chapter 1 hardware anatomy and physiology of a personal...

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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


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


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• 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



• 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)


WHAT?


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


Why?


System components and steps to digital image production


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


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


Density results from the

amount of exposure and

anatomic attenuation in

an images

• Higher mAs = more

dense (overexposed)

• Lower mAs = less

dense

(underexposed).


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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



X-ray film through

chemical processing

converts the

transmitted radiation

by the various types

of tissues (tissue

contrast) into film contrast.



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.


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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.



• 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.



• 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


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• 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………



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?



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)


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Film Gamma

• Calculated from points

surrounding optical

density of 1.0 of

sensitometry curve

• Used for information

about contrast by type of film



Film Latitude

• Wide exposure

latitude = ability to use

a wide range of

exposures

• Narrow exposure

latitude means it

respond to small range of exposures.


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


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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)


Contrast Resolution mm at 0.5% difference

Radiography 10

Nuclear Medicine 20

Sonography 10

Computed Tomography 4

Magnetic Resonance Imaging 1


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.



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.


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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


DATA ACQUISITION


COMPUTER DATA PROCESSING


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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


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


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


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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.


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



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)


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• 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.



• 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


DIGITAL RADIOGRAPHY MODALITIES

Computed Radiography (CR)

Flat-Panel Display Radiography (DR)

Digital Mammography

Digital Fluoroscopy


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COMPUTED RADIOGRAPHY (CR)

Fundamental steps in the production of a CR image.


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.



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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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.



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


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.


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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”


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


DIGITAL FLUOROSCOPY


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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


DIGITAL FLUOROSCOPY

• Temporal subtraction, in which images are

subtracted in time


DIGITAL FLUOROSCOPY

• Energy subtraction, in which images are

subtracted using different kilovoltages.


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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


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


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.


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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.


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


WHAT IS MEDICAL IMAGING INFORMATICS?

IT (Information Technology)

helps use images for:

• Diagnosis

• Assessment and planning

• Guidance of procedures

• Communication

• Education

• Training

• Research.


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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


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



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??

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