Artifacts of Diagnostic Radiology

1
Artifacts of Diagnostic Radiology Clifford R.
Berry, DVM Adjunct Associate Professor,
University of Tennessee Veterinary Specialists
Center, Maitland, FL
2
Special Thanks

• Dr. Crispin Spencer
• Veterinary Radiological Consultants
• Dr. Mary Mahaffey
• University of Georgia
• Dr. Greg Daniel
• University of Tennessee

3
Overview

• Radiographic Artifacts - Definition
• Overview of X-ray production
• Review of Image Geometry, Magnification and Grids
• Review of Image Formation
• Artifacts Common to Exposure/Film Handling
• Review of Image Development
• Manual Processing (Artifacts)
• Automatic Processing (Artifacts)
• Overview of Approach to Artifact Problem Solving
• Artifacts Section Review - 2002 Oral Boards

4
Artifacts

• Definition
• any appearance on a radiograph that is not
  representative of a structure within the patient
  being radiographed.
• Artifacts will
• Degrades image quality
• Can mimic pathology
• Cause visual distractions for radiologist
• Render a radiographic study non-diagnostic

5
Artifacts - Overview

• Descriptions of Artifacts
• Type of processing
• Automatic
• Manual - film holders/cut corners
• Density of Artifact
• Plus Density - (increased or positive optical
  density)
• Minus Density - (decreased or negative optical
  density)
• Potential Timing of Artifact
• Before or after exposure

6
Artifacts - Overview

• Descriptions of Artifacts
• Potential Location of Artifact
• Exposure, Patient, Film-Screen, Grid
• Processing Artifact
• Appearance of Radiographic Film
• Coloration
• View the radiographic film in reflected/transmitte
  d light
• Emulsion torn or missing

7
X-ray Tube

• X-rays were discovered by Wilhelm Roentgen on
  November 8, 1895

8
Modern X-ray Tube

• Cathode
• Anode
• Target
• Tube Housing
• Focal Spot

9
Modern X-ray Tube
Cathode
10
Cathode

• The filament heats like the electrical coils of
  an electric stove

An electron cloud develops around the filament by
a Process called Thermionic Emission
11
Cathode
Focusing Cup
The focusing cup is in a metal shroud that
focuses the electrons To a specific point on the
anode. Negative current (bias) will help keep
electron beam focused.
12
Cathode

• Most x-ray tubes have two filaments
• The small filament is used for low output
  exposures where high detail is needed
• The large filament is used for high output
  exposures

13
Modern X-ray Tube
Anode
14
Modern X-ray Tube
Rotating Anode Target
15
Anode

• The negatively charged electrons are accelerated
  toward the positively charged anode

16
Anode

• The electrons from the cathode interact with the
  tungsten atoms of the anode to produce x-rays

17
Anode Design

• Note the target of the rotating anode of this
  modern x-ray tube

18
Modern X-ray Tube
Window
19
X-ray Tube Housing

• X-ray tube is encased in a metal housing
• The outer casing contains lead to shield x-rays
  produced in directions other than the patient

20
Anode Design

• Rotating the anode will spread the energy of the
  electron beam over a greater area but maintain a
  small focal spot

21
Line Focus Principle

• The smaller the focal spot the better the image
  resolution
• The anode is angled so the the affect focal spot
  will be small than the actual focal spot

22
Anode Angle
Actual Focal Spot Length Effective Focal Spot Length Anode Angle
2.0 x 1.2 .68 x 1.2 20
2.0 x 1.2 .41 x 1.2 12
2.0 x 1.2 .35 x 1.2 10
23
Line Focus Principle - Heel Effect

• The negative consequence of the line focus
  principle is intensity of the beam varies from
  the cathode to anode end of the tube

24
Line Focus Principle - Heel Effect

• Note the x-rays on the anode side must travel a
  greater distance through the target before
  exiting.
• This results in greater absorption by the target
  and this less intensity on the anode side.

25
Line Focus Principle - Heel Effect
Cathode
Anode
26
Bremsstrahlung Radiation

• The electrons from the cathode filament will pass
  near the nucleus of the atom.
• The positive charge of the nucleus will act on
  the negative charge of the electron to decelerate
  it from its original path.
• As the electron slows and bends there is
  release of its kinetic energy as a
  Bremsstrahlung (braking radiation) x-rays.

27
Characteristic Radiation

• X-rays are produced when an electron (from the
  anode electron beam) directly hits an inner shell
  orbital electron, ejecting it from orbit.
• The excess energy is released in the form of an
  x-ray (Characteristic x-ray).
• The energy of the x-ray is the difference in the
  binding energies between the two shells.

28
Polychromatic X-ray Beam

• An x-ray tube produces a combination of both
  general and characteristic x-rays.
• The general x-rays are a variety of energy
  levels.
• The characteristic x-rays are at specific energy
  levels (dependent upon Z of anode material).

29
Electrical Current

• Transfer of electrons along wires
• The United States electrical current is
  alternating which means the electrons change
  direction at 60 cycles per second (60 Hz)

30
X-ray Generator - Single Phase

• An x-ray unit producing 60 pulses of x-ray per
  second is called half wave rectification

31
X-ray Generator - Single Phase

• A circuit can be devised to so that the voltage
  potential applied to the tube always has the
  anode () and the cathode ().
• This is called Full-Wave Rectification.

32
X-ray Generator

• As the voltage potential changes of 0 to the
  maximum so does the energy of the x-ray beam.
• The drop off in x-ray beam intensity is referred
  to as ripple.
• Single-phase generators have a 100 ripple in
  x-ray beam intensity.

33
X-ray Generator

• All voltage waveforms shown up to now are
  produced by a single-phase electrical power
  (standard form of power in the US)
• X-ray machine using this type power are called
  single-phase generators and they produce
• Half-wave rectified 60 pulses of x-rays/sec
• Full-wave rectified 120 pulses of x-rays/sec

34
Filtered X-ray Spectrum

• The x-ray energies range of 0 to the kVp
• The average energy will be equal to 1/3 of the
  kVp (single phase generators).

35
kVp Selector

• Increasing kVp will increase the average energy
  of the beam
• Increasing kVp will also increase the number of
  x-rays produced

36
mAs Spectrum - Quantity

• mAs control the number of x-rays
• Note the energy spectrum and average x-ray photon
  is not changed

37
X-ray Generator

• Three-phase power is the result of sophisticated
  electrical engineering that produces three
  simultaneous voltage waveforms out of step with
  each other.

38
Single Phase - Motion
Three Images Half wave 3/60 1/20 second
time Full-wave 3/120 1/40 second time
39
Three-Phase Generators

• Electrons will continue to flow to the anode
  during the entire time of exposure this producing
  more x-rays per unit of time.
• These generators require special heavy duty
  wiring.
• 6 pulse or 12 pulse ratings.

40
High Frequency Generators

• A high frequency generator increases the
  frequency of the electrical wave form from 60 Hz
  to between 400 to 2000 Hz.
• These generators can operate off single phase
  standard AC current.
• High frequency generators are becoming more
  common in veterinary practices.
• The resulting wave form has less than a 1
  ripple.

41
High Frequency Generators

• The resulting wave form has less than a 1
  ripple

42
High Frequency Generators

• The result is more x-rays per unit time and
  higher average beam energy than single phase and
  three phase generators.

43
High Frequency Generators

• Below is a graph show a comparison of a single
  phase and a high frequency generator of the same
  mA