DHA Diagnostic Imaging & Radiology 1 — Questions and Answers
Question 1: Which unit is used to measure radiation absorbed dose in tissue?
- Becquerel
- Gray (Gy) (Correct answer)
- Sievert (Sv)
- Roentgen
Correct answer: Gray (Gy)
The Gray (Gy) is the SI unit of absorbed dose, defined as one joule of radiation energy absorbed per kilogram of tissue.
Question 2: What does the acronym ALARA stand for in radiation protection?
- As Low As Reasonably Achievable (Correct answer)
- Always Limit All Radiation Amounts
- As Limited As Reasonably Applied
- Avoid Large Areas of Radiation Always
Correct answer: As Low As Reasonably Achievable
ALARA (As Low As Reasonably Achievable) is the guiding principle of radiation protection, aiming to minimize exposure while maintaining diagnostic quality.
Question 3: Which imaging modality uses magnetic fields and radiofrequency waves to produce images?
- CT scan
- PET scan
- MRI (Correct answer)
- Fluoroscopy
Correct answer: MRI
MRI (Magnetic Resonance Imaging) uses strong magnetic fields and radiofrequency pulses to align and then perturb hydrogen nuclei, generating detailed soft-tissue images.
Question 4: The standard diagnostic chest radiograph is taken in which projection?
- Lateral
- Oblique
- Anteroposterior (AP)
- Posteroanterior (PA) (Correct answer)
Correct answer: Posteroanterior (PA)
The standard chest X-ray is taken in the posteroanterior (PA) projection with the patient standing and the X-ray beam passing from back to front, minimizing cardiac magnification.
Question 5: Which contrast agent is most commonly used to enhance MRI images?
- Barium sulfate
- Iodinated contrast
- Gadolinium (Correct answer)
- Technetium-99m
Correct answer: Gadolinium
Gadolinium-based contrast agents (GBCAs) are the standard MRI contrast agents, shortening T1 relaxation times and improving tissue differentiation.
Question 6: Which type of ionizing radiation has the greatest penetrating power?
- Alpha particles
- Beta particles
- Gamma rays (Correct answer)
- Protons
Correct answer: Gamma rays
Gamma rays are high-energy photons with the greatest penetrating power, requiring dense materials like lead or thick concrete for adequate shielding.
Question 7: In nuclear medicine, the 'half-life' of a radiopharmaceutical refers to:
- The time for half the radioactive atoms to decay (Correct answer)
- The time to deliver half the therapeutic dose
- Half the energy emitted per scan
- The time for half the drug to be metabolized
Correct answer: The time for half the radioactive atoms to decay
Physical half-life is the time required for half of the radioactive atoms in a sample to undergo decay, a fixed property of each radionuclide.
DHA Diagnostic Imaging & Radiology 1
Which unit is used to measure radiation absorbed dose in tissue?