ISCD Certified Bone Densitometry Technologist (CBDT®) — Questions and Answers

Question 1: What type of joint connects the femur and pelvis?

Ball-and-socket joint (Correct answer)
Gliding joint
Pivot joint
Hinge joint

Correct answer: Ball-and-socket joint

The joint connecting the femur (thigh bone) and the pelvis (specifically the acetabulum) is a ball-and-socket joint, known as the hip joint. This type of synovial joint allows for a wide range of motion in multiple planes, including flexion, extension, abduction, adduction, rotation, and circumduction. Its structure provides both mobility and stability.

Question 2: What does a T-score represent?

Daily bone change
Fat percentage
Calcium intake
Comparison to young adult average (Correct answer)

Correct answer: Comparison to young adult average

A T-score in DEXA scanning compares a patient's Bone Mineral Density (BMD) to the average BMD of a healthy young adult of the same sex at peak bone mass. This score is used to diagnose osteoporosis or osteopenia in postmenopausal women and men over 50. It helps assess the risk of fractures based on bone density relative to a healthy reference population.

Question 3: Which of the following findings on patient intake would prompt the technologist to select the forearm as the preferred scan site instead of the spine or hip?

Body weight under 100 lbs
Bilateral hip replacements and severe lumbar scoliosis (Correct answer)
Recent calcium supplement use
History of hypertension

Correct answer: Bilateral hip replacements and severe lumbar scoliosis

When both primary DEXA sites (hip and spine) are compromised by implants or anatomical abnormalities, the non-dominant forearm becomes the appropriate alternative site.

Question 4: A 'total body less head' (TBLH) measurement is frequently reported in pediatric DXA because:

The head contains a disproportionately large amount of bone mass in children, skewing whole-body BMD (Correct answer)
Children cannot hold their heads still during the scan
Head bone density is not affected by growth hormone
Radiation to the cranium is prohibited in patients under 18

Correct answer: The head contains a disproportionately large amount of bone mass in children, skewing whole-body BMD

In children, the skull contributes disproportionately to total BMD; excluding the head reduces variability and improves the sensitivity of the measurement for assessing skeletal growth and disease.

Question 5: A patient with severe obesity (BMI > 40) presents for a DXA body composition scan. The main technical limitation to address is:

The DXA software cannot generate a body composition report above a BMI of 35
The scan will overestimate bone mineral density due to beam hardening
The patient may exceed the table weight limit and scan field width, causing tissue truncation (Correct answer)
The radiation dose will be too high for the patient to receive the scan

Correct answer: The patient may exceed the table weight limit and scan field width, causing tissue truncation

Obese patients may exceed the weight limit of the DXA table (commonly 350–450 lbs) and may be wider than the scan field, leading to truncation artifacts that invalidate body composition results.

Question 6: A patient's hip scan shows asymmetric positioning artifacts. Which step should the technologist take before issuing the report?

Use only Ward's triangle for the final BMD value
Note the artifact in the report and rescan if the rotation exceeds acceptable limits (Correct answer)
Apply a 5% correction factor to the T-score
Average both hips and report that value

Correct answer: Note the artifact in the report and rescan if the rotation exceeds acceptable limits

Rotation artifacts can falsely alter BMD; the scan should be repeated if positioning errors exceed acceptable limits, and artifacts must be documented.

Question 7: Which of the following actions demonstrates proper infection control during DEXA patient preparation?

Asking patients with illness to wear a lead apron
Wiping the scan table with an approved disinfectant between patients (Correct answer)
Using a lead apron as a physical barrier between patients
Wearing gloves only when the patient has an open wound

Correct answer: Wiping the scan table with an approved disinfectant between patients

Disinfecting the scan table surface between patients is standard infection control practice in all diagnostic imaging environments.

Question 8: When documenting assessment findings in DEXA practice, which approach is MOST appropriate?

Use jargon only experts understand
Record objective findings, measurements, and observations factually (Correct answer)
Include only positive findings
Summarize verbally without written documentation

Correct answer: Record objective findings, measurements, and observations factually

Assessment documentation must be objective, factual, and comprehensive.

Question 9: What is the primary reason DEXA uses dual-energy X-ray rather than single-energy X-ray?

To increase image resolution
To shorten scan acquisition time
To reduce patient radiation dose
To differentiate bone mineral from soft tissue (Correct answer)

Correct answer: To differentiate bone mineral from soft tissue

Dual-energy X-ray allows mathematical subtraction of soft tissue attenuation, isolating bone mineral density values accurately.

Question 10: A DEXA system's daily QC phantom result falls outside ±1.5% of the long-term average. What is the correct action?

Repeat the phantom scan 10 times and use the average
Reset the system and proceed normally
Do not scan patients; investigate and contact the manufacturer (Correct answer)
Scan patients and document the variance

Correct answer: Do not scan patients; investigate and contact the manufacturer

A phantom result outside the ±1.5% control limit requires halting patient scans and investigating the cause before proceeding.

Question 11: What is the effect of residual metal (e.g., an IUD) in the lumbar spine scan field during DXA?

It decreases BMD values by absorbing photons
It attenuates the X-ray beam and artificially increases BMD at that region (Correct answer)
It has no measurable effect on the scan
It only affects the scan if it is larger than 2 cm

Correct answer: It attenuates the X-ray beam and artificially increases BMD at that region

Metal objects attenuate the DXA beam more than bone, causing the software to overestimate BMD in the overlapping region.

Question 12: Which condition requires DEXA monitoring and is caused by elevated endogenous cortisol due to a pituitary or adrenal tumor?

Fibrous dysplasia
Cushing's syndrome (Correct answer)
Paget's disease of bone
Hyperparathyroidism

Correct answer: Cushing's syndrome

Cushing's syndrome causes endogenous glucocorticoid excess, leading to secondary osteoporosis that requires BMD monitoring via DEXA.

Question 13: Which three compartments does a standard DXA body composition scan quantify?

Water, protein, and mineral
Lean mass, fat mass, and bone mineral content (Correct answer)
Intracellular fluid, extracellular fluid, and bone
Visceral fat, subcutaneous fat, and muscle mass

Correct answer: Lean mass, fat mass, and bone mineral content

DXA partitions the body into lean soft tissue mass, fat mass, and bone mineral content (BMC), making it a three-compartment model.

Question 14: A postmenopausal woman's lumbar spine T-score is -2.7. According to WHO criteria, how should this be classified?

Normal bone density
Osteopenia
Severe osteoporosis
Osteoporosis (Correct answer)

Correct answer: Osteoporosis

A T-score of -2.5 or below is classified as osteoporosis by WHO criteria.

Question 15: A patient's follow-up lumbar spine BMD increased from 0.910 to 0.932 g/cm². The facility's LSC is 0.030 g/cm². How should this change be reported?

Significant increase in BMD
Significant decrease in BMD
No significant change — within measurement error (Correct answer)
Cannot be determined without T-scores

Correct answer: No significant change — within measurement error

A change of 0.022 g/cm² is below the LSC of 0.030 g/cm², so it falls within measurement error and is not statistically significant.

Question 16: What is the primary clinical significance of a high fat mass index (FMI) combined with a low lean mass index (LMI) on DXA body composition analysis?

It suggests sarcopenic obesity, a condition associated with increased metabolic and functional risk (Correct answer)
It is a normal finding in elite endurance athletes
It confirms a diagnosis of anorexia nervosa
It indicates primary hyperparathyroidism

Correct answer: It suggests sarcopenic obesity, a condition associated with increased metabolic and functional risk

Sarcopenic obesity is defined by simultaneous excess fat mass and deficient lean mass, and DXA is a key tool for identifying this high-risk phenotype.

Question 17: According to ISCD, when is a vertebral fracture assessment (VFA) particularly indicated alongside a DEXA scan?

When a vertebral fracture is suspected but spine radiographs are unavailable or not performed (Correct answer)
Only for patients over age 80
Only when lumbar spine BMD is unobtainable
For every patient regardless of clinical history

Correct answer: When a vertebral fracture is suspected but spine radiographs are unavailable or not performed

ISCD recommends VFA when vertebral fractures are suspected clinically (height loss, back pain, history of fragility fracture) and standard radiographs are not available.

Question 18: What BMD change pattern is typically seen in the lumbar spine during the first 1–2 years of teriparatide therapy?

Decrease followed by rebound increase
Modest 1–2% increase similar to bisphosphonates
No detectable change during the first year
Significant BMD increase in the spine, often 8–13% (Correct answer)

Correct answer: Significant BMD increase in the spine, often 8–13%

Teriparatide typically produces robust spine BMD gains of 8–13% over 18–24 months, significantly exceeding gains seen with antiresorptive agents.

Question 19: What is ALARA in radiation safety?

As Low As Reasonably Achievable (Correct answer)
Average Level of Radiation Application
All Lines Are Radiation Approved
Annual Limits of Radiation Amount

Correct answer: As Low As Reasonably Achievable

ALARA stands for "As Low As Reasonably Achievable" and is a fundamental principle in radiation safety. It mandates that all radiation exposure should be kept to the absolute minimum necessary, taking into account economic and social factors. This principle guides practices in DEXA scanning to minimize patient and staff exposure while still achieving diagnostic quality images.

Question 20: When assessment results for a DEXA Bone Density Scan Certification evaluation are inconclusive, the BEST practice is to:

Discard the results and start over
Report the results as definitive anyway
Conduct additional assessment using alternative methods (Correct answer)
Delay reporting until results are favorable

Correct answer: Conduct additional assessment using alternative methods

Inconclusive results require additional assessment using alternative methods for triangulation.

Question 21: When comparing DXA body composition results across serial scans, the technologist should ensure:

Scans are always performed in the morning to control circadian variation
The patient fasts for 24 hours before each scan to standardize hydration
The patient wears the same clothing for all follow-up scans
The same DXA system and software version are used for each scan (Correct answer)

Correct answer: The same DXA system and software version are used for each scan

Using the same DXA machine and software version is critical for longitudinal comparability because cross-calibration between different systems introduces systematic errors.

Question 22: When a DEXA report shows progressive bone loss over three serial scans despite treatment, what additional reporting element is most clinically useful to include?

Cumulative percentage change from baseline and comment on treatment response (Correct answer)
Whole-body fat percentage trend
Z-score comparison to age-matched peers only
A note on scanner calibration date only

Correct answer: Cumulative percentage change from baseline and comment on treatment response

Reporting cumulative percentage change from baseline and noting inadequate treatment response helps clinicians decide whether to reassess therapy or adherence.

Question 23: When scanning the total body, which of the following patient instructions is MOST important before starting the acquisition?

The patient should hold their breath for the entire scan
The patient should cross their arms over the chest
The patient's feet must be elevated on a footrest
The patient must remove all metal objects and lie still with arms at sides, palms down (Correct answer)

Correct answer: The patient must remove all metal objects and lie still with arms at sides, palms down

Metal objects create artifacts, and the arms-at-sides palms-down position with stillness ensures accurate whole-body composition and BMD analysis.

Question 24: In DEXA Bone Density Scan Certification practice, what is the CORRECT sequence when performing a technical procedure?

Execute, then plan and review
Execute immediately and document only if issues arise
Document, execute, then plan
Plan, prepare, execute, verify, and document (Correct answer)

Correct answer: Plan, prepare, execute, verify, and document

The correct sequence follows: plan, prepare, execute, verify, and document.

Question 25: How does temperature and humidity in the scanning room affect DEXA equipment performance?

Room temperature has no measurable effect on DEXA performance
Extreme temperatures and humidity outside manufacturer specs can cause detector drift and electronic instability (Correct answer)
Only humidity affects the X-ray tube output
Temperature only affects the patient table movement

Correct answer: Extreme temperatures and humidity outside manufacturer specs can cause detector drift and electronic instability

DEXA detectors and electronics are sensitive to environmental conditions; rooms must stay within manufacturer-specified temperature and humidity ranges.

Question 26: How long does a typical DEXA scan take?

30–45 minutes
1–2 minutes
Over an hour
10–20 minutes (Correct answer)

Correct answer: 10–20 minutes

A typical DEXA scan is a relatively quick procedure, usually taking between 10 to 20 minutes to complete. The exact duration can vary slightly depending on the number of areas being scanned (e.g., lumbar spine, hip, forearm) and the specific equipment used. This short duration makes it a convenient diagnostic tool.

Question 27: What is the MOST important factor when selecting assessment tools for DEXA certification work?

The cost of the assessment tool
Personal familiarity with the tool
How quickly the tool can be administered
Validity, reliability, and appropriateness for the specific context (Correct answer)

Correct answer: Validity, reliability, and appropriateness for the specific context

Assessment tools must be valid, reliable, and appropriate for the specific context.

Question 28: What does a positive T-score suggest?

Higher than average BMD (Correct answer)
Bone damage
Low calcium
Radiation exposure

Correct answer: Higher than average BMD

A positive T-score suggests that a patient's bone mineral density (BMD) is higher than the average BMD of a healthy young adult at peak bone mass. While less common, it indicates robust bone health and a lower risk of osteoporosis.

Question 29: A patient taking long-term glucocorticoids (prednisone ≥5 mg/day for ≥3 months) presents for a DEXA scan. Why is this clinically important?

Glucocorticoids cause glucocorticoid-induced osteoporosis (GIO), a major secondary cause of bone loss (Correct answer)
Glucocorticoids only affect soft tissue, not bone
Steroids cause artifacts on DEXA images that must be corrected
Glucocorticoids increase bone density and DEXA is used to confirm this

Correct answer: Glucocorticoids cause glucocorticoid-induced osteoporosis (GIO), a major secondary cause of bone loss

Glucocorticoid-induced osteoporosis is the most common secondary cause of osteoporosis, and baseline and monitoring DEXA scans are recommended for these patients.

Question 30: How long should a DEXA technologist wait before performing a follow-up BMD scan to assess treatment response for a patient on bisphosphonate therapy?

Repeat annually regardless of treatment
3 months after starting therapy
At least 1–2 years after initiating therapy (Correct answer)
6 months after starting therapy

Correct answer: At least 1–2 years after initiating therapy

ISCD guidelines recommend waiting 1–2 years before a follow-up DEXA to detect meaningful BMD changes that exceed the LSC on bisphosphonate therapy.

Question 31: Which FRAX input variable directly represents the skeletal impact of chronic glucocorticoid use?

Femoral neck BMD T-score only
Secondary osteoporosis checkbox and glucocorticoid input field (Correct answer)
Body mass index (BMI)
Spine fracture history field

Correct answer: Secondary osteoporosis checkbox and glucocorticoid input field

FRAX includes a secondary osteoporosis field and a separate glucocorticoid input that adjusts fracture probability upward for chronic steroid users.

ISCD Certified Bone Densitometry Technologist (CBDT®)

The CBDT® exam certifies technologists in performing and analyzing DEXA bone density scans, covering bone physiology, radiation safety, DXA equipment, scan acquisition, and clinical data interpretation for osteoporosis assessment.

Questions

35 min

Time Limit

70%

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