Understanding Your REMS Bone Scan
Frequently Asked Questions
Bone health is about more than a single number. Bone mineral density is important, but it is only one part of understanding how strong or fragile your bones may be.
REMS (Radiofrequency Echographic Multi Spectrometry) is an ultrasound-based technology used to evaluate bone health at the lumbar spine and proximal femur (hip). In addition to estimating bone mineral density and T-scores, REMS provides information about skeletal fragility through its Fragility Score.
The questions below address some of the things we hear most often from people trying to understand their bone health and their REMS results.
Understanding Why REMS Is Different
Q. I already had a DXA scan. Why would I want a REMS scan too? A. A DXA scan provides valuable information about bone mineral density (BMD) and remains an established tool for diagnosing osteoporosis and assessing fracture risk. REMS gives us another way to evaluate bone health using ultrasound—and, importantly, provides information about skeletal fragility that goes beyond bone density alone. Bone density is important, but it isn't the same thing as bone strength. BMD tells us how much bone mineral is present. But whether a bone will resist or sustain a fracture also depends on the quality and structural organization of that bone. This broader concept is often called bone quality. Bone quality includes characteristics such as the bone's microarchitecture—the internal organization of its trabecular and cortical structure—as well as its geometry, material properties, remodeling and accumulated microscopic damage. The importance of these characteristics is well established in bone science. Bone mineral density explains an important part of bone strength and fracture risk, but it does not explain all of it. This helps explain why some people fracture even though their BMD is not in the osteoporosis range, while others with very low BMD may not experience a fracture. This is where REMS adds something different. REMS doesn't simply generate another T-score. It analyzes the radiofrequency ultrasound signals returning from the bone. Characteristics within those signals are used to calculate BMD and provide additional information related to skeletal fragility. REMS also provides a Fragility Score, which is designed to identify characteristics associated with fragile versus non-fragile bone independently of the traditional BMD classification. Research has shown that the Fragility Score can provide information about fracture risk beyond BMD T-scores alone. So rather than asking, “Do I need another bone-density test?” a better question may be, “Would additional information about the strength and fragility of my bones help me better understand my bone health?” For many people, that's where REMS can be particularly valuable. REMS also uses ultrasound rather than ionizing radiation, making it well suited to establishing a baseline and following bone health over time.
Q. Isn't my T-score what tells me how strong my bones are? A. Not completely. Your T-score tells us how your bone mineral density (the amount of bone mineral present) compares with the average peak bone density of a healthy young adult reference population. It is an important measurement and is used to classify bone density as normal, osteopenic or osteoporotic. Think about two pieces of building material that contain a similar amount of material. One may be well organized and structurally sound, while the other may contain weaknesses that make it easier to break. Bone works in a similarly complex way. Bone strength = Bone density + Bone Quality and is influenced by factors that include the amount of mineral present, bone geometry and structure, cortical and trabecular characteristics, the organization and properties of the bone tissue, accumulated microscopic damage, age and bone remodeling, previous fractures and other clinical risk factors. This helps explain why not every fracture occurs in someone whose T-score is in the osteoporosis range.
Q. So what exactly is “bone quality,” and how does REMS evaluate it? A. “Bone quality” is a broad term describing characteristics of bone that contribute to strength beyond the amount of mineral measured as BMD. REMS sends ultrasound waves through the tissues to the bone and analyzes the raw radiofrequency signals that return. The spectral characteristics of those signals contain information related to the physical properties of the bone being evaluated. REMS uses these spectral characteristics in its analysis and also generates a Fragility Score, which is intended to provide information about skeletal fragility that is different from BMD alone. You may sometimes hear this described as information about bone microarchitecture. That concept is helpful for understanding why bone quality matters, but REMS does not directly create a microscopic image of the internal trabecular architecture of your bone. A better way to think about it is: BMD tells us how much bone mineral is present and is used to calculate your T-score. REMS spectral analysis provides information related to bone quality and skeletal fragility and is used to generate your Fragility Score.
Q. What is the Fragility Score, and why should I care about it? A. The REMS Fragility Score is different from your T-score. A T-score is primarily a bone-density measurement, while the Fragility Score provides information related to bone quality and skeletal fragility. It is derived from analysis of the ultrasound spectral characteristics of the bone and comparison with reference models associated with fragile and non-fragile bone. That distinction is important. Research following a large study population for five years found that the REMS Fragility Score provided information about future fragility fractures beyond BMD T-scores. The Fragility Score ranges from 0 to 100, and unlike a T-score, lower is better. Lower values represent less skeletal fragility, while higher values represent greater skeletal fragility. In a five-year prospective study, researchers identified different Fragility Score thresholds for women and men. The fracture-risk thresholds were approximately 37 at the lumbar spine and 32 at the femoral neck for women, and approximately 30 at the lumbar spine and 33 at the femoral neck for men. Scores above these thresholds were associated with substantially greater odds of future fragility fracture. These are research-based fracture-risk thresholds rather than simple “good” versus “bad” scores. That means someone can have a relatively reassuring density measurement while still having characteristics associated with increased skeletal fragility. We therefore don't look at your Fragility Score or your T-score in isolation. Looking at them together can provide a more complete picture of both bone density and skeletal fragility.
Q. My T-score and Fragility Score don't seem to match. Is that possible? A. Yes—and that doesn't necessarily mean something is wrong with your scan. Your T-score and Fragility Score are measuring different aspects of bone health, so they don't have to tell exactly the same story. For example, someone may have relatively low bone density but a more favorable Fragility Score. Another person may have better density but a less favorable Fragility Score. Rather than asking which number is “right,” we look at what each measurement is telling us. This distinction is important because bone density alone does not identify everyone who will experience a fragility fracture. Research has shown that >70% of fragility fractures occur in people whose BMD is not in the osteoporosis range. This is one of the reasons REMS can provide useful additional information: two people with similar bone density do not necessarily have identical bone quality or skeletal fragility. It is also why we pay attention to trends in both measurements when following someone over time.
Understanding REMS and DXA Differences
Q. My DXA and REMS results are different. Why—and which one should I believe? A. REMS and DXA are different technologies, and although both report bone mineral density (BMD) and T-scores, their numbers are not expected to be identical in every person. Sometimes REMS will report a lower T-score than DXA. In other people, DXA may report a substantially lower T-score than REMS. A difference by itself does not tell us which measurement better represents that person's bone health. DXA uses low-dose X-rays to measure bone mineral within a two-dimensional field. REMS uses ultrasound and analyzes radiofrequency signals obtained from the bone. Because the technologies acquire and calculate BMD differently, some variation between their results is expected. Results may also be influenced by the skeletal site being measured, positioning and hip rotation, vertebral selection, region-of-interest placement, equipment and analysis methods, body size and composition, and individual anatomy. Certain conditions can affect one measurement more than another. For example, arthritis, osteophytes, vertebral deformity and vascular calcification can sometimes artificially increase lumbar-spine BMD on DXA. Positioning and analysis can also contribute to unexpectedly high or low DXA measurements. So when REMS and DXA disagree, we don't simply choose the better—or worse—number. A significant difference is something to investigate. We look at the actual DXA images when available, individual vertebral and hip measurements, REMS BMD and T-scores, Fragility Score, previous scans, body-composition changes and clinical history. DXA is an established tool for measuring bone mineral density and diagnosing osteoporosis when performed and interpreted properly. REMS gives us another way to evaluate bone density using ultrasound while also providing additional information related to bone quality and skeletal fragility through the Fragility Score, giving us a more comprehensive view. Agreement can strengthen our confidence in what we're seeing. Disagreement can tell us where we need to look more closely. Either way, having more information helps us better understand your bone health.
Q. Can arthritis, degeneration or calcification make my DXA look better than my bones really are? A. They can in certain situations, particularly at the lumbar spine. DXA measures bone mineral within a two-dimensional X-ray field. Dense structures and changes within that field can influence the measurement. Degenerative changes such as osteophytes, vertebral changes and calcification may therefore artificially elevate lumbar spine BMD in some people. This becomes especially relevant as we age because degenerative changes become more common. For example, if someone's lumbar DXA T-score has become progressively better while the hips remain substantially lower—or if the spine appears unusually dense in someone with significant spinal arthritis—we may want to look more closely at the actual DXA images and individual vertebral measurements rather than assuming that the spine has truly gained that much bone. REMS research has also found greater disagreement between REMS and DXA measurements in people with certain vertebral deformities and abdominal aortic calcification. This doesn't make DXA a poor test. It means every bone measurement needs to be interpreted in context.
Q. I have scoliosis. Can positioning during a DXA affect my results? A. Yes. Scoliosis is an especially important situation in which positioning and interpretation deserve closer attention. DXA measurements are most reliable when the spine and hip can be positioned according to standardized protocols. With scoliosis, spinal rotation and curvature can make it difficult to reproduce a standard straight, symmetrical position. Individual vertebrae may be rotated differently relative to the X-ray beam, and degenerative changes can also be more common in an asymmetric or scoliotic spine. As a result, people with scoliosis may show greater differences between individual lumbar vertebrae or greater discordance between the spine and hip measurements. A lumbar spine result therefore sometimes requires closer review rather than relying only on the combined L1–L4 T-score. This does not mean that a DXA scan is automatically invalid in someone with scoliosis. It means that the images, positioning, individual vertebral measurements and hip results become especially important when interpreting the study. Positioning matters even if you don't have scoliosis. At the hip, differences in leg rotation can change the anatomy included in the measurement and influence BMD. At the spine, rotation, positioning, vertebral selection and region-of-interest placement can also influence the result. This becomes particularly important when comparing DXA scans over time. Ideally, the same positioning, analysis technique and machine should be reproduced as closely as possible. That's why an unexpected change on a DXA should sometimes prompt us to look at the actual images and individual measurements, rather than simply comparing today's T-score with the number from several years ago. REMS also requires good scanning technique. No bone-assessment technology is completely independent of acquisition quality. REMS uses automated quality controls and signal-selection processes designed to help identify inappropriate or artifact-containing signals during analysis.
Weight Changes and Your Results
Q. I have lost a significant amount of weight. Can that affect my REMS results? A. Yes. Significant weight change is something we want to know about when interpreting a follow-up REMS scan, and there are two different reasons it matters. First, substantial weight loss can result in real biological changes in bone. Bone is living tissue that continually adapts to the forces placed upon it. When body weight decreases significantly, the skeleton experiences less mechanical loading during everyday activity. Weight loss can also be accompanied by changes in muscle mass, hormones, protein intake and other nutrients important to bone. So some change in bone health after substantial weight loss can be real. Second, significant changes in weight and body composition can influence bone-density measurements themselves. With DXA, research has shown that changes in the amount and distribution of soft tissue surrounding the bone can influence measured BMD. With REMS, ultrasound signals are analyzed from the bone, while demographic and anthropometric information—including age and body size—is incorporated into portions of its reference and calculation process. Research is continuing to examine exactly how much changes in these variables influence REMS-derived measurements. This is an active area of scientific discussion that we continue to follow closely. That means we should not automatically look at a change after significant weight loss and conclude, “My bones definitely lost that much density.” But we also shouldn't dismiss the result as, “It's just because my weight changed.” Both biological change and measurement-related effects may need to be considered. When there has been substantial weight loss, we look at the bigger picture: how much and how quickly weight changed, whether muscle mass was maintained, nutrition and protein intake, exercise and skeletal loading, the magnitude of the BMD and T-score change, Fragility Score, and the pattern across previous scans. For this reason, it is important that accurate current height and weight are entered at every REMS scan. One number rarely tells the entire story.
Following Your Bones Over Time
Q. How much change between REMS scans is actually meaningful? A. Small differences from one measurement to another do not necessarily mean your bones have truly changed. Every medical measurement has some degree of normal measurement variability. This is why bone-density professionals use a concept called Least Significant Change (LSC). LSC helps determine whether a difference between two measurements is large enough that it is more likely to represent a real change rather than normal measurement variation. Published REMS precision studies have reported a Least Significant Change of approximately 1% when repeat scans are performed by the same operator. Reported values have ranged from about 0.9% at the hip to 1.1–1.3% at the lumbar spine, with somewhat higher values when different operators perform the scans. In practical terms, this means that a very small difference between two scans may simply reflect normal measurement variability. Once a change exceeds the expected LSC, we can have greater confidence that we are seeing a true change in measured BMD rather than measurement variation alone. LSC does not tell us whether a change is clinically good or bad—it tells us whether the change is large enough to be considered real. However, we don't want you focusing on tenths or hundredths of a number without context. When reviewing follow-up scans, we look at whether the magnitude of change exceeds expected measurement variability and whether the overall pattern makes sense across BMD, T-score, Fragility Score and your clinical history.
Q. What if my bone density improves but my Fragility Score doesn't—or the other way around? A. This can happen. Remember that these measurements represent different characteristics of your bones. Bone density may change without an identical change in the spectral characteristics used to calculate Fragility Score. Likewise, Fragility Score may improve even when the change in BMD is relatively small. There may also be a biological reason these changes don't always happen at the same time. Newly formed bone continues to mineralize and mature after it is first formed. Its mineral content, structure and material properties continue to develop over time. This means that changes in bone density and changes in characteristics related to bone quality may not necessarily occur at the same rate. It is possible that this ongoing process of bone formation and maturation contributes to some of the differences we see between BMD and Fragility Score over time, although research has not yet established exactly how bone-tissue maturation influences changes in the REMS Fragility Score. So a difference between the two doesn't automatically mean that one measurement is inaccurate—or that positive changes aren't occurring within the bone. In fact, being able to follow both measurements is one of the valuable aspects of REMS for longitudinal bone assessment. Rather than expecting every number to rise and fall together, we ask: What is the overall pattern telling us about this person's bone health over time?
Q. Why is REMS useful for monitoring my bones over time? A. One scan gives us a snapshot. Repeated measurements help us see the pattern. Bone changes slowly. Whether you are exercising to improve bone strength, improving nutrition, addressing hormones, taking medication or making other changes, the long-term trend is usually more meaningful than any single measurement. A baseline scan tells us where you started. Follow-up scans help us determine whether bone density is improving, remaining stable or declining—and whether changes are large enough to be considered meaningful. Additional scans help confirm whether those changes represent a true trend. For example, if someone previously lost 5% and later shows only a 2% loss, that may be encouraging, but another measurement can help determine whether the rate of bone loss has truly slowed. REMS is particularly well suited for follow-up. It is non-ionizing, evaluates the lumbar spine and proximal femur, and provides BMD and T-scores along with Fragility Score information related to bone quality and skeletal fragility. Published REMS precision studies have reported a Least Significant Change (LSC) of approximately 1% under same-operator conditions, allowing relatively small changes in measured BMD to exceed expected measurement variability. (See Question 10 for more about LSC.) With DXA, reliable comparison over time generally requires returning to the same machine with consistent calibration. If a different DXA system is used—or if a machine has undergone a calibration change that affects its measurements—differences between scans may reflect the equipment rather than a true change in your bones. This is why DXA results from different or recalibrated systems cannot always be directly compared. REMS has demonstrated high reproducibility between measurements and trained operators. This means you can have a follow-up REMS scan performed on a different REMS system or at a different location and still compare the results with your previous REMS scan. As with any bone assessment, proper scanning technique and high-quality acquisition remain important. Ultimately, we are interested in the trend—not just one number from one day.
Q. If my T-score stayed the same, does that mean I haven't made progress? A. Not necessarily. Maintaining bone density can itself be a meaningful outcome, particularly during stages of life when bone loss commonly occurs. Bone is constantly undergoing remodeling—older bone is broken down and new bone is formed. Your BMD represents the net result of those ongoing processes at the time it is measured. For someone who has been losing bone, progress may first mean slowing the rate of loss. The next step may be stabilizing bone density. An increase in BMD may come later—or stability itself may be a meaningful outcome. This is why we don't define success only as “my T-score went up.” We look at where you started, your previous rate of change, and the pattern that develops across multiple scans. It is also important to remember that your T-score reflects bone density, not every characteristic that contributes to bone strength. Your Fragility Score provides additional information related to bone quality and skeletal fragility, and these measurements don't necessarily change at exactly the same rate. Progress in bone health isn't always about gaining bone. Sometimes changing the direction—or slowing the rate of loss—is meaningful progress.
Q. Why might my spine improve while my hip stays the same—or vice versa? A. This is completely possible and doesn't necessarily mean that something is wrong with either measurement. Different areas of the skeleton do not necessarily change at the same rate. The spine and hip have different proportions of trabecular and cortical bone, experience different types of mechanical loading, and can respond differently to aging, exercise, hormones, medications and other interventions. The vertebrae contain a large proportion of trabecular bone, which has a high surface area and undergoes active remodeling. The proximal femur contains a different mixture of trabecular and cortical bone and experiences very different mechanical forces during standing, walking and exercise. Because bone remodeling and adaptation are site-specific, you may see measurable improvement at one skeletal site while another remains relatively stable. Stability at one site can also be meaningful, particularly if bone loss might otherwise have been expected. And just as different bones can respond differently, every body is different. Age, hormones, genetics, medications, muscle mass, activity level, nutrition, starting bone health and the way each person loads their skeleton can all influence how—and how quickly—their bones respond. We also consider whether something unrelated to true bone change could be influencing the measurement. For example, degenerative changes can artificially elevate lumbar-spine BMD on DXA, while hip positioning can influence a hip measurement. That's why we don't expect every skeletal site—or every person—to respond in exactly the same way. Your spine and hip are different bones with different structures and loading demands, and your response is uniquely yours. We look at the pattern across both sites and over time—not whether every number changed equally.
Q. What factors can cause my bone health to change over time? A. Bone is living tissue that is constantly being broken down and rebuilt. That process is influenced by much more than any single exercise, supplement or treatment. Factors that can influence bone remodeling and bone health include age and menopause, as bone remodeling changes as we age and declining estrogen during the menopause transition can accelerate bone loss. Hormones also play a role. Estrogen, testosterone, thyroid hormones and other hormonal changes can influence the balance between bone breakdown and formation. Medications can affect bone health in different ways. Some medications can contribute to bone loss, while osteoporosis medications may slow bone breakdown or stimulate bone formation, depending on the medication. Nutrition is also important. Adequate protein, calcium, vitamin D and other nutrients provide the building blocks needed to maintain and remodel bone. Muscle mass matters because muscle and bone work together. Maintaining muscle is important not only for strength and fall prevention, but also because muscle forces provide mechanical signals to the skeleton. Physical activity and skeletal loading also influence bone. Bone responds to the forces placed upon it. Weight-bearing activity, resistance exercise and appropriate mechanical loading help provide signals that encourage the skeleton to maintain or build strength. Weight and body composition can play a role as well. Significant changes in body weight, muscle mass and body composition can change the mechanical forces placed on the skeleton and may influence bone remodeling. Medical conditions and illness can also affect bone health. Certain gastrointestinal, endocrine, inflammatory and other medical conditions can affect bone metabolism or the body's ability to absorb and use nutrients. Lifestyle and genetics matter too. Smoking, alcohol use, genetics, previous activity level and other individual factors can also influence skeletal health. This is why we don't interpret a change in your bone scan in isolation. We want to understand what has been happening in the rest of your body during the time between scans.
Q. Why might two people following the same bone-health program get very different results? A. Because they aren't starting with the same biology. Two people can follow the same exercise or bone-health program consistently and still have very different results. Age, genetics, menopause and hormone status, medications, starting bone density and bone quality, nutrition, muscle mass, previous activity level, medical conditions and fracture history can all influence how the skeleton responds. Their bones may also have been moving in very different directions before they started. For example, someone who had been losing bone relatively quickly may first show a slowing of that loss or stabilization, while another person may demonstrate measurable gains sooner. Both may represent meaningful changes in their individual trajectory. Bone remodeling also occurs over long periods of time, and people do not necessarily respond at the same rate. This is why we compare your results with your own previous results, rather than comparing your percentage change with someone else's. The most meaningful question isn't “How much did someone else improve?” It's “What direction is my bone health moving over time?”
Q. So what should I pay attention to on my REMS report? A. Try not to reduce your entire bone-health story to one T-score. Your REMS report gives us several different pieces of information, and they are most useful when considered together. Bone Mineral Density (BMD): An estimate of the amount of bone mineral present at the area being evaluated. T-score: How your BMD compares with the average peak bone density of a healthy young-adult reference population. T-scores are used to classify bone density as normal, osteopenic or osteoporotic in the populations for whom T-score criteria apply. Z-score: How your BMD compares with what would be expected for someone of a similar age and sex. A Z-score answers a different question from a T-score: rather than comparing you with peak young-adult bone density, it helps show whether your bone density is unusually high or low relative to your peers. Fragility Score — Bone Quality: The Fragility Score provides information related to bone quality and skeletal fragility beyond BMD alone. It ranges from 0–100, with lower scores representing less skeletal fragility and higher scores representing greater skeletal fragility. Research has identified different fracture-risk thresholds for women and men. For women, the thresholds are approximately 37 at the lumbar spine and 32 at the femoral neck. For men, the thresholds are approximately 30 at the lumbar spine and 33 at the femoral neck. Scores above these thresholds were associated with greater odds of future fragility fracture in a five-year prospective study. These numbers are best viewed as research-based fracture-risk thresholds rather than simple “good” or “bad” scores. Your Fragility Score does not necessarily have to “match” your T-score or change in the same direction. They provide different information, which is why we look at both the score itself and how it changes over time as part of the bigger picture. Spine and hip differences: Your spine and hips don't always tell exactly the same story. Differences between skeletal sites can themselves be useful information and may sometimes prompt us to look more closely at positioning, anatomy, degenerative changes or other factors. Changes over time: One measurement is a snapshot. Multiple high-quality measurements allow us to look for trends and determine whether changes are large enough to be meaningful. Your clinical history: Previous fractures, falls, medications, hormonal status, nutrition, muscle strength, exercise, medical conditions and other risk factors all contribute to the bigger picture. No single number should be viewed in isolation.
The Bigger Picture
Bone health isn't simply about getting your T-score above a particular number.
Our goal is to understand as much as possible about your skeletal health, identify factors that may increase fracture risk, and follow meaningful changes over time.
DXA provides valuable information about bone mineral density and remains an important clinical tool. REMS gives us another way to evaluate the skeleton using ultrasound and adds information about bone quality and skeletal fragility that BMD alone may not capture.
Your T-score matters. But your bones are more than a T-score.