Virtual Human Project Page: 2 of 10
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ORNL has been involved in computational human modeling nearly since its inception. In the 1940s, the focus was on building
mathematical phantoms capable of being used in calculations of radiation doses to workers and medical patients. The earliest
computational models represented the body and its organs as homogeneous spheres. By the 1950s the geometries progressed to the
rough descriptions of three shapes, the head, torso, and legs. However, with the need for more accurate calculations of radiation
dose, mathematical phantoms of the human body and its organs were developed (Snyder et al. 1969, Cristy and Eckerman 1987).
These phantoms used simple mathematical expressions to define the surfaces of the body and the organs. The masses of the organs
were consistent with the Reference Man data (ICRP 1975). The 1970s and 1980s saw the application of these models in
epidemiological studies including those of the survivors of the Hiroshima and Nagasaki bombings. In the mid-1980s, a first attempt
was made to develop voxel phantoms for children using physical phantoms of various ages. Capability to use these voxel phantoms
was incorporated into radiation transport codes. The techniques to construct a voxel phantom from CT images have been greatly
improved over the last few years and a detailed phantom of the torso and head was constructed from the National Library of
Medicine's (NLM) Visible Human (Male) image data (www.nlm.nih.gov/research/visible/visible_human.html).
Paralleling the development of mathematical phantoms, efforts were also underway to model the behavior of inhaled or ingested
radionuclides within the body. These models have now evolved to include the relevant physiological and biokinetic processes and
are presented as compartment models. Dosimetric considerations required that the compartments of the biokinetic models be
identified with the specific organs and tissues and that a proper spatial relationship of the organs be reflected in the mathematical
phantom. The latter detail is not generally required by biokinetic or pharmacokinetic models but is required by the dosimetric
The spatial relationships between the organs also play an important role in models used for automotive and aeronautical safety
studies. But these models have not incorporated physiological function such as blood flow or biokinetic behavior. Our hope is that
VH will be able to incorporate both the anatomical information and physiological and biokinetic parameters to make it possible to
integrate these two modeling regimens. In addition, the mechanical, thermal and dielectric properties of human tissue and the
skeletal system and the signaling characteristics of the heart, brain, and neuromuscular system must be added to make possible a
reasonably complete range of modeling on the human body.
3. LUNG SOUNDS MODELING
As an example of the potential of the VHRS in medical research, the problem of lung sound changes with injury or disease could be
modeled. There is a need to develop a capability to monitor and quantify lung pathological disorders from the thorax region. This
need stems from the fact that patient's movements or the existence of chest wounds creates problems for locating the stethoscope.
Another point of major importance is that the throat region provides an ideal place for locating the stethoscope. The key is to be
able to assess from the throat region disorders such as pulmonary fibrosis, lung consolidation, etc., in the thorax region, which are
generally localized to the gas-exchange region of the lung. This capability would enhance medical diagnosis for combat casualty
care as well as civilian clinics. There is a need to develop an effective model of sound transmission from the lungs through the chest
that would provide the needed data to develop such a capability.
The modeling of lung sounds can be divided into two tasks that require the use of high performance computing to solve complex
partial differential equations. The first task involves modeling the propagation of lung sounds in the body. The proposed approach
is to model the body tissues as inhomogeneous fluids, resulting in a non-homogeneous wave equation for the acoustic pressure in
the tissues. This equation derives from Lighthill's equation (reformulation of Navier-Stokes equation) for sound generation by flow
after simplifying assumptions are made. The sound propagation equation requires spatially distributed information for the tissue's
mass density and speed of sound, which is obtainable from the NLM's Visible Human CT scan data.
The second task involves actually modeling the generation of sound sources from the flow of air in the airways. If the entire problem
were solved, computational fluid dynamics (CFD) would be needed to model sound generation due to vortices, turbulence, airway
wall flutter, airway closure, mucosal lining effects, etc. for the entire lung. We will pick one or two sound generation phenomena to
model in this project, but others can be added later. With the current tarascale computational resources, we will only be able to
model the flow in a few branching generations of airways at a time. We will then devise a method for replicating the results over a
distribution of airways of the same generation to use as the sound source to the sound propagation model. Details of the lung sound
modeling will be presented separately at this conference.
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Ward, RD. Virtual Human Project, article, June 12, 2001; Tennessee. (digital.library.unt.edu/ark:/67531/metadc724876/m1/2/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.