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The 2 classifications for X-ray Equipment are?and give examples of each.
Diagnostic - radiographic equipment used to produced images for detection of pathology that aid in the diagnosis of disease
- - Radiographic & fluoroscopic rooms
- •Rooms that have both are called R/F rooms
- - Portable x-ray unit
- - Portable fluoroscopy (C-Arm)
- - Tomography units
- - Mammography units
- - CT scanners
- - Panoramic dental units
- - Simulators (used in radiation therapy – radiographic/fluoroscopic/CT capabilities)
Therapeutic – radiographic equipment used to treat disease (primarily cancer)
- Linear accelerator (used in radiation therapy)
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The 5 main components of a Radiographic Room are?
- - X-ray table
- - Tube support
- - Control console
- - Electronic circuits
- - Generators
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Describe the Radiographic Table.
- Designed to support the patient for an x-ray exam:
- - Uniformly radiolucent
- •Made of carbon graphite fiber
- - Flat, level surface
- •Curved design used in some fluoroscopy rooms & CT scanners
- - Designed to be a smooth, scratch resistant surface that is easy to clean
- - Can accommodate a radiolucent table pad for patient comfortFloating table top (longitudinal & transverse/lateral) – either motor driven or manual operation (electromagnetic foot brake)
- - Most (but not all) height-adjustable to make it easier to get patient on/off
- •Height – designed for a height that reduces physical strain on the operator: 30”-40” (75-100 cm) from the floor
- - Built-in Bucky
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The parts of the Bucky and who invented it.
- Parts:
- - Tray to hold image receptors (cassettes) or a built in DR detector array
- •IR cassettes: CR with PSP plate or flat-panel wireless DR detector
- - Grid with mechanism to move it during exposure
- •Designed to blur out grid lines on image
- - Bucky may be fixed or moveable along the long axis of the table (longitudinally)
Named after Gustav Bucky – inventor of the grid
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Upright Bucky
- Tray to hold image receptors or a built in DR detector array
- •Built in grid
- •Vertical movement for height adjustment
- - Some have tilt capabilities
- •May have build-in handles or overhead bar (chest x-rays)
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Table Types & Accessories
- Fixed – do not tilt
- •Tilting – able to tilt 90° in one direction (erect) & approximately 15°-30° in another direction (Trendelenburg)
- - Usually found in R/F rooms
- •Footboard
- •Shoulder supports
- •Handgrips
- •Compression bands
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The 5 types of Tube Supports are?
- Floor suspension – column mounted on the floor that moves on a track vertically & longitudinally
- Floor to ceiling suspension
– column mounted with a pair of rails on ceiling & floor that allow vertical & longitudinal motion
Overhead suspension (ceiling mounted) – allows movements in all directions (vertical, longitudinal, horizontal)
Mobile – portable units with tube mounted on a vertical column
- C-arm – c-shaped arm that can be rotated & turned in various positions
- •Room or mobile
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The Control Console consists of what?
- Allows control of:
- - X-ray tube current (mA) & voltage (kV) to adjust quantity & quality of x-ray photons produced
- - Exposure time
- - Automatic exposure control (AEC)
- - Focal spot
- •Exposure button/control to activate tube
- •Based on computer technology – some are touch-screen
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Electrical Power
Power supplied by a utility company in the US is usually ___ Hz AC with voltages between ___ - ___ V. This is called the incoming line current (main).
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x-ray imaging systems operate with an incoming line voltage of ___-___ V
210-220
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The incoming line current is supplied 2"hot" wires, each with __-__V.
110-120
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Permits the potential difference (voltage) to drop to zero with every change in the direction of current flow
•Results in a pulsating x-ray beam
- X-rays produced when the waveform voltage is low or near zero are of little diagnostic value because of their low energy (photons do not exit the tube or are absorbed before hitting the IR – low penetrability)
Single Phase Power
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Single-phase full-wave rectified DC waveform
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Designed to help overcome the deficiencies of single-phase power
•High-voltage transformer wired so that as each wave peak begins to drop towards zero, the potential difference (voltage) is boosted back to peak by the next phase
•Seen as 3 voltage waveforms superimposed on one another
•Results in a nearly constant high voltage
•Full wave rectification – produces a voltage ripple
Three-Phase Power
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3 Phase fully rectified DC
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These 10 things make up an X-ray Circuit.
- 1.Main breaker
- 2.Exposure switch
- 3.Autotransformer
- 4.Timer circuit
- 5.High voltage step-up transformer
- 6.Rectifier
- 7.Filament circuit variable resistance
- 8.Filament step-down transformer
- 9.X-ray tube
- 10.Stator
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What's 1?
Main breaker
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What's 2?
Exposure switch
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What's 3?
Autotransformer
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What's 4?
Timer circuit
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What's 5 on the primary (low voltage) side?
Primary side of the step-up transformer
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What's 5 on the Secondary (high voltage) side?
Secondary side of the step-up transformer
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What's 6?
Rectifier
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What's 7?
Filament circuit variable resistance
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What's 8?
Filament step-down transformer
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What's 9?
X-ray tube
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What's 10?
Stator
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Device that receives the incoming line power from utility company?
Main breaker
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Connection that allows current to flow through the circuit
Exposure switch
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Autotransformer
- Device used to vary the incoming line voltage to an appropriate level for the high voltage step-up transformer
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- - Controlled by the kV selector on the control console
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Timer Circuit
Circuit that terminates exposure when desired mAs level achieved
- mAs Timers – monitors product of mA x exposure time
- Automatic Exposure Control Timers (AEC) – monitors exposure time
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Device & connection within circuit that modifies the incoming line power to produce thermionic emission from the filament wire inside the x-ray tube?
Step-Down Transformer &Filament Circuit Variable Resistance
- - Modified to about 3-5 A & 6-12 V by the step-down transformer
- - Controlled by the mA selector on the control console, but:
- •Not labeled by actual amperage (3-5 A)
- •Labeled in increments of mA, representing tube current (i.e., electrons crossing from cathode to anode)
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Device used to increase voltage from the autotransformer & supply it to the rectifier & x-ray tube?
Step-Up Transformer
- High voltage (large potential difference) needed to accelerate electrons from cathode to anode to produce x-ray photons
- Voltage on secondary side of step-up transformer ranges from 40-150 KV on most diagnostic units
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Device used to convert AC from step-up transformer to DC needed for x-ray tube operation?
Rectifier
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Device used to produce radiation (x-ray photons)?
X-Ray Tube
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Device (electromagnets) that employs the principles of electromagnetic induction to move the rotor inside the x-ray tube?
Stator
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Generators
___ ___ (full wave rectified):
- 2 pulses per Hz; 120 pulses per sec.
- 100% voltage ripple
Single Phase
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Generators
___ ___(full wave rectified):
- 6 pulses per Hz; 360 pulses per sec.
- 13%-25% voltage ripple (voltage in tube never falls below 75%-87& of peak kV set)
- Advantage: produces photons with approximately 35% greater average energy than single phase!
Low voltage ripple increases radiation quality because fewer low energy electrons pass from cathode to anode to produce x-rays
Three Phase
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High Frequency Generators
•Utilize AC & DC power converters to change incoming line voltage frequency from 60 Hz to the 6,000 Hz range
•When fully rectified, a 12-13 kHz waveform produced
•Advantage: less voltage ripple (as low as 1%) This increased frequency allows for a peak kV to be supplied to the x-ray tube almost continuously. Although more costly & complex, these generators are smaller in size, weigh less, & allow for more efficient x-ray production.
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Power Ratings
•Indicate the greatest load that a generator is capable of sending to the x-ray tube in ____ (__)
•Useful for comparing the capabilities of various generators
P = IV (Power = current x PD)
Watts = amperes x volts
Kilowatts (kW)
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Specially designed high frequency generators that start at high amperage (mA) & allow it to fall during exposure?
Falling Load Generators
- Maximizes the use of tube limits to shorten exposure times - - Removes the control of mA from the radiographer
- - Example:
- •Constant potential generator: 1000 mA x 500 ms = 500 mAs
•Falling load generator: Starts at 1800 mA & drops down to 1000 mA within 300 ms = 500 mAs
- •Result: 500 mAs achieved within 300 ms exposure time versus 500 ms
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Used on some portable units
- Operate by charging a series of capacitors instead of the x-ray tube
- When capacitors charged to the appropriate level, pressing the exposure switch triggers a discharge of the x-ray tube
- Current supplied by DC batteries (usually nickel-cadmium (NiCd)
- Batteries charged by plugging in portable machine to AC outlet
Advantage: can expose portable machine without having to plug unit into an outlet
Capacitor Discharge Generator
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- A device that measures the amount of radiation reaching the IR to automatically terminate the exposure time
- Functions by measuring a preset quantity of radiation & breaking the timing circuit•Utilizes ionization chambers
- Most AEC systems have 3 rectangular-shaped flat chambers
Advantage: technologist sets kV, but exposure time (& therefore mAs) controlled by the AEC to produce an exposure within the desired range for the part studied
Automatic Exposure Control
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•Flat, parallel plate ionization chambers positioned between the patient & the IR
- Radiolucent – 5 mm thick
- Calibrated upon instillation
•As x-radiation exits the patient, air atoms within the chambers are ionized, creating an electric charge proportional to the amount of radiation received. When the charge is sufficient, it terminates the timing circuit which in turn stops emission of photons from the tube.
Ionization Chambers
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•Required when using AEC because:
- Radiographer may activate the wrong AEC chambers
•Example: table AEC activated when doing chest against wall Bucky – beam would stay on & overexpose the patient because no radiation is reaching the table chambers
- Radiographer may choose the wrong chamber for exam
•Example: the center chamber is chosen when doing a PA chest (should be outer 2 chambers) - beam would stay on & overexpose the patient because the center chamber will not terminate exposure until enough radiation has penetrated the thoracic spine rather than the lungs
•Backup time set manually on the control console by the radiographer or automatically by the machine
- Should be set at no more than 150% of anticipated manual technique
- Maximum exposure per U.S. Public Law: 600 mAs
Backup Time
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