Bone Densitometry No Room For Doubt
Edition: April 2003 - Vol 11 Number 04
Author: Laura Thill
Since the first table X-ray units were introduced in 1987, a new generation of bone densitometers has emerged. Today, while still offering the larger units, manufacturers make portable, more affordable ones as well. Nevertheless, as much as 80 percent of physicians’ offices are not properly equipped to perform bone assessments, notes Bill Elliott, executive vice president of Quidel Corp., in San Diego, Calif. And, only 20 percent of those at risk for osteoporosis actually receive bone densitometry testing, according to Markus Maritz, president of Somerset-N.J.-based Sunlight Medical.
Dual X-ray absorbtiometry (DXA) technology is designed to measure the rate of X-ray absorption in the bone caused by its mineral density, according to Maritz. “A high level of mineral density will absorb X-rays at a higher rate,” he notes.
“DXA is based on the utilization of two specific energy peaks,” adds Gitte Andreasen, a marketing manager at GE Lunar in Madison, Wis. “One peak will be absorbed by both bone and soft tissue as it passes through the body, whereas the other energy peak is preferentially absorbed by bone. The absorption [by] bone can be calculated mathematically and converted to a measurement of bone density,” she explains.
Typically found at larger clinics or specialty providers, these units are larger and more expensive (costing between $45,000 and $90,000, according to Maritz). They measure bone at the spine or hip. Advances in DXA include a lower level of radiation exposure, greater speed and accuracy and computer enhancements.
GE Lunar has enhanced the precision of its bone measurement techniques. For example, through advancements in hip assessment, the company can offer:
• Hip axis length measurement. An adjunct to femur bone density in predicting fracture risk.
• Dual femur. Identifies the weaker femur while improving precision over single-femur measurements.
• Dual-energy vertebral assessment. Identifies and quantifies vertebral fractures. (Existing vertebral fracture doubles a patient’s risk for future fractures, regardless of the bone density.)
• One-scan technology. Acquires typical spine and dual femur sites in one process, from a single patient position. Requires less operator training and patient positioning.
• Computer Assisted Densitometry (CAD). Detects anomalies and then displays explanations and instructions. A computer flags any problems for the operator, rather than leaving that up to operator discretion.
Hologic, of Bedford, Mass., which reportedly introduced the first X-ray table unit in 1987, has also developed more precise devices for evaluating bone. In 1995, the company marketed the clinical Fan-Beam unit, designed to deliver quick, high-resolution images using low radiation doses. In 2002, Hologic introduced Instant Vertebral Assessment IVA technology, targeting the 30 percent of patients who require treatment, but are overlooked by conventional bone mineral density (BMD) results.
Features of Fan-Beam offered today include:
• Express BMD. Scans and reports bone and hip results in 10 seconds with over 1 percent precision.
• Image Pro. Advanced digital imaging.
• CAD fx. Computer-aided fracture assessment tool quantifies vertebral compression.
• Electronic reporting.
• Instant vertebral assessment. Ten-second, single-energy imaging of the spine.
Also new to the market as of 2002 is the Hologic Discovery. Features of this unit include:
• OnePass Technology. Single sweep scanning in 10 seconds.
• True Fan-Beam Geometry. Enables rapid, high-resolution single-energy imaging in addition to dual energy bone density measurements.
• Internal Reference System. Offers
automatic pixel-by-pixel calibration for more precise results.
• Hologic Anthropomorphic QC Phantom. Confirms system stability with a life-like standard.
The Good and Bad of DXA
Central DXA technology is well-established and well-supported by clinical data, according to Maritz. One of the greatest advantages of these units is their capacity to measure at multiple sites and directly at critical fracture sites – for instance, the hip and spine. DXA units are well-suited to larger clinics and hospitals, with trained or certified operators, notes Maritz.
Because patients and operators are exposed to a minimal dose of radiation, however, the technology may be used only with clinical indication – not for general screening. DXA reportedly only measures area density – not volumetric density. And it only measures BMD – no other bone properties.
Nevertheless, “DXA is fast, highly accurate and permits physicians to follow patients over time,” says John Jenkins, senior product manager, Hologic.
“Precision is key when choosing a densitometer,” says Andreasen. “DXA of the spine and femur is considered a standard for diagnosis of osteoporosis,” she notes, adding that the femur is a critical body site to assess for bone density. “Femur fractures are considered the most serious fracture,” she says. “They’re expensive and have a high negative impact on quality of life after surgery, since the patient rarely gets back to [his or her] previous mobility.”
Although this technology may not be as diagnostically sensitive as central DXA, peripheral DXA is considered a good alternative when central DXA is not available, according to Andreasen. It measures the forearm, a critical fracture site, according to Maritz.
Peripheral DXA is geared for use in smaller clinics and primary care offices, notes Maritz. “It’s affordable and, to an extent, transportable.”
At the same time, Maritz continues, “peripheral DXA is limited to a single measurement site. It measures only BMD and no other bone properties.” In addition, he continues, “it may only be used by a certified operator; it requires site registration in many states; and it may be used for public health screening events.”
Peripheral technologies include DXA devices for the forearm and heel, radiographic absorbtiometry devices for the finger and peripheral computed tomography devices, according to Maritz. “They’re typically priced between $15,000 and $25,000, and are often bound to similar registration and certification rules as for central X-ray based technologies,” he says.
An example of peripheral DXA is Pleasanton, Calif.-based Norland Medical System’s Apollo DXA Bone Densitometry System, which measures the weight-bearing trabecular bone in the OS calcis. Features include:
• A 15-second scan time.
• Accuracy of 2 percent or greater.
• Detailed report and readable graph.
• Off- or on-site scanning.
• Dry heel scanning.
• Low radiation exposure (0.2 mRem).
Ultrasound densitometry, available since 1997, has proven to be a popular tool for evaluating bone. These units assess bone by measuring the speed of sound traveling through it. In addition, ultrasound assesses bone elasticity, cortical thickness and micro architecture of the bone. Units range from $10,000 to $20,000, according to Maritz.
Ultrasound has proven to be a popular method for measuring bone density. “Studies show that the heel is the second best site after the femur to predict the risk of fracture,” says Andreasen. Physicians should ask their sales rep for prospective studies showing that a particular device can predict fractures similar to DXA predictions of the hip and spine, she adds.
“Ultrasound units are lightweight, portable and affordable,” says Hologic’s Jenkins. And, of course, they require no X-ray.
“No special room or certified technician is necessary [for ultrasound units],” adds Bill Elliott of Quidel.
Sunlight and Quidel, two pioneers in ultrasonometer technology, offer a number of options for physicians and clinicians.
Sunlight’s Ultrasound Omnipath is designed to measure bone density at multiple skeletal sites – both the wrist and forearm – while eliminating soft tissue effect. Reportedly, it’s easy to use and the operator requires no special certification. The Omnipath applies World Health Organization criteria for test results, similar to that of DXA, notes Maritz. And during use, the operator and patient sit face-to-face for added convenience. The technology is new, says Maritz, and it’s gaining more clinical acceptance.
Another of Sunlight’s products, the Omnisense (7000 and 8000), also employs ultrasound technology, but in a different way. Rather than sending ultrasonic waves across the bone, as is common with heel devices, the Omnisense measures the speed of sound moving along the bone. Referred to as Axial Transmission Technology, the system is designed to avoid soft tissue interference. Precision is reportedly high – less than one percent – and the user error rate is relatively low, according to Maritz.
Quidel’s QUS-2 Calceneal Ultrasonometer is yet another solution in ultrasonometry. The QUS-2 measures the quality of calcneus by sending acoustic energy – or ultrasound – from one transducer to another through the heel bone. The QUS-2 analyzes the ultrasound that crosses the heel to determine the patient’s calcaneal Broadband Ultrasound Attenuation (BUA). The BUA, in turn, can be compared to results from a reference population, notes Quidel.
Designed for a small clinic or physician office, the transportable QUS-2 weighs seven pounds. Because it’s a dry system, traditional clean-up issues associated with wet systems are avoided. Features include:
• Less than two-minute process from start to finish.
• Unit can operate on rechargeable battery power or AC power.
• Water-based gel is easily cleaned up.
During scanning, mobile transducers move along the patient’s heel, sending a broadband ultrasound signal into the heel. The transducers then locate and scan a region of interest – an area about one centimeter large. The system analyzes the resultant signal and calculates the BUA in decibels per megahertz. To determine the T-school, the patient’s BUA is compared to a
For more information on the best bone assessment options for your customers, manufacturers recommend visiting their Web sites for product and reimbursement news.
What You Should Know About Osteoporosis
A disease characterized by low bone mass and deteriorating bone tissue, Osteoporosis is not limited to the elderly, as some may believe. Bone loss generally occurs without symptoms, and patients often are unaware of their condition until they experience a fracture or collapsed vertebra. Collapsed vertebrae usually cause severe back pain and loss of height or kyphosis.
Today, nearly 34 million Americans, or 55 percent of people 50 years and older, have low bone density, according to the National Osteoporosis Foundation (NOF). Eight million women and two million men are afflicted with osteoporosis.
Over 1.5 million fractures occur annually, costing the country more than $47 million daily in hospital and nursing home expenditures. The more typical fracture sites due to osteoporosis include the hip, wrist and ribs, although any bone can be affected. The rate of hip fractures for women is two to three times higher than that for men. Men, on the other hand, have nearly twice as high a risk of dying within a year after fracturing a hip.
The following factors may increase a person’s chances of developing osteoporosis, according to the NOF:
• Personal history of fracture after age 50.
• Being female.
• Being thin or having a small frame.
• Advanced age.
• Current low bone mass.
• Family history of osteoporosis or fractures.
• Postmenopausal estrogen deficiency.
• Anorexia nervosa.
• Diet low in calcium.
• Use of such medications such as glucocorticoids and anticonvulsants.
• Low testosterone levels in males.
• Abnormal absence of menstrual periods.
• Inactive lifestyle.
• Excessive use of alcohol.
Caucasians and Asians have the greatest risk for osteoporosis, although African Americans and Hispanic Americans also have a substantial risk.
The following FDA-approved medications help prevent or treat osteoporosis in postmenopausal women:
• Bisphosphonates (alendronate and risedronate).
• Estrogen/hormone replacement therapy.
• Selective estrogen receptor modulators (SERMs) – specifically, raloxifene.
Of these, alendronate is also approved to treat osteoporosis in men and glucocorticoid-induced osteoporosis in both men and women. Risedronate is approved for preventing or treating glucocortcoid-induced osteoporosis in men and women as well.
Treatments still being investigated include parathyroid hormone, sodium fluoride, vitamin D metabolites and other bisphosphonates and SERMS.
For more information on osteoporosis, visit the National Osteoporosis Foundation at www.nof.org.