Draft:Virtual Population

The Virtual Population (ViP) is a set of whole-body anatomical human phantoms used in computational simulations to study interactions between biological tissues and electromagnetic (EM) fields.^[2] Applications span wireless technology testing, medical device evaluation, radiology safety, and tissue engineering. The collection includes whole-body computational phantoms, specific organ phantoms, and whole-body models of animals and animal tissues from species used in preclinical studies.

The IT'IS Foundation maintains a database of tissue properties — such as EM, thermal, fluid, acoustic, and magnetic resonance imaging (MRI) characteristics — to support parameter assignment in simulations. The database is regularly updated and can be used with the Sim4Life simulation software platform.

The first ViP models, referred to as the Virtual Family, included two adults and two children based on high-resolution magnetic resonance imaging (MRI) data.^[3] These "Version 1.x" models have been made available to the scientific community free-of-charge.^[4]

The ViP collection has grown to include a broader age and sex range and higher anatomical detail with the expansion of the Virtual Family into the Virtual Population, which includes models of both sexes ranging in age from 5 to 84 years old,^[2] used to evaluate the safety of diagnostic and therapeutic applications,^[5] including assessments of medical implant safety.^[6]

Models of specific organs have been developed. The ViP hand library consists of 12 computational right-hand models of different sizes and ages extracted from the full-body ViP models. The Ella Breast Coil model is a modified version of the "Ella" model used in applications such as safety assessments and the design of specialized MRI coils for breast tissue scanning.^[7]

Notable collaborative developments include:

• The MIDA model (head and neck) and IXI Head Models, co-developed with the FDA and segmented from the IXI dataset.^[8] These models offer detailed representations of eyes, deep brain structures, scalp layers, blood vessels, and salivary glands.
• Korean Virtual Population models, made in collaboration between the IT'IS Foundation and Korean research teams using cryosection images to create models for neuronal interaction studies.

Methods for generation of unstructured meshes with geometrically and topologically compatible interfaces from the segmented cross-sections of the ViP models were developed for the purpose of large-scale whole-body simulations.^[9] Finite element method (FEM) simulations, whereby the body is treated as a deformable hyperelastic material with rigid bones for variable posing, were used to enable adaptive posture adjustment. The models were also made morphable to allow simulation of weight gain or loss through changes in the distribution of subcutaneous adipose tissue (SAT) and enable variation in body mass index (BMI).^[10] The introduction of combined morphing and posing of computational models may allow in silico methods to be used to improve the accuracy of estimations of radiofrequency exposure due to MRI scanning.^[11]

The ViP models have also been functionalized to account for physiology-related changes in shape^[12] – e.g., breathing and blood flow^[13] or aspects such as tissue thermoregulation.^[14] Poseable ViP models were used, for example, in simulations to study the influence of anatomy and posture on exposure to induction cooktops, with the conductivities of the human tissues exposed assigned according to the Tissue Properties database.^[15]

Applications of the ViP in computational life sciences (CLS) include:

• Wireless device safety compliance and exposure analyses
• Design and evaluation of medical imaging hardware, e.g., MRI coils
• Study of EM interactions of biological tissues with medical and telecommunication devices
• In silico modeling for personalized medicine and device-tissue interactions

The ViP models have been integrated into the open-source o²S²PARC platform – developed as part of the "Stimulating Peripheral Activity to Relieve Conditions" (SPARC) program of the National Institutes of Health Common Fund to enable collaborative, reproducible, and sustainable computational neurosciences.

The ViP human phantoms and Virtual Zoo (ViZoo) animal phantoms are integrated in the Sim4Life computational simulation platform. The Sim4Life website maintains a selected list of research findings published by users of the ViP models.^[16]

Korean Virtual Population models – male model "Jeduk" and female model "Yoon-sun" – were developed by the IT’IS Foundation and the Visible Korean Human (VKH) project^[17] as part of the Swiss-Korean collaborative project NEUROMAN: Functionalized Anatomical Models for Studying EM-Neuronal Dynamic Interactions.^[18] The ViP model "Eddie" is also based on high-resolution cryosection images obtained from the Visible Human Project of the US National Library of Medicine (NLM). Additional models hosted by the IT'IS Foundation include phantoms based on the Visible Human Project that cover various ages, sexes, and developmental stages.

The ViP project of the IT'IS Foundation hosts the Breast Tumor Patient Models (BTPM) Repository, containing 22 breast models developed at the Erasmus University Medical Center, segmented into 6 tissue types: skin, bone, muscle, tumor, fibroglandular tissue, and fat.^[19]

Computational anatomical models developed by other researchers are also hosted.^[20]

The specifications of the full-body human models are listed here.

¹ Height, weight, and BMI values are based on the latest versions of the models and of the tissue properties database. ² These models are available only as Version 1.x. ³ The pregnant woman models are based on the Ella model; the specifications listed are those of the fetus.

In addition to human computational models, the IT'IS Foundation developed the Virtual Zoo (ViZoo) – a collection of high-resolution anatomical animal models created from MRI or cryosection image data. These computational animal phantoms are used in in silico biophysical simulations to reproduce and analyze results from in vivo animal experiments, with the aim of reducing the use of laboratory animals. The ViZoo models include mouse and rat models of both sexes at various developmental stages, a male pig, and a female Rhesus macaque (developed as part of the NEUROMAN project). A special rat model with neuro-functionalized nerve trajectories – known as the "NeuroRat" – has also been released.