated with the PACS by computer networks
• RIS - Radiology Information Systems can use
PACS systems are being used for
storing/archiving and communicating images
• PACS - Picture Archiving and Communication
Systems store and archive images
Section I: Chapter 1 RADT 3463 Computerized Imaging 38
IMAGE AND DATA COMMUNICATIONS
Networks:
• LANS - local area networks can be used within a
hospital.
• WANS - wide area networks are used for sites
outside and remote of the hospital.
Language:
• Effective management and standards of patient
information
• DICOM - Digital Imaging and Communications
in Medicine and
• HL-7 Health Level-7)
• IHE Integrating the Healthcare Enterprise (ACR,
RSNA, and HIMSS)
Section I: Chapter 1 RADT 3463 Computerized Imaging 39
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IMAGE AND DATA COMMUNICATIONS
• Image Compression
• Storing data in a format that requires less space
than usual.
• Compression techniques are distinguished by
whether they remove detail and color from the
image
• Crucial to radiology and teleradiology because of
large image file sizes.
• The process of compacting an image by
removing redundant information.
Section I: Chapter 1 RADT 3463 Computerized Imaging 40
IMAGE AND DATA COMMUNICATIONS
• Image Compression
• There are two main
types of compression:
• Lossless compression -
on decompression, the
original is restored in
every detail.
• Lossy (lossee)
compression -
unnecessary(?) detail is
thrown away
Section I: Chapter 1 RADT 3463 Computerized Imaging 41
DIGITAL RADIOGRAPHY MODALITIES
Computed Radiography (CR)
Flat-Panel Display Radiography (DR)
Digital Mammography
Digital Fluoroscopy
Section I: Chapter 1 RADT 3463 Computerized Imaging 42
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COMPUTED RADIOGRAPHY (CR)
Fundamental steps in the production of a CR image.
Section I: Chapter 1 RADT 3463 Computerized Imaging 43
FLAT-PANEL DIGITAL RADIOGRAPHY (DR)
• Digital detector is designed as a flat-panel
Two Categories:
• Indirect conversion digital radiography systems
1. Array of electronic elements
2. Charge-coupled devices (CCDs)
• Direct conversion digital radiography systems.
Section I: Chapter 1 RADT 3463 Computerized Imaging 44
FLAT-PANEL DIGITAL RADIOGRAPHY (DR)
Indirect (electronic elements)
• X-rays are converted to light
using a phosphor such as cesium
iodide.
• Emitted light from the phosphor
falls on a matrix array of
electronic elements to create and
store electrical charges in direct
proportion to X-ray exposure.
• Charges produce electrical
signals, which are digitized to
produce an image. Section I: Chapter 1 RADT 3463 Computerized Imaging 45
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FLAT-PANEL DIGITAL RADIOGRAPHY (DR)
Indirect (charge-coupled device)
• Uses an array of charge-
coupled devices (CCDs) which
are coupled to a scintillator
phosphor, cesium iodide
• X-rays fall on the phosphor to
produce light, which then falls
on the CCD array, which in turn
converts the light into electrical
signals that are then digitized
and processed to produce an
image.
Section I: Chapter 1 RADT 3463 Computerized Imaging 46
FLAT-PANEL DIGITAL RADIOGRAPHY (DR)
Direct
• Detectors convert x-rays
directly into electrical signals.
• X-rays fall on a
photoconductor (e.g.-
selenium) that is coupled to a
matrix array of electronic
elements to produce
electrical signals.
• These signals are digitized
and processed to produce an
image. Section I: Chapter 1 RADT 3463 Computerized Imaging 47
FLAT-PANEL DIGITAL RADIOGRAPHY (DR)
Advantages
• Flat-panel digital detector can be erased and
ready to be reused.
• High detective quantum efficiency (DQE) What?
• Spatial resolution comparable to CR systems.
• Characteristic response to radiation exposure
with wide exposure latitude fundamentally
different to the film characteristic curve. – Wide exposure latitude will produce acceptable
images even when the input exposure is low or high.
Section I: Chapter 1 RADT 3463 Computerized Imaging 48
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DIGITAL MAMMOGRAPHY
Benefits
• Overcomes limitations of technique in film-
screen mammography
• Post-processing tools allows enhancement
image for interpretation
• Uses computer-aided diagnosis (CAD) software
to enhance detection of microcalcifications and
malignant lesions • Provides the "second reader”
Section I: Chapter 1 RADT 3463 Computerized Imaging 49
DIGITAL FLUOROSCOPY
Major goal of digital fluoroscopy
• Use digital imaging processing software to
improve the perception of contrast resolution,
compared to conventional fluoroscopy
Advantages
• Gray-scale processing
• Temporal frame averaging
• Edge enhancement
• Produces dynamic images acquired in real time
Section I: Chapter 1 RADT 3463 Computerized Imaging 50
DIGITAL FLUOROSCOPY
Section I: Chapter 1 RADT 3463 Computerized Imaging 51
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DIGITAL FLUOROSCOPY
Application
• Digital subtraction angiography (DSA) in which
pre-contrast and post-contrast images can be
digitally subtracted in real time.
• Why? Improve the perception of low-contrast
vessels by subtracting or removing the tissues
(bones) that interfere with visualization of
vascular structures.
Two subtraction techniques
• Temporal subtraction
• Energy subtraction
Section I: Chapter 1 RADT 3463 Computerized Imaging 52
DIGITAL FLUOROSCOPY
• Temporal subtraction, in which images are
subtracted in time
Section I: Chapter 1 RADT 3463 Computerized Imaging 53
DIGITAL FLUOROSCOPY
• Energy subtraction, in which images are
subtracted using different kilovoltages.
Section I: Chapter 1 RADT 3463 Computerized Imaging 54
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PICTURE ARCHIVING AND
COMMUNICATION SYSTEMS PACS = IMACS (image management and
communications systems
• Digital images must be
• Displayed for interpretation
• Stored and archived for medico-legal purpose
• Stored for retrospective analysis
• Transmitted to remote locations
Section I: Chapter 1 RADT 3463 Computerized Imaging 55
MAJOR SYSTEM COMPONENTS
Major components
include:
• Image acquisition
devices
• PACS computer
• Devices called
interfaces
• Display workstations
• All should be
connected and
linked to HIS and
RIS
Section I: Chapter 1 RADT 3463 Computerized Imaging 56
PICTURE ARCHIVING AND COMMUNICATION SYSTEMS
MAJOR SYSTEM COMPONENTS
PACS systems contains confidential patient data
and information
• Data security is of central importance (HIPAA)
– Health Insurance Portability and Accountability Act
• Interfaces
• Facilitate easy communication between the
image acquisition modalities and the HIS/RIS
with the PACS computer
• Allow individuals to use the World Wide Web
to access the PACS computer.
Section I: Chapter 1 RADT 3463 Computerized Imaging 57
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QUALITY ASSURANCE IN DIGITAL
RADIOGRAPHY
• QA and QC procedures are effective strategies
to ensure continuous quality improvement to:
– Ensure patients are exposed to minimum
radiation using the ALARA (as low as reason-
ably achievable) philosophy.
– Produce optimum image quality for diagnosis.
– Reduce the costs of radiology operations.
Section I: Chapter 1 RADT 3463 Computerized Imaging 58
MEDICAL IMAGING INFORMATICS
Information Technology (IT) concepts are used for
• Digital image acquisition technologies
• Digital image processing
• Digital image display
• Storage and archiving
• Digital image communications
• Rapidly growing field – degrees in informatics
Section I: Chapter 1 RADT 3463 Computerized Imaging 59
WHAT IS MEDICAL IMAGING INFORMATICS?
IT (Information Technology)
helps use images for:
• Diagnosis
• Assessment and planning
• Guidance of procedures
• Communication
• Education
• Training
• Research.
Section I: Chapter 1 RADT 3463 Computerized Imaging 60
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WHAT IS MEDICAL IMAGING INFORMATICS?
IT involves these topics:
• Information systems
• Standards for communicating
(text and images)
• Computer communication
networks
• Web technology
• Image and text handling
• Privacy, security, and
confidentiality issues
• Digital image processing
• Payroll
Section I: Chapter 1 RADT 3463 Computerized Imaging 61
THE TECHNOLOGIST AS INFORMATICIST
• Radiographers need skills related to IT
• Radiology Departments need a PACS
administrator (IT administrator)
• Function is dedicated to ensuring the integrity
of the PACS.
• Radiographers need to learn the skills to
become a informaticist
Section I: Chapter 1 RADT 3463 Computerized Imaging 62
Section I: Chapter 1 RADT 3463 Computerized Imaging 63
Sprawls Educational Foundation
http://www.sprawls.org/ppmi2/FILMCON/
SECOND LOOK:
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Section I: Chapter 1 RADT 3463 Computerized Imaging
What lies behind us and
what lies before us are
small matters compared to
what lies within us.
Ralph Waldo Emerson
64
QUESTIONS??