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Questions and Answers
What material is used for the spacer cone in dental X-ray equipment?
What is the purpose of a sheet of aluminium in X-ray equipment?
Which of the following factors can be controlled in an X-ray machine?
How does increasing the kV affect the continuous spectrum of X-rays?
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What is the recommended thickness of the aluminium filter for X-ray sets operating at 70 kV or less?
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Which of the following accurately describes how X-rays are produced in the glass tube?
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What happens when an electron is slowed down or deflected by a nucleus?
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What is the main function of the X-ray tube's copper block?
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What is produced only when X-ray equipment is operating at 70kV or more?
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How does increasing the milliampere (mA) affect the X-ray image?
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What is the function of the collimator in a dental X-ray unit?
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What is E-max in the context of X-ray production?
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What effect does a higher kV have on patient exposure during an X-ray?
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What is one of the main components of a dental X-ray unit?
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What is characterized by the atomic number (Z) of a substance?
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What happens to the X-ray production graph when combined with continuous and characteristic spectrum at 100kV?
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What is the role of the tungsten target in the X-ray tube?
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What does a longer exposure time in X-ray imaging provide?
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What is the recommended focal spot distance (fsd) according to the 2001 guidelines?
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What effect does a long focal spot distance (fsd) have on patient radiation exposure?
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What is the purpose of the step-up transformer in an X-ray machine?
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Why are low energy X-ray photons considered more dangerous than high energy ones?
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What is a characteristic spectrum in X-ray production?
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What is the recommended collimator dimension for reducing patient dose?
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At what voltage does the alternative method of producing X-rays occur?
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What is the primary reason for surrounding the X-ray tube with oil?
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Why should a dentist never hold the X-ray tube head during exposure?
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What percentage of the X-ray production process is actually converted into X-rays?
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Study Notes
Rectangular Spacer Cone
- Metallic and acts as a collimator
- Determines the distance between the target and the patient (focus-to-skin distance).
Current Dental X-ray Equipment Recommendations
-
Aluminium filter thickness:
- 1.5mm for machines operating at 70kV or less.
- 2.5mm for machines operating at more than 70kV.
-
Collimator:
- Recommended to use rectangular collimation.
- Reduces dose by 50%.
- Dimensions: 40mm x 50mm.
-
Focus-to-skin distance (FSD):
- 200mm fsd is recommended.
- 300mm fsd significantly reduces dose.
- Operating range: 60-70kV
Removing Low Energy Photons
- Aluminium sheet absorbs and filters out the lowest energy photons.
- Low energy photons lack penetrating power and cannot pass through the aluminium.
X-ray Production
- Process: An electric current heats the filament, boiling off electrons which are then accelerated towards the tungsten target.
-
Outcome:
- Produces a continuous spectrum of X-rays, with a range of energies.
- Generates significant heat, conducted away by the copper block.
Continuous Spectrum
-
Higher kV:
- Produces more photons in the continuous spectrum.
- Increases the energy of the photons.
Controlling X-ray Machine
- Voltage (kV): Set/fixed level.
- Milliamperage (mA): Set/fixed level.
- Time: Adjustable, depending on the anatomical region and its thickness.
Characteristic Spectrum
- Produces x-ray photons of specific energies, characteristic of tungsten.
- Only generated when the machine operates at 70kV or more.
X-ray Unit Components
- Tube head
- Glass X-ray tube
- Filament (cathode)
- Tungsten target (anode)
- Copper block
- Oil
- Step-up transformer
- Spacer cone
Density of Substances
- Described by atomic number (Z), which represents the number of protons in the nucleus.
Collimator & Spacer Cone Functions
- Collimator: Limits the size of the x-ray beam.
- Spacer cone: Determines the focus-to-skin distance and directs the beam.
mA & Time Relationship
- Together, they determine the quantity of electrons leaving the tube and the quantity of photons produced.
- Higher mA: Darker image (overexposed).
- Lower mA: Brighter image (underexposed).
- Longer exposure time provides more radiation exposure.
X-ray Spectrum Graph
- Characteristic spectrum has peaks representing a smaller number of X-rays produced.
kV Impact
- Determines: Energy of photons and penetrating power.
- Affects: Film contrast (lower kV = higher contrast).
-
High kV:
- More photons penetrate the patient, reducing absorption and patient dose.
- Low kV: Useful for visualizing foreign objects in the body.
X-ray Tube Function
- Where X-rays are produced.
Combining Spectra at Target
- X-rays produced by both continuous and characteristic spectra result in many low energy photons, which are dangerous and have little diagnostic value.
X-ray Definition
- A wave packet of energy (photons) that can penetrate human tissue.
E-max
- The maximum energy of a single X-ray photon.
- Higher kV produces more photons and increases E-max.
X-ray Production Efficiency
- Inefficient process: 99% heat, 1% X-ray.
Overall Photon Energy
- Determined by the energy of the incoming electron, which is controlled by the voltage applied.
- Higher voltage increases the energy of the electrons and the photons produced.
'Focus-to-Skin Distance' (FSD)
- Distance from the focal spot on the target to the patient's skin (end of the spacer cone).
-
Longer FSD:
- Smaller beam.
- Less irradiation of the patient.
Low vs. High Energy Photons
-
Low energy:
- Low penetrating power.
- Absorbed in soft tissues.
- More dangerous.
-
High energy:
- Pass through patient and hit the film.
- Diagnostically useful.
Alternative X-ray Production Method
- Incoming electron interacts with an orbiting electron in the tungsten atom, knocking it out.
- An electron from an adjacent shell fills the vacancy, releasing energy as an X-ray photon.
- This method produces a characteristic spectrum, with specific energy levels.
- Occurs at 70kV or more.
X-ray Machine Safety Precautions
- Exposure timer switch should be continuously depressed by the operator.
- Audible and visible warning signs during exposure.
Stray Photons
- Some X-ray photons leave the target in directions other than the primary beam.
- This is why you should never hold the tubehead during an exposure.
Why Higher kV is Better
- More photons penetrate the patient, reducing absorption and patient dose.
Step-up Transformer Function
- Increases the mains voltage (240 volts) to the high voltage needed for the X-ray tube (60-70kV).
Short FSD Disadvantages
- The beam diverges, irradiating a wider area of the face.
Oil Surrounding the X-ray Tube
- Facilitates heat removal.
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Description
Explore the latest recommendations for dental X-ray equipment, including details on collimation, filtering, and focus-to-skin distance. This quiz covers critical specifications like aluminum filter thickness and operating ranges for optimal patient safety.
