Bone Density Registry Review Exam with
150 Questions and verified Answers and
Rationales updated 2026
Section 1: Principles of Bone Densitometry (Questions 1–25)
1. Dual-energy X-ray absorptiometry (DXA) uses two distinct X-ray energy levels primarily to:
A) Increase radiation dose for better image quality
B) Differentiate bone from soft tissue based on differential attenuation
C) Eliminate the need for calibration phantoms
D) Measure cortical bone exclusively
Answer: B. Differentiate bone from soft tissue based on differential attenuation.
Rationale: DXA uses two X-ray energies (typically 40 keV and 70–100 keV). Soft tissue attenuates the
two energies differently, allowing calculation of bone mineral content independent of soft tissue
thickness. This dual-energy subtraction technique provides accurate areal bone mineral density
(g/cm²)-4-8.
2. What is the primary clinical application of DXA?
A) Evaluating muscle mass
B) Diagnosing osteoporosis and assessing fracture risk
C) Assessing joint health
D) Measuring bone size
Answer: B. Diagnosing osteoporosis and assessing fracture risk.
Rationale: DXA is the gold standard for measuring bone mineral density (BMD). T-scores from DXA
are used to diagnose osteoporosis (T ≤ –2.5), osteopenia (–2.5 < T < –1.0), and normal bone density
(T ≥ –1.0) according to WHO criteria-4-8.
3. Which anatomical sites are recommended for standard DXA measurement by the International
Society for Clinical Densitometry (ISCD)?
A) Skull and ribs
B) Lumbar spine (L1–L4) and proximal femur (total hip and femoral neck)
C) Tibia and fibula
D) Whole body only
Answer: B. Lumbar spine (L1–L4) and proximal femur (total hip and femoral neck).
Rationale: The ISCD recommends measuring both the spine and hip for initial diagnosis. Forearm
(33% radius) is used when spine or hip cannot be measured or interpreted (e.g., severe degenerative
changes, hyperparathyroidism, very obese patients)-4-8.
4. The T-score compares a patient’s BMD to:
A) The mean BMD of age-matched peers
B) The mean BMD of a young healthy adult reference population at peak bone mass
,C) The patient’s previous BMD measurement
D) The mean BMD of all patients in the facility
Answer: B. The mean BMD of a young healthy adult reference population at peak bone mass.
Rationale: The T-score compares a patient's BMD to the mean BMD of a young healthy adult
reference population at peak bone mass (age 20–29 years, same sex and ethnicity). Z-scores
compare to age-matched populations-4-8.
5. Which of the following is a limitation of DXA?
A) It measures volumetric bone density
B) It can distinguish cortical from trabecular bone
C) It measures areal BMD (g/cm²) and results can be artifactually elevated by degenerative changes
D) It requires high radiation doses
Answer: C. It measures areal BMD (g/cm²) and results can be artifactually elevated by
degenerative changes.
Rationale: DXA is a two-dimensional projection technique. It cannot distinguish cortical from
trabecular bone and is affected by artifacts such as osteophytes, sclerosis, or contrast material.
Degenerative changes, aortic calcification, or vertebral fractures can falsely elevate spine BMD-4-8.
6. The DXA scan acquisition mode (fast, standard, or slow) should be selected based on:
A) Patient preference
B) Patient size and thickness
C) Time of day
D) Insurance reimbursement
Answer: B. Patient size and thickness.
Rationale: Larger patients require higher energy or longer scan times to achieve adequate image
quality. Using an inappropriate mode can increase radiation exposure or reduce accuracy-4.
7. Which of the following best describes the radiation effective dose from a typical DXA scan
(spine and hip)?
A) Approximately 1–5 μSv (microsieverts)
B) Approximately 100–200 μSv
C) Approximately 1–5 mSv (millisieverts)
D) Approximately 10–20 mSv
Answer: A. Approximately 1–5 μSv (microsieverts).
Rationale: DXA uses very low radiation: spine ~1–3 μSv, hip ~0.5–1.5 μSv, total less than a single
chest X-ray (≈20 μSv) and far less than a mammogram (≈400 μSv)-4-8.
8. The precision error of DXA is defined as:
A) The accuracy of the machine
B) The coefficient of variation (CV%) of repeated measurements on the same patient under identical
conditions
C) The difference between T-score and Z-score
D) The radiation dose to the patient
Answer: B. The coefficient of variation (CV%) of repeated measurements on the same patient
under identical conditions.
,Rationale: Precision error is used to calculate the least significant change (LSC). A precision error of
1% means that a change of at least 2.77% (for 95% confidence) is required to be statistically
significant-4-8.
9. Which of the following is an absolute contraindication for DXA scanning?
A) Obesity
B) Pregnancy
C) Recent barium study
D) Metal implants
Answer: B. Pregnancy.
Rationale: Although radiation dose is very low, DXA is contraindicated in pregnant women due to
potential risk to the fetus-4-8. Recent barium or contrast studies are relative contraindications
requiring rescheduling.
10. What is the most common cause of falsely elevated BMD on spine DXA?
A) Osteoporosis
B) Degenerative changes (osteophytes, facet sclerosis), aortic calcification, or vertebral compression
fractures
C) Improper positioning
D) Low calcium intake
Answer: B. Degenerative changes (osteophytes, facet sclerosis), aortic calcification, or vertebral
compression fractures.
Rationale: These artifacts increase bone density artificially, potentially masking osteoporosis. The
technologist should review the image and may need to exclude affected vertebrae-4-8.
11. Which of the following is a potential cause of falsely low BMD on hip DXA?
A) Internal rotation of the leg
B) Rotation of the leg (failure to internally rotate the femur)
C) High calcium intake
D) Recent exercise
Answer: B. Rotation of the leg (failure to internally rotate the femur).
Rationale: Internal rotation aligns the femoral neck parallel to the table, providing a true profile.
Without rotation, the femoral neck appears elongated and BMD is underestimated-4-8.
12. In a pediatric DXA scan, which score should be used for interpretation?
A) T-score
B) Z-score
C) Raw BMD value only
D) FRAX score
Answer: B. Z-score.
Rationale: T-scores are not appropriate for children or adolescents because they have not yet
reached peak bone mass. Z-scores compare to age- and sex-matched pediatric reference data-5-8.
13. What percentage of the adult skeleton is cortical bone?
A) 20%
B) 50%
, C) 80%
D) 100%
Answer: C. 80%.
Rationale: The adult skeleton is about 80% cortical (compact) bone and 20% trabecular (cancellous)
bone. Cortical bone forms the outer shell of long bones; trabecular bone predominates in vertebral
bodies, the ends of long bones, and the pelvis-16.
14. Which skeletal site has the highest percentage of trabecular bone?
A) Lumbar spine (vertebral body)
B) Mid-shaft radius
C) Femoral neck
D) Calcaneus
Answer: A. Lumbar spine (vertebral body).
Rationale: Vertebral bodies are ~75% trabecular bone, which has higher metabolic activity and
shows early bone loss. The femoral neck is ~50% trabecular, 50% cortical-12-15.
15. Osteoblasts are derived from which precursor cells?
A) Mesenchymal stem cells
B) Hematopoietic stem cells
C) Osteoclasts
D) Chondrocytes
Answer: A. Mesenchymal stem cells.
Rationale: Osteoblasts differentiate from mesenchymal stem cells; osteoclasts come from
hematopoietic lineage (monocyte/macrophage)-12-15.
16. The RANK/RANKL/OPG system primarily regulates:
A) Osteoblast differentiation
B) Osteoclast activity
C) Collagen synthesis
D) Calcium absorption
Answer: B. Osteoclast activity.
Rationale: RANKL (on osteoblasts) binds RANK on osteoclast precursors → stimulates
osteoclastogenesis. OPG is a decoy receptor that inhibits this pathway. Denosumab is a monoclonal
antibody to RANKL-12-15-16.
17. Which hormone decreases bone resorption?
A) Parathyroid hormone (PTH)
B) Calcitonin
C) Cortisol
D) Thyroid hormone
Answer: B. Calcitonin.
Rationale: Calcitonin inhibits osteoclast activity. PTH increases resorption (at high sustained levels).
Cortisol and thyroid hormone promote bone loss-12.
150 Questions and verified Answers and
Rationales updated 2026
Section 1: Principles of Bone Densitometry (Questions 1–25)
1. Dual-energy X-ray absorptiometry (DXA) uses two distinct X-ray energy levels primarily to:
A) Increase radiation dose for better image quality
B) Differentiate bone from soft tissue based on differential attenuation
C) Eliminate the need for calibration phantoms
D) Measure cortical bone exclusively
Answer: B. Differentiate bone from soft tissue based on differential attenuation.
Rationale: DXA uses two X-ray energies (typically 40 keV and 70–100 keV). Soft tissue attenuates the
two energies differently, allowing calculation of bone mineral content independent of soft tissue
thickness. This dual-energy subtraction technique provides accurate areal bone mineral density
(g/cm²)-4-8.
2. What is the primary clinical application of DXA?
A) Evaluating muscle mass
B) Diagnosing osteoporosis and assessing fracture risk
C) Assessing joint health
D) Measuring bone size
Answer: B. Diagnosing osteoporosis and assessing fracture risk.
Rationale: DXA is the gold standard for measuring bone mineral density (BMD). T-scores from DXA
are used to diagnose osteoporosis (T ≤ –2.5), osteopenia (–2.5 < T < –1.0), and normal bone density
(T ≥ –1.0) according to WHO criteria-4-8.
3. Which anatomical sites are recommended for standard DXA measurement by the International
Society for Clinical Densitometry (ISCD)?
A) Skull and ribs
B) Lumbar spine (L1–L4) and proximal femur (total hip and femoral neck)
C) Tibia and fibula
D) Whole body only
Answer: B. Lumbar spine (L1–L4) and proximal femur (total hip and femoral neck).
Rationale: The ISCD recommends measuring both the spine and hip for initial diagnosis. Forearm
(33% radius) is used when spine or hip cannot be measured or interpreted (e.g., severe degenerative
changes, hyperparathyroidism, very obese patients)-4-8.
4. The T-score compares a patient’s BMD to:
A) The mean BMD of age-matched peers
B) The mean BMD of a young healthy adult reference population at peak bone mass
,C) The patient’s previous BMD measurement
D) The mean BMD of all patients in the facility
Answer: B. The mean BMD of a young healthy adult reference population at peak bone mass.
Rationale: The T-score compares a patient's BMD to the mean BMD of a young healthy adult
reference population at peak bone mass (age 20–29 years, same sex and ethnicity). Z-scores
compare to age-matched populations-4-8.
5. Which of the following is a limitation of DXA?
A) It measures volumetric bone density
B) It can distinguish cortical from trabecular bone
C) It measures areal BMD (g/cm²) and results can be artifactually elevated by degenerative changes
D) It requires high radiation doses
Answer: C. It measures areal BMD (g/cm²) and results can be artifactually elevated by
degenerative changes.
Rationale: DXA is a two-dimensional projection technique. It cannot distinguish cortical from
trabecular bone and is affected by artifacts such as osteophytes, sclerosis, or contrast material.
Degenerative changes, aortic calcification, or vertebral fractures can falsely elevate spine BMD-4-8.
6. The DXA scan acquisition mode (fast, standard, or slow) should be selected based on:
A) Patient preference
B) Patient size and thickness
C) Time of day
D) Insurance reimbursement
Answer: B. Patient size and thickness.
Rationale: Larger patients require higher energy or longer scan times to achieve adequate image
quality. Using an inappropriate mode can increase radiation exposure or reduce accuracy-4.
7. Which of the following best describes the radiation effective dose from a typical DXA scan
(spine and hip)?
A) Approximately 1–5 μSv (microsieverts)
B) Approximately 100–200 μSv
C) Approximately 1–5 mSv (millisieverts)
D) Approximately 10–20 mSv
Answer: A. Approximately 1–5 μSv (microsieverts).
Rationale: DXA uses very low radiation: spine ~1–3 μSv, hip ~0.5–1.5 μSv, total less than a single
chest X-ray (≈20 μSv) and far less than a mammogram (≈400 μSv)-4-8.
8. The precision error of DXA is defined as:
A) The accuracy of the machine
B) The coefficient of variation (CV%) of repeated measurements on the same patient under identical
conditions
C) The difference between T-score and Z-score
D) The radiation dose to the patient
Answer: B. The coefficient of variation (CV%) of repeated measurements on the same patient
under identical conditions.
,Rationale: Precision error is used to calculate the least significant change (LSC). A precision error of
1% means that a change of at least 2.77% (for 95% confidence) is required to be statistically
significant-4-8.
9. Which of the following is an absolute contraindication for DXA scanning?
A) Obesity
B) Pregnancy
C) Recent barium study
D) Metal implants
Answer: B. Pregnancy.
Rationale: Although radiation dose is very low, DXA is contraindicated in pregnant women due to
potential risk to the fetus-4-8. Recent barium or contrast studies are relative contraindications
requiring rescheduling.
10. What is the most common cause of falsely elevated BMD on spine DXA?
A) Osteoporosis
B) Degenerative changes (osteophytes, facet sclerosis), aortic calcification, or vertebral compression
fractures
C) Improper positioning
D) Low calcium intake
Answer: B. Degenerative changes (osteophytes, facet sclerosis), aortic calcification, or vertebral
compression fractures.
Rationale: These artifacts increase bone density artificially, potentially masking osteoporosis. The
technologist should review the image and may need to exclude affected vertebrae-4-8.
11. Which of the following is a potential cause of falsely low BMD on hip DXA?
A) Internal rotation of the leg
B) Rotation of the leg (failure to internally rotate the femur)
C) High calcium intake
D) Recent exercise
Answer: B. Rotation of the leg (failure to internally rotate the femur).
Rationale: Internal rotation aligns the femoral neck parallel to the table, providing a true profile.
Without rotation, the femoral neck appears elongated and BMD is underestimated-4-8.
12. In a pediatric DXA scan, which score should be used for interpretation?
A) T-score
B) Z-score
C) Raw BMD value only
D) FRAX score
Answer: B. Z-score.
Rationale: T-scores are not appropriate for children or adolescents because they have not yet
reached peak bone mass. Z-scores compare to age- and sex-matched pediatric reference data-5-8.
13. What percentage of the adult skeleton is cortical bone?
A) 20%
B) 50%
, C) 80%
D) 100%
Answer: C. 80%.
Rationale: The adult skeleton is about 80% cortical (compact) bone and 20% trabecular (cancellous)
bone. Cortical bone forms the outer shell of long bones; trabecular bone predominates in vertebral
bodies, the ends of long bones, and the pelvis-16.
14. Which skeletal site has the highest percentage of trabecular bone?
A) Lumbar spine (vertebral body)
B) Mid-shaft radius
C) Femoral neck
D) Calcaneus
Answer: A. Lumbar spine (vertebral body).
Rationale: Vertebral bodies are ~75% trabecular bone, which has higher metabolic activity and
shows early bone loss. The femoral neck is ~50% trabecular, 50% cortical-12-15.
15. Osteoblasts are derived from which precursor cells?
A) Mesenchymal stem cells
B) Hematopoietic stem cells
C) Osteoclasts
D) Chondrocytes
Answer: A. Mesenchymal stem cells.
Rationale: Osteoblasts differentiate from mesenchymal stem cells; osteoclasts come from
hematopoietic lineage (monocyte/macrophage)-12-15.
16. The RANK/RANKL/OPG system primarily regulates:
A) Osteoblast differentiation
B) Osteoclast activity
C) Collagen synthesis
D) Calcium absorption
Answer: B. Osteoclast activity.
Rationale: RANKL (on osteoblasts) binds RANK on osteoclast precursors → stimulates
osteoclastogenesis. OPG is a decoy receptor that inhibits this pathway. Denosumab is a monoclonal
antibody to RANKL-12-15-16.
17. Which hormone decreases bone resorption?
A) Parathyroid hormone (PTH)
B) Calcitonin
C) Cortisol
D) Thyroid hormone
Answer: B. Calcitonin.
Rationale: Calcitonin inhibits osteoclast activity. PTH increases resorption (at high sustained levels).
Cortisol and thyroid hormone promote bone loss-12.
