DHA Diagnostic Imaging & Radiology 5 — Questions and Answers
Question 1: Which nuclear medicine scan is most appropriate for detecting occult bony metastases in a cancer patient?
- Tc-99m bone scan (Correct answer)
- Gallium-67 scan
- FDG-PET scan
- MIBG scan
Correct answer: Tc-99m bone scan
Tc-99m methylene diphosphonate bone scintigraphy is sensitive for osteoblastic metastatic lesions and is widely used for whole-body skeletal survey.
Question 2: In computed tomography, the Hounsfield Unit (HU) value for simple water is:
- -1000 HU
- 0 HU (Correct answer)
- +100 HU
- +1000 HU
Correct answer: 0 HU
The Hounsfield scale sets water at 0 HU as the reference point, with air at -1000 HU and cortical bone at approximately +1000 HU.
Question 3: Which ultrasound artifact is caused by a highly reflective structure that prevents sound from passing through, creating a dark region behind it?
- Posterior acoustic enhancement
- Acoustic shadowing (Correct answer)
- Reverberation artifact
- Side lobe artifact
Correct answer: Acoustic shadowing
Acoustic shadowing occurs when structures like gallstones or bones reflect nearly all the ultrasound beam, creating a shadow of no signal distal to them.
Question 4: A 'Hampton's hump' on chest radiograph is associated with:
- Lung abscess
- Pulmonary embolism with infarction (Correct answer)
- Pneumothorax
- Aortic dissection
Correct answer: Pulmonary embolism with infarction
Hampton's hump is a pleural-based, wedge-shaped opacity caused by pulmonary infarction secondary to embolic occlusion of a pulmonary artery.
Question 5: What is the recommended maximum cumulative dose of ionizing radiation considered acceptable for occupational workers per year according to international radiation protection standards?
- 1 mSv/year
- 5 mSv/year
- 20 mSv/year (Correct answer)
- 50 mSv/year
Correct answer: 20 mSv/year
The ICRP recommends an effective dose limit of 20 mSv per year averaged over 5 years for occupational radiation workers.
Question 6: On fluoroscopy during a barium swallow, a 'bird beak' tapering of the lower esophagus is most consistent with:
- Esophageal carcinoma
- Achalasia (Correct answer)
- Zenker's diverticulum
- Esophageal web
Correct answer: Achalasia
Achalasia causes failure of the lower esophageal sphincter to relax, producing smooth, symmetric tapering resembling a bird's beak on barium studies.
Question 7: Which imaging finding on CT abdomen is most diagnostic of acute appendicitis?
- Dilated loops of small bowel
- Appendix diameter >6 mm with periappendiceal fat stranding (Correct answer)
- Free intraperitoneal air
- Wall thickening of the terminal ileum
Correct answer: Appendix diameter >6 mm with periappendiceal fat stranding
An appendiceal diameter exceeding 6 mm with surrounding inflammatory fat stranding on CT has high sensitivity and specificity for acute appendicitis.
DHA Diagnostic Imaging & Radiology 5
Which nuclear medicine scan is most appropriate for detecting occult bony metastases in a cancer patient?