Transcript Quality Control - Wolters Kluwer Health

CHAPTER 3
EQUIPMENT OPERATION AND
QUALITY CONTROL
EXAMINATION REVIEW FOR RADIOGRAPHY
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ARRT Certification Exam: Equipment
Operation and Quality Control
• Twenty-two questions (11% of the examination)
• Three primary sections
– Principles of Radiation Physics
– Imaging Equipment
– Quality Control of Imaging Equipment and
Accessories
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Principles of Radiation Physics: X-ray
Production
• Primary
requirements
– Source of free
electrons
• Cathode (− charge)
• Heated filament
– Focusing of
electrons
– Acceleration of
electrons
• Applied kVp
– Deceleration of
electrons
• Rotating tungsten
anode (+ charge)
• Focusing cup
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Principles of Radiation Physics: X-ray
Production—(cont.)
• The x-ray tube produces x-rays due to the conversion of
high-speed electrons (kinetic energy) into
electromagnetic energy (x-ray photons, heat, and light).
• X-ray tube efficiency: 1% x-ray production
– 99% of energy produced: heat
• Two primary atomic interactions occur in the x-ray tube
– Bremsstrahlung (85% of radiation produced)
– Characteristic (15% of radiation produced)
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Bremsstrahlung Radiation
• Projectile electron loses kinetic energy (KE) as it interacts
with the nuclear field of a target atom.
– Deceleration occurs due to a change in direction of
the projectile electron.
• Lost KE converted to x-ray photons
• Produces varying energy levels and wavelengths of x-ray
photons
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Characteristic Radiation
• Projectile electron ionizes a k-shell electron of a target
atom.
• Opening in K-orbit replaced by an outer shell electron
(transition)
• Characteristic radiation photon released
• Produces fixed energy x-ray photons
– In a tungsten target, no characteristic radiation will
be produced under 69 kVp.
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Fundamental Properties of
Electromagnetic Radiation and X-ray
Photons
• Descriptive or controlling factors
– Frequency
– Wavelength
– Velocity
– Energy
– Inverse square law
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Characteristics of the X-ray Beam
• Descriptive or controlling factors
– Quality
• Voltage
– Quantity
• Current
– Filtration
– Target material
– Voltage waveforms/generators
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Primary versus Remnant (Exit) Radiation
• Primary radiation
• Primary beam
• Leakage radiation
• Remnant or exit radiation
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Imaging Equipment: Operating Console
• Power: (on/off)
• kVp control
– Provides E for beam penetration
• mA control
– Controls quantity or intensity of x-ray beam
• Timer
– Used in conjunction with mA to control the intensity
of x-ray beam
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Imaging Equipment: Automatic Exposure
Control
• Components
– Ion chambers or sensors
– Density controls
• −2 to +2
– Backup timer
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Imaging Equipment: Circuit Components
• X-ray tube
– Produces x-rays
• Transformers
– Controls and varies
voltage
• Incoming current:
60 Hertz AC
• Rectifers
– Converts AC to DC
• Generators
– Single phase
– Three phase
– Each peak = one
pulse
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Imaging Equipment: Accessory Devices
• Beam restriction
devices
– Adjustable
collimator
• Grids
– Stationary
– Reciprocating
(Bucky device)
– Aperture diaphragm
– Cones and cylinders
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Dedicated X-ray Equipment
• Chest:
freestanding system
for upright imaging
• Often incorporates
– Automatic vertical
tracking
• Tomography:
focuses on a single
plane
• Tube and IR move
synchronously
around a fulcrum
– Automatic
collimation
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Fluoroscopic Equipment
• Used for real-time
imaging
• Components
– X-ray tube
• Conventional and
digital systems
available
– Image intensifier
• Fixed or mobile (Carm) systems
– Display
screen/monitor
– Automatic
brightness control
– Recording device(s)
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Digital Imaging
• Filmless equipment
• Two types
– Computed radiography (CR)
– Digital radiography (DR)
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Digital Imaging: Computed Radiography
(CR)
• Components and
image acquisition
– Reusable imaging
plate
– Photostimulable
phosphor (PSP)
• Stores latent image
– Laser reader
• Stimulates phosphor
to release light
photons
– Monitor
• Displays image
– Fluorescent light
• Erases PSP
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Digital Imaging: Digital Radiography (DR)
• Components and image acquisition (two types)
– Direct panel DR (amorphous selenium)
• Converts x-ray photons directly to an electric
signal, sent to a computer
– Indirect panel DR (amorphous silicon)
• Converts x-ray photons to light to an electric
signal, sent to a computer
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Quality Control (QC) of Equipment and
Accessory Devices
• Beam restriction devices QC tests
– X-ray/light field alignment: ±2% of SID
– Central ray alignment
• Shielding QC tests (aprons, gloves, and gonadal shields)
– Visual inspection for tears or cracks
– Fluoroscopy check for holes or cracks
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Digital Imaging Quality Control: Artifacts
• Types/causes
– Debris/dust
– Scratches
– Incomplete erasure
– Ghost images
– Fog
– Software
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Digital Imaging: Monitor Quality Control
• Checked monthly or quarterly
• SMPTE (Society of Motion Picture and Television
Engineers) test pattern
– Tests monitor for
• Sharpness
• Distortion
• Luminance
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