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CESLab 3.0 THA Torso Model Technical Specifications
CESLab 3.0
THA Torso Model Technical Specifications
Mark Stevans
CESI
http://www.cesinst.com
September 4, 2000
1. Introduction
This document describes the
CESI THA inhomogeneous adult human torso model, which is included with
the HHA Bench distributed with the
CESLab application.
2. Torso Model Component Objects
2.1. Polyhedra
The THA torso model contains the following polyhedra:
-
Lung Polyhedra
The lung polyhedra were originally modelled after Gulrajani and
Mailloux, but were modified to accomodate the CESI HHA series adult human
heart model (described in the document
HHA Bench Series Technical Specifications)
without placing any Regional Dipoles
too close to any lung polyhedral
facets no matter how small a
regional dipole exclusion radius is selected.
Maximum facet size is set to 2.0 centimeters, yielding about 400 facets per lung.
The lung polyhedra are normally
employed
or unemployed in tandem, but simulations can be run with either lung removed.
-
Single Torso Polyhedron
This polyhedron is derived from the single torso shape in the torso
Compound Shape, and is intended to model
the torso surface when the
torso extension paradigm of McFee and Rush is not being employed.
This polyhedron should not be employed if the inner or outer torso
polyhedron is being employed.
The maximum facet size is set to 2.5 centimeters, yielding about
1300 facets.
-
Inner and Outer Torso Polyhedra
These polyhedra are derived from the inner and outer torso shapes
(respectively) in the torso Compound Shape,
and are intended to
model the torso surface when the torso extension paradigm of McFee and Rush
is being employed.
These polyhedra should both be employed if the single torso
polyhedron is unemployed.
The maximum facet size is set to 2.5 centimeters, yielding about 1200
facets on the inner torso polyhedron, and 1500 facets on the outer.
2.2. Tissue Types
The following Tissue Types are part of the THA
torso model:
-
Boundary Tissue Type
Reserved for internal use only.
-
Medium Tissue Type
Reserved for internal use only.
-
Lung Tissue Type
This Tissue Type is intended for modeling
the low-conductivity lungs.
The gross conductivity of this Tissue Type
is used during computation
of Surface Potential Transfer Coefficients if either or both
lungs are employed.
The gross conductivity is set to .05 Siemens/meter after Lorange and
Gulrajani.
-
Generic Torso Tissue Type
This Tissue Type is intended for modeling
the portions of the torso
exclusive of the lungs, skeletal muscle layer, and intracavitary blood
masses.
Its gross conductivity must be equal to the base torso conductivity
specified in the Bench Window.
Its gross conductivity is set to .2 Siemens/meter after Lorange and
Gulrajani.
-
Skeletal Muscle Layer Tissue Type
This Tissue Type is intended for modeling the
high-conductivity
skeletal muscle layer when using the torso extension approach of
McFee and Rush. Please see the document
CESLab Technical Specifications for more information.
The gross conductivity is set to .125 Siemens/meter after Lorange
and Gulrajani.
2.3. Compound Shapes
At present, there is only one Compound Shape
particular to the THA torso model:
Torso Compound Shape. It contains all geometric data used to generate
the THA torso model.
|
Shape Editor view of the torso
Compound Shape 10 cm above the normal position
of the heart as seen from above. The tops of the lungs are nearly circular in this
presentation, and the attachment points of the right and left limb electrodes can be seen.
Click on image to enlarge.
|
The lung shapes have been modified to fit the heart geometry and
rotations as closely as possible, but should be considered very
approximate.
Nine loci correspond with the nine standard electrodes, and are
named accordingly. These loci serve to mark the desired positions of
the associated electrodes. Note that, due to the discretization of the
torso surface into polyhedral facets performed by CESLab for
electrophysiological simulation, the positioning of electrodes is
approximate.
2.4. Matrices
At present, there is only one matrix defined in the THA torso model: Torso Transformation
Matrix. It should be left as an identity matrix.
3. Electrode Placement
3.1. Dependence Upon Polyhedron Facet Size
For the purposes of electrophysiological simulation, each electrode is
associated with exactly one facet of the outermost employed torso
polyhedron ("Single Torso Polyhedron" or "Outer Torso Polyhedron").
The ideal location for each electrode is specified by a correspondingly
named locus in the
Compound Shape named
"Torso CompoundShape".
During polyhedron generation, the facet closest to the ideal position is
designated the electrode attachment point.
Thus, electrode positioning is necessarily inexact. The greater the
number of facets, the more exact the positioning. The number of facets
for a given polyhedron may indirectly modified by adjusting the
maximum facet size of the associated polyhedron: the smaller the
maximum facet size, the more facets will be generated.
However, note that the resources (real time and Macintosh free memory)
for computation of
Surface Potential Transfer Coefficients increases
according to the square of the number of facets.
3.2. Limb Leads
Electrodes ER and EL are placed at the anterior surface of the
corresponding shoulders. Electrode EF is centrally located on the lower
anterior surface of the torso so as to create (in combination with
the other two limb leads) an approximately equilateral triangle.
3.3. Precordial Leads
Precordial electrode placement is after Pilkington and Plonsey. The
horizontal spacing along the torso surface between any two consecutive
precordial leads is approximately equal. E1 and E2 are arranged
symmetrically about
the sternal line, and E6 is at the extreme left aspect of the torso.
The fourth intercostal space is assumed to lie 2.5 cm upwards from the
fifth.
3.4. Vectorcardiographic Leads
Vectorcardiographic electrode placement is after Mailloux and Gulrajani.
4. Modifying the THA Torso Model
Using the CESLab integrated Shape Editor,
the user may modify the geometry of the torso
model. Electrode placements can also be changed by moving the
associated loci.
To alter the heart position or rotation within the torso model, the user
may edit the matrix
named "Heart Transformation Matrix".
Any desired series of rotations and translations may be specified.
5. References
Gulrajani RM, Mailloux GE (1983). A simulation study of the effects of
torso inhomogeneities on electrocardiographic potentials, using realistic
heart and torso models. Circ Res 52: 45-56.
Mailloux GE, Gulrajani RM (1982). Theoretical evaluation of the McFee and
Frank vectorcardiographic lead systems using a numerical
inhomogeneous torso model. IEEE Trans Biomed Eng 29: 322-32.
McFee R, Rush S (1968). Qualitative effects of thoracic resistivity
variations on the interpretation of electrocardiograms: the low
resistance surface layer. Am Heart J 76: 48-61.
Pilkington TC, Plonsey R (1982). Engineering Contributions to
Biophysical Electrocardiography. IEEE Press, New York.
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