Bone Densitometry

NMT 631

Bone Densitometry

A technique to measure bone mineral

content (bone density). It is used to detect

osteoporosis, a disease that causes the

bone to become more porous and

susceptible to fracture.

Decreased bone density increases the risk

of bone fracture.

Bone Density MeasurementsIn the beginning……….

Gamma Source

Shielding - lead (Pb)

patient

Detector – gamma type camera

The DEXA machine today contains an x-ray tube thatgenerates x-rays of two different photon energies

and a detector that measures the amount ofradiation that passes through the bone.

Hologic, Inc.

Dual energy x-ray Absorptiometer (DEXA)

Patient positioned for lumbar spine measurement

Clinical Indications

Indicate if a person has low bone density before a fracture occurs.

Tell if a person’s bone are losing bone density or staying the same when the test is repeated at intervals of 1 year or more.

Predict the chances that a person will have a fracture in the future.

Help decide a treatment plan.

Subject positioned for hip measurement

Risk Factors for Developing Osteoporosis

Uncontrollable Factors

Gender

Race

Heredity

Body habitus

Age

This graph shows how the bone density of the total hip decreases with age. The units are standardized bone density in (mg/cm2). The lines show the average values, and for each age, race and gender a range of values occurs in the ordinary population.

http://courses.washington.edu/bonephys/opbmd.html

Risk Factors for Developing Osteoporosis

Controllable Factors

Calcium/vitamin D intake

Regular exercise

Alcohol consumption

Estrogen intake

Medications

Treatment Options – (no cure)

Fosamax - biphosphonate

Reclast - biphosphonate

Boniva - biphosphonate

Forteo – anabolic (bone forming) – man –made parathyroid hormone (subcutaneous injection daily) increases bone mass & bone strength and decreases chance of fracture

Clinical Procedure for Bone Density Measurements

1) Identify patient; confirm physician’s

order; review clinical indication for exam

2) Explain procedure to patient; obtain

relevant medical history

Relevant Medical History

Height/weight

Any loss of height?

Amount of loss

Right or left handed?

Age at menopause

Medications

Recent imaging tests?

Arthritis

Osteoporosis

Osteopenia

Fractures

Recent surgery

Bone surgery

Chronic illnesses

Dietary habits

Tobacco use

Family history

Body type, eye/hair color

Daily exposure to sunlight

Exercise program

Pregnant?

Clinical Procedure: continued

3) Prepare patient: rule out recent x-ray and nuc med procedures, pregnancy; remove attenuating objects

4) Perform bone density measurements

Measurement sites include lumbar spine (1st 4 lumber vertebrae), hip, and forearm

Results Picture of the scanned area

Comparison of the patient to a database of measurements from age and gender matched peers and to a database of gender matched young adults

Z score: comparison with age-matched peers T score: comparison with gender-matched young

adults

Z-Scores

Pediatricians use percentiles to interpret the height of a child. A child at the 5th percentile (same as Z-score of -1.65) is short for his or her age, and one at the 75th percentile is somewhat taller than average (Z-score of 0.68). The Z-score does not tell how tall a child is, because the average child gets taller as she gets older. On the other hand, if you know that a child is 40" tall, it does not mean anything unless you also know his age. You must know both the age and the percentile to know if this is a healthy height.

For bone density, the Z-score will tell you if the bone density is close to the average value for the person's characteristics such as age, race and gender, but that still does not tell you if the bone is strong. Elderly white women have weak bones even if the bone density is average.

http://courses.washington.edu/bonephys/opbmdtz.html

T-ScoresNotice that when the T-score is zero (average peak bone mass) the bone density is highest in black men and lowest in white women. At very low T-scores, however, the bone density is the same. This is due to differences in the standard deviations of the young populations.

http://courses.washington.edu/bonephys/opbmdtz.html

http://courses.washington.edu/bonephys/opDEXA1.html

Causes of Artifacts Scoliosis

Degenerative arthritis

Compression fractures

Spondylitis Aortic calcifications

Navel jewelry

Surgical changes

Paget’s disease

http://images.google.com/imgres?imgurl=http://tech.snmjournals.org/content/vol34/issue3/images/medium/coverfig.gif&imgrefurl=http://tech.snmjournals.org/content/vol34/issue3/cover.shtml%3Fck%3Dnck&h=440&w=377&sz=96&hl=en&start=1&um=1&usg=__a-r6jHpwn20aAv5iPX9I7ll49zY=&tbnid=28gPXRu4hwFJLM:&tbnh=127&tbnw=109&prev=/images%3Fq%3Dpaget%2527s%2Bimages%2Bnuclear%2Bmedicine%26um%3D1%26hl%3Den%26sa%3DN

Additional Information

Susan Ott, MD. University of Washington, Department of

Medicine

http://courses.washington.edu/bonephys/opDEXA1.html

A comprehensive discussion of bone density measurement

with lots of illustrations and case reviews.

http://courses.washington.edu/bonephys/index.html