The stakes are enormous. Osteoporosis is a systemic metabolic bone disease in which both bone density and the fine internal architecture of the skeleton deteriorate, and it remains one of the leading causes of fractures in old age. In Russia, the study’s authors note, osteoporosis is diagnosed in 34 percent of women and 27 percent of men aged 50 and older, and the burden of fragility fractures after age 50 has been described as a public health threat comparable to dyslipidemia and hypertension. Secondary osteoporosis also shadows many common conditions of aging, including type 2 diabetes, chronic kidney disease, and long-term glucocorticoid use. Under World Health Organization criteria, the diagnosis rests on three pillars: a pathological low-energy fracture of a large bone, a high 10-year fracture probability on the FRAX risk tool, or a bone mineral density deficit of 2.5 or more standard deviations below the young adult mean, the famous T-score, measured by DXA at the lumbar spine or proximal femur.

DXA earned its status as the clinical standard through elegant physics. A detector measures the differential attenuation of two X-ray energies passing through bone and soft tissue, allowing the machine to calculate areal bone mineral density in grams per square centimeter and to separate out body composition. The patient’s result is then compared with reference values from a young healthy population, expressed as the standard-deviation difference from that reference mean. But the technology has practical drawbacks. Access and affordability remain limited in many regions, including Russia, and although the radiation dose is very low, it is not zero. Those constraints have driven a search for alternatives, and REMS has emerged as one of the most intriguing candidates.

REMS works on an entirely different physical principle. Instead of measuring how X-rays are absorbed, it records how ultrasound vibrations scatter as they pass through bone. A convex transducer, operating at a nominal frequency of 3.5 megahertz, scans the lumbar vertebrae or the femoral neck, and the raw radiofrequency data are compared against an extensive database of reference ultrasound spectral models. From that comparison, the software calculates bone mineral density, T-scores, Z-scores, and even a 10-year fracture risk estimate, all without ionizing radiation. Scanning a single region takes roughly 80 to 90 seconds, guided by on-screen instructions and audio signals. The method’s proponents argue it could be a cost-effective, straightforward alternative to DXA, particularly for primary screening, and a 2026 meta-analysis by R.Y. Liu and E. Liu reported a strong correlation between the two techniques overall. That same meta-analysis, however, flagged substantial heterogeneity across studies and warned that the correlation may be considerably weaker in certain clinical settings and populations.

To find out where REMS stands in the Russian population, researchers at the Russian Gerontology Clinical Research Centre and Pirogov Russian National Research Medical University in Moscow conducted a single-center longitudinal study. They recruited 40 patients, of whom 32 met clinical indications for bone densitometry and 25 completed the full protocol: women aged 49 to 88, with a mean age of about 72 years and body mass index ranging from 22 to 41.9 kilograms per square meter. Each participant underwent both DXA, using a GE HealthCare Lunar Prodigy Advance system, and REMS, using an Echo Station ultrasound machine from EchoLight in Italy, at two visits separated by one year. Measurements targeted the lumbar spine from L1 to L4 and the femoral neck, the two sites where fracture risk is assessed most reliably. Between visits, all participants received standardized anti-osteoporotic therapy under Russian Ministry of Health guidelines, including therapeutic exercise, dietary correction, cholecalciferol at 2,000 to 7,000 international units daily, calcium supplements, and antiresorptive treatment with either annual intravenous zoledronic acid or twice-yearly subcutaneous denosumab. Fourteen patients received zoledronic acid and eleven received denosumab, and adherence was high across the cohort.

The baseline results revealed a picture of moderate, not stellar, diagnostic performance. Mean lumbar T-scores at the first visit were -1.89 by DXA and -2.33 by REMS; at the femoral neck, they were -1.95 and -2.20 respectively. Diagnostic agreement for osteoporosis between the two methods across both bone sites was 64 percent, with a Cohen’s kappa of just 0.28, a statistic indicating that much of that agreement could be attributed to chance. Sensitivity of REMS relative to DXA was 0.63, with a 95 percent confidence interval stretching from 0.33 to 0.94, and specificity was 0.64, with an interval from 0.39 to 0.89. The positive predictive value was 0.58 and the negative predictive value 0.69. In practical terms, REMS caught only about two-thirds of the women whom DXA classified as osteoporotic, and it misclassified roughly a third of those DXA cleared. The correlation between T-scores was moderate at the lumbar spine, 0.65 with a p-value below 0.001, but weak and statistically insignificant at the femoral neck, where the correlation was 0.35 with a p-value of 0.089.

Agreement analysis deepened the concern. Bland-Altman plots, which directly assess how closely two measurement methods track each other across a range of values, showed poor agreement for both bone regions, with wide 95 percent limits. For the lumbar spine, the limits ran from -1.543 to 1.919 T-score units; for the femoral neck, from -1.516 to 2.116. Although the mean bias was close to zero, 0.188 and 0.299 respectively, meaning the methods did not systematically overestimate or underestimate on average, the enormous spread meant that for any individual patient, REMS could deviate from DXA by nearly two full standard deviations in either direction. That is a clinically meaningful margin, given that the diagnostic threshold itself sits at -2.5.

The most striking finding emerged at the one-year follow-up, after antiresorptive therapy had begun. Correlations between REMS and DXA dropped to 0.47 for the lumbar spine, with a p-value of 0.022, and to 0.22 for the femoral neck, with a p-value of 0.307, rendering the femoral neck comparison statistically insignificant. In other words, once patients started receiving zoledronic acid or denosumab, the two methods diverged even further. The authors suggest this may reflect differences in the physical basis of the two techniques: after a year of therapy, the drugs may have altered the amount of hydroxyapatite in bone without yet significantly changing the microarchitecture that ultrasound spectra capture, or vice versa. Whatever the mechanism, the implication is clear: REMS cannot yet be trusted to tell clinicians whether a specific patient’s bone density is responding to treatment.

The authors are careful to contextualize their findings. Many large multicenter studies have demonstrated high agreement between REMS and DXA, and a Russian comparability study of 50 patients published in 2025 also reported a high correlation. But smaller studies have produced results similar to those seen here; in a study by Caffarelli and colleagues with 77 participants, correlations were 0.35 and 0.54 for the lumbar spine and femoral neck respectively. Even in the largest trials, sensitivity and specificity for osteoporosis detection by REMS were comparable to the values seen in this cohort. The structure of the study population may have played a role: elevated body mass index, prior pathological fractures, type 2 diabetes, and other conditions have all been shown to reduce agreement between the two methods, and no trial data exist for REMS devices in patients with a BMI above 40 kilograms per square meter. The femoral neck has consistently shown lower agreement than the lumbar spine across many studies, partly because REMS’s claimed advantage, the automatic exclusion of bone osteophytes and soft tissue calcifications, applies most cleanly to the lumbar region, where degenerative changes often inflate DXA readings.

The study’s limitations are acknowledged candidly: only 25 women completed the protocol, all participants were female, and the sample size could not be expanded within the initial administrative and diagnostic capabilities of the center. The authors conclude that REMS demonstrated statistically significant diagnostic value for osteoporosis, but that the comparability and agreement of its bone mineral density data with DXA was near low, varied widely by bone region, and decreased further during active antiresorptive therapy. The results, they write, are not sufficiently precise or statistically robust to validate REMS unequivocally for bone mineral density monitoring in Russia, but they provide a basis for further research. A larger follow-up study is already underway, with plans to expand the demographic spectrum, analyze inter-rater and test-retest reliability, stratify subgroups by obesity, pathological fractures, and diabetes, and record the device’s fragility score. For now, the message for patients and clinicians is measured: ultrasound-based bone assessment is a promising screening tool with real diagnostic value, but the gold standard for diagnosis and treatment monitoring remains DXA, and REMS must earn its place through larger, more diverse trials before it can claim parity.

Subject of Research: Diagnostic capabilities and monitoring the effectiveness of osteoporosis therapy using radiofrequency echographic multispectrometry in comparison with dual-energy x-ray absorptiometry

Article Title: Diagnostic capabilities and monitoring the effectiveness of osteoporosis therapy using radiofrequency echographic multispectrometry in comparison with dual-energy x-ray absorptiometry

Article References: Sharashkina, N. V., Rodionov, D. V., Runikhina, N. K., & Tkacheva, O. N. (2026). Diagnostic capabilities and monitoring the effectiveness of osteoporosis therapy using radiofrequency echographic multispectrometry in comparison with dual-energy x-ray absorptiometry. Frontiers in Endocrinology, 17, Article 1889333. https://doi.org/10.3389/fendo.2026.1889333

Image Credits: AI Generated

DOI: 10.3389/fendo.2026.1889333

Keywords: osteoporosis, REMS, DXA, bone mineral density, ultrasound imaging, antiresorptive therapy, T-score, fragility fractures, geriatric medicine, diagnostic agreement, Bland-Altman analysis, Russian population