1-5 Bone Densitometr1- Dr. Omar Hussien

8/14/2019 1-5 Bone Densitometr1- Dr. Omar Hussien

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Bone densitometry:

The ideal detector for Osteoporosis

By Dr Omar Hussein

Professor of Radiodiagnosis

Osteoporosis is a disease characterized by:

Low bone mass

Microarchitectural deterioration of the bone leading to Hip,

Colles, and vertebral fractures

Microarchitectural Changes in Osteoporosis includedecreased Bone Mass,

Trabecular Thickness, Trabecular Number, Horizontal

Struts and Connectivity

It is worth saying that Bone Resorption takes 7-10 days to

happen , while Bone formation takes 10-12 weeks

BMD Testing Techniques

A. Traditional methods

Conventional radiography

Radiographic absorptiometry (RA)

Ultrasound densitometry

Dual-energy X-ray absorptiometry(DEXA)

B. Non traditional methods

New DEXA techniques

Quantitative computed tomography (QCT) and Finite Element

Analysis

MRI

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The Basics of BMD Measurement

Measurement of BMD at any skeletal site has a value in predicting

fracture risk. A variety of densitometers are in clinical use andprovide reliable assessment of fracture risk.

However, hip BMD is the best predictor of hip fractures, and

spine BMD is the best predictor of spine fractures.

Dual energy X-ray Absorptiometry DXA

Better than Isotope-based absorptiometry

X-ray based

Excellent precision and accuracy (1%)

Reliable and versatile

Economic exam cost

High-intensity beam

Fast scans, low dose

High image quality

Can measure all skeletal sites: central and peripheral

Best Clinical Utility

Clinical uses:

Site - specific measurements, essential for prediction of BMD,

fracture risk rate of loss.

Comprehensive evaluation:

Lumbar spine

Proximal femur

Total body is important in children, metabolic bone disease,

severe osteoporosis.

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DEXA allows us to determine :

A- Bone Tissue

BMD (g/m)

Bone Mass (g)

Area

A- Soft Tissue

%Fat (R Value)

Soft Tissue Mass (g) ( Fat Free Mass)

Fat Mass (g)

Lean Mass (g) (Fat free and Bone free Mass)

Problems in the interpretation of BMD by DEXA:

Osteomalacia

Osteoarthritis (especially the spine)

Vascular calcification (especially the spine)

Overlying metal objects

Contrast media (spine)

Previous fracture (spine, hip and wrist)

Severe scoliosis

Vertebral deformities due to osteoarthrosis, Scheuermann`s

disease

Who should be tested?

1. All postmenopausal women under age 65 who have one or

more additional risk factor for osteoporosis.

2. All women aged 65 and older regardless of additional riskfactors.

3. Postmenopausal women who present with fractures (to

confirm diagnosis and determine disease severity)

4. Women who are considering therapy for osteoporosis, if BMD

testing would facilitate the decision.

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5. Women who have been on hormone replacement therapy for

prolonged periods.

Because absolute values can vary with different densitometers,

BMD is expressed as a relationship to two norms:

a. The expected BMD for the patients age and sex (Z-score)

b. The young adult normal BMD for the same sex (T-score).

The difference between the patients score and norm (T-score or

Z-score) is expressed as a standard deviation (SD) above or

below the mean.

Usually, 1 SD equals a 10% to 12% difference in bone density.

In general, when talking about fracture risk, we talk in terms ofT-score.

T-score is used because fracture risk increases as BMD declines

from young normal levels.

Because in older adults, low BMD is very common, comparison

with age matched levels (Z-score) can be misleading

WHO definition of Osteoporosis:

Values of T score:

> -1 SD is normal

-2.5 to -1 SD equals osteopenia

< -2.5 SD equals osteoporosis

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Dual energy X-ray Absorptiometry DXA Interval

Annual:Post-menopausal osteoporosis, appropriate for age.

Biannual:Post-menopausal osteoporosis not appropriate for age.

Steroid induced Osteoporosis

Hyperthyroidism

Hyperparathyroidism

Therapy other than HRT

Recommendations for extremely precise follow up

test

To follow interval change in bone density, it is essential to

choose a measurement site that is responsive to treatment.

Because BMD values in the forearm change very little with all

treatment for osteoporosis, the spine or proximal femur are the

preferred measurement sites. The important value to monitor

when assessing interval change is the absolute difference

between tests ( in gm/cm2), rather than the T- or Z-score.

In addition, it is essential to have bone density test results

interpreted by an experienced practitioner. This is important

because many factors may influence test results, such as

osteoarthritis, scoliosis, and arterial calcification.

Clinical Practice of Osteoporosis:

Where we are going tomorrow ?

Newer technologiesthat may help measure components of

bone quality and how they contribute to bone strength.

A- Specialized DEXA techniques:

Lat. Vert. Morphometry

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Advanced Hip Assessment New Regions of Interest

B- QCT :Quantitative Computed Tomography

C- FEA :Finite Element AnalysisD- High Resolution MRI:Magnetic Resonance Imaging,

E- MRS :MR Spectroscopy

A- Specialized DEXA techniques:

Lateral DEXA Vertebral Morphometry

A relatively new DXA technique has been developed to evaluate

vertebral deformity using a lateral DXA scan of the spine from T4

to L4.

Compared with radiographs, this technique is potentially

advantageous with lower cost and lower radiation exposure, and

Because it is quick and can be done in the same visit for BMD

measurement.

According to Hurxthal criteria, 6 measurement points are

selected in each vertebra between T4 and L4, corresponding

respectively to the four corners and the mid-points of the

endplates.

Computer measures anterior (Ha), middle (Hm) and posterior

(Hp) heights and calculates the following ratios:

Ha/Hp (wedging), Hm/Hp (biconcavity) and Hp/Hp+1 or Hp/Hp1

(crushing or compression), where Hp+1 and Hp1 indicate the

posterior height of the vertebra above or below the one under

examination, respectively

A vertebra is considered fractured if any of the three ratios of

vertebral body heights (Ha/Hp, Hm/Hp, Hp/Hp+1 or Hp/Hp1) is :

4 SD (grade 1 deformity)

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Advanced Hip Assessment (AHA)

Includes all the standard femoral regions of interest previously

available. In addition, AHA provides a measurement of two new

regions of interest-upper and lower femoral neck, automated

determination of hip axis length, and hip strength values.

1. Lower Femoral Neck

2. Trochanter

3. Ward's

4. Shaft

5. Total Hip (defined as the density of the combined region of the

femoral neck, trochanter, and shaft regions.6. Upper Femoral Neck

7. Hip axis length (HAL)

Each centimeter (10%) increase in HAL increases hip fracture risk by50-80%. For short-term prediction of hip fracture (within 2 years), HALwas shown to predict hip fractures independent of BMD.

Bone around prosthesis

(DXA) has proven to be a useful technique for quantifyingperiprosthetic (BMD) changes around proximal femoral implants,

but relatively few studies have assessed BMD changes in bone

surrounding knee implants.

Tibial bone loss may result from altered loading conditions

imposed by the implant (stress shielding) and periprosthetic

bone resorption caused by a variety of factors .

These factors may contribute to aseptic loosening and ultimate

implant failure. Measurement of BMD change can detect anybiological change over time.

A- Quantitative Computed Tomography

Advantages

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Flexible measurements: pure trabecular bone or mix of

cortical and trabecular

Disadvantages

spine .forearm .femur only relatively high radiation dose (100-1000 mR for spine)

Low precision (2-5% error)

expensive

No validation of results (WHO, )

- High Resolution- pQuantitative CT

- 3D QCT:Evaluates Bone Geometry and Cancellous and Cortical Bone

Density

- Finite Element Analysis:

An analytical method to predict bone strength that integrates

material and structural information

Uses QCT imaging data for geometry and density

Strengths of HR- pQCT:

3D assessment of architecture and density

Short imaging time

Low radiation dose

Age-related changes and fracture discrimination studies

exist

Limitations of HR- pQCT:

Limited to radius and tibia only

Requires specialized equipment

No prospective fracture data

Limited reference and therapy related data

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A- Magnetic Resonance Imaging: Magnetic Resonance Microscopy (MMR):

High resolution images provide information about trabecular

microarchitecture

MR Spectroscopy of bone marrow:

Provides information about bone marrow chemical composition

MRS divides the global MR signal from bone into 2 major

segments: water and lipid.

Water signal comes mostly from red marrow

Most lipid stem from yellow marrow.

The spectra of MRS have a water peak and a lipid peak

Strengths of HR- MRI

a. Non-invasive, non-ionizing radiation

b. 3D assessment of cortical and trabecular structure

c. Clinical scanners can be adapted

d. Treatment related effects ( calcitonin, testosterone)

Limitations:

a. Limited to appendicular skeleton

b. Limited Reference data, no prospective fracture data

c. Technically demanding

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1-5 Bone Densitometr1- Dr. Omar Hussien