Physics in medicine and biology最新文献

{"title":"Electrode-specific dosimetric robustness of group-level optimized transcranial alternating current and temporal interference stimulation montages under placement variability.","authors":"Eikei Yamada, Taiga Inoue, Naofumi Otsuru, Makoto Suzuki, Shintaro Uehara, Yohei Otaka, Akimasa Hirata","doi":"10.1088/1361-6560/aeae9c","DOIUrl":"10.1088/1361-6560/aeae9c","url":null,"abstract":"<p><p><i>Objective.</i>The objective of this study was to characterize, for selected group-level optimized montages, electrode-specific dosimetric sensitivity to placement variability in transcranial alternating current stimulation (tACS) and transcranial temporal interference stimulation (tTIS).<i>Approach.</i>Electric fields (EFs) were computed using the scalar-potential finite-difference method in 60 paired model instances generated from magnetic resonance imaging data of 30 male participants (30 original models and their left-right mirrored counterparts). Three anatomically defined targets spanning cortical and subcortical structures were examined: the primary somatosensory hand area (S1 Hand), the insula, and the hippocampus. Every electrode constituting each selected montage was independently displaced from -10 mm to +10 mm in 5 mm increments on a 5 × 5 tangential grid. Three descriptive outcomes were evaluated: intensity sensitivity, defined as the absolute percentage change in the region-of-interest mean; hotspot displacement; and position-dependent intensity variability, defined as the standard deviation (SD) of the percentage change across the full ±10 mm grid.<i>Main results.</i>Across all 16 displaced electrodes, intensity sensitivity ranged from 0.41%-14.88%, and hotspot displacement ranged from 0.63-6.86 mm. Marked within-pair asymmetries were observed in several montages, and position-dependent intensity variability differed across electrodes and model instances. These patterns were descriptively associated with montage geometry and current allocation.<i>Significance</i>. The independent all-electrode perturbation framework introduced here enables electrode-specific robustness assessment of group-level optimized tACS and tTIS montages. The results identify montage-specific electrodes for which placement control is particularly important within the studied configurations, informing the practical implementation of these montages.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149113758","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Feasibility of an ultrafast and low-cost image sensor based on single-pulse photomechanical with minimal electronics electromagnetic detection (SPEED).","authors":"A Alonso, S Contador, E Lage, J Aguirre","doi":"10.1088/1361-6560/aea7f5","DOIUrl":"10.1088/1361-6560/aea7f5","url":null,"abstract":"<p><p><i>Objective.</i>Image sensors are the backbone of numerous imaging technologies that underpin modern science and engineering, being particularly important for biomedical imaging systems. The ideal sensor technology should be compatible with any region of the electromagnetic spectrum as each spectral range interrogates matter uniquely, support ultrahigh imaging rates (millions of frames per second (fps)), and remain cost-effective. These requirements become particularly challenging in the terahertz (THz) spectral domain, which is of growing interest for biomedical imaging. Here, we present an alternative image sensor concept, termed single-pulse photomechanical with minimal electronics electromagnetic detection (SPEED), with potential to overcome the THz imaging challenges. Moreover, we demonstrate its feasibility for the THz spectral region through realistic simulations.<i>Approach.</i>SPEED sensors leverage the principles of optoacoustic biomedical imaging. They use the optoacoustic effect to transduce incident electromagnetic radiation into acoustic waves, rather than relying on conventional photoelectric or photothermal approaches. By exploiting the principles of optoacoustic tomography, SPEED can be implemented with a highly simplified electronic readout scheme that boosts imaging speed while substantially reducing overall cost. We evaluated the concept with numerical simulations representative of THz operation, quantifying achievable frame rates, reconstruction fidelity, expected sensitivity and practical implementation constraints relevant to medical imaging systems.<i>Main results.</i>Our results demonstrate that a SPEED image sensor operating at 10⁵-10⁶fps is feasible for the THz domain, surpassing the fastest existing THz image sensors by 2-3 orders of magnitude. The architecture supports broadband operation and can be tailored to other spectral regions while maintaining ultrahigh frame rates. Moreover, we show that such a sensor can be implemented at low cost due to the highly simplified electronic readout.<i>Significance.</i>This work lays the foundations for a new generation of ultrafast, low-cost cameras for the THz and other spectral domains, with clear relevance to emerging imaging tasks in biomedicine where high temporal resolution and low-cost hardware are critical.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148977513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Integrated isocenter and sector duration optimization (ISDO) for gamma knife radiosurgery.","authors":"Jingjie Yu, Dante P I Capaldi, Olivier Morin, Ke Sheng, Qihui Lyu","doi":"10.1088/1361-6560/aeae9d","DOIUrl":"10.1088/1361-6560/aeae9d","url":null,"abstract":"<p><p><i>Objective.</i>Current Gamma Knife (GK) treatment planning algorithms typically determine isocenter locations using geometric heuristics rather than dose-driven optimization. Isocenters are either placed automatically (using center-of-mass, skeleton-based, or curvature-based algorithms) or manually by planners, followed by a separate sector duration optimization (SDO) with fixed isocenter locations. Since the isocenter selection is separate from the dosimetry optimization, the SDO step is often constrained by a suboptimal isocenter configuration, limiting achievable plan quality and leading to unnecessarily long beam-on time (BOT).<i>Approach.</i>We introduce an integrated isocenter and SDO framework (ISDO) that replaces heuristic isocenter placement with a dose-driven joint ISDO. The framework includes a group-sparsity regularization for isocenter selection and an explicit BOT regularization for delivery efficiency. The selected isocenters are further refined through an SDO module, followed by a post-processing stage that converts the optimized sector-collimator patterns into deliverable shot configuration. The framework was evaluated using 12 GK cases spanning a variety of clinical indications, including arteriovenous malformation, vestibular schwannoma, meningioma, and pituitary adenoma.<i>Main Results.</i>With similar or better plan quality, ISDO plans used fewer or equal shots and substantially reduced the BOT. Across all cases, ISDO reduced the number of shots by 15.06% and BOT by 20.77%. With similar target coverage, the selectivity and Paddick conformity index increased by 5.77% and 5.82%, and<i>R</i>₅₀and<i>D</i>_{2 cm}decreased by 6.45% and 5.23%. The maximum and mean doses of organs-at-risk were also reduced by 16.0% and 28.8% respectively.<i>Significance.</i>By incorporating isocenter selection directly into the BOT-aware inverse-planning framework and driving the isocenter selection through a group sparsity term, the proposed ISDO method achieved more efficient and conformal GK plans than current clinical GK treatment planning approaches.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149113761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A convergent electron beam approach for small-field irradiation with reduced bremsstrahlung.","authors":"Y Hayashi, A Myojoyama","doi":"10.1088/1361-6560/aeaf41","DOIUrl":"10.1088/1361-6560/aeaf41","url":null,"abstract":"<p><p><i>Objective</i>. To investigate whether converging electron beams using quadrupole electromagnets can mitigate fluence loss and bremsstrahlung contamination in small irradiation fields.<i>Approach</i>. A three-stage quadrupole electromagnet system was installed beneath a linear accelerator head to converge 6, 9, 12, and 15 MeV electron beams. Dose distributions, dose rate, and bremsstrahlung contamination were evaluated for 2 cm and 1 cm fields. The 2 cm convergent field was compared with a 2 cm tubular applicator, whereas the 1 cm convergent field was evaluated at 5.1 and 10 cm air gaps. Monte Carlo simulations at 6 and 9 MeV assessed detector volume-averaging effects and the origins of bremsstrahlung photons.<i>Main results</i>. The dose rate of the 2 cm convergent field was 1.05-2.53 times higher than that of the 2 cm tubular applicator, while bremsstrahlung contamination was reduced by 0.40-1.79 percentage points. The 1 cm convergent field achieved a therapeutic field width ⩽1 cm and penumbra ⩽0.85 cm at all energies. At a 5.1 cm air gap, the dose rate was comparable to that of a 3 cm tubular applicator at 9 MeV and exceeded that of a 10 × 10 cm²applicator at 12 and 15 MeV. Bremsstrahlung contamination was 1.08%, 0.87%, 1.04%, and 1.32% at 6, 9, 12, and 15 MeV, respectively, and remained lower than that of the 2 cm tubular applicator at all energies. At a 10 cm air gap, output decreased and dose profiles broadened. Bremsstrahlung contamination increased to 2.56%, 1.70%, 1.72%, and 2.11%, respectively, but remained lower than that of the 2 cm tubular applicator at 12 MeV and above.<i>Significance</i>. Converging electron beams can mitigate fluence loss while reducing bremsstrahlung contamination in small fields. This externally mounted system provides proof of concept for high-spatial-resolution electron beam delivery and future electromagnetic spot-scanning applications.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149113648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Fractal geometry-governed oxygen diffusion: tumors vs. normal tissues.","authors":"Neda Valizadeh, Robabeh Rahimi, Ramin Abolfath","doi":"10.1088/1361-6560/aeabe7","DOIUrl":"10.1088/1361-6560/aeabe7","url":null,"abstract":"<p><p><i>Objective.</i>To develop a geometry-governed diffusion framework that explains differential tissue response under FLASH ultra-high dose rate (UHDR) irradiation by explicitly accounting for structural heterogeneity and anomalous transport in biological tissues.<i>Approach.</i>We formulate a generalized diffusion-reaction model on fractal substrates to describe molecular transport in heterogeneous media. Tissue architecture is characterized by a fractal (Hausdorff) dimension, while scale-dependent transport inefficiency and memory effects are captured by a fractional parameter. Analytical solutions for radially symmetric geometries are derived and compared with classical normal (Euclidean) diffusion and a Gaussian reference model under identical physical conditions. Transport behavior is quantified through transient probability distributions and steady-state spatial profiles.<i>Main results.</i>The model reveals systematic suppression of long-range transport and enhanced localization as tissue structural complexity increases. Increasingleads to subdiffusive dynamics, reduced effective diffusion lengths, and persistent non-Gaussian concentration profiles, even in the steady state. While increasingalone enhances spatial accessibility, fractional dynamics dominate transport behavior when, counteracting geometric connectivity. These effects produce a separation between regimes characterized by efficient inter-track overlap and rapid homogenization, and regimes marked by isolated, long-lived reactive domains.<i>Conclusion.</i>Fractal geometry provides a unifying physical framework for understanding tissue-dependent transport and differential response under FLASH UHDR irradiation. Normal tissues, characterized by near-Euclidean geometry and weak anomalous effects, permit greater inter-track interaction and recombination, whereas tumor-like tissues with elevated structural complexity exhibit localized transport and reduced collective chemical reactivity. This proof-of-principle study establishes tissue architecture as a fundamental determinant of transport efficiency and offers a mechanistic basis for experimentally observed FLASH tissue sparing, motivating geometry-aware modeling of radiobiological response.<i>Significance.</i>This work shifts the emphasis from purely chemical kinetics toward a geometry-governed description of oxygen and reactive oxygen species transport in cells and tissues.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149031065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ReCo-Diff: residual-conditioned deterministic sampling for cold diffusion in sparse-view CT.","authors":"YongEun Choi, Hyoung Suk Park, Kiwan Jeon, Hyun-Cheol Park, Sung Ho Kang","doi":"10.1088/1361-6560/aeb34a","DOIUrl":"https://doi.org/10.1088/1361-6560/aeb34a","url":null,"abstract":"<p><strong>Objective: </strong>Sparse-view computed tomography (CT) reduces radiation dose and&#xD;acquisition time but introduces structured streak artifacts that make reconstruction&#xD;severely ill-posed. Cold-diffusion approaches can model such deterministic degradation&#xD;processes, but existing sampling strategies may rely on scalar similarity criteria and&#xD;predefined thresholds to trigger sample-adaptive resets of the degradation-level trajectory.&#xD;We aim to replace this threshold-based sampling control with spatially resolved residual&#xD;conditioning.</p><p><strong>Approach: </strong>We propose ReCo-Diff, a residual-conditioned cold-diffusion&#xD;framework for sparse-view CT reconstruction. At each reverse step, a zero-residual&#xD;baseline prediction is re-degraded using the CT degradation operator, and the resulting&#xD;signed image-domain re-degradation discrepancy is used as a spatial conditioning map for&#xD;a second restoration pass. ReCo-Diff does not require an adaptive reset during&#xD;residual-conditioned sampling and instead follows a predetermined degradation schedule.&#xD;A one-time level transition is additionally used for highly sparse inputs. The method was&#xD;evaluated on the AAPM Low-Dose CT dataset under 18-, 36-, and 72-view settings using a&#xD;patient-wise split with one held-out test volume.</p><p><strong>Main results: </strong>ReCo-Diff achieved&#xD;PSNR values of 38.54, 42.57, and 46.98 dB at 18, 36, and 72 views, respectively. At 18&#xD;views, matched-computation analysis showed that ReCo-Diff achieved 38.54 dB compared&#xD;with 38.25 dB for a two-pass zero-residual control under the same 18-NFE budget. A&#xD;spatially shifted-residual control achieved 37.65 dB, indicating that effective residual&#xD;conditioning benefits from spatial correspondence with the current degraded state.&#xD;Significance. ReCo-Diff replaces adaptive trajectory control with step-wise spatial&#xD;residual conditioning in deterministic cold diffusion. Matched-computation analysis shows&#xD;that the reconstruction benefit depends on spatially aligned residual information rather&#xD;than on the additional network evaluation alone. The proposed strategy provides an&#xD;alternative approach to controlling error propagation under a predetermined degradation&#xD;schedule without relying on sample-adaptive reset decisions.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149167000","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Applying exponential data consistency conditions to non-homogeneous attenuation.","authors":"Taylon Clark, Rolf Clackdoyle, R Glenn Wells","doi":"10.1088/1361-6560/aeabe9","DOIUrl":"10.1088/1361-6560/aeabe9","url":null,"abstract":"<p><p><i>Objective.</i>Exponential data consistency conditions (eDCCs) have shown feasibility for motion correction and attenuation map alignment in single photon emission computed tomography (SPECT). The eDCCs require all the activity to be contained within a convex region of homogeneous attenuation. In a non-homogeneous attenuation, activity outside the convex region can violate this assumption, introducing an additional source of inconsistency and inhibiting eDCC-based methods. We present the mathematical foundations of the sine-amplitude approach for coping with activity outside the region of constant attenuation and validate it using SPECT computer simulations.<i>Approach</i>. The sine-amplitude method uses the time-varying aspect of the cardiac signal in ECG-gated SPECT studies to extract a component of the measured data that satisfies the eDCCs, even if the overall activity does not. Four noise-free activity distributions were simulated: a time-varying point source inside the heart, the point source with static liver activity, time-varying left-ventricle (LV) activity, and the LV with static liver activity. The liver activity violated the eDCC constraints. The method was evaluated with different levels of Poisson noise and liver activity. Consistency between exponential projections was assessed using the mean normalised difference (MND) over single- and multi-slice axial ranges.<i>Main Results</i>. In noise-free simulations, the liver activity outside the region of constant attenuation increased the LV activity single-slice MND fromto. For the eleven-slice range, the presence of liver increased the LV activity MND fromto. The sine-amplitude method reduced the LV single-slice MND toand the eleven-slice MND to. With noisy data, the sine-amplitude method improved the average MND values for all tested liver levels when the total heart counts were 2.1-53 times a typical clinical acquisition, depending on the axial range.<i>Significance.</i>For time-varying SPECT data, the sine-amplitude approach can broaden the applicability of exponential data consistency conditions in non-homogeneous attenuation.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149031082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"An imaging framework for nuclei-based three-dimensional cell quantification in intact tissue using phase-contrast x-ray CT.","authors":"T Partridge, R Ahmad, A Astolfo, I Buchanan, M Endrizzi, M A Hawkins, A Olivo, M Esposito","doi":"10.1088/1361-6560/aeadec","DOIUrl":"10.1088/1361-6560/aeadec","url":null,"abstract":"<p><p><i>Objective.</i>Quantitative analysis of cellular morphology and spatial organisation within intact tissue remains challenging, particularly when three-dimensional information must be preserved. This study investigates whether laboratory propagation-based phase-contrast x-ray computed tomography (CT) can support nuclei-based quantitative analysis in unstained tissue while retaining the surrounding tissue architecture.<i>Approach.</i>We propose a nuclei-based quantitative imaging workflow that combines laboratory propagation-based phase-contrast x-ray CT with volumetric segmentation. Intact unstained liver tissue was imaged at cellular resolution, then nuclei were segmented throughout the reconstructed volume and quantitative metrics describing the nuclear morphology and spatial organisation were extracted. The resulting measurements were evaluated in two non-overlapping volumes of interest and compared with histological reference data using thickness-matched virtual CT slices.<i>Main results.</i>The proposed workflow enabled visualisation and segmentation of individual nuclei throughout intact unstained liver tissue. Comparable nuclear morphology and spatial organisation metrics were obtained from two non-overlapping volumes of interest, indicating stable segmentation performance within the analysed specimen. Comparison with H&E histology demonstrated broad agreement in nuclear morphology.<i>Significance.</i>This work demonstrates the feasibility of nuclei-based quantitative analysis using laboratory phase-contrast x-ray CT in intact unstained tissue. The approach provides volumetric cellular information while preserving tissue architecture and may complement conventional histological assessment in applications requiring three-dimensional analysis. These findings highlight the potential of laboratory phase-contrast CT for quantitative tissue characterisation and spatial cellular analysis.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149081928","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exact analytical PGSE signal for diffusion confined to a cylindrical surface using a spectral Laplacian formalism.","authors":"Erick Jorge Canales-Rodríguez, Chantal M Tax, Juan M Gorriz Saez, Derek K Jones, Jean-Philippe Thiran, Jonathan Rafael-Patiño","doi":"10.1088/1361-6560/aeb2a0","DOIUrl":"https://doi.org/10.1088/1361-6560/aeb2a0","url":null,"abstract":"<p><strong>Objective: </strong>To derive an exact analytical expression for the diffusion MRI signal arising from diffusion confined to a cylindrical surface under finite rectangular pulsed-gradient spin-echo (PGSE) gradients, and to develop computationally efficient strategies for repeated model evaluations.</p><p><strong>Approach: </strong>The Bloch-Torrey equation was solved using a spectral matrix formalism of the Laplace operator in the eigenbasis of the cylindrical surface. The resulting signal is expressed as a product of non-commuting matrix exponentials and is valid for arbitrary rectangular gradient durations and separations, without approximations to the diffusion propagator or spin phase distribution. A reduced real spectral basis was introduced to decrease the dimensionality of the problem. Accelerated implementations based on Strang&#xD;splitting and Gauss-Legendre quadrature were developed for repeated signal evaluations and computation of the spherical mean. The analytical signal was validated against Monte Carlo diffusion simulations.</p><p><strong>Main results: </strong>The exact formulation showed excellent agreement with Monte Carlo simulations over a wide range of cylinder radii and acquisition parameters. The spectral expansion&#xD;converged rapidly with mode order, and the reduced basis substantially decreased computational cost without loss of accuracy. The accelerated implementations provided large additional speed-ups while retaining controllable errors relative to the exact solution.</p><p><strong>Significance: </strong>The proposed framework extends exact finite-pulse solutions of the Bloch-Torrey equation to diffusion confined to cylindrical surfaces and provides practical implementations for directional and orientationally averaged diffusion MRI signals. It therefore offers an approximation-free reference for assessing faster signal approximations and for applications requiring large numbers of model evaluations.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149149069","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Simultaneously quantifyingK1,k2, and blood volume in myocardial imaging with overlapping volumes of interest: structural identifiability.","authors":"Scott D Metzler, Dale J Stentz, Marie A Guerraty","doi":"10.1088/1361-6560/ae968a","DOIUrl":"10.1088/1361-6560/ae968a","url":null,"abstract":"<p><p>Dynamic imaging in emission computed tomography allows the determination of physiological parameters that have important clinical implications. In myocardial imaging, three parameters of interest are the uptake and washout rates,and, respectively, and the blood-volume fraction,. These parameters can be determined from time-activity curves (TACs) of the blood (i.e. the input function) and the myocardium. However, the volumes of interest for the dynamic images may show overlap of these regions; this overlap can be expressed as a mixing matrix. Herein, we address the requirements for mathematical uniqueness of the solutions. The relationship of the TACs of the myocardium and blood pool with model parameters is evaluated under the structural identifiability criterion, which requires equal observed TACs to have a one-to-one mapping with the model parameters. This leads to constraints on the model parameters. Those constraints lead to system invariants, specifying the relationship between the true solution of the equations and other candidate solutions consistent with the observations for the TACs. Structural identifiability is achieved for,, andif all parameters of the mixing matrix are known. These results provide a complete structural identifiability analysis for a one-tissue compartment model with a mixing matrix that accounts for partial-volume effects and spill-in/out of volumes of interest. Prior results showed a more relaxed condition whenwas assumed to be zero.</p>","PeriodicalId":20185,"journal":{"name":"Physics in medicine and biology","volume":" ","pages":""},"PeriodicalIF":3.1,"publicationDate":"2026-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148685482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}