17-11-2012, 04:40 PM
A Comprehensive Model of Human Ear for Analysis of Implantable Hearing Devices
[attachment=40053]
Abstract
A finite element (FE) model of the human ear including
the ear canal, middle ear, and spiral cochlea was constructed
from histological sections of human temporal bone. Multiphysics
analysis of the acoustics, structure, and fluid coupling in the ear
was conducted in the model. The viscoelasticmaterial behavior was
applied to the middle ear soft tissues based on dynamic measurements
of tissues in our laboratory. The FEmodel was first validated
using the experimental data obtained in human cadaver ears, and
then used to investigate the efficiency of the forward and reverse
mechanical driving with middle ear implant, and the passive vibration
of basilar membrane (BM) with cochlear implant placed
in the cochlear scala tympani. The middle ear transfer function
and the cochlear function of the BM vibration were derived from
the model. This comprehensive ear model provides a novel computational
tool to visualize and compute the implantable hearing
devices and surgical procedures.
INTRODUCTION
HUMAN ear is a complicated and multiphysics system including
air in the ear canal and middle ear cavity, ossicular
bones, tympanic membrane ™ and middle ear ligaments, and
viscous fluid inside cochlea. A finite element (FE) model based
on the anatomy of human ear with realistic material properties
will be a powerful tool to study the acoustic–structure–fluid
coupled functions in normal and diseased ears and to characterize
the functions of various implantable hearing devices.
The FE models of human ear have been reported in the literature
[1]–[4], but no comprehensive ear model including the ear
canal, middle ear, and spiral cochlea exists. It is critical and
important to build a spiral cochlea with three chambers of the
scala vestibule (SV), scala media (SM), and scala tympani (ST)
separated by cochlear basilar membrane (BM) and Reissner’s
membrane (RM), for understanding the cochlear function and
the interactions between the middle ear and cochlea.
METHODS
FE Model of the Human Ear
A FE model of human ear was built based on a complete
set of histological sections of a human temporal bone (male,
age 52, left ear). The model consists of the external ear canal,
TM, middle ear ossicular chain with suspensory ligaments, and
spiral cochlea [see Fig. 1(a)]. The ear canal and middle ear
parts are same as our previous published model [1]. The spiral
cochlea having two and a half turns is connected to the footplate
(FP) at the oval window and to the middle ear cavity at the
round window. The space inside cochlea was divided by the
RM and BM into three chambers: SV, SM, and ST and filled
with viscous perilymphatic fluid [see Fig. 1(b) and ©]. The
ratio of cross-section area between SV, SM, and ST was 5:3:8.
The total cross-section area of cochlea chambers changed from
2.55mm2 at the base to 1.13mm2 at the apex.
FE Modeling of Implantable Hearing Devices
Forward mechanical driving was simulated by placing a floating
mass transducer onto the ossicles at two different locations:
Forward-1 at the long process end of incus, and Forward-2 at
the stapes head [see Fig. 2(a)]. The transducer has the diameter
of 1.8 mm, length of 2.0 mm, and weight of 25 mg. A sinusoidal
driving force with amplitude of 0.05 mN was applied onto the
transducer along the piston direction of stapes vibration.
Reverse driving was simulated by placing floatingmass transducer
on the middle ear side surface of RWM and coupling the
nodes at the contact surface [see Fig. 2(b)]. Two types of transducer
were used in FE analysis: Reverse-1 with large transducer:
7 mg in weight, 1.2mm in length, and 1mm2 in cross-section
area; Reverse-2 with small transducer: 2.2 mg in weight, 1.2mm
in length, and 0.314mm2 in cross-section area. Driving force
with amplitude of 0.05 mN was applied onto the transducers
along the normal direction of RWM for both transducers.
CONCLUSION
It is the first time of a 3-D comprehensive FE model of the
human ear including the ear canal,middle ear, and spiral cochlea
with three chambers separated by BM and RM is reported. The
frequency-dependent dynamic properties are applied to the ear
soft tissues in FE modeling analysis. Preliminary studies on
surgical implantation of middle ear devices and passive function
of cochlear implant indicate that 1) the reverse driving on RWM
has higher efficiency than the forward driving through ossicles;
2) cochlear implant diminishes the passive vibration of BM at
high frequencies, but reserves certain levels at low frequencies
[attachment=40053]
Abstract
A finite element (FE) model of the human ear including
the ear canal, middle ear, and spiral cochlea was constructed
from histological sections of human temporal bone. Multiphysics
analysis of the acoustics, structure, and fluid coupling in the ear
was conducted in the model. The viscoelasticmaterial behavior was
applied to the middle ear soft tissues based on dynamic measurements
of tissues in our laboratory. The FEmodel was first validated
using the experimental data obtained in human cadaver ears, and
then used to investigate the efficiency of the forward and reverse
mechanical driving with middle ear implant, and the passive vibration
of basilar membrane (BM) with cochlear implant placed
in the cochlear scala tympani. The middle ear transfer function
and the cochlear function of the BM vibration were derived from
the model. This comprehensive ear model provides a novel computational
tool to visualize and compute the implantable hearing
devices and surgical procedures.
INTRODUCTION
HUMAN ear is a complicated and multiphysics system including
air in the ear canal and middle ear cavity, ossicular
bones, tympanic membrane ™ and middle ear ligaments, and
viscous fluid inside cochlea. A finite element (FE) model based
on the anatomy of human ear with realistic material properties
will be a powerful tool to study the acoustic–structure–fluid
coupled functions in normal and diseased ears and to characterize
the functions of various implantable hearing devices.
The FE models of human ear have been reported in the literature
[1]–[4], but no comprehensive ear model including the ear
canal, middle ear, and spiral cochlea exists. It is critical and
important to build a spiral cochlea with three chambers of the
scala vestibule (SV), scala media (SM), and scala tympani (ST)
separated by cochlear basilar membrane (BM) and Reissner’s
membrane (RM), for understanding the cochlear function and
the interactions between the middle ear and cochlea.
METHODS
FE Model of the Human Ear
A FE model of human ear was built based on a complete
set of histological sections of a human temporal bone (male,
age 52, left ear). The model consists of the external ear canal,
TM, middle ear ossicular chain with suspensory ligaments, and
spiral cochlea [see Fig. 1(a)]. The ear canal and middle ear
parts are same as our previous published model [1]. The spiral
cochlea having two and a half turns is connected to the footplate
(FP) at the oval window and to the middle ear cavity at the
round window. The space inside cochlea was divided by the
RM and BM into three chambers: SV, SM, and ST and filled
with viscous perilymphatic fluid [see Fig. 1(b) and ©]. The
ratio of cross-section area between SV, SM, and ST was 5:3:8.
The total cross-section area of cochlea chambers changed from
2.55mm2 at the base to 1.13mm2 at the apex.
FE Modeling of Implantable Hearing Devices
Forward mechanical driving was simulated by placing a floating
mass transducer onto the ossicles at two different locations:
Forward-1 at the long process end of incus, and Forward-2 at
the stapes head [see Fig. 2(a)]. The transducer has the diameter
of 1.8 mm, length of 2.0 mm, and weight of 25 mg. A sinusoidal
driving force with amplitude of 0.05 mN was applied onto the
transducer along the piston direction of stapes vibration.
Reverse driving was simulated by placing floatingmass transducer
on the middle ear side surface of RWM and coupling the
nodes at the contact surface [see Fig. 2(b)]. Two types of transducer
were used in FE analysis: Reverse-1 with large transducer:
7 mg in weight, 1.2mm in length, and 1mm2 in cross-section
area; Reverse-2 with small transducer: 2.2 mg in weight, 1.2mm
in length, and 0.314mm2 in cross-section area. Driving force
with amplitude of 0.05 mN was applied onto the transducers
along the normal direction of RWM for both transducers.
CONCLUSION
It is the first time of a 3-D comprehensive FE model of the
human ear including the ear canal,middle ear, and spiral cochlea
with three chambers separated by BM and RM is reported. The
frequency-dependent dynamic properties are applied to the ear
soft tissues in FE modeling analysis. Preliminary studies on
surgical implantation of middle ear devices and passive function
of cochlear implant indicate that 1) the reverse driving on RWM
has higher efficiency than the forward driving through ossicles;
2) cochlear implant diminishes the passive vibration of BM at
high frequencies, but reserves certain levels at low frequencies