Medical Physics Papers

ALT Magnetic resonance imaging (MRI) pulse sequences organize radiofrequency excitation, gradient encoding, and signal acquisition, determining magnetization evolution and image formation. Sequence research requires translating imaging objectives into executable protocols meeting physical and acquisition constraints, refined via physical simulation, signal reconstruction, and scientific evaluation. Sequence construction, physical verification, parameter search, and assessment involve many tools and manual decisions, limiting automation from objective to verifiable sequence. We develop SmartBloch-Agent, an integrated framework for automated MRI sequence design and optimization. Given objectives and scientific constraints in natural language, an AI agent interprets goals, plans tasks, orchestrates tools, and makes feedback-informed decisions, drawing on a construction module and optimizers for structural design and parameter search. Our GPU-accelerated SmartBloch engine supplies physical com

ALT Ultrasound spectral Doppler imaging provides quantitative blood flow information for vascular diagnosis, but its accuracy is limited by the one-dimensional (1D) sample volume (SV). Motion from respiration, patient movement, and probe manipulation can move the target vessel out of the SV, causing spectral broadening, signal reduction, or loss of the spectrum. A two-dimensional (2D) SV can address this, but sequential focused-beam transmission reduces the pulse-repetition frequency (PRF), and plane-wave transmission lowers the signal-to-noise ratio (SNR). In this study, we propose a wide-beam transmission method that acquires a 2D SV from a single transmit event while preserving the PRF. A Hamming network, which requires no prior training, tracks axial and lateral motion within the 2D SV and updates the position of an adaptive 1D SV for each frame. Field II simulations showed that the wide-beam transmission had a spectral SNR comparable to that of focused-beam transmission and approximat

ALT Background: The temporal misregistration in conventional X-ray digital subtraction angiography (DSA) remains a key challenge for its practical application in cardiac catheterization, leading to incomplete separation of cardiac vessels from background anatomical structures. Purpose: In this study, the X-ray spectral information is unveiled for DSA imaging to generate better visualization of cardiac vessels with negligible anatomical background. Methods: A dedicated dual-energy DSA imaging model is proposed based on the subtraction residuals between pre-contrast and post-contrast spectral projections, enabling accurate material decomposition without requiring precise scatter correction. Specifically, a dual-layer flat-panel detector (DL-FPD) is assumed to acquire the needed temporally registered low-energy and high-energy projections. Moreover, a penalized likelihood material decomposition algorithm is proposed to enhance the material decomposition performance. To validate, in vivo swine

ALT Over 50 million diagnostic procedures involving medical radioisotopes are performed per year and the number of therapeutic and theranostic agents continues to climb. Yet, the global supply chain is far from stable and many regions are underserved. This is the second of a Series of two review papers providing a comprehensive overview of the landscape of medically relevant radioisotopes. This paper focuses on the supply chain. It presents a critical overview of the 2025-2026 status quo, case studies of acute stressors and disruptions they caused, and methods in place to secure a stable supply. A literature-based analysis is paired with expert interviews. We argue that the ageing fleet of nuclear reactors currently used for the centralised production of many isotopes should be complemented by regional accelerator-based centres, alleviating single-point failures and cross-border logistics complications, and increasing access to short-lived isotopes in harder-to-reach regions and low- and m

ALT Over 40 radioisotopes are currently in use or under development across virtually all fields of modern medicine. Their availability relies on a complex interplay of nuclear physics, radiochemistry, and nuclear medicine. This review provides an isotope-by-isotope map of medically important radioisotopes from the perspective of these disparate yet complementary fields. We address the landscape grouped into three tiers: the established clinical core, including, familiar workhorses such as Tc-99m, F-18, Lu-177; an under-leveraged middle tier including Re-186, Re-188, and Sm-153, and the emerging frontier, radioisotopes with demonstrated but underutilised clinical promise such as Ac-225, At-211, Cu-67, and Sc-47. We discuss the properties of these radioisotopes with respect to clinical applications and their production pathways, as well as the associated nuclear and radiochemical challenges. We synthesise these disparate perspectives to identify situations in which alleviating production-sid

ALT Reliable localization and characterization of cavitation activity are central to many ultrasound imaging and therapy monitoring applications. Passive acoustic mapping (PAM) can estimate cavitation distributions without prior assumptions but remains limited by the system point spread function. While advanced PAM methods improve spatial resolution, their performance may degrade for transient emissions with uncertain emission times. In this work, we propose a parametric source localization framework based on the Space-Alternating Generalized Expectation-Maximization (SAGE) algorithm to estimate source positions and emitted waveforms directly from array channel data. A greedy source extraction and localization procedure is first used to initialize the model order and source parameters, after which SAGE iteratively refines each source estimate. The proposed method was validated on 49 simulated acquisitions containing up to seven simultaneously emitting sources with emission time uncertainti

ALT Computed tomography (CT) is used ubiquitously for diagnostic imaging, with novel iterative reconstructions such as hybrid iterative reconstruction with partial model-based component (ASiR-V) and deep learning image reconstruction (DLIR) increasingly utilized. In conjunction, CT vendors have developed a noise index (NI) to reduce radiation dose during protocol development. However, it is unclear how these reconstruction algorithms reduce noise as NI changes, particularly across multiple organs. The goal of this study was to utilize an anthropomorphic phantom to evaluate image noise against the prescribed NI across different organs, determine if DLIR reduces image noise compared to ASiR-V, and use this relationship to determine the maximum volume CT dose index (CTDIvol) reduction at equivalent noise levels. Repeat images were acquired on a GE HealthCare Revolution Apex CT scanner across NI values in an anthropomorphic adult-sized phantom from Kyoto Kagaku with ASiR-V and DLIR. Organs-of-

ALT Prompt-gamma (PG) imaging is a promising approach for in vivo verification in proton therapy, but existing methods are primarily limited to reconstructing the PG emission profile, which provides only indirect information on proton transport. In this work, we introduce Prompt-Gamma Time Imaging (PGTI), an iterative reconstruction method based on the PG Timing (PGT) technique that jointly estimates the PG emission distribution and the proton velocity profile from Time-Of-Flight (TOF) measurements acquired with multiple detector modules. Unlike the PG distribution, the proton velocity is directly related to the stopping power and therefore provides access to both the tissue composition traversed by the beam and a first-order estimation of the delivered dose. The method was validated using experimental data acquired with the eight-module TIARA prototype previously developed by our collaboration. The anthropomorphic RANDO head phantom was irradiated with 100 MeV protons in two anatomical co

ALT Purpose: Ventilation Perfusion SPECT is important in the diagnostics of e.g. pulmonary embolism and chronic obstructive pulmonary disease. Classical and reverse mismatched defects can be identified by utilizing the ventilation-perfusion ratio. Unfortunately, this ratio is only linear in the ventilation, the scale is not symmetrical regarding classical and reversed mismatches and small perfusion values give rise to artifacts. The ventilation-perfusion (VQ) difference is developed as an alternative. Methods: For both VQ-ratio and VQ-difference a scaling factor for the perfusion is computed, so that voxels with matched ventilation and perfusion (on average) yield zero signal. The relative VQ-difference is calculated by scaling with the summed VQ-signal in each voxel. The scaled VQ-difference is calculated by scaling with the global maximum of this sum. Results: The relative and scaled differences have a scale from -1 (perfusion only) to +1 (ventilation only). Image quality of relative VQ-

ALT Very high energy electron (VHEE) beams offer several promising properties for radiotherapy. Accurate beam delivery requires a beam model that accounts for scattering along the beam propagation path. This work develops and validates a beam model incorporating Multiple Coulomb Scattering (MCS) to estimate beam parameters. MCS is incorporated as an additive term to the covariance matrix transformation for a drift space, allowing conventional quadrupole scans to estimate beam parameters in the presence of a downstream scatterer. The scattering correction factor is fitted to Monte Carlo (MC) simulations for a range of materials and thicknesses. The model is then validated by recovering the initial beam parameters from simulated quadrupole scans of a realistic beamline. Finally, the method is applied to in-air screen measurements at the Pulsed Energetic Electrons for Research (PEER) end station of the Australian Synchrotron. After fitting the correction factors, the mean and standard deviati

ALT Background: Quantitative Cherenkov-to-dose conversion depends on beam spectrum, field size, depth, and material properties. Purpose: To distinguish dose contributions with and without accompanying Cherenkov production and assess their implications for calibration. Methods: Geant4 simulations paired dose and local Cherenkov distributions in water for flattened 6, 10, and 15 MV and flattening-filter-free (FFF) 6 and 10 MV beams with 3 × 3 and 10 × 10 cm² fields. Energy deposition was tagged by whether its transport step produced at least one Cherenkov photon. Component fractions were calculated over the phantom. Distributions were independently normalized within a shared reference region and compared using voxelwise ratios, lateral profiles, and spatial partitioning. Results: Emission-tagged fractions were 37%-61%, increasing with beam energy and lower for FFF beams. Fractions differed by less than 1.3 percentage points between field sizes. Emission-tagged ratios clustered near unity, wi

ALT Machine learning models in radiotherapy are commissioned by testing them on cases with known answers, which may not reveal a shortcut that the test cases share with the training data. Frontier language models have recently been reported to read and write the raw weights of small neural networks, an ability called weight-space programming. The purpose of this study was to determine whether such a model, given only a clinical protocol and a network's weights, can audit and repair the network. Networks with 433 to 4,801 parameters were trained to screen head-and-neck planning requests against four rules. Flaws were planted through the training data: confounds that hid each rule, a 3 Gy shift in the cord threshold, and a hidden trigger. Claude Opus 5.5 audited each network blind, without tools, data or code execution, and every claim and repair was tested on about 420,000 requests. The language model named the broken rule in 16 of 18 flawed networks (95% CI 67% to 97%), including all 15 wi

ALT Medical physicists turn a prescription into a delivered dose and check one another's calculations, because one error in a beam calibration or a monitor-unit (MU) calculation can affect every patient treated with it. MedPhysBench has ten seeded generators of calculation items in radiation therapy, diagnostic imaging, nuclear medicine and radiation protection, up to clinical tasks such as a TG-51 calibration worksheet. Reference answers come from code implementing the governing protocols, and a grader converts units and applies tolerance bands. From the same inputs, separate checking items test error detection, showing a colleague's worksheet or only the colleague's result, half correct and half with one planted error. On a held-out test split of 1,200 items (half for two models), 12 models scored 33.3 to 100.0% on calculation. Of the nine answers graded incorrect for the four best (99.3-100.0%), five contained model errors and four followed NCRP Report 151 on points our items misstate o

ALT Skin meshing increases graft coverage, yet the clinically achieved expansion often falls below the manufacturer's nominal meshing ratio. Previous elastic analyses have demonstrated that mesh topology and skin anisotropy strongly influence graft expansion; however, the effect of progressive damage at larger deformation remains unexplored. This study therefore investigates how progressive damage affects the expansion and mechanical response of skin meshes. The performance of auxetic mesh geometries is compared with conventional Zimmer mesher (ZM) geometry. Human back skin was modelled using a one-term Ogden ground matrix and a Gasser Ogden Holzapfel (GOH) collagen network, with separate scalar Kachanov-type continuum damage variables for each constituent. The auxetic geometries, including 1st- and 2nd-order alternative slits (AS1 and AS2), I-shaped (IS) and H-shaped (HS) re-entrant patterns, and ZM, were analysed with Langer's lines oriented either parallel or perpendicular to the loadin

ALT OBJECTIVE Shear wave elastography (SWE) is a recent method for evaluating soft tissue stiffness. Its application to the spinal cord is limited by the ultrasound bone barrier. Spinal dysraphism can cause neurological symptoms impairing bladder, bowel, and lower limb function due to a mechanical stress known as tethered cord syndrome. Detethering of the spinal cord is a part of surgical treatment. This study aimed to assess the feasibility of intraoperative elastography to guide surgery in patients with spinal dysraphism involving traction of the spinal cord. METHODS This single-center retrospective study included all patients who underwent surgery for spinal dysraphism between November 2023 and July 2024. SWE was performed under general anesthesia with the patient in the prone position before and after spinal cord detethering. All SWE measurements were performed using the Aixplorer system. Demographic, clinical, and radiological data (age at surgery, neurological status, and MRI finding

ALT Compton camera imaging relies on the positions and energies of multiple photon interactions recorded in the detector. In silicon detectors that resolve individual interactions, these measurements do not directly provide the causal interaction order, and in nuclear medicine applications the photon may also have scattered in the object before entering the detector. We present a probabilistic model for photon interaction chains in a silicon detector and use it for two inference tasks at the event level: interaction order inference and classification of primary versus object-scattered photons. The model combines photon transport based on Compton scattering and attenuation with a detector response model. It is evaluated on Monte Carlo data for monoenergetic point sources at 140 keV and 511 keV, with and without a cylindrical water phantom. For interaction chains of length two to four, the maximum a posteriori order estimate gives high accuracy in the case without a phantom, exceeding 0.95 f

ALT Adrenal gland-induced hypertension results from underlying adrenal gland disorders including Conn's syndrome, Cushing's syndrome, and Pheochromocytoma. Due to the limitations of existing pharmaceutical and surgical treatment methods, minimally invasive treatment options like microwave ablation (MWA) have received significant attention for treating adrenal gland disorders. A precise comprehension of the dielectric properties of human adrenal glands will help to tailor energy delivery for MWA therapy, thus offering the potential to optimise treatments and minimise damage to surrounding tissues. This study reports the ex vivo dielectric properties of human adrenal glands, including the cortex, medulla, capsule, and tumours, based on the data obtained from four patients (diagnosed with Conn's syndrome, Cushing's syndrome, and Pheochromocytoma) who underwent unilateral adrenalectomy at the University Hospital Galway, Ireland. An open-ended coaxial probe measurement technique was used to mea

ALT The dielectric properties of biological tissues are used to investigate the interaction of electromagnetic (EM) fields with the human body. These properties are integrated into EM numerical simulations, such as the finite difference time domain (FDTD) method, using dielectric models such as Cole-Cole and Debye models. These computational tools are employed to study the propagation of EM waves within the human body. This paper has developed the one-pole and two-pole Cole-Cole and Debye models for the dielectric properties of normal and diseased human trabecular bone tissue at microwave frequencies (0.5-8.5 GHz). The dielectric properties of normal trabecular and cortical bone were derived based on the literature, while those of diseased human trabecular bones (osteoporotic and osteoarthritis) were acquired from a previous study conducted by the authors, which characterised the properties within the 0.5-8.5 GHz frequency range. This study has employed a weighted least squares method to o

ALT This study presents a transformation scheme for converting measured Hounsfield units (HUs) into linear attenuation coefficients (LACs) for 511 keV gamma photons in iodine contrast-enhanced angiographic CT images. The method is based on spectral CT data acquired from tissue-equivalent inserts of the Sun Nuclear electron density phantom. The resulting transformation will be used to develop an attenuation map template for our in-house developed BrainPET 7T system. Three approaches were used to obtain the attenuation maps. The first approach is based on angiographic spectral CT scans with iodinated contrast agent administration, and the computation of virtual non contrast (VNC) and virtual non-iodine (VNI) images. In this case, two images are combined: bone regions are segmented from the VNI images, and the corresponding voxel values in the VNC images are replaced, yielding a single quantitative monochromatic CT image. The second approach relies exclusively on VNC images, whereas the third

ALT The clinical translation of artificial intelligence (AI) is a critical step toward precision medicine. The implementation study presented here focuses specifically on barriers to AI adoption in the diagnostic medicine workflow. Successful clinical adoption of AI requires more than technical performance; it depends on addressing real-world organizational, ethical, infrastructural, and workflow-related barriers that may prevent promising systems from moving beyond research settings. To examine these barriers, we used structured concept mapping (CM) to operationalize stakeholder engagement and to integrate a knowledge translation (iKT) approach within the Knowledge-to-Action (KTA) framework. Stakeholders co-generated 96 statements describing barriers to AI implementation and organized them into 11 clusters, including infrastructure limitations, ethical and legal concerns, workflow integration challenges, and distrust in algorithmic reasoning. These findings provide actionable knowledge fo