DXA (Dual-Energy X-ray Absorptiometry) Comprehensive
Exam – 200 Questions with Answers and Short Rationales
(2026/2027)
Overview:
This comprehensive exam guide is designed for students, radiology technologists, and healthcare
professionals studying DXA (Dual-Energy X-ray Absorptiometry). It covers all critical areas
of DXA practice, including physics, positioning, scanning techniques, artifacts, quality
control, BMD interpretation, and body composition analysis.
The 200 questions are divided into six sections:
1. DXA Physics & Principles (1–30): Covers energy types, beam technology, and
fundamental physics concepts.
2. Positioning & Scanning Protocols (31–60): Focuses on proper patient positioning, ROI
selection, and scan protocols.
3. Artifacts & Errors (61–90): Identifies common scan artifacts, errors, and methods to
minimize them.
4. Quality Control & Calibration (91–120): Addresses QC procedures, phantom use,
LSC, and machine drift.
5. BMD Interpretation (121–150): Includes T-score, Z-score, osteoporosis diagnosis, and
fracture risk assessment.
6. Body Composition & Total Body DXA (151–200): Discusses fat mass, lean mass,
appendicular lean mass, sarcopenia, and regional fat assessment.
Each question includes the correct answer in bold and a rationale, making this an ideal
resource for exam preparation, review, and self-assessment.
SECTION 1 — DXA PHYSICS
1. What type of energy does DXA primarily use for bone density measurement?
A. Gamma rays
B. Dual-energy X-rays
,C. Ultrasound
D. Proton beams
Rationale: DXA uses two X-ray energies to differentiate tissue types.
2. Dual-energy in DXA refers to:
A. Two scans of different speeds
B. Two X-ray beam energies
C. Two detectors
D. Two body segments
Rationale: “Dual-energy” means two distinct photon energies are emitted and analyzed.
3. Beam type used in modern fan-beam scanners:
A. Pencil beam
B. Narrow beam
C. Wide-angle fan beam
D. Cone beam
Rationale: Newer DXA machines primarily use wide-angle fan-beam technology for faster
scans.
4. The purpose of dual energy is to distinguish between:
A. Bone and fat
B. Fat and muscle
C. Bone and soft tissue
D. Air and soft tissue
Rationale: DXA separates bone density from surrounding soft tissue using attenuation
differences at two energies.
5. What does X-ray attenuation primarily depend on?
A. Temperature
B. Patient hydration
C. Tissue density and thickness
,D. Patient age
Rationale: Denser and thicker tissue absorbs more X-rays.
6. The photoelectric effect is most significant in which tissue type?
A. Fat
B. Muscle
C. Bone
D. Skin
Rationale: Bone has higher atomic number, increasing photoelectric absorption.
7. DXA uses two energy peaks to:
A. Speed up scanning
B. Reduce radiation exposure
C. Separate bone from soft tissue
D. Improve image color
Rationale: Two energies allow mathematical differentiation of tissues.
8. Which element in bone contributes most to X-ray absorption?
A. Sodium
B. Calcium
C. Iron
D. Carbon
Rationale: Calcium’s high atomic number causes high attenuation.
9. A key advantage of fan-beam DXA over pencil-beam is:
A. Lower radiation
B. Faster scan time
C. No magnification
, D. Higher patient dose
Rationale: Fan-beam scans multiple slices at once, speeding scans.
10. Pencil-beam scanners are known for:
A. Less magnification error
B. Higher radiation
C. Faster scans
D. Lower precision
Rationale: The narrow beam reduces geometric distortion.
11. DXA uses which principle to compute BMD?
A. MRI resonance
B. Differential X-ray attenuation
C. Electrical impedance
D. Ultrasound reflection
Rationale: It analyzes attenuation changes at two energies.
12. What does BMD stand for?
A. Bone mass detection
B. Bone mineral density
C. Bone measurement depth
D. Bone metabolic data
Rationale: DXA measures mineral density in g/cm².
13. DXA radiation dose is closest to:
A. CT abdomen
B. Chest X-ray
C. A few microsieverts
Exam – 200 Questions with Answers and Short Rationales
(2026/2027)
Overview:
This comprehensive exam guide is designed for students, radiology technologists, and healthcare
professionals studying DXA (Dual-Energy X-ray Absorptiometry). It covers all critical areas
of DXA practice, including physics, positioning, scanning techniques, artifacts, quality
control, BMD interpretation, and body composition analysis.
The 200 questions are divided into six sections:
1. DXA Physics & Principles (1–30): Covers energy types, beam technology, and
fundamental physics concepts.
2. Positioning & Scanning Protocols (31–60): Focuses on proper patient positioning, ROI
selection, and scan protocols.
3. Artifacts & Errors (61–90): Identifies common scan artifacts, errors, and methods to
minimize them.
4. Quality Control & Calibration (91–120): Addresses QC procedures, phantom use,
LSC, and machine drift.
5. BMD Interpretation (121–150): Includes T-score, Z-score, osteoporosis diagnosis, and
fracture risk assessment.
6. Body Composition & Total Body DXA (151–200): Discusses fat mass, lean mass,
appendicular lean mass, sarcopenia, and regional fat assessment.
Each question includes the correct answer in bold and a rationale, making this an ideal
resource for exam preparation, review, and self-assessment.
SECTION 1 — DXA PHYSICS
1. What type of energy does DXA primarily use for bone density measurement?
A. Gamma rays
B. Dual-energy X-rays
,C. Ultrasound
D. Proton beams
Rationale: DXA uses two X-ray energies to differentiate tissue types.
2. Dual-energy in DXA refers to:
A. Two scans of different speeds
B. Two X-ray beam energies
C. Two detectors
D. Two body segments
Rationale: “Dual-energy” means two distinct photon energies are emitted and analyzed.
3. Beam type used in modern fan-beam scanners:
A. Pencil beam
B. Narrow beam
C. Wide-angle fan beam
D. Cone beam
Rationale: Newer DXA machines primarily use wide-angle fan-beam technology for faster
scans.
4. The purpose of dual energy is to distinguish between:
A. Bone and fat
B. Fat and muscle
C. Bone and soft tissue
D. Air and soft tissue
Rationale: DXA separates bone density from surrounding soft tissue using attenuation
differences at two energies.
5. What does X-ray attenuation primarily depend on?
A. Temperature
B. Patient hydration
C. Tissue density and thickness
,D. Patient age
Rationale: Denser and thicker tissue absorbs more X-rays.
6. The photoelectric effect is most significant in which tissue type?
A. Fat
B. Muscle
C. Bone
D. Skin
Rationale: Bone has higher atomic number, increasing photoelectric absorption.
7. DXA uses two energy peaks to:
A. Speed up scanning
B. Reduce radiation exposure
C. Separate bone from soft tissue
D. Improve image color
Rationale: Two energies allow mathematical differentiation of tissues.
8. Which element in bone contributes most to X-ray absorption?
A. Sodium
B. Calcium
C. Iron
D. Carbon
Rationale: Calcium’s high atomic number causes high attenuation.
9. A key advantage of fan-beam DXA over pencil-beam is:
A. Lower radiation
B. Faster scan time
C. No magnification
, D. Higher patient dose
Rationale: Fan-beam scans multiple slices at once, speeding scans.
10. Pencil-beam scanners are known for:
A. Less magnification error
B. Higher radiation
C. Faster scans
D. Lower precision
Rationale: The narrow beam reduces geometric distortion.
11. DXA uses which principle to compute BMD?
A. MRI resonance
B. Differential X-ray attenuation
C. Electrical impedance
D. Ultrasound reflection
Rationale: It analyzes attenuation changes at two energies.
12. What does BMD stand for?
A. Bone mass detection
B. Bone mineral density
C. Bone measurement depth
D. Bone metabolic data
Rationale: DXA measures mineral density in g/cm².
13. DXA radiation dose is closest to:
A. CT abdomen
B. Chest X-ray
C. A few microsieverts
