Free ABR Diagnostic Medical Physics Questions and Answers — Questions and Answers
Question 1: What is the primary mechanism of x-ray production in an x-ray tube?
- Bremsstrahlung radiation (Correct answer)
- Photoelectric effect
- Compton scattering
- Pair production
Correct answer: Bremsstrahlung radiation
In an x-ray tube, x-rays are primarily produced through Bremsstrahlung radiation, which means 'braking radiation' in German. This process occurs when high-speed electrons from the cathode are decelerated as they pass near the nuclei of the anode material, causing them to lose kinetic energy. This lost energy is then emitted as x-ray photons, forming the continuous x-ray spectrum.
Question 2: Which imaging modality uses Hounsfield units to represent tissue density?
- MRI
- CT (Correct answer)
- Ultrasound
- Nuclear Medicine
Correct answer: CT
Computed Tomography (CT) imaging uses Hounsfield units (HU) to quantify and represent tissue density. Each voxel in a CT image is assigned an HU value, where 0 HU represents water and -1000 HU represents air, allowing for precise differentiation of various tissues and pathologies based on their x-ray attenuation properties. Other modalities like MRI use different signal intensity scales.
Question 3: What does a modulation transfer function (MTF) measure in diagnostic imaging?
- Spatial resolution (Correct answer)
- Contrast resolution
- Temporal resolution
- Noise
Correct answer: Spatial resolution
The Modulation Transfer Function (MTF) is a quantitative measure used in diagnostic imaging to assess the system's ability to transfer details from the object to the image, which directly relates to spatial resolution. It describes how well an imaging system can reproduce different spatial frequencies (fine details) present in the object. A higher MTF value indicates better spatial resolution and image sharpness.
Question 4: Which of the following is the most effective method to reduce patient dose during fluoroscopic procedures?
- Increasing frame rate
- Increasing source-to-skin distance (Correct answer)
- Using a smaller focal spot
- Decreasing tube voltage
Correct answer: Increasing source-to-skin distance
Increasing the source-to-skin distance (SSD) during fluoroscopic procedures is an effective method to reduce patient dose. A larger SSD spreads the x-ray beam over a wider area before reaching the patient's skin, reducing the entrance skin dose due to the inverse square law. This helps to minimize the dose rate to the patient's skin while maintaining image quality.
Question 5: What is the purpose of beam filtration in diagnostic radiography?
- Enhance spatial resolution
- Improve image contrast
- Remove low-energy photons (Correct answer)
- Increase patient dose
Correct answer: Remove low-energy photons
Beam filtration in diagnostic radiography is primarily used to remove low-energy (soft) x-ray photons from the beam. These low-energy photons contribute significantly to patient dose because they are readily absorbed by superficial tissues without contributing to image formation. By filtering them out, the average energy of the beam increases, improving image quality and reducing patient exposure.
Free ABR Diagnostic Medical Physics Questions and Answers
What is the primary mechanism of x-ray production in an x-ray tube?