Acoustic and Intraluminal Ultrasonic Technologies in the Diagnosis of Diseases in Gastrointestinal Tract: A Review

doi:10.4236/eng.2013.55B015

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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

Email: *[email protected]

Received 2013

ABSTRACT

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

1. Introduction

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 [1] 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 [2],

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 [3].

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

[6].

The introduction of the electronic stethoscope allowed

amplification of the weak body sound signals [7]. 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 [8]. 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 [8].

Campbell et al [9] 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.

*Corresponding author.

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 [10] 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

sounds.

Later studies tried to correlate bowel sounds related to

drug-induced episodes with simultaneous manometry

findings. Tomomasa et al [11] 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 [12] 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

sound alterations.

Dimoulas et al [13,14] proposed prolonged abdominal

sound monitoring and processing using a wavelet-based

method [13] and time-frequency features [14]. 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 [16] 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 [15] 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

controls.

3. Intraluminal Ultrasonic Technology

3.1. Principle of Intraluminal Ultrasonic

Technology

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 [21].

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 [33].

3.2. Instrumentation on Intraluminal Ultrasonic

Technology

Depending on the direction of the image formed, in-

traluminal ultrasonic devices can be divided into two

types: radial and curvilinear [21]. 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 [29]. 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 [29]. Although such images are difficult to in-

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 [29]. 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 [34].

3.3. Ultrasonic Applications for GI Disorders

Mittal et al [21] 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 [28].

Studies have shown that imaging can measure esophag-

eal cross-sectional area (CSA) distensions during liquid

GER episodes [25].

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

[35]. 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 [28].

Ultrasound has been greatly applied for diagnosing

malignant gastric disorders [29], ultrasound has added

greatly to the staging of gastric cancers, especially when

the cancers are limited to the mucosa level [29]. 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 [29].

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 [33].

In the past two decades, studies have shown that in-

traluminal ultrasound is consistently accurate in staging

rectal cancers, especially those in early stages [31],

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 [32].

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.

5. Acknowledgements

This study was sponsored in part by the National Sci-

ences and Engineering Research Council of Canada, and

by the Gastrointestinal Motility Laboratory, Faculty of

Medicine, University of Alberta, Edmonton, Alberta,

Canada.

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