24-01-2013, 04:26 PM
Capsule Endoscopy: From Current Achievements to Open Challenges
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Abstract—
Wireless capsule endoscopy (WCE) can be considered
an example of disruptive technology since it represents an
appealing alternative to traditional diagnostic techniques. This
technology enables inspection of the digestive system without
discomfort or need for sedation, thus preventing the risks of conventional
endoscopy, and has the potential of encouraging patients
to undergo gastrointestinal (GI) tract examinations. However,
currently available clinical products are passive devices whose
locomotion is driven by natural peristalsis, with the drawback of
failing to capture the images of important GI tract regions, since
the doctor is unable to control the capsule’s motion and orientation.
To address these limitations, many research groups are
working to develop active locomotion devices that allow capsule
endoscopy to be performed in a totally controlled manner. This
would enable the doctor to steer the capsule towards interesting
pathological areas and to accomplish medical tasks. This review
presents a research update on WCE and describes the state of the
art of the basic modules of current swallowable devices, together
with a perspective on WCE potential for screening, diagnostic,
and therapeutic endoscopic procedures.
Index Terms—Endoscopy of the gastrointestinal (GI) tract,medical
robots, passive and active locomotion capsule and vision, wireless
capsule endoscopy (WCE).
INTRODUCTION
I N 1868, G. and R. Schindler pioneered methodologies for
inspecting the mucosa of the gastrointestinal (GI) tract with
semi-flexible endoscopes, paving the way to the advent of endoscopic
procedures [1].
Nowadays, traditional endoscopic techniques enable effective
and reliable operation through different districts of the GI
apparatus, i.e., esophagus, stomach, large bowel or colon and
part of the small bowel, with diagnostic, therapeutic and surgical
capabilities [2]. Flexible endoscopes, which are introduced
into the oral or rectal orifices, consist of a steerable tip that orients
the device toward the regions of interest, by means of cable
actuation driven by an external control knob [3]. The rigidity
of the instrument, due to the presence of the actuation mechanism
running through the whole length of the instrument, and
Manuscript received June 13, 2011; revised September 06, 2011; accepted
Digital Object Identifier 10.1109/RBME.2011.2171182
its diameter (from 11 mm up to 13 mm for a standard colonoscope)
result in limited accessibility and make endoscopic procedures
significantly traumatic and poorly tolerated by patients
[4]. Pain or problems with sedation make patients quite reluctant
to undergo endoscopy and consistently limits the pervasiveness
of a potential mass screening campaign. On the other hand,
only mass screening could lead patients to periodically undergo
endoscopy with the benefit of discovering and treating asymptomatic
pathologies. A further medical drawback of flexible endoscopy
is that certain areas of the GI tract cannot be reached,
such as most of the small bowel [5].
camera pill for imaging of the entire GI tract. Limits in technologies
prevented the realization of a swallowable camera capsule,
although in the mid 1990s experimental trials were performed
on a larger prototype by P. Swain et al. [6].
In the recent past, the availability of low-power and lowcost
miniaturized image sensors based on complementary metal
oxide semiconductor (CMOS) technology, application-specific
integrated circuits (ASIC) andminiaturized light-emitted diodes
(LEDs) enabled the realization of swallowable wireless camera
pills. In fact, in 2000 Given Imaging Inc. (Yoqneam, Israel),
thanks to G. Iddan patents, introduced the wireless capsule endoscopy
(WCE) that entails the ingestion of a miniaturized pillsize
camera that navigates passively along the GI tract by means
of peristaltic contractions, thus visualizing the surrounding wall
[7]. WCE enables inspection of the digestive system without
discomfort or need for sedation, thus preventing the risks of
conventional endoscopy [8]. In this way,WCE has the potential
additional benefit of encouraging patients to undergo GI tract
examinations [9].
In 2003, PillCam SB (M2A capsule, Given Imaging Inc.) received
approval from the Food and Drug Administration (FDA)
and clearance to market capsule endoscopy for use in pediatric
patients aged 10 to 18 years, specifically designed for the diagnosis
of pathologies of the small bowel. The capsule, provided
with a CMOS camera, acquires two images per second
and has a battery life of approximately 8 hours [10], [11]. Initially
conceived for the investigation of the small bowel, WCE
is now spreading to other GI districts. In addition to the M2A
capsule, and exploiting similar technology, Given Imaging Inc.
produced double-head camera capsules for the inspection of
the esophagus (PillCam ESO, Given Imaging Inc.) and of the
colon (PillCam COLON, Given Imaging Inc.) [12], [13]. Up
until 2009, more than 750,000 patients had undergone WCE in
clinical trials, although the sensitivity of capsule endoscopy for
the detection of colonic lesions is still low compared to the use
of traditional colonoscopy [14].
Several other companies produce endoscopic capsules, such
as Olympus Inc. (EndoCapsule, Olympus Medical Systems
Corp., Tokyo, Japan), Chongqing Jinshan Science and Technology
(OMOM capsule, Chongqing Jinshan Science and
Technology, Chongqing, China) and Intromedic Co. (MiRo
capsule, Intromedic Co. Seoul, South Korea) [15].
AlthoughWCE has entered the medical scene as a disruptive
technology, it presents a number of limitations, e.g., the impossibility
to actively control capsule locomotion and camera orientation
which leads to low diagnostic specificity and to false-positive
results, mainly in the colonic tract. Therefore, the natural
evolution of WCE consists of integrating mechanisms for
active locomotion and also providing the capsule with microsensors
and micro-tools for diagnosis and therapy [16]–[18].
In this regard, many research centers and private companies
are exploiting mechatronic knowledge and background for the
enhancement of WCE capabilities, ranging from simple diagnostic
cameras to complete and autonomous diagnostic and therapeutic
robotic platforms.
SYSTEM ARCHITECTURE FOR ENDOSCOPIC CAPSULES
The human GI tract is composed of the esophagus, stomach,
small bowel and colon. The esophagus consists of a muscular
tube throughwhich food passes from the pharynx to the stomach
and is approximately 250 to 300mm long and 10 to 20mm large
in diameter. The stomach is located between the esophagus and
the small intestine. It is a deflected elastic cavity characterized
by a thick mucous membrane that secretes protein-digesting enzymes
and acids. The small intestine is an elastic lumen with
villi coating its internal surface; it is 30 to 40 mm in diameter
and is the longest portion of the GI tract (approximately 6.5 to
7.5 m in length). The last segment of the GI tract is the large
intestine or colon, that is about 1.6 m in length and 60 mm in
diameter [28]. Each segment of the GI tract is characterized by
different anatomical and physiological properties, thus leading
to different challenges for the design of endoscopic capsules.
A complete capsule platform comprises six primary modules:
locomotion, vision, telemetry, localization, power and diagnosis/
tissue manipulation tools (Fig. 1). However, most capsules
developed to date include a subset of the modules described
above, of primary importance due to space constraints.
Each miniature module represents an engineering challenge per
se, however, thanks to current technological progresses in microsystem
development, interface and integration, devices can
be designed that embed all these modules and that are able to
provide both diagnostic and treatment functionalities. Alternatively,
a possible solution may be to use several task-specific
capsules that operate independently or that are self-assembled
into a single operating system [19], [20]. The next sections illustrate
the different modules of an endoscopic capsule, with specific
focus on the locomotion module (Section II-A). In fact, locomotion
is the feature that distinguishes an uncontrolled probe
navigating in the bowel from a teleoperated miniature robot performing
diagnostic and surgical tasks.