19-09-2012, 03:29 PM
Modification of the Phased-Tracking Method for Reduction of Artifacts in Estimated Artery Wall Deformation
[attachment=34080]
Abstract
Noninvasive measurement of mechanical properties,
such as elasticity, of the arterial wall, is useful for
diagnosis of atherosclerosis. For assessment of mechanical
properties, it is necessary to measure the deformation of
the arterial wall. In this study, a modification of the previously
proposed phased-tracking method was conducted to
improve measurement of the small change in thickness (deformation)
of the arterial wall due to the heartbeat. In our
previous method, a set of two points along an ultrasonic
beam was initially assigned, and the change in thickness of
the layer between these two points during an entire cardiac
cycle was estimated. In motion estimation with ultrasound,
the motion of an interface or a scatterer, which generates
an echo, can be obtained by estimating the change in time
delay of the echo. For example, in the case of a carotid
artery of a healthy subject, there are only two dominant
echoes from the lumen-intima and media-adventitia interfaces.
Thus, only the displacements of the lumen-intima and
media-adventitia interfaces can be estimated, which means
that ultrasound can estimate only the change in distance
(thickness) between these two interfaces. However, even in
this case, our previous method gives different estimates of
the change in thickness
Introduction
Noninvasive measurement of mechanical properties of
the arterial wall, such as elasticity, is useful for diagnosing
atherosclerosis because there are significant differences
between the elastic moduli of normal arterial walls
and those affected by atherosclerosis [1], [2].
For assessment of mechanical properties, various methods
have been proposed to measure the displacement of the
arterial wall. Elasticity based on estimation of the pulse
wave velocity (PWV) [3]–[6] and the homogeneity of distensibility
[7], which is evaluated by the change in diameter
obtained from displacements of near and far walls, can
be noninvasively evaluated by measuring displacements at
multiple points in the axial direction of the artery. Of
course, measurement of the change in diameter at one
point is widely used for assessment of mechanical properties
of the arterial wall [8]–[10]. In such case, however,
the arterial wall must be assumed to be an isotropic, cylindrical
shell with a uniform wall thickness.
Drawbacks of Previously Proposed
Phased-Tracking Method
Fig. 4(a) shows a B-mode image of a carotid artery of
a 30-year-old, healthy male. The B-mode image was acquired
using a 10 MHz linear-type ultrasonic probe of ultrasonic
diagnostic equipment (SSD-6500, Aloka Co., Ltd.,
Tokyo, Japan). Figs. 4(b) and © show RF echoes from
the posterior wall along the white arrow in Fig. 4(a).
The region shown in Figs. 4(b) and © is indicated by
a white dashed line in Fig. 4(a). In healthy subjects, there
are only two dominant echoes from the lumen-intima and
media-adventitia interfaces [30]. In this study, as shown
in Figs. 4(b) and ©, the intima-media thickness (IMT)
is defined by the region between the rises of echoes from
the lumen-intima and media-adventitia interfaces. In this
study, these rises were manually assigned by inspecting
a B-mode or M-mode image. In motion estimation with
ultrasound, we can estimate the motion of a reflector (interface
or scatterer) by analyzing its echo. Therefore, in
the case of a healthy subject, we can estimate only displacements
of the lumen-intima and media-adventitia interfaces.
In Vitro Experiments Using Excised
Diseased Arteries
Figs. 13(a) and (b) show B-mode images of femoral arteries
excised from two patients, 78-year-old and 72-yearold
males, with arteriosclerosis obliterans, respectively. After
surgical extraction, arteries were immediately kept in
cold storage and were measured within 5 days. These two
arteries were placed in a water tank filled with 0.9% saline
solution at the room temperature, and the change in internal
pressure was applied by a flow pump. During the application
of the change in internal pressure, RF lines were
acquired along the ultrasonic beams as shown by white vertical
arrows in Figs. 13(a) and (b). Then, as in the in vivo
experiments, changes in thickness of the arterial walls were
estimated by the previous and proposed methods as shown
in Figs. 14–17. Figs. 14(a), 15(a), 16(a), and 17(a) show
waveforms of internal pressure measured with a catheter
(model 110-4, Camino Co., Ltd., San Diego, CA) located
at the edge of the distal side of the artery
Conclusions
In the present study, our previous method for measuring
the change in thickness of the arterial wall caused by
the heartbeat was modified to reduce an artifact in a deformation
image of the arterial wall.
In the case of a carotid artery of a healthy subject,
there are only two dominant echoes from the lumen-intima
and media-adventitia interfaces. In such a situation, only
the change in the entire intima-media thickness can be estimated
using ultrasound. However, changes in thickness
estimated by the previous phased-tracking method show
the artificial spatial variation. In this study, the phasedtracking
method was modified to reduce this artifact. In
simulation experiments, it was found that such artificial
spatial variation was reduced by the proposed method, and
changes in thickness estimated by the proposed method
corresponded to that in the entire intima-media thickness.
[attachment=34080]
Abstract
Noninvasive measurement of mechanical properties,
such as elasticity, of the arterial wall, is useful for
diagnosis of atherosclerosis. For assessment of mechanical
properties, it is necessary to measure the deformation of
the arterial wall. In this study, a modification of the previously
proposed phased-tracking method was conducted to
improve measurement of the small change in thickness (deformation)
of the arterial wall due to the heartbeat. In our
previous method, a set of two points along an ultrasonic
beam was initially assigned, and the change in thickness of
the layer between these two points during an entire cardiac
cycle was estimated. In motion estimation with ultrasound,
the motion of an interface or a scatterer, which generates
an echo, can be obtained by estimating the change in time
delay of the echo. For example, in the case of a carotid
artery of a healthy subject, there are only two dominant
echoes from the lumen-intima and media-adventitia interfaces.
Thus, only the displacements of the lumen-intima and
media-adventitia interfaces can be estimated, which means
that ultrasound can estimate only the change in distance
(thickness) between these two interfaces. However, even in
this case, our previous method gives different estimates of
the change in thickness
Introduction
Noninvasive measurement of mechanical properties of
the arterial wall, such as elasticity, is useful for diagnosing
atherosclerosis because there are significant differences
between the elastic moduli of normal arterial walls
and those affected by atherosclerosis [1], [2].
For assessment of mechanical properties, various methods
have been proposed to measure the displacement of the
arterial wall. Elasticity based on estimation of the pulse
wave velocity (PWV) [3]–[6] and the homogeneity of distensibility
[7], which is evaluated by the change in diameter
obtained from displacements of near and far walls, can
be noninvasively evaluated by measuring displacements at
multiple points in the axial direction of the artery. Of
course, measurement of the change in diameter at one
point is widely used for assessment of mechanical properties
of the arterial wall [8]–[10]. In such case, however,
the arterial wall must be assumed to be an isotropic, cylindrical
shell with a uniform wall thickness.
Drawbacks of Previously Proposed
Phased-Tracking Method
Fig. 4(a) shows a B-mode image of a carotid artery of
a 30-year-old, healthy male. The B-mode image was acquired
using a 10 MHz linear-type ultrasonic probe of ultrasonic
diagnostic equipment (SSD-6500, Aloka Co., Ltd.,
Tokyo, Japan). Figs. 4(b) and © show RF echoes from
the posterior wall along the white arrow in Fig. 4(a).
The region shown in Figs. 4(b) and © is indicated by
a white dashed line in Fig. 4(a). In healthy subjects, there
are only two dominant echoes from the lumen-intima and
media-adventitia interfaces [30]. In this study, as shown
in Figs. 4(b) and ©, the intima-media thickness (IMT)
is defined by the region between the rises of echoes from
the lumen-intima and media-adventitia interfaces. In this
study, these rises were manually assigned by inspecting
a B-mode or M-mode image. In motion estimation with
ultrasound, we can estimate the motion of a reflector (interface
or scatterer) by analyzing its echo. Therefore, in
the case of a healthy subject, we can estimate only displacements
of the lumen-intima and media-adventitia interfaces.
In Vitro Experiments Using Excised
Diseased Arteries
Figs. 13(a) and (b) show B-mode images of femoral arteries
excised from two patients, 78-year-old and 72-yearold
males, with arteriosclerosis obliterans, respectively. After
surgical extraction, arteries were immediately kept in
cold storage and were measured within 5 days. These two
arteries were placed in a water tank filled with 0.9% saline
solution at the room temperature, and the change in internal
pressure was applied by a flow pump. During the application
of the change in internal pressure, RF lines were
acquired along the ultrasonic beams as shown by white vertical
arrows in Figs. 13(a) and (b). Then, as in the in vivo
experiments, changes in thickness of the arterial walls were
estimated by the previous and proposed methods as shown
in Figs. 14–17. Figs. 14(a), 15(a), 16(a), and 17(a) show
waveforms of internal pressure measured with a catheter
(model 110-4, Camino Co., Ltd., San Diego, CA) located
at the edge of the distal side of the artery
Conclusions
In the present study, our previous method for measuring
the change in thickness of the arterial wall caused by
the heartbeat was modified to reduce an artifact in a deformation
image of the arterial wall.
In the case of a carotid artery of a healthy subject,
there are only two dominant echoes from the lumen-intima
and media-adventitia interfaces. In such a situation, only
the change in the entire intima-media thickness can be estimated
using ultrasound. However, changes in thickness
estimated by the previous phased-tracking method show
the artificial spatial variation. In this study, the phasedtracking
method was modified to reduce this artifact. In
simulation experiments, it was found that such artificial
spatial variation was reduced by the proposed method, and
changes in thickness estimated by the proposed method
corresponded to that in the entire intima-media thickness.