Imaging Systems

1
Imaging Systems

• X-Rays

2
Imaging Systems Shared Elements

• Where did the energy come from?
• What happens when the energy interacts with
  matter?
• How is the energy collected after that
  interaction?
• How is the collected energy captured?
• How is the signal manipulated?
• What do you do with the information?
• How is the information shown?
• How does the brain interpret that information?

3
Source

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

1. Where did the energy come from?
X rays are a form of electromagnetic
radiation. They have enough energy to liberate
electrons from the atoms that bind them ?
ionizing radiation. X rays can be produced by
different methods Synchrotron, free electron
lasers, x-ray tubes that emit bremsstrahlung and
characteristic x rays.
4
Source

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

Energetic electrons may be attracted into partial
orbit around the nucleus of a target atom. They
slow down, losing kinetic energy. The energy lost
is converted into a photon of electromagnetic
radiation, called bremsstrahlung radiation. The
energy lost by the incoming electron may be of
any amount, up to the total kinetic energy
carried by the electron. Similarly, the photon
emitted may have any value up to the total
kinetic energy of the electron.
5
Source
E1

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

E2
e1
e2
e3
E3
www.mcw.edu/medphys/learning
6
Object

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

2. What happens when the energy interacts with
matter?
Interaction between X rays and matter usually
results in the deposition of energy. Different
types of interactions include Photoelectric
effect, Rayleigh scattering, Compton scattering,
pair and triplet production. These mechanisms
combine to produce attenuation of the incident
x-ray photon beam as it passes through matter.
7
Object

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

Penetrate
Photoelectric interaction
Release kinetic energy
Scatter
Compton interaction
8
Collection and Detection

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

3. How is the energy collected after that
interaction?

• There are two basic ways to create x-ray images
• Pass an x-ray beam through a body section and
  project a shadow image onto a receptor.
• Computer tomography use a computer to
  reconstruct an image from the penetration data.

9
Detection

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

4. How is the collected energy captured?
In conventional radiography the receptor consists
of the film mounted in contact with an
intensifier screen. The contrast that appears in
the image is determined by several factors
penetration characteristics, scattered radiation,
contrast characteristics of the film.
10
Processing

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

5. How is the signal manipulated?

• The most important effect of the intensifying
  screens on image quality is that they blur the
  image.
• Motion blur
• Finite size of x-ray tube focal spot

11
Processing

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

5. How is the signal manipulated?
If the image is stored in computer memory
processing for noise reduction is
possible. Contrast can be manipulated. Images may
be subtracted form each other to show a
difference or change between them.
12
Compression/Storage/Transmission

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

6. What do you do with the information?
In conventional radiography hospitals store
films In digital radiography images are stored in
computer memory. Image files may be compressed
for transmission.
13
Display
7. How is the information shown?

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

In conventional radiography the image is a
photographic film. Digital radiography can be
displayed in either a CRT monitor or a laser film
printer. But these are not able to display full
dynamic range. One way to overcome limitations is
to use image processing techniques to enhance
lesion visibility.
14
Perception

• MRI
• PET scan
• Film photography
• Digital photography
• Television
• VCR
• DVD
• Microscopes
• Telescopes
• CRT
• LCD
• Plasma display
• Thermal imagers
• Passive IR sensors
• Radar
• Movies
• Overhead projector
• Slide projector
• Holography

8. How does the brain interpret that
information?
Human observers are integral part of imaging
system. Relationship between physical image
quality and diagnostic performance is known as
psychophysics. Use of ROC (receiver operating
characteristics) is one of the major statistical
analytical tools to characterize human
performance.
15
The Imaging Chain

• The common thread in these imaging systems can be
  described in terms of the component black boxes
  that make them up.

• Source
• Object
• Collection
• Detection
• Processing
• Compression/storage/transmission
• Display
• Perception