Pulmonary function testing revealed a severe obstructive defect, with her forced expiratory volume in one second, or FEV1, measuring only 40 percent of the predicted value for her age and size. FEV1 is one of the most widely used benchmarks in respiratory medicine: the patient takes a maximal breath and then exhales as hard and fast as possible, and the machine records how much air leaves the lungs in the first second. A healthy child typically clears the large majority of their vital capacity in that window, so a value of 40 percent signaled that air was having trouble escaping her lungs, the hallmark of an obstruction in the small airways. In children, such a pattern raises particular concern for bronchiolitis obliterans, a disease in which inflammation and fibrosis progressively narrow and destroy the bronchioles, the tiniest branches of the airway tree.

Bronchiolitis obliterans after stem cell transplantation is generally understood to be a manifestation of chronic graft-versus-host disease, the process by which donor immune cells recognize the recipient’s tissues as foreign and attack them. In the lungs, this attack targets the small airways, producing scarring that is essentially irreversible once established. The condition is a leading cause of late non-relapse mortality in long-term transplant survivors, which makes early detection and careful monitoring critically important. Yet the disease is notoriously difficult to assess precisely, because the small airways where the damage occurs are far below the resolution of even the best conventional imaging, and the functional consequences are scattered unevenly across the lung in a patchwork of affected and spared regions.

To visualize that patchwork, the clinical team turned to expiratory coronal chest computed tomography. The CT images demonstrated diffuse mosaic attenuation, a pattern in which the lung parenchyma appears as a patchwork of darker and lighter regions, like a quilt of alternating density. In the context of small airway disease, the darker areas represent air trapping: regions of lung where obstructed bronchioles prevent air from emptying during exhalation, leaving those territories abnormally inflated and under-perfused. Mosaic attenuation on an expiratory scan is a classic radiological signature of air trapping and supported the diagnosis of bronchiolitis obliterans in this patient. But while CT can show that some regions are denser and others less dense than they should be, it cannot directly measure whether those regions are actually participating in ventilation, and it delivers a dose of ionizing radiation, a meaningful consideration in a child who will need repeated surveillance over many years.

That is where hyperpolarized xenon-129 MRI enters the picture, and it represents one of the most striking technical achievements in modern medical imaging. Ordinary MRI excels at imaging soft tissue rich in hydrogen nuclei, but it is nearly blind to the air inside the lungs, because air contains almost no hydrogen and produces essentially no signal. The solution is to image a gas instead, and to boost that gas’s signal to extraordinary levels through a process called hyperpolarization. Xenon-129, a stable, non-radioactive isotope of the noble gas xenon, is paired with rubidium vapor and exposed to laser light in a process known as spin-exchange optical pumping. This transfers angular momentum from the laser-polarized rubidium atoms to the xenon nuclei, aligning their nuclear spins far beyond what is possible at normal thermal equilibrium, sometimes amplifying the available MRI signal by tens of thousands of times.

Once hyperpolarized, the xenon gas is inhaled by the patient inside the MR scanner, and because the nuclei are polarized, the gas itself becomes visible to the MRI system. In this case, the xenon-129 was inhaled and ventilation images were acquired during a single breath hold, meaning the entire three-dimensional picture of where the gas reached within the lungs was captured in the few seconds the child could comfortably hold her breath. This is a crucial practical advantage in pediatric imaging, where long scan times and repeated breath holds are often impossible for young patients to tolerate. Regions of the lung that received the gas appear as high signal on the images, while regions that the gas could not reach, because of obstructed or destroyed airways, appear as low signal, or ventilation defects. The result is a direct, functional map of breathing, region by region, rather than an inference drawn from density patterns.

The raw ventilation images were then processed into a color map, translating signal intensity into an intuitive visual display of lung function. In the published images, the areas of decreased attenuation on the CT scan corresponded closely to the ventilation defects highlighted on the xenon-129 MRI, providing a compelling side-by-side demonstration that the two modalities were capturing the same underlying pathology. More importantly, the technique allowed the team to calculate a single quantitative metric: the ventilation defect percentage, or VDP, which expresses the proportion of total lung volume showing impaired ventilation. In this patient, the VDP was 36 percent, a dramatic figure compared with the normal threshold of less than 5 percent. In other words, more than a third of her lung volume was effectively silent on the ventilation map, unable to participate in gas exchange through the damaged airways.

The significance of a reproducible number like VDP is difficult to overstate for a disease that has long been monitored indirectly. FEV1, the workhorse of pulmonary function testing, reflects the summed behavior of millions of airways and can be influenced by the patient’s effort and cooperation, which is a particular challenge in young children. It also cannot say anything about where in the lungs the obstruction is concentrated or how the pattern of disease evolves over time. Xenon-129 MRI, by contrast, offers a spatially resolved, quantitative, and radiation-free measure that can be repeated at regular intervals. For a teenager facing decades of surveillance after stem cell transplantation, the ability to track her ventilation defect percentage over time, and to see whether it worsens, stabilizes, or improves in response to treatment, represents a fundamentally more informative way to manage her disease.

The case, published in the journal Pediatric Radiology by Tyler Obermark, Kathryn Donohue, Elizabeth Kramer, Laura Walkup, and Cara Morin of the University of Cincinnati College of Medicine and Cincinnati Children’s Hospital Medical Center, is presented as a demonstration of what hyperpolarized gas imaging can offer in pediatric practice. The authors note that xenon-129 MRI provides a reproducible quantitative measure for longitudinal surveillance and assessment of treatment response in children with bronchiolitis obliterans. The report is open access, allowing clinicians and researchers anywhere to examine the images and methods in full detail, and the work reflects a broader movement to bring hyperpolarized gas MRI from the research laboratory into routine clinical care for pediatric lung disease.

For the field of pediatric pulmonology, the implications extend well beyond a single patient. Bronchiolitis obliterans is not limited to stem cell transplant recipients; it can also follow severe viral infections, including adenovirus and other pathogens, and it shares features with the small airway damage seen in chronic obstructive pulmonary disease in adults. A technique that maps ventilation directly, quantifies it precisely, and avoids ionizing radiation could reshape how all of these conditions are diagnosed and followed in children. The image of a teenager’s lungs, painted in color by a magnetically aligned noble gas she breathed in for a single breath hold, captures a moment when physics, chemistry, and clinical medicine converge to make the invisible visible, and to give clinicians a number they can actually act on in the long fight to preserve a child’s breathing.

Subject of Research: Hyperpolarized xenon-129 MRI ventilation imaging for assessing bronchiolitis obliterans after pediatric stem cell transplantation

Article Title: Xenon-129 ventilation imaging in pediatric bronchiolitis obliterans patient

Article References: Obermark, T., Donohoe, K., Kramer, E., Walkup, L., & Morin, C. (2026). Xenon-129 ventilation imaging in pediatric bronchiolitis obliterans patient. Pediatric Radiology. https://doi.org/10.1007/s00247-026-06799-5

Image Credits: AI Generated

DOI: 10.1007/s00247-026-06799-5

Keywords: xenon-129 MRI, hyperpolarized gas imaging, bronchiolitis obliterans, pediatric radiology, stem cell transplantation, ventilation defects, FEV1, air trapping, chronic graft-versus-host disease, lung imaging, ventilation defect percentage, Xenon-129

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 new platform, described in the open-access journal HardwareX by Jerry Febrico and Basari of Universitas Indonesia, is built around two inexpensive, widely available integrated circuits: the STM32F407VGT6 microcontroller and the AD5933 impedance converter. EIT works by injecting a small, safe alternating current into a subject or phantom through an array of surface electrodes and measuring the faint voltages that appear at the boundary. Because different tissues conduct electricity differently, the pattern of these boundary voltages encodes information about the internal distribution of conductivity, which a computer algorithm can then reconstruct into a cross-sectional image. For the lungs, this is particularly powerful: as air flows in and out during breathing, the local impedance of lung tissue changes dramatically, allowing EIT to track regional ventilation at the bedside without a single X-ray. Diseases such as chronic obstructive pulmonary disease and pulmonary edema, which demand repeated monitoring rather than one-off snapshots, are precisely the conditions where this continuous, non-ionizing approach holds the greatest clinical promise.

What distinguishes the new design from earlier open-source efforts is its deliberately modular analog front-end. The heart of the system is the AD5933, a chip that combines a direct digital synthesizer signal generator and a 12-bit impedance converter on a single die. In this implementation, the AD5933 is configured to output a sinusoidal excitation signal at 50 kilohertz, which is fed into a voltage-controlled current source that injects a constant current of roughly 1.44 milliamperes peak-to-peak into the imaging domain. On the receive side, weak differential voltages picked up from the electrodes are amplified by an instrumentation amplifier and routed back into the AD5933, whose on-chip digital signal processor applies a discrete Fourier transform to extract the real and imaginary components of the measured signal. The STM32 microcontroller orchestrates the entire sequence over an I2C bus, computes impedance magnitudes, and streams the results over USB to a personal computer running Python-based reconstruction software.

The modularity is not an abstract design philosophy; it is physically built into the circuit board. The single custom PCB, measuring 177.8 by 155.83 millimeters, carries two alternative voltage-controlled current source topologies, a Load-in-the-Loop design and a Mirrored Howland current pump, alongside two instrumentation amplifier options, a discrete INA118P chip and an AD620 module. Manual DIP switches on the board let researchers route the signal through any combination of these circuits, enabling direct, empirical comparison of four distinct analog front-end configurations under identical operating conditions. The board is assembled with IC sockets, female headers, and through-hole resistors specifically so that users can swap components, replace damaged parts, and experiment with their own circuit modifications without fabricating a new board. Every component is listed in a bill of materials with purchase links from global suppliers such as DigiKey and AliExpress, and the complete design files, from EasyEDA schematics to PCB Gerber files, are released under CERN-OHL, MIT, and CC BY 4.0 open-source licenses.

Data acquisition follows the classic adjacent four-terminal sensing pattern used across the EIT field. Four 16-channel CD74HC4067 analog multiplexers, steered by the microcontroller, dynamically connect the current source and the measurement amplifier to a ring of 16 stainless steel electrodes mounted on a 3D-printed polylactic acid container. Current is injected through one adjacent electrode pair while differential voltages are measured sequentially across all remaining neighboring pairs; the injection pair then rotates around the ring, and the process repeats. One complete sweep yields 208 impedance measurements, which the firmware collects in just two seconds. The authors tested alternative injection patterns, including opposite and diagonal schemes that push current deeper into the domain, but found in their comparative experiments that the adjacent pattern best preserved the shape and location of target inclusions, while cross and opposite patterns introduced excessive noise that obscured objects entirely.

Validation of the hardware was thorough and refreshingly candid. Signal-to-noise ratio measurements, taken across 50 consecutive frames in a saline-filled phantom with a conductivity of 966 millisiemens per meter, ranged from 21.5 to 43.7 decibels depending on the front-end configuration. The Mirrored Howland paired with the AD620 achieved the highest peak SNR of 43.7 decibels, a figure the authors note is comparable to the clinically validated Sheffield Mk 3.5 system, which operated at roughly 40 decibels. The Load-in-the-Loop configurations delivered more uniform channel-to-channel performance, around 37 to 38 decibels, because this topology does not depend on precisely matched resistor networks, whereas the Howland pump’s high output impedance degrades rapidly when built with standard 1 percent tolerance components. Precision testing with standard resistors from 100 to 1000 ohms revealed exceptionally tight repeatability, with standard deviations between 0.54 and 6.33 ohms across all configurations and coefficients of determination reaching as high as 0.9997.

Perhaps the most instructive finding concerns absolute accuracy. The system exhibited a systematic positive offset, producing relative errors that ranged from 0.60 percent to as much as 37.82 percent for the lowest resistor values. In most measurement contexts, such errors would be disqualifying. But EIT, as practiced here, relies on time-difference imaging: a baseline reference dataset is captured in a homogeneous medium, and images are reconstructed from the changes that occur relative to that baseline. Static hardware offsets, parasitic capacitances, and multiplexer channel resistances are mathematically subtracted during this differential process, which means repeatability, not absolute accuracy, is the metric that matters. By this standard, the platform performs admirably, and the authors are transparent that the fixed additive error, traced through linear regression to positive y-intercepts between 11.2 and 99.4 ohms, is effectively cancelled by the reconstruction algorithm.

Imaging experiments confirmed the system’s practical capability. Using cylindrical phantom targets, one highly conductive stainless steel tube and one non-conductive plastic tube, placed at various positions inside the saline tank, the team reconstructed 2D images using three algorithms available in the open-source pyEIT library: Back-Projection, the Jacobian-based JAC method, and GREIT. Back-Projection was favored for its speed and low computational cost. Quantitative comparison against simulated ground-truth images, scored with the Structural Similarity Index Measure and Root Mean Square Error, showed strong reconstruction fidelity, with the HOW-INA118 configuration achieving a peak SSIM of 0.9242 and the HOW-AD620 configuration delivering the lowest RMSE of 28.29. The reconstructed inclusions showed the characteristic boundary smearing and spatial deformation inherent to adjacent-drive EIT with linear reconstruction, particularly near the center of the domain, but the system reliably detected and localized both conductive and non-conductive anomalies across all four hardware configurations and all tested positions.

The team is explicit that this prototype is intended strictly for education and non-human phantom experiments; it lacks the medical-grade patient isolation required by the IEC 60601-1 safety standard, and no commercial analog currently exists at this price point. Yet the significance of the work extends well beyond the laboratory bench. Existing open-source EIT systems that support standard 16-electrode arrays typically cost between 250 and 330 dollars, while cheaper designs sacrifice electrode count or capability. By delivering a full 16-electrode, 50-kilohertz system with an end-to-end open-source software pipeline, including a Tkinter-based graphical interface, STM32 firmware, 3D-printable container files, and even a step-by-step video calibration tutorial, for under 100 dollars, the researchers have lowered the barrier to entry for students and early-career researchers to a fraction of its previous level. Future plans include upgrading to next-generation impedance converters with multi-frequency capability, compressing acquisition below one second for true real-time respiration monitoring, boosting SNR with active-shielded cabling, and exploring generative deep-learning models such as conditional variational autoencoders and diffusion models to push image quality beyond the physical limits of conventional reconstruction. For a field whose clinical value has long been constrained by hardware cost and complexity, a 95-dollar, fully open imaging platform is a genuinely democratizing development.

Subject of Research: A portable, low-cost, open-source electrical impedance tomography system with a modular analog front-end based on an STM32 microcontroller and AD5933 impedance converter.

Article Title: A portable, low-cost, and open-source electrical impedance tomography system with a modular analog front-end based on STM32 and AD5933

Article References: Febrico, J., & Basari (2026). A portable, low-cost, and open-source electrical impedance tomography system with a modular analog front-end based on STM32 and AD5933. HardwareX, Article e00836. https://doi.org/10.1016/j.ohx.2026.e00836

Image Credits: AI Generated

DOI: 10.1016/j.ohx.2026.e00836

Keywords: electrical impedance tomography, open-source hardware, STM32, AD5933, lung imaging, biomedical engineering, analog front-end, pyEIT, medical imaging, respiratory monitoring, low-cost instrumentation, phantom experiments