Engineering, 2013, 5, 73-77
doi:10.4236/eng.2013.55B015 Published Online May 2013 (http://www.scirp.org/journal/eng)
Acoustic and Intraluminal Ultrasonic Technologies in the
Diagnosis of Diseases in Gastrointestinal Tract: A Review
Qian Lu1*, Orly Yadid-Pecht1, Dan Sadowski2, Martin P. Mintchev1
1Department of Elect r i ca l and Computer Engineering, University of Calgary, Calgary, Alberta, Canada
2Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada
Gastrointestinal (GI) auscu ltation (listening to sounds from stomach and bowel) has b een applied for abdominal physi-
cal assessment for many years. This article evaluates the technique involved in listening to both bowel and stomach
sounds and the significance of both normal and abnormal GI auscultation findings. Moreover, intraluminal ultrasonic
techniques have been widely used for gastrointestinal disease diagnosis by providing intraluminal images since 1980s,
this article also reviews the existing intraluminal ultrasonic technolo gy fo r di ag no si n g of GI di s or der s.
Keywords: Auscultation; Gastrointestinal Diseases; Sound; Intraluminal Ultrasonic
Sonic signals generated from both sto mach and the bow-
els during the peristalsis could be clinically useful for the
diagnosis of gastrointestinal diseases. In addition, in-
traluminal ultrasonic techniques provide clear images to
visually monitor stomach and bowel anatomy and func-
tion in real time. Both sonic and ultrasonic technologies
are relatively cheap and non-invasive by nature. In this
paper, we will discuss both technologies, with an empha-
sis on the medical devices related to them and the associ-
ated methods for clinical applications.
2. Acoustic Technology
2.1. Why Acoustic Technology?
For centuries, clinicians performed auscultation by plac-
ing a stethoscope, an acoustic device, on patient’s skin to
listen to the sounds coming from adjacent internal organs
in order to make a diagnosis. For example, lung and heart
auscultation is now a routine clinical practice to exclude
certain pulmonary and cardiac diseases. Cannon  pio-
neered abdominal auscultation for investigating sounds
originally from GI organs more than a century ago. Due
to its low cost and non-invasiveness compared to other
modalities such as manometry and X-ray imaging ,
abdominal auscultation became attractive and was once a
popular part of any clinical examination. However, due
to the lack of scientific support, clinicians gradually
turned away from abdominal auscultation .
Thanks to the advances in electronics and computer
science, computerized analysis the abdominal sounds
become possible [4,5].
2.2. Contemporary Acoustic Technology Devices
Earlier investigators wore acoustic stethoscope to listen
to the abdominal sound s and manually recorded the data.
Their data logging carried limited information and the
data could be erroneous due to low sound levels. Further,
the clinical criteria were generally considered subjective
The introduction of the electronic stethoscope allowed
amplification of the weak body sound signals . More
importantly, the signals could now be digitized and
stored for offline computer-aided analysis. The electronic
stethoscope further incorporated skin-adhesive and seal-
ing features . The advantages are twofold: Firstly, the
sealing can effectively prevent the stethoscope from en-
vironmental interferences transmitted through air. Sec-
ond, the adhesion permits long and unsupervised auscul-
tation for hours .
Campbell et al  introduced what they referred to as
“surface vibration analysis” device, the technology be-
hind which is transferred from industrial applications.
Rather than utilizing a diaphragm that transforms body
vibrations to an acoustic signal, it utilizes a piezoelectric
transducer, which has a minimal response to acoustic
signals but is very sensitive to vibrational energy trans-
mitted from internal organs through the abdominal wall.
Copyright © 2013 SciRes. ENG
Q. LU ET AL.
2.3. Acoustic Applications in GI Diseases
Computerized acoustic technologies in the diagnosis of
diseases in the GI tract can be classified according to the
GI organs they target.
Extensive research has been going on to understand
bowel sounds [10-12]. With CASAS, an advanced signal
processing software, Sugrue and Redfern  explored
bowel sounds in controls and patients with several acute
abdominal conditions, including appendicitis, cholecysti-
tis and intestinal obstruction. They recorded the abdomi-
nal sounds for 10 minutes for each patient and defined
five different acoustic parameters: a) sound length, b)
number of sounds over a unit time, c) sound amplitude, d)
interval between sounds and e) sound to silence ratio.
Several interesting differences between controls and pa-
tients with various acute abdominal disorders are ob-
served. However, the experiments failed to offer a reli-
able scientific explanation ab out the origins of the bowel
Later studies tried to correlate bowel sounds related to
drug-induced episodes with simultaneous manometry
findings. Tomomasa et al  compared bowel sound
index (i.e. sound amplitude) to small intestinal transit
time in subjects that were intraduodenally administered
lactulose that can change the duodenal motility for 15
minutes. The correlation of their sound recordings with
manometry suggested that the stimulated contractions
can increase bowel sounds and these sounds are more
likely to reflect the movement of food con tent rather than
the movement of the lumen wall.
Yuki et al  conducted two-minute recordings on
controls, inflammatory bowel disease (IBD) patients and
those with increased bowel motility that was induced by
a prokinetic drug. After comparing the mean sound-
sound interval and number of detectable sounds per min-
ute among the groups, they failed to identify any statisti-
cal difference, suggesting that the 2-minute sampling
period may not be long enough to capture the bowel
Dimoulas et al [13,14] proposed prolonged abdominal
sound monitoring and processing using a wavelet-based
method  and time-frequency features . The
methods they developed were able to classify abdominal
sounds into intestinal bursts (IB), i.e. those abrupt sounds
in a very short duration, and regularly sustained (RS), i.e.
those clustered sounds in a long duration. Further, they
could identify three type of interfering noises: silent pe-
riod, respiration and snoring, as well as motion-related
moving noi ses.
Acoustic studies from GI organs other than intestines
we re als o stud ied. Tomoma sa et al  conducted stom-
ach sound measurements with a microphone placed 3 cm
below the umbilicus on infants with pyloric stenosis be-
fore and after pyloromyotomy. Gastric emptying was
measured simultaneously. Sound index (SI) was calcu-
lated. They found that there was a significant positive
correlation between SI and gastric emptying, which is
suggesting that SI was a useful indicator of gastric emp-
tying after the surgery.
Yamaguchi et al  measured stomach sounds while
monitoring the motility of the gastric antrum using ultra-
sonography. Sounds were classified as gastroduodenal
sounds and intestinal sounds based on whether antral
movement was observed using ultrasonography. Diabetic
patients and controls underwent measurements after food
intake. In diabetics, the SI of the gastroduodenal sounds
was significantly lower after food intake compared to
3. Intraluminal Ultrasonic Technology
3.1. Principle of Intraluminal Ultrasonic
Intraluminal ultrasound imaging techniques were origi-
nally developed for the visualization of plaques when
investigating cardiac valves and vessels [17,18]. They
had been applied to study gastrointestinal diseases since
the 1980s [19,20]. The technique is a derivative of
B-mode and M-mode ultrasonography, which are able to
provide high-resolu tion images for both linear and cross-
sectional images. Typically, the radial resonant frequen-
cies of ultrasonic transducers vary from 9 to 40MHz .
Since the ultrasonic technique records in real time and is
noninvasive, it has been widely adopted to study the dy-
namics of the GI tract. In recent years, due to device
miniaturization, it becomes feasible to incorporate fine
needle aspiration (FNA) biopsy mechanism with in-
traluminal ultrasound devices .
3.2. Instrumentation on Intraluminal Ultrasonic
Depending on the direction of the image formed, in-
traluminal ultrasonic devices can be divided into two
types: radial and curvilinear . Intraluminal ultrasonic
devices can be inserted alone or within a standard endo-
scope. Radial imaging devices, they utilize a 360º rotat-
ing ultrasound transducer. All ultrasonic waves travel
within a plane that is perpendicular to the direction of the
endoscope insertion. As a result, the image formed is
parallel to those axial CT images, but it is more intuitive
to interpret ultrasonic images compared to their com-
puted tomography (CT) counterparts . As for the
curvilinear imaging devices, the transducer is positioned
at the tip of the endoscope and is producing sector im-
ages which are parallel to the direction of the endoscope
insertion . Although such images are difficult to in-
Copyright © 2013 SciRes. ENG
Q. LU ET AL. 75
terpret, they present a significant advantage over radial
imaging when used for guiding FNA that is inserted at an
oblique angle from the endoscope . Moreover, Dop-
pler imaging can be implemented in the curvilinear de-
vices to detect blood flow in blood vessels. It is useful to
prevent bleeding when performing FNA .
3.3. Ultrasonic Applications for GI Disorders
Mittal et al  performed preliminary studies of utiliz-
ing ultrasonic techniques in evaluating various esophag-
eal diseases. The cross-sectional structure of the eso-
phageal lumen during liquid swallows and liquid gas-
troesophageal reflux (GER) can be measured by a ultra-
sound probe. Meanwhile, analysis of the esophageal
contents and dimensions during transient lower eso-
phageal sphincter (LES) relaxations can be performed as
well [21-24]. Extremely small ultrasonic crystal arrays
are often mounted circumferentially on a single site of an
intraluminal catheter to inspect visually the cross-sec-
tional image of the esophagus at a specific level .
Studies have shown that imaging can measure esophag-
eal cross-sectional area (CSA) distensions during liquid
GER episodes .
Comparison of esophageal CSAs between GER pa-
tients and controls showed that the peak esophageal lu-
minal CSAs was significantly dilated in GER patients
than that in controls [26,27]. However, there are still
limitations for the u ltrasonic techn ique in GER diagno sis.
For example, the current intraluminal ultrasound device
can only measure esophageal luminal distension at one
level of the esophagus, because there is only one ultra-
sonic sensor integrated on the catheter. Therefore, it was
suggested to mo unt multiple ultrasonic sen sors at various
levels of a catheter for more comprehensive GER testing
. This has not been implemented, most likely due to
the limited room left in the catheter, the high manufac-
turing cost of the ultrasonic sensors, as well as the tedi-
ous image analysis process .
Ultrasound has been greatly applied for diagnosing
malignant gastric disorders , ultrasound has added
greatly to the staging of gastric cancers, especially when
the cancers are limited to the mucosa level . Ultra-
sound is also more favorably used than CT because it can
be combined with endoscopic mucosa resection for his-
tologic confirmation. As for staging cancers evolving
into the muscularis mucosa, high-frequency miniprobes
can be used, which can delineate the fine details of the
gastric wall as a 9- or 1l-layer structure as opposed to the
5 layers shown in lower frequency ultrasound [29, 30].
Ultrasound is also outperforming traditional endo-
scopy in characterizing submucosal tumors in the GI
tract because it is able to distinguish whether a tumor is
cystic, solid or hypervascular from its echo pattern .
However, ultrasound alone is difficult to differentiate
malignant and benign tumors. Biopsy exam from ultra-
sound-guided FNA can impro ve the diagnosis, especially
when the tumors are in the first few layers shown on the
ultrasonic images .
In the past two decades, studies have shown that in-
traluminal ultrasound is consistently accurate in staging
rectal cancers, especially those in early stages ,
which CT or magnetic resonance imaging (MRI) are un-
able to resolve. Ultrasound is also an alternative modality
for assessing inflammatory bowel disease through ob-
serving features such as increased bowel wall thickness
and enlarged vessels .
4. Discussion and Conclusions
The idea of diagnosing GI diseases using sound and ul-
trasound devices is very attractive because of their rela-
tively low manufacturing costs and non-invasiveness to
the human body. This paper reviewed the relevant re-
search on them in the past 20 years. With the advances in
device miniaturization and computing capacity, new di-
agnosing devices and associated methods evolve and are
being clinically tested. Intraluminal ultrasound has been
gradually accepted in the diagnosis of many GI diseases.
Sonic technologies, which are capable of revealing many
interesting features of the GI organs though, are still un-
der investigation. More understanding on the origins of
the abdominal sounds is needed. In the future, more pre-
cise sonic detection and analysis devices and methods are
expected for accurate diagnosis of GI diseases.
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ences and Engineering Research Council of Canada, and
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