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categories: ["bodies", "foundations"]categories: ["bodies", "foundations"]tags: ["simulation", "in silico trials", "personalized medicine", "computational modelling", "medical devices", "cardiology"]tags: ["simulation", "in silico trials", "personalized medicine", "computational modelling", "medical devices", "cardiology"]summary: "Computational models of an individual person's physiology, built from that person's own data and run to predict what an intervention would do before it is attempted."summary: "Computational models of an individual person's physiology, built from that person's own data and run to predict what an intervention would do before it is attempted."updated: "2026-08-22"updated: "2026-10-27"humanEvidence: "In patients, simulation is routine only for radiotherapy dose and CT-derived coronary physiology; virtual-heart ablation planning rests on small studies. No whole-body twin exists for any person."humanEvidence: "In patients, simulation is routine only for radiotherapy dose and CT-derived coronary physiology; virtual-heart ablation planning rests on small studies. No whole-body twin exists for any person."access: "Organ-specific models are sold as regulated software and reimbursed in some health systems, notably CT-derived coronary flow analysis. Products marketed as whole-person twins are usually dashboards."access: "Organ-specific models are sold as regulated software and reimbursed in some health systems, notably CT-derived coronary flow analysis. Products marketed as whole-person twins are usually dashboards."reversibility: "reversible"reversibility: "reversible"lines 106–112 → 106–11291 unchanged lines not shown
**No counterfactual to check against.** If the model recommends ablating one site and the clinician ablates it, the outcome of the alternative is never observed. Validating a predictive model of an individual therefore requires randomising against ordinary care, which is expensive and rarely done. A related shortage of checkable ground truth slows the validation of [[aging-biomarkers]].**No counterfactual to check against.** If the model recommends ablating one site and the clinician ablates it, the outcome of the alternative is never observed. Validating a predictive model of an individual therefore requires randomising against ordinary care, which is expensive and rarely done. A related shortage of checkable ground truth slows the validation of [[aging-biomarkers]]. **Scope.** A model represents what its builders chose to represent. Cardiac mechanics and drug distribution are tractable because the physics is well characterised and the geometry does much of the work. Immune response, metabolism, wound healing and the brain are not in that position, and a whole-body twin needs all of them at once, coupled. The same parameter shortage recurs one level down, where [[virtual-cell-models]] confront it at the scale of a single cell.**Scope.** A model represents what its builders chose to represent. Cardiac mechanics and drug distribution are tractable because the physics is well characterised and the geometry does much of the work. Immune response, metabolism, wound healing and the brain are not in that position, and a whole-body twin needs all of them at once, coupled. The same parameter shortage recurs one level down, where [[virtual-cell-models]] confront it at the scale of a single cell. What its partners call the largest coordinated effort to supply the missing measurements is aimed at that level rather than at people: in October 2026 [[biohub]], the US Department of Energy and the National Institutes of Health expanded the Virtual Biology Initiative, a programme to generate open, AI-ready data on how cells respond to perturbation, into a package the partners value at $1.8 billion, part of it existing federal datasets rather than new money.[^biohub2026] **Drift.** A person is not a fixed system. Anatomy remodels, drugs change physiology, disease progresses. A model validated at one moment silently expires, and there is usually no signal telling anyone when.**Drift.** A person is not a fixed system. Anatomy remodels, drugs change physiology, disease progresses. A model validated at one moment silently expires, and there is usually no signal telling anyone when. lines 148–152 → 148–15335 unchanged lines not shown
[^badano2018]: `paper` Badano, A. et al. "Evaluation of Digital Breast Tomosynthesis as Replacement of Full-Field Digital Mammography Using an In Silico Imaging Trial." *JAMA Network Open*, 2018. {Synthetic anatomy sampled from population statistics, not models of individual patients, and a comparison of imaging methods rather than of treatments.}[^badano2018]: `paper` Badano, A. et al. "Evaluation of Digital Breast Tomosynthesis as Replacement of Full-Field Digital Mammography Using an In Silico Imaging Trial." *JAMA Network Open*, 2018. {Synthetic anatomy sampled from population statistics, not models of individual patients, and a comparison of imaging methods rather than of treatments.}[^fda2016]: `regulator` U.S. Food and Drug Administration. *Reporting of Computational Modeling Studies in Medical Device Submissions: Guidance for Industry and Food and Drug Administration Staff*, 2016.[^fda2016]: `regulator` U.S. Food and Drug Administration. *Reporting of Computational Modeling Studies in Medical Device Submissions: Guidance for Industry and Food and Drug Administration Staff*, 2016.[^asme2018]: `report` American Society of Mechanical Engineers. *V&V 40-2018: Assessing Credibility of Computational Modeling Through Verification and Validation: Application to Medical Devices*, 2018. {Credibility is graded against the decision a model informs, so the same model can be adequate for one question and inadequate for another.}[^asme2018]: `report` American Society of Mechanical Engineers. *V&V 40-2018: Assessing Credibility of Computational Modeling Through Verification and Validation: Application to Medical Devices*, 2018. {Credibility is graded against the decision a model informs, so the same model can be adequate for one question and inadequate for another.}[^biohub2026]: `statement` Biohub. "International, cross-sector collaboration commits nearly $2 billion to build foundational data for AI models to predict and treat disease." Press release, 7 October 2026. {The partners' own valuation; it combines new funding, planned agency spending, datasets from earlier federal investment and in-kind computing.}[^delp2007]: `paper` Delp, S.L. et al. "OpenSim: Open-Source Software to Create and Analyze Dynamic Simulations of Movement." *IEEE Transactions on Biomedical Engineering*, 2007.[^delp2007]: `paper` Delp, S.L. et al. "OpenSim: Open-Source Software to Create and Analyze Dynamic Simulations of Movement." *IEEE Transactions on Biomedical Engineering*, 2007. removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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