Module 6: Bone Mineral Densitometry (BMD)

These practice flashcards cover the key clinical concepts, equipment specifications, radiation safety, and scoring metrics for Bone Mineral Densitometry (BMD) as outlined in the Module 6 transcript.

What does Bone Mineral Densitometry (BMD) measure?

The amount of calcium hydroxyapatite (bone mineral) per unit area of bone.

What is the primary purpose of a BMD examination?

To detect bone loss, diagnose osteoporosis, assess fracture risk, and monitor treatment effectiveness.

What is the most commonly used modality for BMD?

Dual-Energy X-ray Absorptiometry (DXA).

What are the three most common anatomical sites used for BMD assessment?

Lumbar spine, hip, and forearm.

What T-score defines osteoporosis?

$T\text{-score} \le -2.5$.

What happens to fracture risk for every 1 SD decrease in T-score?

Fracture risk doubles.

If a patient's T-score decreases by 2 SD, how much does fracture risk increase?

Approximately fourfold.

What medication examples were listed for osteoporosis treatment?

Premarin and Fosamax.

What structures make up the central skeleton?

Vertebral column, ribs, sternum, pelvis, and proximal femur.

What structures make up the peripheral skeleton?

Upper and lower extremities excluding the proximal femur.

Which BMD devices are classified as central devices?

DXA and QCT.

Why is DXA considered the gold standard for BMD?

Excellent reproducibility and strong correlation with fracture risk.

What anatomical areas can pDXA measure?

Forearm, finger, and heel.

What does pQCT measure?

Volumetric bone density of the forearm.

What does Quantitative Ultrasound (QUS) measure?

Speed of sound through bone.

What three major components are found in a DXA system?

X-ray tube, collimator, and detector.

What type of collimation is used in a pencil beam scanner?

Circular pinhole collimation.

What is the major disadvantage of a pencil beam scanner?

Longer scan time.

What is the major advantage of a fan beam scanner?

Faster scan times.

What is the major disadvantage of a fan beam scanner?

Higher radiation dose and lower resolution.

Why can't single-energy absorptiometry accurately measure bone density?

It cannot separate bone attenuation from soft tissue attenuation.

How does DXA overcome the limitations of single-energy absorptiometry?

Uses two photon energies to subtract soft tissue attenuation from bone attenuation.

What does BMC stand for?

Bone Mineral Content.

What units are used for BMC?

Grams ($g$).

What is the formula for calculating Bone Mineral Density?

$BMD = \frac{BMC}{\text{Area}}$.

What units are used for BMD?

$g/cm^2$.

Name the two methods used to generate dual energies in DXA.

K-edge filtering and voltage switching.

What is the purpose of a K-edge filter?

To split the x-ray beam into high- and low-energy components.

What detector is used with K-edge filtering systems?

Energy-discriminating detector.

What detector is used with voltage switching systems?

Current-integrating detector.

What is the typical effective dose from a DXA examination?

$1-5\,\mu Sv$.

Why should repeat DXA scans not be denied if positioning is questionable?

Radiation dose is negligible compared with the risk of an incorrect diagnosis.

How far should a technologist stand from a pencil beam scanner?

At least $1\,\text{metre}$.

How far should a technologist stand from a fan beam scanner?

At least $3\,\text{metres}$.

Why are DXA rooms typically not required to have special shielding?

Most systems have internal shielding.

Why must extra care be taken when assisting elderly DXA patients?

They are at increased risk of fragility fractures.

What is the major contraindication for a DXA examination?

Pregnancy.

How long should a patient wait after receiving IV contrast before a DXA scan?

2 days.

How long should a patient wait after a barium study before a DXA scan?

At least 1 week.

Why should BMD results only be compared when performed on the same equipment?

Different manufacturers use different protocols and analysis methods.

What is the most important principle for follow-up DXA examinations?

Consistency.

What is the purpose of daily phantom testing?

To assess equipment accuracy and calibration.

In BMD quality assurance, what does accuracy mean?

The ability to measure the true value.

In BMD quality assurance, what does precision mean?

The ability to reproduce results consistently.

Which is more important for monitoring a patient's bone density over time: accuracy or precision?

Precision.

What lumbar vertebral levels are included in a standard spine DXA study?

L1-L4.

What positioning device is used during lumbar spine DXA to reduce lordosis?

Leg-positioning block.

What is considered the best predictor of hip fragility fracture risk?

Hip BMD.

Why should a hip containing a prosthesis not be scanned?

Metal artificially increases bone density measurements.

What are the WHO T-score classifications?

Normal: $> -1.0$; Osteopenia: $-1.0$ to $-2.5$; Osteoporosis: $\le -2.5$; Severe Osteoporosis: $\le -2.5$ with a fragility fracture.