Biology subjects

Bonmassar, G.

Publications and source records attributed to Bonmassar, G..

6 recordsLinked to original sources

bioRxiv2026

Development and Validation of Thalia: A High-ResolutionPediatric Computational Model of a 10-Month-Old Infant

Numerical human models are essential to advance medical device design, safety assessment, and study how anatomical development influences physiological processes. Despite increasing availability of pediatric models, a critical gap remains in high-resolution, non-morphed whole-body models representing children around one year of age. Existing pediatric models are often derived from morphing older anatomies or lack sufficient tissue segmentation to accurately capture early developmental anatomy. This study introduces Thalia, a non-morphed, high-resolution numerical model of a healthy 10-month-old female. The model was constructed by segmenting 442 tissues from Magnetic Resonance Imaging data. Brain tissues were automatically segmented using an infant-specific FreeSurfer framework, followed by semi-automated and manual refinement in 3DSlicer. The model was validated by expert review and quantitative comparison with age-matched anatomical values reported in the literature. The resulting whole-body model provides detailed anatomical representation across the brain, musculoskeletal system, vasculature, and internal organs, enabling realistic assignment of tissue-specific properties for computational studies. It provides a versatile platform for pediatric medical device development, dosimetry, safety assessment, and bioelectromagnetic simulations. This pediatric numerical anatomical model is openly available as an open-source resource. HighlightsO_LIHigh-resolution model of a 10-month-old child developed from MRI data C_LIO_LI442 tissues segmented to capture early anatomical development accurately C_LIO_LIModel validated against expert review and age-matched anatomical data C_LIO_LIIllustrative Example of a pediatric transcranial magnetic stimulation use case C_LI

bioengineering↗

bioRxiv2026

Cumulative Transfer Function for Assessment of MRI-Induced RF Heating Risk in Pediatric Patients Implanted with Bifurcated Leads

PurposeRF-induced heating remains a major barrier to MRI access for patients with epicardial cardiac implantable electronic devices (CIEDs). Although ISO/TS 10974 Tier-3 transfer function (TF) methods are established for unbranched leads, no analogous framework exists for bifurcated leads, in which branch asymmetry and inter-branch coupling may substantially alter heating. We developed and validated a cumulative transfer function (cTF) framework to address this gap. MethodsFollowing ISO/TS 10974 Tier-3 formalism, we measured, calibrated, and validated cTFs for a commercial 35 cm bipolar epicardial lead at 1.5 T. The framework explicitly accounts for branch-specific response and cross-branch coupling. Validation was performed with 24 canonical lead configurations in a homogeneous phantom and, without recalibration, in a heterogeneous anthropomorphic pediatric phantom with clinically derived trajectories. A single-branch TF approximation served as a comparator. The validated cTF was applied to predict RF heating across adult and pediatric human models at multiple imaging landmarks. ResultsCompared with the single-branch TF approximation, the cTF reduced prediction error by nearly 70% in the primary validation dataset. In secondary validation, the cTF maintained low error across clinically relevant trajectories and imaging landmarks. In human models, the framework revealed marked anatomy- and landmark-dependent variation in predicted heating for the tested 35 cm lead, with low predicted heating in pediatric models and substantially higher heating in selected adult chest and upper abdominal imaging scenarios. ConclusionThe cTF provides a validated framework for RF-heating assessment of bifurcated leads and substantially improves prediction accuracy over single-branch TF approximations that neglect branch coupling.

bioengineering↗

bioRxiv2022

Age and lead configuration matter: A comparative study of RF-induced heating of epicardial and endocardial electronic devices in adult and pediatric anthropomorphic phantoms in 1.5 T MR

BackgroundChildren with congenital heart defects often have life-sustaining indications for a cardiac implantable electronic device (CIED). In children, these devices are typically sewn to the heart epicardium, but the FDA has never licensed an epicardial system as MR-Conditional due to limited data. Childrens hospitals default to either refusing MRI service to a vast majority of pediatric CIED patients or adopting a scan-all strategy based on results from adult studies. We argue that both approaches are flawed, and the risk-benefit decisions should be made on an individual basis. PurposeTo provide evidence-based knowledge on RF-induced heating of CIEDs in children and adults with epicardial and endocardial leads of different lengths. Study TypePhantom Field Strength/Sequence1.5 T. Assessment120 clinically relevant epicardial and endocardial device configurations were implemented in adult and pediatric anthropomorphic phantoms. Temperature rise was recorded during RF exposure at 1.5 T. Statistical TestsMeans comparisons were implemented using two-sample t-tests, reliability analysis using interclass correlation coefficient based on a single rating, absolute-agreement, 2-way mixed-effects model. ResultsThere was significantly higher RF heating of epicardial leads compared to endocardial leads in the pediatric phantom (3.4 {+/-} 3.0 vs. 0.6 {+/-} 0.4 {degrees}C, p<0.001); however, there was no significant difference in the adult phantom (3.0 {+/-} 3.2 vs. 2.0 {+/-} 1.8, p=0.16). Endocardial leads in the pediatric phantom generated significantly less RF heating than in the adult phantom (0.6 {+/-} 0.4 {degrees}C vs. 2.0 {+/-} 1.8 {degrees}C, p<0.001). Data ConclusionBody size and lead length significantly affected RF heating. For models based on younger children with short epicardial leads (e.g., 25cm), RF heating up to 12 {degrees}C was observed, delivering a cumulative thermal dose previously associated with tissue necrosis. In contrast, RF heating in model based on children with endocardial leads was well below the heating expected from physiologic fever (3 {degrees}C).

biophysics↗

bioRxiv2022

Modifying the trajectory of epicardial leads can substantially reduce MRI-induced RF heating in pediatric patients with a cardiac implantable electronic device

PurposeInfants and children with congenital heart defects, inherited arrhythmia syndromes, and congenital cardiac conduction disorders often receive epicardial implantable electronic devices. Unfortunately, once an epicardial device is implanted, the patient is no longer eligible to receive MRI exams due to an elevated risk of RF heating. Here we show that a simple modification in the trajectory of epicardial leads can substantially and reliably reduce RF heating during MRI at 1.5 T, with benefits extending to abandoned leads. MethodsElectromagnetic simulations were performed to assess RF heating of two common epicardial lead trajectories exhibiting different degrees of coupling with MRI incident electric fields. Experiments in anthropomorphic phantoms implanted with commercial cardiac implantable electronic devices (CIEDs) confirmed the findings. ResultsSimulations of an epicardial lead with a trajectory where the excess length of the lead was looped and placed on the anterior surface of the heart showed a 9-fold reduction in 0.1g-averaged SAR compared to the lead with excess length looped on the inferior surface of the heart. Repeated experiments with a commercial epicardial device confirmed the results, showing a 16-fold reduction in the average temperature rise for fully implanted systems with leads following low-SAR trajectories, and a 20-fold reduction in RF heating on an abandoned lead. ConclusionSurgical modification of epicardial lead trajectory can substantially reduce RF heating at 1.5 T, with benefits extending to abandoned leads.

biophysics↗

bioRxiv2021

A temporal sequence of thalamic activity unfolds at transitions in behavioral arousal state

The moment of awakening from sleep reflects a profound transformation in neural activity and behavior. The thalamus is a key controller of arousal state, but whether its diverse nuclei exhibit coordinated or distinct activity at transitions in behavioral arousal state is not known. Using fast fMRI at ultra-high field (7 Tesla), we measured sub-second activity across thalamocortical networks and within nine thalamic nuclei to delineate these dynamics during spontaneous transitions in behavioral arousal state. We discovered a stereotyped sequence of activity across thalamic nuclei that preceded behavioral arousal after a period of inactivity, followed by widespread cortical deactivation. These thalamic dynamics were linked to whether participants remained awake or fell back asleep, with unified thalamic activation reflecting subsequent maintenance of awake behavior. These results provide an outline of the complex interactions across thalamocortical circuits that orchestrate arousal state transitions, and additionally, demonstrate that fast fMRI can resolve sub-second subcortical dynamics in the human brain.

neuroscience↗

bioRxiv2018

Reducing RF-Induced Heating Near Implanted Leads Through High-Dielectric Capacitive Bleeding of Current (CBLOC)

Patients with implanted medical devices such as deep brain stimulation or spinal cord stimulation are often unable to receive magnetic resonance imaging (MRI). This is because once the device is within the radiofrequency (RF) field of the MRI scanner, electrically conductive leads act as antenna, amplifying the RF energy deposition in the tissue and causing possible excessive tissue heating. Here we propose a novel concept in lead design in which 40cm lead wires are coated with a ~1.2mm layer of high dielectric constant material (155 <{varepsilon} r < 250) embedded in a weakly conductive insulation ({sigma} = 20 S/m). The technique called High-Dielectric Capacitive Bleeding of Current, or CBLOC, works by forming a distributed capacitance along the lengths of the lead, efficiently dissipating RF energy before it reaches the exposed tip. Measurements during RF exposure at 64 MHz and 123 MHz demonstrated that CBLOC leads generated 20-fold less heating at 1.5 T, and 40-fold less heating at 3 T compared to control leads. Numerical simulations of RF exposure at 297 MHz (7T) predicted a 15-fold reduction in specific absorption rate (SAR) of RF energy around the tip of CBLOC leads compared to control leads.

biophysics↗