DEXA Radiation Safety & Patient Preparation 5 — Questions and Answers
Question 1: A patient who weighs 350 lbs (159 kg) arrives for a DEXA scan. What is the primary concern the technologist should address first?
- The scan will require double the radiation dose
- The patient may exceed the table weight limit of the DEXA system (Correct answer)
- Obesity makes all DEXA results clinically invalid
- A lead apron must be used to shield the abdomen
Correct answer: The patient may exceed the table weight limit of the DEXA system
Most DEXA tables have a weight limit (commonly 300–450 lbs), and exceeding it is a safety concern for both the patient and equipment.
Question 2: Which of the following actions demonstrates proper infection control during DEXA patient preparation?
- Wearing gloves only when the patient has an open wound
- Wiping the scan table with an approved disinfectant between patients (Correct answer)
- Using a lead apron as a physical barrier between patients
- Asking patients with illness to wear a lead apron
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 3: The T-score threshold defined by the WHO for diagnosing osteoporosis is:
- -1.0 or above
- Between -1.0 and -2.5
- -2.5 or below (Correct answer)
- -3.0 or below
Correct answer: -2.5 or below
The WHO defines osteoporosis as a T-score of -2.5 or lower, indicating bone density 2.5 standard deviations below the young adult mean.
Question 4: A patient asks if they need to fast before their DEXA scan. The correct response is:
- Yes, fast for 4 hours to reduce bowel gas artifact
- No fasting required, but avoid calcium supplements on the morning of the scan (Correct answer)
- Fast for 8 hours exactly as with blood work
- Fasting is required only for hip scans
Correct answer: No fasting required, but avoid calcium supplements on the morning of the scan
Patients should not fast before DEXA, but are advised to avoid calcium supplements on the day of the scan as they can minimally affect results.
Question 5: Scatter radiation from a fan-beam DEXA system is greater than from a pencil-beam system. What does this mean for staff safety?
- Staff must wear lead aprons at all times with fan-beam units
- Staff should exit the room or stand behind a barrier during fan-beam scans (Correct answer)
- Fan-beam units require a dedicated radiation-shielded room only
- Staff dose is identical for both systems
Correct answer: Staff should exit the room or stand behind a barrier during fan-beam scans
Fan-beam DEXA produces more scatter radiation than pencil-beam, so technologists should not stand in the direct scatter field during acquisition.
Question 6: 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?
- History of hypertension
- Bilateral hip replacements and severe lumbar scoliosis (Correct answer)
- Body weight under 100 lbs
- Recent calcium supplement use
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 7: What does the Z-score measure in a DEXA report, and why is it particularly useful in younger patients?
- Compares BMD to a young healthy adult reference; used for fracture risk in all ages
- Compares BMD to age- and sex-matched peers; helps identify secondary causes of bone loss (Correct answer)
- Measures the rate of bone loss over serial scans; used for monitoring therapy
- Converts T-score to absolute BMD values for easier clinical interpretation
Correct answer: Compares BMD to age- and sex-matched peers; helps identify secondary causes of bone loss
The Z-score compares a patient's BMD to age- and sex-matched norms, making it useful for identifying whether bone density is unexpectedly low for the patient's age group.
DEXA Radiation Safety & Patient Preparation 5
A patient who weighs 350 lbs (159 kg) arrives for a DEXA scan.
What is the primary concern the technologist should address first?