The field of bone health made a giant leap forward with the development of bone mass measurement devices. A standard x-ray can confirm the diagnosis of a fracture. However, an x-ray can only begin to detect low bone density after an estimated 30 percent loss of bone mass. Therefore, more sensitive devices have been developed.
The current best noninvasive test for bone mass measurement is dual-energy x-ray absorptiometry (DXA), commonly referred to as a bone density scan. It is a simple and painless test that uses low doses of radiation.
The amount of bone mass measured is called bone mineral density (BMD). Because minerals contribute to bone strength, bone mineral density serves as an important indicator for risk of a fracture. An estimated 60 to 80 percent of bone strength is related to bone mineral density. Lower bone mineral density predicts a higher risk of fractures; conversely, improvement in bone mineral density reduces the risk of fractures.
The best predictor for a specific fracture is to measure bone density at that skeletal site. Typically, bone density scans are done of the hip and the lower back (lumbar) region of the spine, which are sites of major osteoporotic fractures. The diagnosis of osteoporosis is based on results from the hip and spine, and in some circumstances, the forearm also may be used. Bone loss at the hip and spine may occur at different rates. Changes in bone density can be assessed with repeat scans, usually at intervals of two years or, if indicated, at shorter intervals.
WHAT DOES DXA MEAN?
The term DXA is short for dual-energy x-ray absorptiometry. The full name is descriptive of the technique. The dual-energy x-ray part of the name accounts for the use of two different energy levels of x-ray. Absorptiometry refers to the radiation passing through the various body tissues that have different patterns of absorption. The differences in the two beams of radiation that pass through your body's tissues allow the bone measurement to be subtracted from the surrounding tissues. The result is a calculated measure of bone mineral density quantified in grams per square centimeter (g/cm2).
The DXA system that measures your hip and spine consists of a table, a radiation source usually beneath the table, a radiation detector above the table, and a computer. The DXA measures the lower area of the spine (lumbar spine, first to fourth levels) and hip (femur). The regions of the hip that are scanned and reported on vary a bit between scanners of different manufacturers.
The manufacturers of DXA machines most widely used in the United States are General Electric (GE) Healthcare and Hologic. A small number of Norland machines are also in use.
Many of these machines are also able to scan other parts of the body including the forearm and the whole body. The whole body scan also provides information on body composition, such as percent fat and lean muscle mass. Some scanners can provide a vertebral fracture assessment, which is a picture of the upper and lower spine that is used to discover silent spine fractures.
The amount of radiation exposure is extremely small and equivalent to about an hour-long flight on a jet airplane. The x-ray is a small beam that is focused on the table and does not scatter beyond it. Therefore, the technologist performing the test can stay in the room adjacent to the table. The test is safe and each site measured only takes a few minutes to complete.
Smaller portable units are used to scan the forearm, heel, shin (tibia), or finger. These may be useful in predicting fracture risk, but they are not used for diagnosis (except at the forearm).
HOW DO YOU KNOW IF YOU NEED A DXA?
Bone density scans are done in women near to menopause (perimenopause) or after menopause and in older men. In general, premenopausal women, with a few exceptions, do not need to be tested. However, a premenopausal woman may need a bone density scan if she is taking certain medicines such as steroids, has certain conditions such as celiac disease or an eating disorder, or is being evaluated for recurrent fractures.
If you are perimenopausal or postmenopausal, you should discuss with your doctor whether a DXA is an appropriate test for you. Men fifty and older should have the same discussion. The timing of your initial test depends on the presence of risk factors for osteoporosis and fractures. Recommendations for testing include:
- Screening. If you do not have any known risk factors, a screening DXA is recommended at age sixty-five for women and at age seventy for men. Similar to screening mammograms or colonoscopies, you get tested to check for the presence of a disease in the absence of symptoms. However, since most fractures occur in women with low bone mass, these screening recommendations may not go far enough in identifying women at higher risk for fracture. An earlier DXA following menopause may be helpful in establishing your baseline. Men have higher bone mass to start with and slower bone loss; therefore, the age for screening is set higher.
- At Risk. If you do have risk factors for osteoporosis and fractures, a DXA test should be done earlier than age sixty-five for women and seventy for men. The goal is early identification and interventions to prevent fractures.
WHEN TO GET A DXA TEST
Screening
- Women age sixty-five and older
- Men age seventy and older
Risk Factors Present
- Women during the menopausal transition with risk factors for fracture
- Postmenopausal women under age sixty-five with risk factors for fracture
- Postmenopausal women discontinuing estrogen therapy
- Men under age seventy with risk factors for fracture
- Adults with a fracture after age fifty
- Adults with a disease or condition associated with low bone mass or bone loss
- Adults taking medicines associated with low bone mass or bone loss
- Anyone considering prescription medicines for treatment of osteoporosis
- Anyone being treated for osteoporosis to monitor treatment
- Anyone not receiving therapy in whom evidence of bone loss would lead to treatment
Sources: International Society for Clinical Densitometry and National Osteoporosis Foundation
HOW DO YOU SELECT WHERE YOU HAVE A DXA?
In most cases, you don't have a choice. Your doctor orders the test and you go to the location he uses. Your bone density results are determined by many factors that are in the hands of the center where your bone density is performed. Assurance of quality is important for accurate results.
Attempts at establishing a system for standardization of DXA centers have fallen flat after a pilot program. Unfortunately, no current standardization is in place for DXA tests as there is for other tests such as mammograms. This translates into wide variability in quality. However, technologists who run the DXA tests and physicians who interpret the DXA tests may have certification in bone densitometry. The International Society for Clinical Densitometry (ISCD) provides educational courses and a standardized testing process for clinicians and technologists. Those clinicians who successfully meet knowledge requirements are designated certified clinical technologists (CCD), and technologists are designated as certified bone density technologists (CBDT).
HOW DO YOU PREPARE FOR A DXA?
No special preparation is required. For comfort, you may want to wear pants without a zipper or metal closures. Often you will be asked to change into a patient gown. In the event that you have undergone a test in the radiology department that required oral contrast within two weeks prior to your testing date, you will need to reschedule your DXA. The contrast might not have fully cleared from your system, and this could influence the DXA.
HOW IS THE DXA DONE?
For a central DXA that includes imaging of your hip and spine, you will lie on a flat, padded surface.
Positioning for the hip depends on the DXA machine. Some machines have the capability of imaging both hips simultaneously. You will lie on your back for all machines. One foot or both feet are moved into a positioning device to hold your hip in place at the correct angle.
For the spine scan, you lie still on your back and your legs may be raised on a cushion to flatten your back against the table.
Examples of scans from Hologic and GE Healthcare DXA machines are shown on the following pages.
Bone Density-Hip
| Name: | Sex: Female | Height: 60.0 in. |
| Patient: | Ethnicity: White | Weight: 114.0 lb |
| DOB: | Age: 55 |
Bone Density-Lumbar Spine
| Name: | Sex: Female | Height: 60.0 in. |
| Patient: | Ethnicity: White | Weight: 114.0 lb |
| DOB: | Age: 55 |
| Patient: | Patient ID: |
| Birth Date: age 52 | Referring Physician: |
| Height/Weight: | Measured: |
| Sex/Ethnic: Female/White | Analyzed: |
Bone Density-Left forearm
| Name: | Sex: Female | Height: 63.0 in. |
| Patient: | Ethnicity: White | Weight: 124.0 lb |
| DOB: | Age: 79 |
WHAT YOU NEED TO KNOW ABOUT YOUR DXA RESULTS
Test results may vary depending on the protocol from the DXA center. The majority of the time, only the report of the DXA is provided to you and your doctor. I encourage both you and your doctor to also get a copy of your complete bone density scan (what some people call “the pictures and the graphics”) to review and keep for your records.
As an aside, keeping a copy of all your records, laboratory results, and reports is a good idea. Even with the move to electronic data records, your personal records will help you track your own information. You will have the comparison data readily available. It helps to stay informed and understand the measures of your health status.
If you were sitting down with me, I would systematically guide you through all the parts of the DXA scan printout and report. In this book, I am trying to do the virtual equivalent. And fortunately, we have the luxury of time. Don't expect your busy primary care doctor to do this. You will want to spend your time with him discussing what to do on the basis of the results. If you are not taking osteoporosis medicines, ask your doctor to calculate your FRAX score if it was not done as part of the DXA.
If you have a copy of the actual printout showing the images of your hip and spine, follow along with your papers out in front of you. On the other hand, if you have a summary report, you will find the descriptions helpful in giving you an idea of what the report is talking about. If you are reading for general knowledge, the accompanying pictures will illustrate each step. Examples are given from scans done on GE Healthcare and Hologic DXA machines.
STEP-BY-STEP
Step 1: Look at your identifying information.
Make sure all your demographic information is listed correctly. An inadvertent transposition of a birth date or selection of wrong race will throw off the results. This does happen!
- Your name
- Date of birth
- Age
- Race
- Height
- Weight
Step 2: Look at the image.
The image tells you right away which body site is being reported, hip or lumbar spine, or in some instances, forearm as well.
Hip
As shown on the images, the neck region (also known as the femoral neck) is the narrowest part of the hip. Other regions of interest that may be reported include the greater trochanter (troch) and intertrochanteric region (inter) or shaft. Depending on the manufacturer, the total hip is comprised of the neck, trochanter, and intertrochanteric, or shaft areas.
Lumbar Spine
The first through the fourth lumbar vertebrae are scanned. The abbreviations L1, L2, L3, and L4 are used for each level. The total lumbar spine is referred to as L1-4. If fewer levels are used, the level not used is grayed out. A minimum of two lumbar levels are required for diagnosis.
Step 3: Look at the numbers—BMD and Standardized T-scores and Z-scores
Bone mineral density (BMD) quantifies your bone mass. It is a calculated measurement. The bone mineral content (BMC, a measurement of the amount of calcium) of each region is measured and divided by the area of that region. The resulting number is BMD.
Your BMD results are compared to two different reference populations to derive the T-score and Z-score. The T-score is the comparison of your results with young adults of the same sex at the time of peak bone mass. Regardless of ethnicity, you are compared to the reference group of young Caucasian women ages twenty to thirty. Men are compared to a reference group of young Caucasian adult males.
The Z-score is the comparison with individuals of the same age and ethnicity from a reference database. For example, if you are female, age fifty-five, and Asian, your BMD results for each region are compared to a reference group of fifty-five-year-old Asian women.
The conversion of BMD to standardized scores allows for a systematic assessment of results. The diagnosis of osteoporosis is based on T-scores for postmenopausal women and men age fifty and older. Z-scores are used for assessment of premenopausal women, men under the age of fifty, and children.
The summary data boxes give the numbers for each scanned region.
As shown above, the regions of the hip displayed on the report vary between manufacturers, though all provide neck and total hip scores. For each region listed, look at the numbers one column at a time. On the GE report, the standardized scores follow the BMD column. The T-scores and Z-scores are expressed in two ways: by number and by percentage. The Hologic example provides area, BMC, BMD, T-score, and Z-score for each region of the hip.
Note the area of the hip called Ward's area or Ward's triangle. Many times, it is the lowest score. Ward's area does not have any clinical relevance and should not be used for diagnosis. This area is not included in the total hip. In short, you can ignore this measurement altogether.
Some machines have the capability of scanning both hips at the same time. Each side, left and right, is reported separately. In addition, the average or mean of both hips is given, as well as the difference between hips. The lowest scores are used for diagnosis.
Each level of the lumbar vertebrae is individually measured and scored. The average of L1-L4 or Total is given for all four vertebrae unless one or two levels are excluded.
Step 4: Look at the graph.
Look at the top of the box to see which site is being displayed. These two examples are total hip. On the graph, BMD of the total hip is plotted by age. The reference curves are age-matched; therefore, the dots plotted represent the Z-score. The middle line represents the reference average equivalent to a Z-score of zero. On the GE graph, the upper line represents 1.0 standard deviation above average or a Z-score of 1.0. The lower line represents a Z-score of -1.0. For the GE example shown below, the total hip BMD result of 1.099 is plotted at age fifty-two and marked with a small box. This corresponds to a total hip Z-score of 1.1 and a T-score of 0.7.
On the Hologic graph, the reference curves are for 2.0 standard deviations above and below average. This printout shows the area between the average line and 2.0 filled in with a light shade and the area between the average line and -2.0 filled in with a darker shade. The symbol used is a plus sign within a circle. For the Hologic example, the total hip BMD of 0.785 is plotted at age fifty-five. This represents a Z-score of -0.6 shown below the average line in the dark shaded area.
Step 5: Look at the DXA report for diagnosis.
The physician who reads the DXA will make a summary report and give a diagnosis. The diagnosis is based on set of criteria that are used universally. The lowest of three sites—femoral neck, total hip, or lumbar spine—is used to make the diagnosis. It is common to have different results at the different sites of measurement. For example, in early menopause, it is common to see the spine lower than the hip. When estrogen levels drop, the spine loses bone faster than the hip.
DIAGNOSIS OF OSTEOPOROSIS
In 1994, the World Health Organization (WHO) established the criteria for diagnosis of osteoporosis based on known fracture levels for white postmenopausal women. The T-score results are used to define the different categories.
| Diagnosis | T-score |
| Normal | -1.0 and higher |
| Osteopenia or low bone mass | Between -1.0 and -2.5 |
| Osteoporosis | -2.5 and lower |
| Severe Osteoporosis | -2.5 and lower with fracture |
These criteria can only be applied to measurements of the lumbar spine, total hip, or the narrowest region of the hip called the femoral neck. The diagnosis is based on the lowest T-score among these sites. The forearm region called the distal one-third radius may also be used for diagnosis.
If a DXA scan of the hip and spine had the following T-scores,
| Femoral Neck | -2.2 |
| Total Hip | -1.8 |
| L1–L4 | -2.6 |
then the diagnosis would be osteoporosis based on the results of the lumbar spine.
In women prior to menopause or men under age fifty, Z-scores are used for diagnosis. A Z-score of -2.0 or lower is defined as “below the expected range for age.” A Z-score above -2.0 is “within the expected range for age.”
A low Z-Score (level lower than -2.0), at any age, may indicate that some other process or disease may be contributing to low bone density. An evaluation to look for the causes of low bone density may be indicated.
Step 6: Calculate FRAX for fracture risk if you have low bone density.
Some of the newer DXA machines have the software to calculate the FRAX after you have provided information for the risk factors. Otherwise, the FRAX may be calculated online (Google FRAX to find it). It also can be accessed via a dedicated smart phone application. An assessment of risk factors, along with your bone density, will provide a more complete picture of your fracture risk. Talk with your doctor to see if this is an appropriate evaluation for you.
Note: This tool is to be used in individuals with low bone mass who have not received any prescription osteoporosis medicines or estrogen therapy. The reason for this restriction is that the relationship between bone density and fracture risk changes with treatment. A small increase in bone density makes a much larger improvement in fracture risk. The FRAX tool is based on untreated women and men. This is important. Do not use it inappropriately; if you do, you will not get the correct information. There is currently no assessment tool for individuals who are already receiving treatment.
How does adding FRAX change your evaluation? Use of T-scores alone does not identify all the individuals at high risk for fracture, since not everyone at the same T-score is alike. Other factors must be taken into account. FRAX is a more comprehensive tool for identifying the individuals who will benefit most from treatment because it quantifies your fracture risk using the combination of risk factors and bone density.
For instance, age is a strong risk factor for fracture. If you are fifty years old and have a T-score of -2.0, your risk of fracture is much lower than the risk faced by an older woman with the same score. This relates to the microstructure or quality of bone. With age, there is more accumulated microstructure loss. Therefore, the quality of bone is poorer, making the bones weaker and more likely to fracture than in a younger person with the same score. The higher risk individual may benefit from prescription therapy even though she doesn't have the diagnosis of osteoporosis. On the other hand, someone at low risk of fractures does not need to go beyond the general measures.
The best way to illustrate this point is with an example.
My college girlfriend Kitty contacted me after having her first DXA scan. Without using FRAX to account for her risk factors, her physician had recommended she start prescription osteoporosis medication based on the results of the DXA scan. She wanted to know if this was the right thing to do. I told her, “Send me your information. After reviewing your bone density results, I will be happy to give you my opinion.”
I asked her for a copy of the actual DXA scan. However, she was only able to get a copy of the radiology report, which she forwarded to me. Her findings were as follows:
The lumbar spine (L2-L4) BMD is 0.924 g/cm2 with a T score of -1.10 and Z score of -0.76. The hip (femoral neck) BMD is 0.838 g/cm2 with a T score of -1.27 and a Z score of 0.04 and the Ward's Triangle BMD score is 0.6398 g/cm2 with a T score of -1.69 and a Z score of 0.07.
Based on the World Health Organization (WHO) criteria, her diagnosis is osteopenia, or low bone mass, as it is preferably called. To answer the question of whether Kitty needed to take medication, several other factors had to be taken into consideration. The overall goal is to prevent fractures.
Does Kitty have any risk factors that would contribute to a high risk of fracture? Looking into her personal and family health histories, she has never had a fracture, both of her parents are healthy and active into their late eighties, and her parents have neither experienced fractures nor been diagnosed with osteoporosis. In addition, Kitty has never taken steroids or smoked. She is healthy and has no chronic diseases such as rheumatoid arthritis. She does not take any medications that may be harmful to the bone. She is a social drinker (one or two glasses of wine per week) and she exercises regularly, mixing a gym routine with weights and walking. Her health history shows that she does not have any significant risk factors associated with osteoporosis.
I entered Kitty's information into the FRAX calculation tool for US (Caucasian), which included her weight (130 pounds converted to kilograms by the program), her height (66 inches converted to centimeters), her age (55), her gender (female), and answered “no” for the clinical risk factors of:
Previous fracture
Hip fracture in her mother or father
Current smoking
Steroid use
Rheumatoid arthritis
Secondary osteoporosis (this risk factor is not used in the calculation if BMD is entered)
Alcohol three or more units a day (one unit equals 10 ounces of beer, a one-ounce shot of liquor, or a four-ounce glass of wine)
Her femoral neck BMD was the last piece of information I entered. Then, I hit the “calculate” button. Note: If you forget to input any of the necessary information, an error message will be displayed.
A bright red box appeared, which showed the ten-year probability of fracture for the categories of major osteoporotic fracture and hip fracture. Four types of fracture comprise the major osteoporotic fracture category: forearm, shoulder, hip, and clinical spine fractures (these are the ones that are associated with symptoms, most commonly pain).
Kitty's ten-year probability of fracture with a femoral neck BMD T-score of -1.27 and no clinical risk factors for major osteoporotic fracture is 5.6 percent; and for hip fracture alone, her ten-year probability is 0.4 percent. Using the FRAX tool, Kitty's calculated ten-year risk of major osteoporotic or hip fractures is quite low.
Although the FRAX tool uses only one skeletal site of measurement, the femoral neck, the lumbar spine measurement should not be ignored. It needs to be taken into account as well. If the BMD at the lumbar spine is lower than at the hip, actual fracture risk may be higher than estimated by the FRAX score. For Kitty, the lumbar spine T-score of -1.10 was similar to the results of her femoral neck T-score.
The National Osteoporosis Foundation's treatment guidelines, which were released in 2008, incorporate the FRAX tool. For a postmenopausal woman with low bone mass (T-score of -1 to -2.5), FDA-approved therapies are recommended if the ten-year fracture probability for hip is 3 percent or greater or the ten-year fracture probability for major osteoporotic fractures is 20 percent or greater.
Based on these treatment recommendations, her lumbar spine BMD, and no other contributing risks, Kitty does not need to take any bone-specific drug at this time. She should continue with her bone-healthy regimen that includes adequate calcium, vitamin D, and exercise. A repeat DXA would be recommended in two to three years.
Armed with the information about risk, Kitty talked with her doctor, who agreed with the new assessment and plan.
Step 7: Make decisions.
Now that you have your T-score and ten-year probability of fracture, what should you do with the information?
Let's look at another example.
Leslie, age fifty-five, is five years postmenopausal and has just had her DXA. She, too, wonders: “Should I be taking a medicine for my bones?”
Because she is adopted, she does not know her family history. She is healthy, has no chronic problems, and takes no prescription medications. She takes a daily calcium supplement that includes vitamin D and a multivitamin for a total of 1,000 mg of supplemental calcium and 1,000 International Units (IUs) of vitamin D. She exercises regularly.
The results of her DXA are:
| Region | BMD | T-Score |
| Left femoral neck | 1.003 | -0.2 |
| Left hip total | 1.009 | 0.7 |
| Right femoral neck | 1.019 | -0.1 |
| Right hip total | 1.089 | 0.6 |
| Lumbar spine L1–L4 | 0.857 | -2.8 |
Leslie has quite different results at the spine and hip. Her spine bone density is much lower than her bone density at the hip. This is called skeletal discordance, which is a common occurrence, particularly in early menopause. Her spine BMD is lower than -2.5. Therefore, her diagnosis is osteoporosis. In addition, she had a lateral vertebral fracture assessment (VFA) that showed no evidence of any fractures.
Since the FRAX model only uses the femoral neck BMD to calculate the ten-year fracture probability, Lisa's fracture probability will be underestimated if the lumbar spine is not taken into account. Since Lisa's diagnosis is osteoporosis, it is not necessary to calculate her FRAX score.
This is one scenario where the fracture risk assessment tool is limited. In early postmenopausal women, because of rapid bone loss at the spine, the spine BMD commonly is lower than the BMD of the hip regions. Just as with any tool, the FRAX model has limitations, so you must consider your entire medical picture.
Lisa's vitamin D levels were reported to her as normal and other evaluations for bone loss did not yield any other factors. Her gynecologist recommended FDA-approved medicine options for her to consider.
TREATMENT GUIDELINES
The National Osteoporosis Foundation's guidelines for treatment using FDA-approved medicines for postmenopausal women and men fifty and over include:
- History of a hip or spine fracture;
- Osteoporosis by T-score at the hip or spine; or
- Low bone mass (T-score of -1.0 to -2.5)
AND
ten-year fracture probability (FRAX score)
for hip fracture of 3 percent or greater OR
for major osteoporotic fractures of 20 percent or greater
WHAT OTHER DXA EVALUATION MAY BE ORDERED FOR ASSESSMENT OF YOUR BONE HEALTH?
The newer DXA machines are able to scan the upper and lower areas of the spine in order to detect spinal fractures. This test is referred to as a vertebral fracture assessment (VFA). Since the majority of spine fractures are silent, identification of a fracture through this imaging would change your risk profile. The VFA information combined with results of your DXA, plus the evaluation of risk factors, will provide a comprehensive picture of your overall risk.
If you have the test done on a Hologic machine, their scan is called instant vertebral assessment (IVA). The GE Healthcare machine refers to their test as dual-energy vertebral assessment (DVA).
In the example with fracture of the first lumbar vertebra, this level would also be seen on the regular DXA spine scan. If the fracture were located in the thoracic spine, then vertebral fracture assessment would identify the spine fracture that the lumbar DXA would have missed.
POSSIBLE LIMITATIONS OF THE LUMBAR SPINE DXA
The lumbar spine DXA may give results for bone mineral density that appear to be good numbers but actually are not. Particularly with aging, degenerative changes may occur that distort the vertebral bodies. A good example of this would be arthritis, which shows up as higher bone density, giving a misleading reading. Calcifications in other places may also falsely increase density results. For example, calcification in the aorta, which lies just in front of the spine, would do this. A fracture of one of the lumbar vertebrae, if not excluded, would also show up as a denser bone when, in fact, it is not.
If underlying problems are identified, one or two of the four levels of lumbar vertebrae that are scanned can be omitted from the analysis, but a minimum of two levels are necessary for a valid evaluation. In some situations, the spine bone density results may not be useful because the changes take place in three or all four of the vertebral bodies (L1-L4), which necessitates reliance on the hip site only. In addition, the nondominant forearm can be scanned as an alternative site to the lumbar spine.
WHAT DXA SCANS DON'T TELL YOU
Bone density results from a DXA are two-dimensional and do not adjust for bone size. However, bone size matters. If you have a small frame, your bone density tends to be lower than the bone density of someone taller with a larger frame.
Bone mineral density is a static measure. For your first bone density, it is not known how you arrived at your present level. Did you start out with much better bone and then lose bone to get to your present point, or have you had low bone density for quite a while? You may have started with less than optimal peak bone mass.
If you are in early menopause, your baseline bone density may look great but your bone turnover may be high, putting you at risk for fast bone loss. The baseline scan tells your past history, but it does not give any information about the current rate of loss. The rate of bone loss is an independent risk factor for fracture.
Bone quality or microstructure is not evaluated. Two individuals with the same bone density may not have the same fracture risk. If one is age fifty-five and the other is seventy-five, the older person has a much greater risk. This is where fracture assessment is helpful, since bone density DXA scans provide no direct measurement of bone quality.
Nevertheless, DXA is the best test for assessing bone density. Newer technologies with increased capabilities are under development that will go beyond quantifying bone density and will examine the quality of the microstructure. These newer technologies will expand and improve the capabilities of bone mass assessment.
|
The Bare Bones
|