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Questions and Answers
What are the components of a fixed radiographic unit?
What are the components of a fixed radiographic unit?
- Designed for diagnostic radiographic work only (correct)
- Permit tilting of the table
- Produces high frequency output
- Operates on rechargeable batteries
Which of the following best describes mobile (portable) radiographic units?
Which of the following best describes mobile (portable) radiographic units?
- Fixed and cannot be moved
- Do not permit tilting of the table
- Operate on rechargeable batteries (correct)
- Designed for diagnostic radiographic work only
What is the primary purpose of a dedicated chest radiographic unit?
What is the primary purpose of a dedicated chest radiographic unit?
Designed specifically to perform radiographic chest x-rays.
What is the function of the operating console in a radiographic unit?
What is the function of the operating console in a radiographic unit?
What is the purpose of the glass envelope in a radiographic unit?
What is the purpose of the glass envelope in a radiographic unit?
What is the atomic number of tungsten?
What is the atomic number of tungsten?
What material is used for the stationary anode in X-ray tubes?
What material is used for the stationary anode in X-ray tubes?
What material is the rotating anode typically made of?
What material is the rotating anode typically made of?
Induction motor consists of the _____________
Induction motor consists of the _____________
Induction motor operates the ________ which spins the anode.
Induction motor operates the ________ which spins the anode.
An induction motor obtains the electric current in the rotor by ________ _________ from the magnetic field of the stator winding.
An induction motor obtains the electric current in the rotor by ________ _________ from the magnetic field of the stator winding.
Where is the induction motor located?
Where is the induction motor located?
Where is the rotor located in the induction motor?
Where is the rotor located in the induction motor?
What is the high-speed rotation range of the rotor?
What is the high-speed rotation range of the rotor?
What is the maximum allowable leakage radiation at 1 meter?
What is the maximum allowable leakage radiation at 1 meter?
X-rays are produced _____________ (equal intensity in all directions).
X-rays are produced _____________ (equal intensity in all directions).
What is the role of insulating oil in a radiographic unit?
What is the role of insulating oil in a radiographic unit?
What does Automatic Exposure Control (AEC) do?
What does Automatic Exposure Control (AEC) do?
The single function of an AEC is to eliminate the need for the radiographer to set an ______ _______.
The single function of an AEC is to eliminate the need for the radiographer to set an ______ _______.
Back-up times for AEC should be set at _______ of the anticipated manual exposure time.
Back-up times for AEC should be set at _______ of the anticipated manual exposure time.
What protects the patient from excessive radiation exposure due to AEC malfunctions?
What protects the patient from excessive radiation exposure due to AEC malfunctions?
Proper use of the density controls is accomplished when the configuration of the ______________________ cannot be adapted.
Proper use of the density controls is accomplished when the configuration of the ______________________ cannot be adapted.
Minimum response time in the region of __________.
Minimum response time in the region of __________.
MA should be _________ to permit longer AEC time.
MA should be _________ to permit longer AEC time.
What type of controls require the use of a technique chart?
What type of controls require the use of a technique chart?
What is the purpose of bottom shutters in collimators?
What is the purpose of bottom shutters in collimators?
What do upper shutters in collimators reduce?
What do upper shutters in collimators reduce?
What automatically collimates to IR size?
What automatically collimates to IR size?
Collimator results in some filtration of the beam =
Collimator results in some filtration of the beam =
What is the simplest of all beam-restricting devices?
What is the simplest of all beam-restricting devices?
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Study Notes
Components of Radiographic Units
- Fixed Units: Do not allow table tilting and are specifically designed for diagnostic radiographic work.
- Mobile Units: Operate on rechargeable batteries and utilize generators to produce high-frequency output.
- Dedicated Chest Units: Specifically designed for performing radiographic chest x-rays.
Operating Console
- Controls enable selection of kVp, mA, exposure time, and AEC (Automatic Exposure Control).
- Includes indicators for tube energization (e.g., bell, beeper, tube current meter).
- Features a power switch to turn off the unit.
Glass Envelope
- Made of leaded pyrex glass, characterized by a high melting point.
- Protects internal tube components and maintains a vacuum.
- Contains a window port where x-rays are directed.
Tungsten Properties
- Tungsten's atomic number is 74, making it a key material in radiography.
- Stationary Anode: Constructed from rhenium-alloyed tungsten to provide greater elasticity under heat expansion.
- Rotating Anode: Made of molybdenum, providing weight reduction benefits.
Induction Motor Components
- Consists of a stator with windings and a rotor to drive the anode.
- The rotor spins the anode for increased surface area, enhancing heat capacity and tube efficiency.
- Operates through electromagnetic induction, utilizing the stator's magnetic field.
Rotor and Speed
- The rotor is located inside the stator and the vacuum envelope, attached to the anode disk.
- Electromagnetic fields cause the rotor to spin at a high speed of 10,000 - 12,000 rpm.
Radiation Safety
- Leakage radiation limit is 100 mR/hr at 1 meter, ensuring patient safety.
- X-rays are produced isotropically, meaning they have equal intensity in all directions.
Insulating Oil
- Helps with cooling and is located outside the glass envelope.
- Contributes to inherent filtration of x-rays.
Automatic Exposure Control (AEC)
- AEC is designed to ensure a consistent exposure to the IR, compensating for patient variations.
- The primary function of AEC is to eliminate manual exposure time settings by the radiographer.
- Backup time for AEC should not exceed 150% of the expected manual exposure time.
- Includes a backup timer to prevent excessive radiation exposure during AEC malfunctions.
Exposure Time Management
- Proper use of density controls is essential when ionization chamber cells cannot be adapted for positioning.
- The minimum response time for AEC is approximately 0.001 seconds.
- Reducing mA allows for a longer AEC time during exposure.
Manual Exposure Controls
- Require a technique chart and involve determining exposure factors based on part size or thickness.
- AEC feature is inactivated under manual controls.
Collimator and Beam Restriction
- Bottom Shutters: Reduce penumbra along the periphery of the x-ray beam.
- Upper Shutters: Reduce off-focus (stem) radiation.
- Positive Beam Limitation (PBL): Automatically collimate the beam to match IR size.
- Provides some filtration of the x-ray beam, equating to 1 mm of aluminum.
Diaphragm and Cones
- Aperture Diaphragm: A flat lead sheet with a central opening, attached to the x-ray tube port; the simplest beam-restricting device.
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