Bone Densitometry

Bone: A Dynamic Tissue

Supports muscles, protects vital organs and stores calcium Built and stored efficiently until about the age of 30 Affected by diet and exercise Breaks down faster than formation of new bone as we get older Osteoporosis results in reduced bone mass and altered structure

T-score

peak bone mass

Normals

**Normal Bone density is within 1 SD (+1 or −1) of the young adult mean. ***Low bone mass Bone density is between 1 and 2.5 SD below the young adult mean (−1 to −2.5 SD). ***Osteoporosis Bone density is 2.5 SD or more below the young adult mean (−2.5 SD or lower). ****Severe (established) osteoporosis Bone density is more than 2.5 SD below the young adult mean, and there have been one or more osteoporotic fractures.

History

**Radiography (plain films) Demineralization only becomes apparent after 40% loss of BMD **Single Photon Absorptiometry (SPA) used a single energy photon beam that passed through bone and soft tissue. **Dual photon Absorptiometry (DPA) used an isotope that emitted photon energy at two distinct photoelectric peaks. **Dual Energy X-Ray (DXA) An x-ray tube replaced the radioactive isotope source of photon energy.

DEXA Scanning Principles

*2 different photon energies are used to seporater the x-ray attenuating effects of soft tissue and bone. *Filters (Lunar Corp., Norland Medical Systems). *Synchronously switching between two kilivoltage peaks (Hologic, Inc.).

Economic Impact

Osteoporotic fractures cost the U.S. healthcare system $14 billion in 1995 Osteoporosis is the direct cause of: 2.5 million physician visits 432,000 annual hospital admissions 180,000 nursing home admissions The number of hip fractures and associated costs could more than triple by the year 2040

T-scores are used to decide whether a patient has reduced BMD consistent with osteoporosis and osteopenia.

T-score Classification T> -1.0 SD Normal -1.0 SD <T< -2.5 SD Osteopenic T < -2.5 SD Osteoporotic **For every SD of decline, fracture risk increases 2-3x!**

Results T & Z score

T-score between +1 and −1 is considered normal or healthy. A T-score between −1 and −2.5 indicates that you have low bone mass, although not low enough to be diagnosed with osteoporosis. A T-score of −2.5 or lower indicates that you have osteoporosis. The greater the negative number, the more severe the osteoporosis.

Bone Loss in Women After Menopause

Trabecular bone

Risk for Osteoporosis in Men

2 million American men have Osteoporosis (20%). 3 million American men have low bone mass. Suffer 33% of all hip fractures.

An Epidemic of Fractures

28 million Americans currently suffer from osteoporosis or have low bone mass [1] Over the next 20 years, this number could rise to 40 million [1] Low bone mass causes 1.5 million fractures a year [1] 700,000 vertebral fractures [1] 300,000 hip fractures a year [1] 20% mortality rate [2] 50% require some form of assisted living [2]

Osteoporosis

A disease characterized by low bone mineral density with the presents of fracture. Primary Type I - bone resorption exceeds bone formation, due to estrogen deprivation (post menopausal). Type II - a decreased ability to build bone due to age. Secondary Skeletal disorders resulting in bone turnover(genetic, endocrine, hematologic, malignancy).

Osteopenia

A disease characterized by low bone mineral density without the presents of fracture. *Left untreated can lead to osteoporosis

Peripheral DEXA (pDEXA)

A small, portable device that works similarly to DEXA but is used to examine bone density in peripheral bones, such as the oscalsis, radious and ulna(best for single event measurment).

Osteoporosis: A Multifactorial Disease

Age, gender, race , body size, Lifestyle factors, Menospause,family history , drug treatments, and other illnesses

Industry Momentum

Approved drugs are now available for prevention and treatment of osteoporosis At least 45 companies are currently developing additional therapies Increased attention to women's health Increased focus on "graying of America" Increased focus on disease prevention

Women Are Most Susceptible

Approximately 13 to 18% of postmenopausal Caucasian Americans (4 to 6 million) have osteoporosis Another 30 to 50% (13 to 17 million) have low bone density Almost one out of two will suffer an osteoporotic fracture (for men, it is one in five) Risk of a hip fracture alone exceeds the combined risk of developing breast, uterine or ovarian cancer

BMD Test Results

BMD=g/cm2 of bone mineral ***Z-scores normalize a patient's BMD by assessing the amount of bone loss compared to the expected loss for age-matched peers*** ***T-scores indicate the amount of bone loss, by quantifying the difference between a patient's BMD at his/her current age, and the peak bone mass for young normals ***

Two Types of Bone

Cortical bone: makes up 80% of the skeletal mass, but accounts for only a small proportion of the total bone turnover (functions mainly mechanical and protection). Trabecular (calcaneus) bone: represents 20% of the skeletal mass, but due to its large surface-to-mass ratio, a far greater percentage (80%) of bone turnover (function mainly metabolic).

DXA (DEXA): The Gold Standard

Detects early bone loss and monitors therapeutic effectiveness. Measures axial skeletal sites where early bone loss occurs High precision (<1.0%) Low patient dose High-resolution imaging (images are used for positioning purposes NOT diagnostic quality). Most common problems are operator related.

Pharmacologic Options for Osteoporosis

Estrogen Replacement Therapy (ERT): Approved for prevention and treatment of osteoporosis. Hormone Replacement Therapy (HRT): To eliminate the risk of increased chance of developing cancer of the uterine lining. Alendronate [Fosomax, Merck & Co.]: Fosomax most widely used for osteoporosis Approved by the FDA for prevention and treatment of osteoporosis. Calcitonin [Miacalcin, Novartis]: FDA-approved for treatment of osteoporosis. Raloxifene [Evista, Eli Lilly & Co.]: FDA-approved for the prevention of osteoporosis. Investigational Treatments: New forms of bisphosphonates, selective estrogen receptor modulators, sodium fluoride, parathyroid hormone and vitamin D metabolites.

Fractures associated with Osteoporosis

Fragility Fractures minimal trauma standing height or less spontaneous

Peak Bone Mass: Determinants PEAK BONE MASS (about 30 years old)

GENETIC INFLUENCE, Hormonal Factors,Nutritional Factors,Exercise & Environmental Factors

Women Are Most Susceptible

Generally at greater risk of developing osteoporosis than men Tend to build less bone than men when they are young Experience a rapid skeletal bone loss due to the decrease in estrogen production, following the menopause Seventy-five percent, aged 45-75, have never even discussed osteoporosis with their physicians

Dual Energy X-Ray Absorptiometry DEXA)

In this technique, an x-ray tube emits two x-ray beams of dual energy or filters are used that result in two seperate energy beams, which pass through the bone and are picked up by a detector or detectors, as in the case of fan beam technology. A computer is then used to analyze the resulting images and calculate bone density based on the amount of radiation absorbed by the bone.

Advantages of Tube over DPA

No source decay Greater source intensity(can increase keV) A smaller focal spot(better pinpoint) Increased beam collimation Less dose Better image resolution Faster scan times Improved precision

Behavior Modification

Prevention of falls. Weight bearing exercise.

DEXA Patient Preparation

Provide patient with explanation of exam Remove any metallic objects (some facilities require changing into a gown). No exams within 7 days with radiopharmaceuticals or contrast media.(No barium) No calcium supplements 2 hours prior to exam

BMD Testing Methods

Quantitative computed tomography (QCT), uses a standard CT scanner—fitted with special equipment and software to measure bone mass—to deliver x-rays to the spine at many different angles.

BMD Testing methods

Quantitative ultrasound (QUS), the only technique for measuring bone density that does not use x-rays, works by transmitting high-frequency sound waves through the heel bone to a signal receiver.

Bone Mineral Density (BMD)

Refers to amount of mineral contained within a certain amount of bone: Helps determine bone strength and fracture risk Provides clinicians with a practical way to identify individuals with osteoporosis and those at risk of developing the disease Useful in monitoring therapy efficacy

BMD Testing Methods

Single x-ray absorptiometry (SXA) uses a small, portable device that works similarly to DEXA, but emits a single x-ray beam. It is used to examine the heel bone or forearm.

DXA / DEXA Imaging procedure

The DEXA machine sends a thin, invisible beam of low dose x-rays through the bones via two energy streams. One energy peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount can be subtracted from the total, and what remains is a patient's bone mineral density. ***90% of all DEXA scans are preformed on the spine and proximal femur (hip).Forearm is used as an alternate site. **

Bone Densitometry

The art and science of measuring bone mineral content and density.

This patient has osteoporosis.

This patient (indicated by X) has a bone density that is 1 SD below age-matched normals and 2.5 below the mean bone density of young normals. Based on the World Health Organization's definition, this patient has osteoporosis.

Purpose of Bone Density Exams

To aid in the diagnosis of diseases associated with low bone density (Osteoporosis). Predict risk of fractures. Asses the need for pharmacological interventions. Monitor the effects of drug therapy

Osteoporosis: A Huge Unmet Need

Undiagnosed, Untreated( 77%) Diagnosed, Treated(9%) Diagnosed, Untreated (14%)

National Osteoporosis Foundation Guidelines of who should have a BMD test:

Women 65 and older, regardless of other risk factors Postmenopausal women with one or more risk factors All postmenopausal women who have had a fracture

Z- score

age matched