The study, published in Pediatric Radiology, comes from Wuhan Children’s Hospital and its affiliated medical college, where a prospective cross-sectional trial enrolled 144 consecutive outpatients between September 2023 and September 2024. The cohort was deliberately balanced, with 72 boys and 72 girls, and covered an extraordinarily wide developmental window: boys ranged in chronological age from 0.2 to 17.8 years, and girls from 0.4 to 17.8 years. Every child underwent both a conventional left-wrist radiograph and a multi-joint ultrasound examination of the wrist, elbow, shoulder, and knee, allowing the researchers to compare their new ultrasound parameter directly against the established radiographic benchmark.

The technical heart of the method lies in a quantity the researchers call the ossification ratio, or OR. On an ultrasound image, each ossification center appears as a discrete, variably sized echogenic focus wrapped in a circumferential halo of hypoechoic cartilage. The sonographer measures the maximum epiphyseal diameter, denoted D, and the diameter of the ossification center within it, denoted d, along the longitudinal axis of the bone. The ratio of these two values, d divided by D, expresses how far that particular growth center has progressed toward full ossification. Because cartilage and bone reflect sound waves differently, ultrasound can visualize these structures even before they are visible on X-ray, and it does so without any radiation exposure at all.

In the study, seven ossification centers and epiphyses were evaluated: the proximal first metacarpal, the distal radius, the distal ulna, the capitellum of the humerus, the proximal radius, the proximal humerus, and the medial epicondyle of the femur. All scans were acquired with a GE LOGIQ e system equipped with a 7.0 to 12.5 MHz high-frequency linear-array transducer, following standardized probe positioning protocols adapted from previous work. A single musculoskeletal sonographer with eight years of pediatric experience performed every scan while remaining blinded to each participant’s chronological age and radiographic bone age, a design feature intended to eliminate expectation bias from the measurements.

The headline result is a correlation so strong it borders on the theoretical limit. When the researchers summed the ossification ratios of just three bones, the distal radius, the distal ulna, and the proximal radius, the resulting composite parameter correlated with radiographic bone age, as assessed by the Greulich-Pyle atlas, at a Pearson coefficient of 0.98 in boys and 0.97 in girls. For context, a coefficient of 1.0 would indicate perfect correlation. Strikingly, adding the ossification ratios of other bones did not improve the correlation, and summing the ratios of all seven assessed bones actually reduced it slightly, to 0.97 in boys and 0.96 in girls. The three-bone combination appears to hit a sweet spot of information density without diluting the signal.

Reproducibility, the other pillar of any clinical measurement, proved equally impressive. The researchers evaluated both intra-observer and inter-observer reliability using intraclass correlation coefficients, with two blinded orthopedic surgeons of differing experience levels repeating measurements on images two months apart. For the summed three-bone parameter, intra-observer reliability reached an ICC of 0.99, with a 95 percent confidence interval of 0.98 to 0.99, and inter-observer reliability was also 0.99. Both values were significantly higher than those of any single sonographic parameter. The first metacarpal, by contrast, showed the weakest correlation with bone age of any individual bone, at 0.80 in boys and 0.77 in girls, and the lowest inter-observer reliability at an ICC of 0.84, underscoring why the composite approach outperforms single-bone measurements.

The choice of the proximal radius as a component of the index was not arbitrary. Among all seven bones examined, the proximal radius showed the strongest individual correlation with radiographic bone age, at 0.95 in boys and 0.94 in girls. This aligns with earlier forensic and orthopedic research showing that proximal radial epiphyseal fusion scores correlate most strongly with chronological age among elbow landmarks. Ossification of the proximal radius begins between three and six years of age, with the ossification center fusing at a mean age of 14.8 years in boys and 12.5 years in girls, making it a powerful developmental marker across a broad age range. The humeral capitellum and proximal humerus, by contrast, showed only moderate correlations of roughly 0.81 to 0.87 and were excluded from the final index.

The practical numbers behind the new parameter are easy to grasp. In adolescents with a bone age of 14 to 16 years, boys in the study exhibited ossification ratios of 82.3 percent for the distal radius, 61.7 percent for the distal ulna, and 79.1 percent for the proximal radius, summing to 232 percent. Girls in the same bone-age group showed corresponding values of 90.1, 81.6, and 76.1 percent, for a total of 247.5 percent. By ages 16 to 18, individual ratios approached 80 to 90 percent and the composite sum reached 250 to 260 percent, reflecting near-complete ossification as skeletal maturity arrives. These reference values, organized by bone-age group and sex, give clinicians a lookup framework for translating an ultrasound measurement into an estimated skeletal age.

Why does eliminating radiation matter so much? Although the effective dose from a single wrist radiograph is very low, children with growth disorders, short stature, or idiopathic scoliosis frequently require bone age assessments multiple times per year over many years, and the cumulative exposure adds up. Magnetic resonance imaging can assess skeletal maturity without ionizing radiation, but its high cost, long scan times, and limited accessibility make it impractical for routine repeated use. Ultrasound, by contrast, is inexpensive, widely available, well tolerated by children, and fast. The new three-bone index offers a further logistical advantage over a previously proposed composite that combined the radius, ulna, and femur: it requires only a single upper-limb scan, eliminating femoral imaging and repeated repositioning, which shortens preparation time, reduces discomfort, and improves cooperation in young or restless patients.

The authors are candid about the limitations that must be addressed before the method becomes standard practice. The study was conducted at a single center and enrolled a nearly homogeneous population of Han children from central China, raising questions about generalizability to other ethnic and regional groups, particularly given evidence that the historical Greulich-Pyle atlas itself fits contemporary Asian children imperfectly. Adolescents with already closed epiphyses were excluded, and in children aged zero to two years the ossification centers are often absent or extremely tiny, which markedly reduces ultrasound measurement accuracy in that youngest group. Ultrasound is also inherently operator-dependent, and although standardized scan planes and numeric ratios mitigate variability, multi-center and multi-operator validation studies remain necessary. Even so, the combination of a 0.98 correlation, 0.99 reliability, zero radiation, and a single-limb scanning protocol makes this summed ossification ratio one of the most compelling candidates yet for bringing bone age assessment out of the X-ray room and into the pediatric clinic.

Subject of Research: A radiation-free ultrasound parameter for pediatric bone age assessment based on summed ossification ratios

Article Title: Summation of ossification ratios of the distal radius, distal ulna, and proximal radius: a novel parameter for pediatric bone age assessment

Article References: Zeng, F., Shen, X., Xiao, X., & Wu, X. (2026). Summation of ossification ratios of the distal radius, distal ulna, and proximal radius: a novel parameter for pediatric bone age assessment. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06772-2

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06772-2

Keywords: bone age, ultrasound, ossification ratio, pediatrics, Greulich-Pyle atlas, radiation-free imaging, distal radius, proximal radius, skeletal maturity, pediatric radiology, growth disorders, diagnostic imaging

The research, led by Xin Miao of Children’s Hospital Los Angeles and the Keck School of Medicine of the University of Southern California, together with colleagues across multiple institutions, set out to test whether a single eight-minute scan on a commercial 0.55-tesla MRI system could simultaneously capture both the structure and the function of diseased infant lungs. Eleven preterm infants diagnosed with bronchopulmonary dysplasia were recruited from the neonatal intensive care unit, all of whom were already scheduled for clinically indicated brain MRI. After their routine brain scan, the infants were transferred to an adjacent 0.55-tesla scanner for the research lung examination. The cohort spanned a wide range of clinical circumstances: gestational ages at birth ranged from 23 to 32 weeks, post-menstrual ages at scanning ranged from 40 to 57 weeks, and body weights ranged from 2.3 to 6.4 kilograms. Nine infants had severe bronchopulmonary dysplasia and two had moderate disease, with five on non-invasive oxygen support and six on mechanical ventilation at the time of imaging.

The technical heart of the study is a prototype sequence called bSTAR, short for balanced steady-state free precession with half-radial dual-echo readout. The choice of sequence and field strength is not arbitrary. Lung MRI has historically been notoriously difficult because air-filled tissue is sparse in hydrogen protons and riddled with microscopic air-tissue interfaces that rapidly dephase the magnetic resonance signal. At conventional field strengths of 1.5 and 3 tesla, researchers have relied on ultrashort echo time sequences to catch the signal before it decays, but the parenchymal signal-to-noise ratio remains a fundamental constraint, especially in preterm infants whose tiny lungs demand high spatial resolution. At 0.55 tesla, the lung’s transverse relaxation time, T2*, stretches roughly tenfold, from about one millisecond at 1.5 tesla to approximately ten milliseconds, and susceptibility artifacts are markedly reduced. That longer signal lifetime gives the scanner far more room to work with.

Lower field strength also unlocks a sequence that has long been underused in the chest. Balanced steady-state free precession offers inherently high signal-to-noise efficiency, but at conventional field strengths it has been hobbled by banding artifacts and by specific absorption rate limits that constrain how fast the sequence can run. Both problems ease substantially at 0.55 tesla, allowing the full advantage of the sequence’s contrast to be exploited for lung parenchymal imaging. In adults, this combination has already produced submillimeter isotropic images with CT-like depiction of lung tissue. The bSTAR sequence in this study acquired three-dimensional data at 1.3-millimeter isotropic resolution over an eight-minute acquisition, using a 340-millimeter field of view, a flip angle of 25 degrees, and echo and repetition times of 0.2, 2.3, and 2.5 milliseconds respectively. Crucially, the infants were not sedated for the lung scan and did not need to hold their breath. Those on non-invasive support breathed freely through a nasal cannula, while ventilated infants breathed under controlled respiratory patterns, with clinically ordered respiratory support maintained throughout.

Handling motion from a freely breathing, sometimes crying infant is where the signal processing becomes as important as the physics. The team extracted respiratory self-navigation waveforms directly from the center of k-space, sampled every 2.5 milliseconds, then filtered and selected the channel with the highest variance as the breathing signal. Data contaminated by bulk motion, identified from waveform irregularity, were discarded. The remaining data were sorted into three respiratory motion states, and each state and each echo was reconstructed independently using non-Cartesian compressed sensing with wavelet regularization, implemented through the Berkeley Advanced Reconstruction Toolbox. Reconstructing a single three-dimensional volume took roughly an hour on a 64-core Linux server. To derive functional information, the end-exhalation volume was deformably registered to the end-inhalation volume, and fractional ventilation was calculated at every lung voxel from the signal change between the two states, following a formula originally established by Zapke and colleagues. Two quantitative biomarkers emerged from these maps: ventilation defect percentage, the share of lung volume with ventilation below 0.75 times the median, and ventilation inhomogeneity, the coefficient of variation of ventilation values across the lung.

The structural results were striking. Two pediatric radiologists, one with nine years of post-fellowship experience and one fellow, independently scored the images using the Ochiai system, a scoring scheme originally developed for chest CT that evaluates eight features including hyper-expansion, mosaic attenuation, bullae and blebs, triangular subpleural opacities, bronchovascular distortion, intercostal bulging, and consolidation, with total scores from 0 to 18. The MRI captured every BPD-associated feature, and in the three patients who also had a clinical chest CT within a week of the scan, feature-by-feature comparison showed largely consistent scoring, with a mean total score difference of 2.8. Inter-reader agreement for the total score was substantial, with a weighted Cohen’s kappa of 0.80, and for individual features such as hyper-expansion, bronchovascular distortion, and bleb size the kappa values of 0.91, 0.94, and 0.85 were numerically higher than those typically reported for CT-based scoring of the same features. Notably, the researchers applied the original, unmodified Ochiai system, including intercostal bulging, which prior MRI studies had excluded and which proved to be among the more frequently observed features in this cohort.

Every one of the eleven scans produced diagnostic image quality, regardless of whether the infant was breathing spontaneously or on a ventilator. The median overall image quality score was 4.0 on a five-point scale, and nine cases scored above the diagnostic threshold with minimal to mild motion blurring. The two remaining cases, blurred by multiple crying episodes, still remained diagnostic. The Ochiai structural score correlated significantly with clinically meaningful variables: it was higher in infants on mechanical ventilation at the time of scanning compared with those on non-invasive oxygen support, a difference that reached statistical significance at P equals 0.035, and it correlated inversely with birth weight, with a Spearman coefficient of minus 0.70, and positively with the duration of mechanical ventilation at discharge, with a coefficient of 0.82. In a cohort where nine of eleven infants had severe disease, these associations suggest that what the scanner sees tracks what the clinical team experiences.

Perhaps the most intriguing findings came from the ventilation maps, which repeatedly resolved ambiguities that structural images alone could not. In one infant whose two lungs showed diffusely different signal intensities, the ventilation map identified markedly reduced ventilation in the right lung, confirming hyper-expansion as the underlying pathology. In another, hyper-expansion in the anterior lung was detectable on structural images only through subtle intercostal bulging, with no corresponding signal change, while the ventilation map provided clear functional confirmation. Elevated signal in the posterior lungs of two infants, which could have represented either consolidation or a normal gravity-induced density gradient, was clarified by matching low ventilation, favoring consolidation. In one case the reverse occurred: a region that mimicked a bleb on structural images showed relatively high ventilation, suggesting preserved function rather than true air trapping. Ventilation defect percentage and inhomogeneity were numerically higher in infants with severe disease and in those still on mechanical ventilation at discharge, though these differences did not reach statistical significance in this small pilot cohort, and the two biomarkers were strongly correlated with each other.

The authors are careful about the limits of the work. The cohort was small and skewed toward severe disease, most subgroup comparisons involved only two or three subjects, and the ventilation biomarker definitions were adapted from other fields with empirically chosen post-processing parameters that can influence absolute values. Absolute fractional ventilation also cannot be fully interpreted without normative models of how infant lung ventilation changes with development, which do not yet exist. Still, the study establishes something genuinely new: that a single free-breathing, radiation-free, sedation-free acquisition on a compact 0.55-tesla scanner can deliver both high-resolution structural images and quantitative three-dimensional ventilation maps in critically ill preterm infants. Because lung density changes rapidly with normal development and overlaps with the course of bronchopulmonary dysplasia, pairing structural and functional measures may prove especially powerful for distinguishing disease from normal physiology. Larger studies spanning the full severity spectrum will determine whether combined structural-functional MRI can improve diagnostic confidence beyond structural imaging alone, and whether it can finally give clinicians an objective, repeatable window into the lungs of their tiniest patients.

Subject of Research: Low-field MRI for structural and functional lung imaging in preterm infants with bronchopulmonary dysplasia

Article Title: Feasibility of free-breathing 0.55-T lung MRI for structural and functional characterization in preterm infants with bronchopulmonary dysplasia

Article References: Miao, X., Nguyen, H. N., Lee, N. G., Uribe, J., Doyle, E. K., Capaldi, D. P., Arrioja, L., Kato, R. M., Durazo-Arvizu, R. A., Nayak, K. S., & Iyer, N. P. (2026). Feasibility of free-breathing 0.55-T lung MRI for structural and functional characterization in preterm infants with bronchopulmonary dysplasia. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06793-x

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06793-x

Keywords: bronchopulmonary dysplasia, preterm infants, 0.55-T MRI, lung imaging, bSSFP, bSTAR, ventilation mapping, neonatal intensive care, Ochiai score, fractional ventilation, pediatric radiology, radiation-free imaging

The work centers on the proximal tibial epiphysis, the growth plate at the upper end of the shinbone just below the knee joint. In 2018, Vieth and colleagues introduced an MRI-based staging system for this region that has since been validated by several independent research groups. The system’s most celebrated feature is its stage 6, which in male individuals was observed only after the eighteenth birthday, making it a potential marker of legal adulthood. Because magnetic resonance imaging involves no ionizing radiation, unlike computed tomography of the clavicles that is currently recommended when hand skeletal development is complete, MRI of the knee has been promoted as a more ethically acceptable tool for age estimation in living subjects.

Yet the earlier validation work by the same German group hinted at something else: stage 4, a mid-range category in which the growth plate is partially fused, might contain hidden structure. If the stage could be subdivided, perhaps the substages would align more closely with legally relevant ages such as fourteen, sixteen, or eighteen years. The new pilot study, led by Natia Chitavishvili of Jena University Hospital together with Daniel Wittschieber, Maria L. Hahnemann, and colleagues, set out to test that idea using a cohort of fifty-seven T1-weighted MRI examinations, twenty-four from males and thirty-three from females, all previously assigned to Vieth stage 4.

The technical logic behind the subclassification rests on a thin line of intermediate signal intensity that appears within the growth plate on T1-weighted turbo spin-echo images. This line represents the advancing front of bony fusion across the metaphysis. The researchers divided its extent relative to the total metaphyseal width into three categories: substage 4a when the line spans less than one-third of the width, substage 4b when it spans between one-third and two-thirds, and substage 4c when it exceeds two-thirds. Three experienced readers, a clinical radiologist, a pediatric radiologist, and a forensic medicine specialist, assessed only coronal images and evaluated every slice of the epiphysis, blinded to each subject’s age and sex throughout.

The results confirmed that every one of the fifty-seven cases could be placed into one of the three substages, demonstrating that the morphological criteria are workable in practice. Reliability statistics supported the scheme as well. Intra-observer agreement, measured when the first reader repeated all assessments two months after the initial consensus reading, yielded a Cohen’s kappa of 0.751, and inter-observer agreement between the first two readers reached 0.663. Under the conventional interpretation scale, both values fall within the range of good agreement, suggesting that different trained readers can apply the substages consistently.

The age data, however, tell a more complicated story. Among male subjects, the minimum ages at which substages 4a, 4b, and 4c were first observed were 15.45, 15.68, and 15.23 years respectively, meaning all three substages appeared only after the fourteenth birthday. Among females, the corresponding minimum ages were 12.64, 12.57, and 13.18 years. Statistically significant sex differences emerged for substages 4b and 4c, consistent with the well-documented pattern in which girls reach skeletal milestones roughly two years earlier than boys. In both sexes, substage 4c showed a particularly wide spread of chronological ages, weakening its value as a narrow age indicator.

What does this mean for the courtroom? The authors conclude that the substages may assist in verifying completion of the fourteenth year of life, at least in males, since no male in the cohort displayed any substage before age 15. But the crucial thresholds of sixteen and eighteen years, which drive decisions about criminal responsibility, asylum, and majority in many jurisdictions, could not be reliably verified with this subclassification. The broad age distributions, especially within substage 4c, mean that an individual at that substage could plausibly be anywhere within a multi-year window that straddles the legal boundaries that matter most.

The findings fit into a broader research landscape. Krämer and colleagues demonstrated as early as 2014 that substage assessment of the proximal tibial epiphysis by MRI was feasible, using an adapted system derived from the clavicle staging schemes of Schmeling and Kellinghaus, and reported minimum ages in comparable ranges. Ottow and colleagues expanded on that work in 2017 with 658 knee MRI scans from individuals aged twelve to twenty-four. More recently, Ekizoglu and colleagues introduced novel substages based on the Dedouit classification using MERGE sequences in 559 individuals, reporting minimum ages that likewise fell within similar age bands. Notably, the Dedouit approach has been criticized because it relies on absolute measurements of growth plate layer thickness, which may vary with body size and thereby introduce bias, whereas the Vieth system and its new substages rest on proportional, morphological criteria.

The authors are candid about the limitations of their pilot. With only fifty-seven cases, the numbers assigned to each substage were small, and substage 4a appeared in just five individuals, which limits the statistical power of the analysis. The retrospective design meant that scans came from different scanners at 1.5 and 3.0 Tesla with non-uniform clinical protocols, a heterogeneity that mirrors real-world practice but complicates precise morphological differentiation. The cohort, drawn from hospital records in Thuringia, was also predominantly Western Caucasian with a largely high socioeconomic background, raising questions about generalizability to the diverse populations that forensic age estimation actually serves. The researchers emphasize that the subclassification cannot currently be recommended for routine forensic practice without validation in larger, independent study populations.

Even so, the study adds a meaningful piece to the puzzle of skeletal maturation. It demonstrates that the intermediate signal line within the fusing tibial growth plate progresses in a graded, readable fashion, and it maps that progression onto chronological age with sex-specific reference values. Future prospective studies with standardized MRI protocols and larger multicenter cohorts may clarify whether the substages gain diagnostic value, particularly around the fourteenth-year threshold in males. For now, the message for forensic science is one of tempered expectation: the knee can speak about age, but its vocabulary at stage 4 remains too coarse to settle the sixteen- and eighteen-year questions that matter most in law.

Subject of Research: MRI-based subclassification of proximal tibial epiphysis ossification for forensic age estimation

Article Title: Subclassification of Vieth stage 4 in MRI of the proximal tibial epiphysis: a pilot study for forensic age estimation

Article References: Chitavishvili, N., Wittschieber, D., Papageorgiou, I., Malich, A., Mentzel, H.-J., & Hahnemann, M. L. (2026). Subclassification of Vieth stage 4 in MRI of the proximal tibial epiphysis: a pilot study for forensic age estimation. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-03991-y

Image Credits: AI Generated

DOI: 10.1007/s00414-026-03991-y

Keywords: forensic age estimation, MRI, proximal tibial epiphysis, Vieth staging, growth plate, ossification, knee joint, forensic radiology, radiation-free imaging, skeletal maturation, legal age thresholds, pilot study