Presentation on theme: "ACVR Artifacts Artifacts of Diagnostic Radiology"— Presentation transcript:
1ACVR Artifacts Artifacts of Diagnostic Radiology Clifford R. Berry, DVMAdjunct Associate Professor, University of TennesseeVeterinary Specialists Center, Maitland, FL
2Special Thanks Dr. Crispin Spencer Dr. Mary Mahaffey Dr. Greg Daniel Veterinary Radiological ConsultantsDr. Mary MahaffeyUniversity of GeorgiaDr. Greg DanielUniversity of Tennessee
3Overview Radiographic Artifacts - Definition Overview of X-ray productionReview of Image Geometry, Magnification and GridsReview of Image FormationArtifacts Common to Exposure/Film HandlingReview of Image DevelopmentManual Processing (Artifacts)Automatic Processing (Artifacts)Overview of Approach to Artifact Problem SolvingArtifacts Section Review Oral Boards
4Artifacts Definition: “any appearance on a radiograph that is not representative of a structure within the patient being radiographed.”Artifacts will:Degrades image qualityCan mimic pathologyCause visual distractions for radiologistRender a radiographic study non-diagnostic
5Artifacts - Overview Descriptions of Artifacts: Type of processing AutomaticManual - film holders/cut cornersDensity of ArtifactPlus Density - (increased or positive optical density)Minus Density - (decreased or negative optical density)Potential Timing of ArtifactBefore or after exposure
6Artifacts - Overview Descriptions of Artifacts: Potential Location of ArtifactExposure, Patient, Film-Screen, GridProcessing ArtifactAppearance of Radiographic FilmColorationView the radiographic film in reflected/transmitted lightEmulsion torn or missing
7X-ray TubeX-rays were discovered by Wilhelm Roentgen on November 8, 1895
19X-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
20Anode DesignRotating the anode will spread the energy of the electron beam over a greater area but maintain a small focal spot
21Line Focus PrincipleThe smaller the focal spot the better the image resolutionThe anode is angled so the the affect focal spot will be small than the actual focal spot
22Actual Focal Spot Length Effective Focal Spot Length Anode AngleActual Focal Spot LengthEffective Focal Spot LengthAnode Angle2.0 x 1.2.68 x 1.220.41 x 1.212.35 x 1.210
23Line 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
24Line 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.
26Bremsstrahlung 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 it’s kinetic energy as a Bremsstrahlung (braking radiation) x-rays.
27Characteristic 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.
28Polychromatic 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).
29Electrical 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)
30X-ray Generator - Single Phase An x-ray unit producing 60 pulses of x-ray per second is called half wave rectification
31X-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.
32X-ray GeneratorAs 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.
33X-ray GeneratorAll 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/secFull-wave rectified = 120 pulses of x-rays/sec
34Filtered X-ray Spectrum The x-ray energies range of 0 to the kVpThe average energy will be equal to 1/3 of the kVp (single phase generators).
35kVp SelectorIncreasing kVp will increase the average energy of the beamIncreasing kVp will also increase the number of x-rays produced
36mAs Spectrum - Quantity mAs control the number of x-raysNote the energy spectrum and average x-ray photon is not changed
37X-ray GeneratorThree-phase power is the result of sophisticated electrical engineering that produces three simultaneous voltage waveforms out of step with each other.
38Single Phase - Motion Three Images Half wave 3/60 = 1/20 second time Full-wave3/120 = 1/40 second time
39Three-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.
40High 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.
41High Frequency Generators The resulting wave form has less than a 1 % ripple
42High Frequency Generators The result is more x-rays per unit time and higher average beam energy than single phase and three phase generators.
43High Frequency Generators Below is a graph show a comparison of a single phase and a high frequency generator of the same mA