CRI Contrast & Exposure Parameters 3 ā Questions and Answers
Question 1: The inverse square law in radiography states that radiation intensity varies:
- Directly with distance
- Inversely with the square of the distance (Correct answer)
- Directly with the square of the distance
- Inversely with distance
Correct answer: Inversely with the square of the distance
The inverse square law states that intensity is proportional to 1/dĀ², so doubling the distance reduces intensity to one-quarter.
Question 2: In industrial radiography, what is the primary purpose of using lead screens with X-ray film?
- To increase scatter radiation and improve contrast
- To filter scatter radiation and intensify the direct beam effect (Correct answer)
- To protect the film from physical damage
- To reduce the required kVp setting
Correct answer: To filter scatter radiation and intensify the direct beam effect
Lead screens absorb scatter radiation (improving contrast) and emit photoelectrons that intensify the film's response to the primary beam.
Question 3: A radiograph of a weld shows an image that is overall too dark (overexposed). To correct this while maintaining the same geometry, the interpreter would recommend:
- Increasing mAs or decreasing SFD
- Decreasing mAs or increasing SFD (Correct answer)
- Switching to a faster film class only
- Reducing the kVp while increasing mAs proportionally
Correct answer: Decreasing mAs or increasing SFD
Reducing mAs decreases the number of X-ray photons reaching the film, and increasing SFD reduces intensity per the inverse square law, both lightening the radiograph.
Question 4: In computed radiography (CR), the exposure indicator value primarily reflects:
- The radiation dose delivered to the patient or object
- The amount of radiation that exposed the imaging plate (Correct answer)
- The processed image contrast setting
- The sensitivity class of the phosphor screen
Correct answer: The amount of radiation that exposed the imaging plate
The exposure indicator (EI) in CR systems is a measure of the radiation exposure received by the imaging plate, used to assess if exposure was adequate.
Question 5: Which of the following conditions would most reduce radiographic contrast in a steel weldment?
- Using very low kVp with a fine-grain film
- Using high kVp with a fast, coarse-grain film (Correct answer)
- Increasing exposure time while reducing mA
- Using a small focal spot with a long SFD
Correct answer: Using high kVp with a fast, coarse-grain film
High kVp reduces differential absorption (lowering subject contrast), and coarse-grain film has lower inherent contrast, both combining to reduce overall radiographic contrast.
Question 6: When radiographing a tapered weld with significant thickness variation, the most appropriate technique to achieve acceptable density across the entire area is:
- Use the lowest possible kVp for maximum contrast
- Use a higher kVp or compensating filters to accommodate thickness variation (Correct answer)
- Perform multiple exposures at different film placements
- Increase mAs to its maximum value
Correct answer: Use a higher kVp or compensating filters to accommodate thickness variation
Higher kVp increases the exposure latitude, allowing acceptable density across a range of thicknesses in a single exposure.
Question 7: The H&D (Hurter and Driffield) curve of a radiographic film is used to:
- Determine the safe handling temperature for film storage
- Relate optical density to relative exposure and determine contrast characteristics (Correct answer)
- Calculate the required source-to-film distance
- Measure the radiation energy spectrum of the source
Correct answer: Relate optical density to relative exposure and determine contrast characteristics
The H&D curve (characteristic curve) plots optical density versus log relative exposure, revealing the film's speed, contrast (gamma), and latitude.
CRI Contrast & Exposure Parameters 3
The inverse square law in radiography states that radiation intensity varies: