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Phantom and Human Experiments for
Breast Cancer Detection by Ultrasound
Transmission Technique
Yoshinori Hayakawa, Aya Sakasegawa, and Kiichi Tsuji
Summary. A new technique named the ultrasound transmission technique has been
proposed by the authors. The idea was developed from the clinical findings that sound
velocity in breast cancer is higher than in normal tissue by 49–90 m/s. Phantom experiments were conducted. Plexiglas (PMMA) plates 3 mm, 2 mm, or 1 mm thick were put
into a cubic container (86 ¥ 86 ¥ 86 mm) filled with degassed water. In the echogram,
the apparent distance between the back wall of the container and transducer was
shortened because of the higher velocity of sound waves in plexiglas (2700 m/s) than
degassed water (1500 m/s). This result showed the validity of the method. A breast to
be examined can be sandwiched between a planar ultrasound transducer and reflector plate. Similar experiments were performed using a slice of pork (42 mm thick)
instead of degassed water. The shortening of the reflector was apparent. The forearm
of a human volunteer was also examined with plexiglas 2 mm or 1 mm thick with
similar results, suggesting the validity of the method.
Key words. Breast cancer, Early detection, Ultrasound, Transmission period, Sound
velocity
Introduction
Breast cancer is the leading cause of death among American women and the second
most common cause among Japanese women. The disease is related to the Westernstyle diet and is increasing in incidence.
In every cancer, early detection and early treatment are the best ways to decrease
mortality of patients. Moreover, early detection of breast cancer increases the possibility of breast conservation treatment. Although mammography is the most powerful modality for early detection, it is hazardous for use in young women due to X-ray
exposure. Another modality of image diagnosis is ultrasound echo technique, but it
is not as powerful in detecting breast cancer as mammography. Palpation, another
modality, is largely dependent on the skill and experience of medical doctors. A new
Department of Biomedical Engineering, Toin University of Yokohama, 1614 Kuragane-cho,
Aoba-ku, Yokohama 225-8502, Japan
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171
Fig. 1. Schematic view of proposed breast examination apparatus. A breast will be
sandwiched between an ultrasound transmitting plate and a
reflector, and examined on an
ultrasound transducer using the
echo technique
technique, which has been proposed by some of the authors, was named the ultrasound transmission technique [1] (Fig. 1).
In the present report, phantom experiments were conducted to obtain good results.
The idea was developed from clinical findings using ultrasound computed tomography that the velocity of sound in a malignant tumor is greater by 49 to 90 m/s than in
the normal tissue of the same patient [2]. The attenuation coefficient of a malignant
tumor and normal tissue are approximately the same. The sound velocity in normal
tissue is 1350 to 1500 m/s depending on the tissue, being greater in parenchyma and
less in fat [2].
Materials and Methods
Phantom experiments were conducted to verify the validity of the technique. The
Toshiba Ultrasound Diagnostic System SSA-390A with a linear transducer of 9 MHz
was employed for the experiment. First, the sound velocity of plexiglas to be used in
the phantom experiment was measured by the echo technique. The echogram of plexiglas of 30.2 mm thickness was taken in degassed water, and the apparent thickness
was compared. The result was analyzed using the published datum of sound velocity
in water (1500 m/s), yielding the velocity of sound in the plexiglas to be 2670 m/s, compared to the published datum of 2720 m/s.
Second, plexiglas (PMMA) plates 3 mm, 2 mm, or 1 mm thick were put in degassed
water in a cubic container (86 ¥ 86 ¥ 86 mm). Apparent protrusion of the container
wall behind each PMMA plate was eminent, which is due to higher sound velocity in
PMMA than in water.
Next, pork slices were sandwiched between PMMA plates 4 mm thick, and examined from above with the ultrasound transducer. A PMMA plate of 2 mm or 1 mm was
inserted between 4 mm PMMA plates. Approximately the same result was achieved
with no PMMA plate inserted.
Third, the forearm of a human volunteer was sandwiched between PMMA plates
4 mm thick, and examined in approximately the same manner as the pork slices
(Fig. 2).
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Fig. 2. Experimental setup
of volunteer human forearm
with plexiglas (PMMA) plate
inserted
Results
Experiment with Pork Slices
Protrusion of the lower PMMA plate, which serves as a reflector, was apparent behind
the 2-mm and 1-mm PMMA plate insertion, mocking a tumor. No such protrusion
was observed without the PMMA plate insertion (Fig. 3).
Experiment with Human Forearm
Two kinds of experiments were achieved using different thickness of forearm (46 mm
and 65 mm). Protrusion of the lower PMMA plate, which serves as a reflector, was
apparent behind the 2-mm PMMA plate insertion, mocking a tumor. No such protrusion was observed without the PMMA plate insertion (Fig. 4). In the case of the
1-mm PMMA plate insertion, the protrusion was not so apparent. B-mode images of
forearm with the sound velocity of 1600 m/s of muscle and with PMMA plate of 1 mm
(or 2 mm), corresponds approximately to 11 mm (or 22 mm) of tumor thickness in the
case of the sound velocity difference of 49 m/s and corresponds approximately to
6 mm (or 12 mm) of tumor thickness in the case of the sound velocity difference of
90 m/s. This relationship is derived from the equation
Y (1 1600 - 1 2720) = X (1 v - 1 ( v + dv ))
where Y is the thickness of PMMA, X is the corresponding tumor thickness, v is the
sound velocity of normal tissue, and dv is the difference of sound velocity of 49 m/s
or 90 m/s.
Discussion
The present work shows that the proposed method may be used for mass screening
of breast cancer for young females. The PMMA plate mocking the tumor seems to
be useful to represent a tumor on a patient’s breast to check the operation of the
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a
b
c
Fig. 3. a Pork slices of thickness of 49 mm with 2-mm-thick PMMA plate. b Pork slices of thickness of 49 mm with 1-mm-thick PMMA plate. c Pork slices of thickness of 49 mm without
PMMA plate. All the B-mode image is zoomed to enlarge the apparent protrusion. Apparently
three-layered echo signals are due to multiple scattering in the upper and lower PMMA plates.
Uppermost reflection is indicated by an arrow
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a
b
c
Fig. 4. a Forearm of thickness of 46 mm with 2-mm-thick PMMA plate. b Forearm of thickness
of 46 mm with 1-mm-thick PMMA plate. c Forearm of thickness of 46 mm without PMMA plate.
All the B-mode image is zoomed to enlarge the apparent protrusion. Apparently three-layered
echo signals are due to multiple scattering in the upper and lower PMMA plates. Uppermost
reflection is indicated by an arrow
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transducer. Echo images may also be useful to observe the reflector position, which
may be apparently protruding due to the higher sound velocity of the tumor. The
echoic volume may be useful to estimate the sound velocity of the region. The reason
we have examined a forearm instead of an actual breast is the lack of volunteers. The
examination of the forearm, however, does not seem to be so inadequate because the
present method seems to be most suitable for examination of dense breasts of young
females less than 40 years of age with scirrhous cancer, and the velocity of sound is
greater compared to older, fatty breasts [3].
References
1. Hayakawa Y, Inada T, Ueno E, et al (1984) Mass screening of breast cancer by
ultrasound transmission technique: theoretical considerations. Jpn J Appl Phys 24(suppl
24-1):82–83
2. Carson PL, Scherzinger AL, Brand PH, et al (1983) Ultrasonic computed tomography
instrumentation and human studies. In: Ultrasonic examination of the breast. Wiley,
Chichester, pp 187–199, Fig. 4
3. Bamber JC (1983) Ultrasonic propagation profiles of the breast. In: Ultrasonic
examination of the breast. Wiley, Chichester, pp 37–44, Fig. 2