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DXA Information

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DXA scans are considered the gold standard technique for measuring bone density and detecting the possibility of osteoporosis (see below for further details). We pride ourselves on high quality bone density testing.

At both of our locations, we have state-of-the-art DXA scanners. These machines are equal to or often exceed the quality and advances of the scanners seen in hospitals and outpatient imaging centers. At our center, we exclusively use Hologic Discovery Scanners (Discovery W and Discovery C). These scanners are the most advanced scanners available today and incorporate One Pass Technology which affords fast scanning and both superior image quality and precision.

In addition, all of our machines are capable of High Definition Instant Vertebral Fracture Assessment (VFA-see below), a 15-second scan which is a powerful tool that detects silent vertebral fractures. Competing bone densitometers from other companies take three minutes to acquire a similar scan that has inferior resolution. All of our providers are capable of performing, analyzing and interpreting these scans. Our providers are certified to read DXA scans by the International Society of Clinical Densitometry.

Vertebral Fracture Assessment (VFA)

Vertebral Fracture Assessment (VFA)

When appropriately indicated, our facility looks to include Vertebral Fracture Assessment along with standard bone density testing. This study, although considered separate from Bone Density (DXA) testing, is done in conjunction with the DXA and improves the diagnosis of Osteoporosis and helps in treatment decisions. A Vertebral Fracture is a lateral image of the lumbar and thoracic spine that takes about 15 seconds to acquire on our machines. This study helps to identify Vertebral Fractures. The vast majority of Vertebral Fractures are silent, but the presence of a vertebral fracture helps to make a diagnosis of Osteoporosis and predicts the potential development of other fractures.

Compared to a standard lateral spine x-ray, the VFA is less expensive, more convenient, and offers significantly less radiation exposure (about 100x less). The VFA fits perfectly in our concept of a comprehensive bone health evaluation.

What is Bone Density Testing?

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Bone Mineral Density Testing is one of the most common methods used to diagnose Osteoporosis or low bone mass. Although there are various methods available to assess bone density, the worldwide accepted gold standard is Central Dual Energy X-ray Absorptiometry (commonly referred to as a DXA or DEXA scan).

dxa page photoThe DXA is a simple, painless scan that involves lying on a table for several minutes while a small x-ray detector scans your spine, hip, or forearm. Patients can choose to leave their clothes on as long as they are not wearing any metal. Patients who are scanned will be asked to lift their legs onto a support to straighten the back for the test. The test is safe and does not require any injections or any other discomfort. There is a very small amount of radiation from the DXA test. In fact, the amount of radiation a patient gets exposed to during a DXA scan is similar to the dose we receive every day from the environment's natural background radiation. The radiation from a DXA scan is actually less than the radiation exposure we get with two hours of direct sun exposure or the radiation exposure we get on an average airline flight.

How does a bone densitometer measure bone density?

A bone densitometer uses a detector to measure the transmission of small amounts of x-rays (light) through the bones. The amount of light that passes through the bone is measured and this value is converted into a value that is commonly used to measure the density (mass/unit volume) of a material or compound. Although an image is produced during the scanning, the physician who reads a DXA scan does not really interpret the image like he/she would when looking at an x-ray, CAT scan, or MRI. The key value is a machine-generated number that represents the bone mineral density, which, by convention, is expressed in grams/cm2 (this describes how "thick or thin" the bones are).

Although the bone density values are helpful, these are somewhat cumbersome to use in the setting of patient care. In addition, these values don't have much meaning when expressed individually and not referenced to a "normal value." In a series of meetings held in Rome (1992), the World Health Organization convened a panel of experts (WHO Study Group) to help assign reference ranges for the raw bone density scores which were obtained by densitometers. In 1994, the WHO Study Group published a report that coined the term "T-score"; these "T-scores" were values that referenced measured Bone Mineral Density against the "normal" bone density expected to be found in young pre-menopausal adult women. T-scores are, in fact, standard deviations of difference from the values seen in a young healthy premenopausal woman. The following are the agreed-upon definitions of the T-scores

  1. T score greater than or equal to (=) -1.0 = Normal
  2. T score less than or equal to (=) -2.5 = Osteoporosis

Who Should have Bone Density Testing?

  • Women aged 65 and older
  • Postmenopausal women under age 65 with risk factors for fracture
  • Men aged 70 and older
  • Men under age 70 with clinical risk factors for fracture
  • Adults with a fragility fracture
  • Women during the menopausal transition with clinical risk factors for fracture
  • Adults with a disease or condition associated with low bone mass or bone loss
  • Adults taking medications associated with low bone mass or bone loss
  • Anyone being considered for pharmacologic therapy
  • Anyone being treated, to monitor treatment effect
  • Anyone not receiving therapy in whom evidence of bone loss would lead to treatment

Reporting

Our DXA reports are clear, concise and timely. Furthermore, when indicated, all of our reports include the World Health Organization's FRAX® absolute fracture risk values. This absolute fracture risk helps make treatment decisions and has been endorsed by the National Osteoporosis Foundation.

FRAX®

While we are intimately aware of the terms "T-scores", "Osteopenia" and "Osteoporosis", we are most strongly focused on preventing a fracture, whether this is a patient's potential first fracture or future fractures in patients who have already fractured.

In keeping with this philosophy, we have espoused the World Health Organization's absolute fracture risk algorithm (FRAX®). This validated tool integrates clinical information about a patient (age, weight, sex, prior fracture, smoking/alcohol use, steroid use, family history of hip fracture, secondary causes of osteoporosis, rheumatoid arthritis) and combines this with the bone density values to come up with a meaningful 10 year probability of fracture. This tool has been endorsed by the National Osteoporosis Foundation and the results serve as a guide to help decide which patients would benefit from drug treatment for their osteoporosis.

The Arthritis & Osteoporosis Center of Southwest Ohio is a member of the National Osteoporosis Foundation's Professional Partners Network®


References:

  1. International Society of Clinical Densitometry, Official Positions Brochure (www.iscd.org), 1997.
  2. International Society of Clinical Densitometery, Bone Density Course Clinician Syllabus, 2008.
  3. Faulkner, K. The tale of the T-score; review and perspectives. Osteoporosis International (2005) 16: 347-352.