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Sunday 9 August

Medical Physics

Toward CT-Equivalent Image Quality in Low-Dose Radiotherapy Planning: Conditional Diffusion-Based CBCT-to-CT Synthesis and the Impact of CBCT Input Representation

Alzahra Altalib, Chunhui Li, Christopher Hamill Taylor et al. (+2 more)

During standard radiotherapy planning, repeated CT acquisitions are often required for patient registration, verification, and adaptive planning, resulting in increased cumulative X-ray dose. To mitigate this, low-dose cone-beam CT (CBCT) is routinely acquired during treatment delivery. However, CBCT image quality remains insufficient for accurate dose calculation and adaptive radiotherapy planning due to increased scatter, noise, beam hardening, and reconstruction related artifacts. This study develops a supervised deep learning based CBCT to CT synthesis framework using a conditional denoising diffusion probabilistic model (DDPM), where the generation of a CT-based planning for accurate positioning and dose calculation is obtained using generative models with low dose CBCT imaging. Beyond demonstrating CBCT to CT synthesis, the primary objective is to investigate how the representation of CBCT input data, either standard clinical DICOM CBCT images or filtered back-projection (FDK) reconstructions from raw projection data, affects the performance of diffusion based CT synthesis. The overarching aim is to assess whether physics aware CBCT representations better support CT-equivalent image quality while maintaining reduced imaging dose in radiotherapy workflows.
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All authors Alzahra Altalib, Chunhui Li, Christopher Hamill Taylor, Sankar Pillai, Alessandro Perelli

Medical Physics · Cross-listed from eess.SY

Preview-Based Relative-Motion Control of an Insertion Tool for Neural-Thread Placement in Pulsating Tissue

Yongyan Cao and Xiaobo Li

Flexible neural electrode threads must be placed at a prescribed depth while the cortical surface moves with cardiac and respiratory pulsation. A controller tracking a fixed point in the laboratory frame cannot distinguish commanded insertion from tissue motion; the error appears as both a depth offset and relative tip–tissue velocity during contact. This paper formulates thread insertion in tissue-relative coordinates: a harmonic observer predicts delayed cortical-surface motion over the control horizon, a constrained MPC regulates the tip relative to that prediction while limiting actuator effort and lateral relative velocity, and an augmented disturbance state removes the steady offset from persistent contact force and model mismatch. In a 1-DOF MuJoCo benchmark, the controller reaches RMS relative-placement errors of 12.0\um\ free-space and 1.9\um\ in contact, versus 18.3/176.8\um\ for delayed-feedback impedance and 286.1/275.5\um\ for laboratory-frame PD – the lower contact offset costs more peak contact force (3.43 vs.\ 2.00~mN), since it drives to commanded depth rather than yielding to tissue. A 3-DOF extension reduces lateral shear velocity from 1.34 to 0.50~mm/s at 2.1\um\ lateral placement error, and a feasibility-restoring soft-slack formulation keeps the shear constraint solvable under degraded sensing where a matched hard-constraint controller fails. A two-vertex Lyapunov certificate for the finite-horizon gain holds over $-40\%/{+}50\%$ reflected-mass mismatch, and the 1-DOF QP solves in under 0.4~ms at the 95th percentile. These results are a simulation-based control benchmark, not a clinical safety claim: the modeled tip is a rigid contact point, and flexible-thread mechanics, a validated force constraint, biological damage thresholds, and hardware-realistic sensing and timing remain necessary before deployment.
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Medical Physics · Cross-listed from cs.CV

MRI super-resolution in ten sampling steps using a diffusion bridge model

Mojtaba Safari, Hang Yu, Zach Eidex et al. (+10 more)

Objective. MRI provides excellent soft-tissue contrast, but long acquisition times can cause patient discomfort and lead to motion artifacts, forcing a trade-off between spatial resolution and scan time. Diffusion-based super-resolution (SR) reconstructs high-resolution (HR) images from low-resolution (LR) inputs, but typically needs many sampling steps and initializes from a Gaussian prior ill-suited to image restoration. We developed an efficient diffusion framework that reconstructs HR MRI directly from LR data. Approach. We propose super-resolution diffusion bridge model (SR-DBM), a super-resolution diffusion bridge model that casts SR as a stochastic transport between the LR and HR image distributions. Through a Doob's h-transform of a mean-reverting stochastic differential equation, SR-DBM pins the process to the paired HR and LR images at its endpoints, initializing reconstruction from the measured anatomy rather than from Gaussian noise. The HR image is recovered by a deterministic reverse trajectory in which a network predicts the clean image at each of only ten sampling steps. We evaluated SR-DBM on ultra-high-field 7T brain T1 MP2RAGE maps and pelvic T2-weighted prostate images against nine comparison methods using PSNR, SSIM, GMSD, and LPIPS. Main results. SR-DBM attained the highest PSNR and SSIM and the lowest GMSD on both datasets (brain: 27.66+-1.52 dB, 0.96+-0.02, 7.96+-1.86$; prostate: 27.87+-2.29 dB, 0.80+-0.05, 8.38+- 1.44), with statistically significant gains over every comparison method (two-sided Wilcoxon signed-rank test with Holm correction, p<0.05). The strongest baseline, SR-EMamba, ranked second. Qualitatively, SR-DBM produced the smallest residual errors and best preserved fine structures and lesions.
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All authors Mojtaba Safari, Hang Yu, Zach Eidex, Mingzhe Hu, Ryan J. Sanford, Alexandru Florea, Shansong Wang, Chih-Wei Chang, Erik H Middlebrooks, Aditya Juloori, Stanley L. Liauw, Ralph Weichselbaum, Xiaofeng Yang

Friday 7 August

Medical Physics

Vendor-Agnostic Joint Relaxometry and Myelin Water Fraction Mapping with B1 and Motion Correction

Unay Dorken Gallastegi, Shohei Fujita, Yohan Jun et al. (+19 more)

Obtaining consistent quantitative maps of myelin content and relaxation times across different sites and vendors is essential for advancing our understanding of brain development. Herein, we present a harmonized, vendor-agnostic magnetic resonance acquisition method designed for joint T1, T2, and myelin water fraction mapping, along with a method for rapid B1+ and B1- field estimation. We used our dictionary-based fitting and multi-compartment modeling for joint mapping of T1, T2 and myelin water fraction. Self-navigation-based retrospective motion correction was integrated with subspace reconstruction to track and correct rigid head motion during scanning, operating without the need for external hardware. Simulations, phantom and in vivo experiments confirmed the sensitivity and accuracy of the method, particularly for short T2 values corresponding to myelin, and demonstrated consistent performance across multiple scanner types. Coupled with the harmonized calibration scan, the proposed package offers a practical tool for multi-site, multi-vendor neuroimaging studies in both adult and pediatric populations.
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All authors Unay Dorken Gallastegi, Shohei Fujita, Yohan Jun, Antoine Delattre-Klauser, Gian Franco Piredda, Tom Hilbert, Cemre Ariyurek, Eugene Milshteyn, Shizhuo Li, Yuting Chen, Xingwang Yong, Kwok-Shing Chan, Qiang Liu, Seonghwan Yee, Yogesh Rathi, Maxim Zaitsev, Jon-Fredrik Nielsen, Onur Afacan, Camilo Jaimes, Patricia Ellen Grant, Borjan Gagoski, Berkin Bilgic

Medical Physics

An Angular Spectrum Method for Nonlinear Propagation in Heterogeneous Tissue with Immersed Sources for Ultrasound

Gianmarco Pinton

A modified angular spectrum method (ASM) is developed for three-dimensional nonlinear acoustic propagation through heterogeneous tissue, targeting transcranial and therapeutic ultrasound. First, a consistent obliquity correction is applied to both the linear and nonlinear operators of the split-step update. The attenuation and dispersion filter carries a per-mode k/kz factor on the full wavenumber-frequency grid, so each component accumulates absorption and phase over its true path length dz/cos(theta), while the Burgers coefficient is scaled by the power-weighted mean beam obliquity. Second, the retarded-time Burgers update is discretized with a second-order Kurganov-Tadmor central-upwind flux using MUSCL reconstruction and SSP-RK2 time integration, composed with diffraction and attenuation through Strang splitting with adaptive CFL sub-cycling, resolving fully developed shocks without the temporal refinement that the CFL coupling imposes on FDTD. Third, a plane-by-plane source-injection scheme decomposes deeply curved bowl transducers into axial slices injected at their correct propagation depths, preserving the aperture-dependent shock-formation distance. Phase-and-amplitude screens derived from skull CT data model transcranial aberration and insertion loss, and three enhanced absorbing-boundary treatments reduce boundary reflections by a factor of 2.4. Analytical validation reproduces the baffled-piston far-field pattern to 0.014 RMS and the focused-piston focal pressure to within 2.3 percent. In a transcranial benchmark through an ex vivo human skull, the ASM matches the Fullwave 2 focal-plane intensity to 1.1 percent RMS and predicts a 5.4 dB through-skull insertion loss. For a bowl transducer (R = 80 mm, f0 = 1 MHz), the ASM matches the Fullwave 2 focal depth to within 2.3 percent with 9x less memory and 2.9x less wall time.
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Medical Physics

Measurements Automatically Extracted from Zero Echo Time MRI Using Deep Learning Image Segmentation and Geometric Modeling Agree with Expert Manual Readings

Jack Consolini, Eric A. Bogner, Meghan Sahr et al. (+3 more)

Computed tomography (CT) remains the reference for 3D osseous morphometry in femoroacetabular impingement (FAI) but requires ionizing radiation and manual measurement. Zero echo time (ZTE) MRI visualizes cortical bone and yields FAI angles that agree with CT, but automated angle extraction remains limited. We developed and validated automated FAI angle computation from ZTE MRI and assessed agreement with expert manual measurements in a cross-sectional study (level of evidence, 3). Pelvic ZTE MRI was acquired in 73 participants (mean age 36.8 +/- 18.5 years; 51 women, 22 men), yielding 135 hips. nnU-Net was trained on 100 manually curated hips to segment the femur, pelvis, and three osseous landmarks. Custom geometric algorithms computed alpha, femoral neck-shaft, Tonnis, coronal and sagittal center-edge, and acetabular version angles from inferred segmentations. Measurements on 35 test hips were compared with the mean of two radiologists' manual measures using intraclass correlation (ICC) and Bland-Altman analysis. Dice exceeded 0.96 for bone and ranged from 0.65 to 0.83 for landmarks. Median landmark error was 0.38 mm (femoral head), 0.82 mm (lateral acetabulum), and <2.5 mm (medial acetabulum, greater trochanter). Interrater ICC was excellent for acetabular version, coronal center-edge, and Tonnis (>=0.82) but poor for alpha and femoral neck-shaft. Model versus rater-mean agreement was excellent for acetabular version, coronal center-edge, and Tonnis (0.92-0.96), good for mid-acetabular sagittal center-edge (0.74), and fair for alpha (0.45) and femoral neck-shaft (0.55). Model Bland-Altman limits of agreement were narrower than interrater limits for most angles. Fully automated morphometric assessment from ZTE MRI is feasible and performs comparably to expert readers for most coverage and version angles.
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All authors Jack Consolini, Eric A. Bogner, Meghan Sahr, Matthew F. Koff, Kevin M. Koch, Hollis G. Potter

Medical Physics · Cross-listed from cs.LG

Machine Learning-Based Inter-Crystal Scatter Recovery for Ultra-High Resolution PET Imaging

Alexandre Bernier, Roger Lecomte and Jean-Baptiste Michaud

Inter-crystal scatter (ICS) events pose a significant challenge in ultrahigh- resolution positron emission tomography (UHR-PET), especially as detector crystals become smaller and their readouts increasingly segmented. Current approaches either reject these events, reducing sensitivity, or accept them with suboptimal positioning algorithms, degrading image resolution. We present a feed forward neural network to optimize ICS event recovery by inferring the line-of-response belonging to the first Compton interaction. Our approach was validated using both Monte Carlo simulations and experimental data from the fully pixelated LabPET-IIbased preclinical and brain UHR-PET scanners.Results demonstrate a 70% to 106% increase in sensitivity while preserving sub-millimeter spatial resolvability (down to 1.6 mm) compared to conventional methods. This ICS recovery approach is an effective solution that compensates for the lower detection efficiency of small, pixelated detectors in UHR-PET, enabling reduced scan times and lower radiation doses while largely preserving image quality.
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Medical Physics

Lens-Aware Differentiable Beamforming for In Vivo Distributed Aberration Correction with Curvilinear Transducers

Benjamin N. Frey, Robin van Velzen, Hoda S. Hashemi et al. (+7 more)

We previously introduced ultrasound autofocusing, an iterative model-based aberration correction technique that estimates local sound speed and incorporates it into beamforming to correct image distortion from heterogeneous media. In this work, we extend ultrasound autofocusing to curvilinear arrays and introduce advancements to the underlying model. A differentiable bent-ray tracing approach accounts for refraction through the transducer lens, while a new adaptive-grid initialization accounts for changes in speckle position with sound speed. The method is validated in silico and in calibrated sound speed phantoms. Our distributed aberration-correction method is then applied to a first large-scale in vivo evaluation comprising 313 liver acquisitions from 76 high-BMI human subjects. In images containing anechoic regions, contrast and CNR improved by $1.38 \pm 1.60$ dB (+18.0%) and $0.09 \pm 0.14$ (+10.2%), respectively. Improvements were also observed in speckle brightness (+20.3%), coherence factor (+13.1%), lag-one coherence (+2.7%), common-midpoint correlation coefficient (+0.7%), and common-midpoint phase error (-9.1%; lower is better), with all metric improvements statistically significant. Target structure and visibility also improved significantly. These results demonstrate the potential of ultrasound autofocusing for clinically applicable distributed aberration correction.
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All authors Benjamin N. Frey, Robin van Velzen, Hoda S. Hashemi, Samuel Beuret, Martin Schneider, Alice C. Fan, Christian R. Hoerner, Aya Kamaya, Sergio J. Sanabria, Jeremy J. Dahl

Medical Physics

108 ps coincidence time resolution through optimized scintillators, photodetectors, readout electronics, and DOI-based timing correction in orthogonally stacked detector configurations

Arisa Sanzen, Yuya Onishi, Takahiro Moriya et al. (+2 more)

Objective. Existing commercial time-of-flight positron emission tomography (TOF-PET) systems yield a coincidence time resolution (CTR) of ~200 ps or less full width at half maximum (FWHM). Recently, there has been a challenge to achieve a CTR of 100 ps FWHM at the system level. However, current silicon photomultipliers (SiPMs) and 20-mm-thick scintillators in conventional single-ended readout scheme is difficult to achieve 100 ps CTR; the photon transport time spread (PTS) within the scintillator crystal is a major barrier. Differences in the interaction position result in variations in PTS on the order of several tens of ps, thereby degrading the CTR. A shorter scintillator can improve CTR; however, this can degrade detection efficiency. Approach. To overcome this trade-off between the CTR and detection efficiency, we previously proposed xDetector, an orthogonally stacked configuration along the longitudinal axis of scintillator crystals. We investigated the CTR potential of the xDetector by improving the scintillator, photodetector, and readout electronics, and by applying CTR correction based on a three-dimensional interaction within the scintillator. Main results. Based on error propagation, the CTR of the paired xDetector was calculated as 113.5 $\pm$ 2.7 ps FWHM. Furthermore, the CTR of the xDetector was measured at four positions along the longitudinal axis by manually sliding the xDetector, and the corrected achieved CTR was 108.6 $\pm$ 1.9 ps FWHM. Moreover, compared with the conventional single detector using a 20.0 mm scintillator, CTR improved by an average of 10.3%. Significance. The xDetector offers potential as a PET detector concept to achieve a CTR of 100 ps FWHM. Such timing performance is expected to improve TOF-PET image quality and quantitative accuracy, contributing to more reliable disease detection and diagnosis than current PET detectors.
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All authors Arisa Sanzen, Yuya Onishi, Takahiro Moriya, Tomohide Omura, Ryosuke Ota

Thursday 6 August

Medical Physics

An open-source framework for predicting ultrasound neuromodulation: bridging tissue elastomechanics and neuron firing dynamics

Gianmarco Pinton

Transcranial focused ultrasound is a non-invasive neuromodulation modality with millimetre-scale resolution, but its biophysical mechanism of action remains unresolved. Exposure is conventionally specified by transducer surface or derated focal pressure, quantities only indirectly related to what matters for therapy: which neurons fire and through which pathway. We address this gap with an end-to-end computational framework that maps a transcranial acoustic field to per-voxel neural firing maps registered to anatomy. The pipeline couples heterogeneous nonlinear full-wave acoustic propagation, viscoelastic shear-wave propagation, Pennes bioheat diffusion, a bilayer-mechanics conversion from tissue strain to membrane tension, and a multi-compartment Hodgkin-Huxley neuron carrying mechanosensitive, cavitation-coupled, calcium-coupled, thermosensitive, astrocytic-gliotransmitter, and mechanosensitive-synaptic pathways. Six candidate mechanisms are implemented as interchangeable components on a shared neuron model, so their firing predictions can be compared directly on the same field, and every numerical parameter is classified by source and bracketed by sensitivity analysis. We demonstrate the framework on a theta-burst sonication delivered through a micro-CT human-skull specimen targeting the left dorsal anterior cingulate cortex, predicting a focal firing zone of approximately 8,500 mm^3 at a focal thermal rise well within ITRUSST consensus safety envelopes. The principal output is a per-voxel firing-volume map resolved jointly with the acoustic, elastic, and thermal field histories that drive it, giving spatially resolved, falsifiable predictions that are testable against high-density extracellular recordings and support parameter estimation, cell-type-resolved mechanism identification, and quantitative safety assessment for ultrasound neuromodulation.
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Medical Physics

Evaluation of Silicon-Based Photon-Counting CT for Coronary Stenosis Quantification with Realistic Coronary Artery Phantoms

Maria Jose Medrano, Jed Pack, Stephen Araujo et al. (+5 more)

Objective: To quantify the impact of high-resolution deep silicon photon-counting CT (dSi-PCCT) on coronary stenosis quantification in anatomically realistic calcified coronary artery phantoms using Micro-CT as ground truth. Methods: Twelve vessel sections representing four calcification geometries (Type I-IV) and three luminal iodine concentrations (10, 15, and 20 mg/mL) were scanned under static conditions using energy-integrating detector CT (EID-CT), dSi-PCCT, and Micro-CT. Images were registered to Micro-CT and segmented using an automated threshold-based pipeline. The primary analysis compared longitudinal profiles of Micro-CT-referenced percent area stenosis and segmented vessel area. A secondary analysis evaluated ellipse-derived percent area stenosis and percent vessel-area deviation at the maximum-calcification cross-section. Results: dSi-PCCT reduced whole-profile mean absolute error in Micro-CT-referenced percent area stenosis from 3.10% with EID-CT to 1.62% (p=0.027) and reduced segmented vessel-area error from 0.55 to 0.31 mm2 (p=0.001). In the secondary analysis, absolute deviations in ellipse-derived percent area stenosis ranged from 0.1% to 6.5% for dSi-PCCT and from 0.8% to 24.2% for EID-CT (p<0.001). Mean absolute differences in percent vessel-area deviation from Micro-CT were also lower with dSi-PCCT than with EID-CT (15.0% vs 26.6%, p<0.001). Conclusion: Under static, resolution-optimized conditions, dSi-PCCT improved task-based coronary stenosis quantification and vessel delineation relative to EID-CT, supporting further evaluation in dynamic phantoms and clinical CCTA.
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All authors Maria Jose Medrano, Jed Pack, Stephen Araujo, Grant M. Stevens, Koen Nieman, Ge Wang, Bruno De Man, Adam S. Wang

Medical Physics

A Unified Analytical Framework for LYSO-SiPM Scintillation Pulse Dynamics

Ao Qiu and Qingguo Xie

Existing scintillation-detector models typically treat scintillation kinetics, optical transport, silicon photomultiplier (SiPM) response, and timing statistics separately, limiting end-to-end prediction of waveform formation and detector performance. We present a unified analytical framework for lutetium-yttrium oxyorthosilicate (LYSO)-SiPM scintillation detectors that links these processes within a single forward model. The framework incorporates finite thermalization, depth-dependent optical transit-time spread, and microcell occupancy dynamics to provide a physics-based description of macroscopic pulse formation. It yields closed-form exponentially modified Gaussian pulses in the linear regime, state-dependent integral solutions in saturation, and recovers the conventional bi-exponential pulse model—ubiquitously used yet hitherto only empirically justified in scintillation pulse fitting and sparse-sampling reconstruction—as a controlled reduction of the full optoelectronic cascade. Experimental validation on 10,000 directly digitized Na-22 pulses shows that the dynamic saturation model captures amplitude-dependent waveform distortion and is favored by the Akaike information criterion (AIC) over a matched bi-exponential baseline in 100/100 high-amplitude pulses and 98/100 medium-amplitude pulses. By coupling the dynamic triggering rate to compound Poisson statistics, the framework also predicts current-variance envelopes and Fisher-information-based timing limits, including an intrinsic coincidence timing resolution lower bound of about 100 ps full width at half maximum (FWHM) for a reference 511-keV LYSO-SiPM configuration. These results deepen the physical understanding of scintillation-detector waveform formation and timing limits by clarifying how scintillation kinetics, optical transport, and SiPM microcell dynamics jointly shape the observed response.
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Medical Physics

The Virtual Hearing Clinic (VHC)- a modular online platform for hearing research and hearing health care

Lena Schell-Majoor, Kim M. Rullmann, Tobias Bruns et al. (+4 more)

Objective: The aim is to introduce the concept of the Virtual Hearing Clinic (VHC), give an overview of the current status and exemplify its feasibility with data from a diagnostics module obtaining hearing thresholds. Design: The architecture of the VHC is described and an overview of functional modules that have been developed and tested in respective studies is given. As a functional example data from an experiment is presented. Hearing thresholds were obtained from 20 subjects with hearing loss with the VHC using the Graded Response Bracketing (GraBr) procedure and compared to reference thresholds obtained with a clinical audiometer. Results: Median VHC-based hearing thresholds over all frequencies did not differ significantly from the reference with values of 57.4 dB SPL (VHC) and 55.5 dB SPL (reference). The shape of the frequency-dependent thresholds was also found to be very similar for 250 Hz to 4 kHz. Results for 6 kHz showed larger differences. Conclusion: The VHC is suitable as a mobile hearing health application and to collect data for audiological research. By offering flexibility in time and location it can lower barriers for hearing health care and enable collecting large datasets that are needed for the advancement of data-driven audiology.
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All authors Lena Schell-Majoor, Kim M. Rullmann, Tobias Bruns, Theresa Jansen, Volker Hohmann, Hendrik Kayser, Birger Kollmeier

Wednesday 5 August

Medical Physics · Cross-listed from eess.IV

A Foundational EDM2-Based Generative Model for High-Resolution Synthetic Fetal Ultrasound Imaging from Open Datasets

Harvey Mannering, Yilin Zhang, Ziao Liu et al. (+3 more)

Prenatal ultrasound imaging is key for assessing fetal health, but AI progress is limited by scarce, privacy-restricted, and hard-to-annotate datasets. We propose a high-resolution fetal ultrasound synthesis framework based on the EDM2 diffusion architecture, trained on multiple public datasets to generate 512x512 images across six anatomical classes. Our method achieved improved image quality with lower FID scores and enhanced downstream fetal plane classification, reaching 93.36% ensemble accuracy after fine-tuning, surpassing real-data-only training. Clinical evaluation by an experienced fetal ultrasound specialist (10+ years) on 100 images yielded a mean realism score of 2.67/5, with real images rated higher than synthetic. Artefacts included smoothing, speckle irregularities, and anatomical inconsistencies. Code, data, models and other resources to reproduce this work are available at https://github.com/xfetus/fetal-ultrasound-edm2.
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All authors Harvey Mannering, Yilin Zhang, Ziao Liu, Zhiwu Huang, Jacqueline Matthew, Miguel Xochicale

Medical Physics

Prior-Based Multi-Voltage Threshold Sampling as a Structured Inverse Problem

Ao Qiu and Qingguo Xie

Prior-based Multi-Voltage Threshold (MVT) sampling reconstructs pulse parameters from sparse threshold-crossing times rather than full waveforms, making parameter recovery inherently a model-dependent inverse problem. However, prior-based MVT has lacked a formal mathematical statement, leaving identifiability, stochastic error propagation, and threshold design without a unified theoretical foundation. We formalize prior-based MVT for strictly unimodal pulse families as a structured inverse problem. On that foundation, we develop the first unified theory of prior-based MVT, comprising deterministic identifiability conditions, a stochastic timing-error model with leading-order mismatch bias, and a nuisance-profiled threshold-design theory centered on an effective-information equation for robust single-event and partial-trigger multi-event operation. We instantiate the framework for the bi-exponential pulse model, derive executable design recipes, and validate the resulting predictions on a 10,000-pulse $^{22}$Na/LYSO/SiPM dataset. The experiments confirm that the framework yields useful threshold designs in the photopeak regime while also revealing the regime boundary at which partial triggering and model mismatch limit the predictive power of Fisher-guided optimization. These results provide the first unified mathematical foundation for prior-based MVT and recast it from an empirical threshold heuristic as a principled inferential framework.
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Tuesday 4 August

Medical Physics · Cross-listed from physics.ins-det

Spectacular - A Modular DAQ System for Microdosimetry

Matthias Knopf, Simon Waid, Daniel Radmanovac et al. (+8 more)

Particle therapy using light ions like protons, helium ions or carbon ions enables precise tumor targeting with enhanced biological effectiveness while minimizing damage to healthy tissue. Successful treatment planning depends not only on the absorbed dose but also on quality of the radiation, as quantified by the linear energy transfer (LET). Microdosimetry provides a direct experimental determination of such quantities by measuring the energy deposited per incoming particle in micrometer-sized solid-state detectors representing the relevant biological scales. However, the small signal amplitudes and high particle rates in therapeutic ion beams challenge existing readout systems, which are not sufficiently optimized for reliable operation with respect to pileup and signal-to-noise ratio (SNR). To address this, a modular data acquisition (DAQ) system was developed to accelerate the design of custom readout electronics and sensor characterization in microdosimetry and related spectroscopic applications. Centered around a Xilinx Zynq system-on-chip, it combines real-time processing, high-bandwidth streaming, and high-resolution digitization (16 bit at 100 MSas$^{-1}$) to enable advanced digital signal processing. The platform integrates programmable power supplies, a bias-voltage filter, test-pulse generators, and flexible I/O. Detector and preamplifier front-ends are hosted on interchangeable daugtherboards connected via a standardized interface, allowing different hardware configurations and readout algorithms to be evaluated on the same platform. The Spectacular DAQ system was successfully tested at the MedAustron ion therapy facility with custom charge-sensitive amplifiers and a diamond microdosimeter. First results demonstrate the feasibility and provide a proof-of-concept for potential future applications in clinical practice.
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All authors Matthias Knopf, Simon Waid, Daniel Radmanovac, Sebastian Onder, Richard Thalmeier, Peter Fischer, Stefan Gundacker, Claudio Verona, Edoardo Domenicone, Thomas Bergauer, Albert Hirtl

Monday 3 August

Medical Physics

Real-time tissue-equivalent measurement of individual clinical radiotherapy pulses

Fernanda C. Rodrigues-Machado, Katherine Szabo, Jingyi Bian et al. (+5 more)

We apply the precision tools of cavity-enhanced absorption sensing to clinical oncology, demonstrating a dosimeter paradigm in which a centimeter-scale volume of water serves as a tissue-equivalent sensing medium. Our proof-of-concept, all-optical scheme achieves real-time readout of clinical radiation pulses with a nominal single-pulse resolution of 90 $\mu$Gy. This demonstration paves the way toward fiber-integrated, micron-scale devices for $\textit{in situ}$ universal absolute dosimetry during treatment.
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All authors Fernanda C. Rodrigues-Machado, Katherine Szabo, Jingyi Bian, Simon Bernard, Tanner Connell, Shirin A. Enger, Lilian Childress, Jack C. Sankey

Medical Physics

Cardiovascular Digital Twins from Physics Based to Data Driven Approaches

Emmanuel Lwele and Francis Chikweto

Cardiovascular digital twins aim to create patient-specific computational models that evolve with clinical data to support diagnosis, prognosis, and therapy optimisation. Mechanistic models provide physiological interpretability but remain computationally demanding, whereas data-driven approaches improve scalability yet risk limited robustness. Emerging physics-informed, graph-based, and hybrid methods integrate physical constraints with relational learning across vascular networks. We review modelling paradigms, data assimilation frameworks, validation challenges, and translational pathways toward clinically deployable cardiovascular digital twins.
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Medical Physics · Cross-listed from physics.ins-det

Performance and prospects of polyurethane-based scintillators for neutron and gamma radiation detection

Olga Maiatska, Torsten Duennebacke, Roland Hillebrands et al. (+6 more)

Organic scintillators have been used for decades to detect gamma rays or fast neutrons at low cost. Despite extensive efforts it is still difficult to combine stability, ruggedness, high light yield, and decent pulse-shape discrimination (PSD) in a single scintillator material. We took the unusual approach of embedding phosphors and wavelengths shifters in a solid polyurethane matrix, trying to combine the robustness of a common construction material with scintillating properties and PSD performance. The plastic scintillators resulting from years of research ultimately meet these intentions. Moreover, the production process is less demanding and less complex than that of conventional plastic scintillators. It allows to directly integrate light sensors or electronics into the scintillator. This opens the door for the construction of extremely compact and robust plastic detectors for the simultaneous detection of fast neutrons and gamma rays. This paper presents basic recipes and properties of scintillators based on this novel conception and discusses first applications in neutron imaging and personal radiation protection.
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All authors Olga Maiatska, Torsten Duennebacke, Roland Hillebrands, Achim Kreuels, Martin Kreuels, Guntram Pausch, Falko Scherwinski, Andreas Wolf, Juergen Stein