Japanese Journal of Applied Physics
Vol. 46, No. 7B, 2007, pp. 4897–4899#2007 The Japan Society of Applied Physics

Measurement of Angular Dependence of Ultrasonic Scatteringfrom Wire Phantom Mimicking Myocardial Fiber
Teppei O NODERA, Hideyuki HASEGAWA, and Hiroshi K ANAI
Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan(Received November 24, 2006; accepted March 22, 2007; published online July 26, 2007)

The diﬀerence between a normal and a hypertrophic heart is whether the direction of regional myocardial ﬁbers arehomogeneously aligned along one direction. In order to investigate the angle dependence of ultrasonic scattering in relation to
the ﬁber direction, we measured the ultrasonic echoes from a metal wire phantom, which mimics a bundle of myocardium
ﬁbers, as a function of the insoniﬁcation angle. In this study, we focused on ultrasonic scattering properties in relation to theazimuth and elevation angles of insoniﬁcation and reception. Experimental results showed that the amplitude of the reﬂectedecho from the metal wire became maximum when the ultrasonic beam was insoniﬁed parallel to the ﬁber direction. In the caseof such parallel insoniﬁcation, echoes from the wire showed directivity like those from an interface. Such directivity wasconsidered to contribute to the dependence of echoes on the azimuth angle. [DOI: 10.1143/JJAP.46.4897]
KEYWORDS: angle dependence, ultrasonic scattering, myocardial fiber

1.

Introduction

Directions of myocardial ﬁbers in a normal human heart
wall change gradually from the epicardium to the endocardium and are homogeneously aligned in each plane that isparallel to the luminal surface of the heart wall.1–3) However,in a heart wall aﬀected by hypertrophic heart disease, themyocardial ﬁber direction becomes disarrayed.4,5) Therefore,
it is important to diagnose the myocardial ﬁber direction fordiﬀerentiation of normal hearts from those aﬀected byhypertrophic heart disease. It is expected that ultrasonicscattering from a heart wall can reveal such changes in the
direction of myocardial ﬁbers. Basic research based onbackscattered echoes from the myocardium has been conducted for quantitative tissue characterization.6)
In order to quantify the correspondence between theacoustic properties of an object and ultrasonic backscattering, ultrasonic backscattering from a reference phantom ofknown acoustic properties was measured with the inﬂuencesof the measurement system being eliminated.7,8) Baldwin
and co-workers measured the ultrasonic myocardial attenuation while changing the angle of ultrasonic propagation
relative to the myocardial ﬁbers for quantitative ultrasoniccardiac tissue characterization.1,6) By measuring ultrasonicbackscattering from the myocardium at each insoniﬁcation
angle  relative to the direction of the myocardial ﬁbers, one
can show that the ultrasonic attenuation in the myocardium
is maximum when  is zero (parallel) relative to themyocardial ﬁbers and minimum when  is 90 (perpendicular) relative to the ﬁbers. In previous studies, it was foundthat ultrasound-integrated backscattering from the myocardium exhibits cyclic variation during one cardiac cycle.9–12)
One of the reasons is considered to be the change in theangle between the ultrasonic beam and the direction of
myocardial ﬁbers.13) Recchia et al. measured the ultrasoundbackscattering from the inside of an excised canine
myocardium specimen.3) There was a strong relationshipbetween the backscattering intensity and ﬁber orientation.
They explained such an angular dependence using amathematical model of the principal structure in a normal
E-mail address: hkanai@ecei.tohoku.ac.jp

myocardium.3) Holland et al. measured the angular dependence of the integrated backscattering from a bovine
tendon.14) Their results showed that the inherent anisotropyof the tissue structure inﬂuences the spectral properties ofthe ultrasound backscattering. They also investgated theeﬀect of the angle dependence of ultrasound backscatteringin the short-axis view of a mouse heart at end systole andend diastole.15)
In this study, we focused on ultrasonic scattering properties in relation to the azimuth and elevation angles of
insoniﬁcation relative to the ﬁber direction. For this purpose,
ultrasonic echoes from a wire phantom (with a diameter lessthan the wavelength) that mimics a bundle of myocardium
ﬁbers were measured as a function of the insoniﬁcationangle.
2.

Experimental Methods

The experimental setup is illustrated in Fig. 1. As shownin Fig. 1(a), two focused transducers were used for transmitting and receiving ultrasonic beams. The transmission
and reception elevation angles are 1 and 2 , respectively. In
this paper, ultrasonic echoes from a wire phantom weremeasured at various angles, 1 , 2 , and azimuth angle .
During the experiment, focal points of both transducers arerequired to be set at the same point on the phantom. Bykeeping the focal points at the same position, the object wasrevolved around that point to change the azimuth angle .
Furthermore, the elevation angle  was changed by moving
the transducers along a circle with its center at the same
point as the focal point on the phantom. To realize suchoperations, a custom-made apparatus was used. The measurement apparatus is shown in Fig. 1(b).
Both transducers for transmission and reception were
single-element concave transducers (Tokimec 7Z10I-PF30C-K445). The focal distances of the transducers are 30 mm
and the center frequency is 7.0 MHz. The wire phantom wasplaced in a water tank, as shown in Fig. 1(b), and ﬁxed onto
the center of the cylindrical pedestal. The azimuth angle  ofinsoniﬁcation relative to the ﬁber direction was changed byrotating the pedestal. There was a hole of 20 mm diameter at
the center of the top of the pedestal in order to receive only
the signal reﬂected from the object. A sine wave of one cycle

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T. ONODERA et al.

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φ2wire

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Generator

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φ1θ350(a)300transducers(a)090180angle θ [deg]Fig. 3. Maximum amplitude of the received signals at each azimuth angle
. (a) 1 ¼ 2 ¼ 30 . (b) 1 ¼ 2 ¼ 40 . (c) 1 ¼ 2 ¼ 50 . (d) 1 ¼
2 ¼ 60 . (e) 1 ¼ 2 ¼ 70 .

wire

Fig. 1. Illustrations of (a) the measurement, (b) custom-made apparatus,and (c) experimental setup.
350

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amplitude [mV]

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amplitude [mV]Fig. 2. Examples of the received signals from the wire ( ¼ 0 ). (a)1 ¼ 2 ¼ 30 . (b) 1 ¼ 2 ¼ 50 .

020
φ 2−φ 1 [deg]4060" φ 1 = 30 deg"
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was applied to the transmitting transducer. The signal
reﬂected from the object was received by the receiving
transducer. The digitized data were acquired after averaging
the reﬂected signals 128 times using a digital oscilloscope(Tektronix TDS220).
The diameter of a human myocardial ﬁber (10 –15 mm)5) isthinner than the wavelength of ultrasound (400 – 500 mm)
used in ultrasonic diagnostic equipment. Therefore, ultrasonic echoes from human myocardium ﬁbers are scatteredwaves. The phantom used in this study was a copper wire ofabout 170 mm in diameter. The wavelength of insoniﬁed
ultrasound was 214 mm. Thus, ultrasonic echoes were also
scattered waves.
3.

Results

Figure 2 shows the received RF signals when the ultrasonic beam was insoniﬁed parallel to the wire ( ¼ 0 ) at
two settings of the elevation angles (1 ¼ 2 ¼ 30 and 50 ).
As shown in Fig. 2, the peak value was measured at eachsetting of the azimuth and elevation angles.
Figure 3 shows the angular dependence of the maximum
amplitude of the reﬂected signals at each azimuth angle, .

0–60

–40

–20

020
φ 2−φ1 [deg]4060

Fig. 4. Maximum amplitude of the received signals at each angle
diﬀerence (2  1 ) between receiving and insoniﬁcation elevation
angles, 1 and 2 . (a)  ¼ 90 . (b)  ¼ 0 .

The amplitude of the reﬂected signal changed with azimuth
angle, . Although the pedestal was rotated three times,reproducible measurements were achieved with respect tothe azimuth angle, . At the same elevation angle (1 ¼ 2 ),the amplitude became maximum when the ultrasonic beam
was insoniﬁed parallel to the wire ( ¼ 0 and 180 ). On theother hand, when the ultrasonic beam was insoniﬁed
perpendicularly to the wire ( ¼ 90 and 270 ), the amplitudetended to be the smallest.
Figure 4 shows the maximum amplitude of the received
signals at each diﬀerence between elevation angles(2  1 ). The azimuth angle  was kept at 90 in Fig. 4(a)and  ¼ 0 in Fig. 4(b), respectively. Amplitude proﬁles andamplitudes showed similar tendencies at each insoniﬁcation
elevation angle 1 .

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T. ONODERA et al.

angle diﬀerence, (2  1 ), did not change greatly withinsoniﬁcation elevation angle, 1 , in the case of insoniﬁcation perpendicular to the wire ( ¼ 90 ). On the other hand,in the case of insoniﬁcation parallel to the wire ( ¼ 0 ), thewire acts as an interface. Such a diﬀerence in amplitude
proﬁles with respect to the angle diﬀerence between
transmitting and receiving elevation angles provides a clue
to the cause of the dependence of echo on the azimuth angle.

" φ 1 = 40 deg"
" φ 1 = 50 deg"

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Acknowledgement–1001020
φ 2−φ1 [deg]304050

The authors would like to thank Mr. Hiroaki Kamada forhis helpful comments in this study.

Fig. 5. Maximum amplitude of the received signals from an aluminum
plate at each angle diﬀerence (2  1 ).

In the case of insoniﬁcation perpendicular to the wire( ¼ 90 ), the amplitude does not change greatly withrespect to (2  1 ), and decreases as the angle diﬀerence(2  1 ) increases. On the other hand, in the case of
insoniﬁcation parallel to the wire direction ( ¼ 0 ), amplitudes become maximum when the angle diﬀerence (2  1 )is 0 . When the absolute value of the angle diﬀerence ismore than 20 degrees, the amplitude is almost zero.
Figure 5 shows the echo amplitude from a ﬂat aluminum
plate measured by a similar procedure as that in the case ofFig. 4(b). Echoes from the aluminum plate are maximum
when the angle diﬀerence (2  1 ) is 0 . When the absolutevalue of the angle diﬀerence is greater than 20 , theamplitudes are again almost zero. These results suggest thatthe wire acts as an interface in the case of parallel
insoniﬁcation ( ¼ 0 ).
4.

Conclusions

In this study, in order to investigate the angle dependenceof ultrasonic scattering from a wire, we constructed anexperimental system that allows us to change the elevation
and azimuth angles. The amplitude of the reﬂected signal
from the wire changed with azimuth angle, .
The maximum amplitude of the received signals at each

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