Presentation on theme: "Artifacts of Diagnostic Radiology Clifford R. Berry, DVM Adjunct Associate Professor, University of Tennessee Veterinary Specialists Center, Maitland,"— Presentation transcript:
Artifacts of Diagnostic Radiology Clifford R. Berry, DVM Adjunct Associate Professor, University of Tennessee Veterinary Specialists Center, Maitland, FL ACVR Artifacts
Special Thanks Dr. Crispin Spencer Veterinary Radiological Consultants Dr. Mary Mahaffey University of Georgia Dr. Greg Daniel University of Tennessee
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 Oral Boards
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
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
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/transmitted light Emulsion torn or missing
X-ray Tube X-rays were discovered by Wilhelm Roentgen on November 8, 1895
The filament heats like the electrical coils of an electric stove An electron cloud develops around the filament by a Process called Thermionic Emission
Cathode 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. Focusing Cup
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
Modern X-ray Tube Anode
Modern X-ray Tube Rotating Anode Target
Anode The negatively charged electrons are accelerated toward the positively charged anode
Anode The electrons from the cathode interact with the tungsten atoms of the anode to produce x-rays
Anode Design Note the target of the rotating anode of this modern x-ray tube Note the anode has splits to allow for heat expansion
Modern X-ray Tube Window
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
Anode Design Rotating the anode will spread the energy of the electron beam over a greater area but maintain a small focal spot
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
Anode Angle Actual Focal Spot Length Effective Focal Spot Length Anode Angle 2.0 x x x x x x
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
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.
Line Focus Principle - Heel Effect CathodeAnode
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 it’s kinetic energy as a Bremsstrahlung (braking radiation) x-rays.
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.
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).
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)
X-ray Generator - Single Phase An x-ray unit producing 60 pulses of x-ray per second is called half wave rectification
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.
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.
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
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).
kVp Selector Increasing kVp will increase the average energy of the beam Increasing kVp will also increase the number of x-rays produced
mAs Spectrum - Quantity mAs control the number of x-rays Note the energy spectrum and average x-ray photon is not changed
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.
Single Phase - Motion Three Images Half wave 3/60 = 1/20 second time Full-wave 3/120 = 1/40 second time
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.
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.
High Frequency Generators The resulting wave form has less than a 1 % ripple
High Frequency Generators The result is more x-rays per unit time and higher average beam energy than single phase and three phase generators.
High Frequency Generators Below is a graph show a comparison of a single phase and a high frequency generator of the same mA