Progress in Self-stabilizing Capsules for
Imaging of the Large Intestine
Dobromir Filip, orty Yadid-Pecht and Martin P. Mintchev
Abstract - This work reports on the progress and development
advances in the design of self-stabilizing capsules for imaging the
lower part of the gastro-intestinal tract, namely the large
intestine (the colon). Macro-level design is reviewed, and the new
miniaturized design and its
Preliminary performance results are discussed.
components are described.
Keywords - Capsule endoscopy, Gastrointestinal tract, Imaging,
Capsule-based imaging of gastrointestinal (GI) organs was
introduced in 1997 . Since then it has become the preferred
imaging modality in the small intestine due to its non
invasiveness and its capability to deliver important wireless
information via video imaging -. Usually it takes 8 to 24
hours for a video capsule endoscope (VCE) to traverse
through the entire GI tract as a result of its passive movement.
In view of the fact that the movement of these capsules is not
controlled, missing diagnosis is likely and extensive
observation of many interesting areas alongside the G I tract is
difficult, if not impossible. The application of VCE is
currently limited to small-lumen organs. In larger lumen
organs, such as stomach or the colon, the capsules tend to
tumble, which leads to incorrect recognition of a given organ
segment by the capsule imaging system, thus rendering them
unsuitable for use. Another problem that results from the
tumbling of a capsule is that the perceived dimensions of a
polyp or another lesion are widely influenced by the distance
between the capsule and the lesion. An innovative method of
imaging of the GI tract was proposed in . This method can
facilitate capsule-based imaging in the GI tract by enabling
imaging of large-lumen organs without the effects of
tumbling. The idea includes a capsule coating capable of
dissolving in the colon, hence enabling a permeable, swellable
container attached to the back of the imaging component to be
exposed. The expandable container swells at exposure to
colonic liquids and enables a stabilized structure with better
imaging capabilities. The device is equipped with all
components necessary for imaging and communication with
the outside world, namely an imaging component, an
illumination component, an RF transmitter, and batteries.
The macro-level design is described in Section 2. Sections 3
and 4 describe the test results, while Section 5 concludes the
current work and outlines the remaining challenges.
978-1-4244-8157-6/10/$26.00 ©2010 IEEE
II. MACRO-LEVEL DESIGN
The macro-level design consisted of an outer casing that
targeted the colon, an inner capsule endoscope, coupled to an
expandable stabilizing component comprising a liquid
permeable sac filled with dry superabsorbent polymer granules
Fig. I. Fully expanded self-stabilizing capsule endoscope
The outer casing was made of the colon targeting agent
Eudragit (Evonik Industries - Pharma Polymers, Piscataway,
New Jersey, USA), a coating resistant to gastric acid that
dissolves only in the intestinal tract at a pH between 6.5 and 7
. Thus, when the capsule reaches the colon, this outer shell
breaks and allows the superabsorbent polymer granules placed
within a knitted, permeable polyglycolic acid (PGA), mesh
like container attached to the end of the capsule to expand.
Simultaneously, a moisture switch placed on the surface of the
capsule activates the electronics inside the capsule, turning on
the device. The expansion is completed relatively quickly,
thus allowing quality imaging of the colon. The expanded
container touches the walls of the colon and stabilizes the
capsule precluding it from tumbling.
As a safety measure, once the expandable component has
been activated it can be electronically separated from the
capsule at any time using a specially designed wirelessly
controlled mechanism. The expandable component is attached
very tightly to the capsule using PGA (USP 6-0) absorbable
suture (Ethicon, Inc. in Somerville, NJ, USA). This separation
safety mechanism comprises of a micro-heater which activates
the heating of a filament in the presence of a magnetic field.
The heating filament reaches a suitable local temperature to
melt the PGA suture (:::: : 220 'C) when a current passes through
it, which separates the capsule away from the expandable
material leaving open the PGA mesh while the temperature of
the shell of the capsule does not change by more than 0.2 'c.
The natural peristaltic movement of the colon completes the
separation of the expandable component from the VCE. The
expandable component is biocompatible and is able to
disintegrate in the Gl tract after a certain period of time.
III. PROPOSED SPECIFIC DESIGN
Presently, we have designed a 1: 1 prototype of this self
stabilizing VCE. The complete block diagram of the proposed
miniature self-stabilizing wireless
prototype is shown on Figure 2.
Fig. 2. Wireless Endoscopic Capsule Prototype. I - External capsule (outer
casing), 2 - optical dome , 3 - longitudinally positioned CMOS color camera,
4 - Illumination system (LEDs), 5 - transmitter/antenna, 6 - battery, 7 -
micro-heater, 8 - tapered cylinder, 9 - sealable lid, 10 - expandable
This design consists of an outer casing, inner capsule, and
expandable component. The inner capsule is comprised of a
CMOS camera, RF transmitter, light emitting diodes (LEOs),
magnetic switch and a micro-heater. After the expandable
component has been activated it can be electronically detached
from the capsule at the operator's command by magnetically
enabling the fast-reacting micro-heater.
For the initial prototype model, the outer casing is a hard
shell gelatin capsule from Torpac, Inc. (Fairfield, NJ,
USA) which dissolves very rapidly (2-4 minutes) in water.
This capsule is sized for animal testing, and with the design
limitations in mind, a capsule of size #13 (1/8 oz. 3.2 ml) was
chosen. The gelatin capsule provides adequate space for the
inner capsule containing the electronics and the expandable
component. In the present prototype, the emphasis is on
demonstrating stabilization and separation, and the testing
assumes that the outer casing has reached the targeted organ.
The colon targeting agent EUDRAGIT® FS 30 0  (Evonik
Industries - Pharma Polymers, Piscataway, New Jersey, USA)
was considered for the final application, but further study is
B. Inner Capsule
The inner capsule must protect the internal components
from conditions inside the patient's body. It is composed of
three parts, a tapered cylinder, an optical dome window, and a
sealable cap. The shape of the capsule is specially designed to
enable the increase in volume of the expandable material. The
dimensions of the capsule were determined to allow it to fit
inside the outer casing (Torpac #13 3.2 ml), and leave enough
space for the 1.5 ml of expandable component required for the
stabilization. Fig. 3 shows the designed inner capsule in
comparison with the commercially available P ill cam ™ Colon
capsule (Given Imaging Ltd, Yoqnem, Israel).
Fig. 3. I: 1 Prototype compared to a commercial capsule endoscope
Electronics Inside the Capsule
/) CMOS imager:
The proposed design has a CMOS imager which captures
images of the colon walls and also suits the space constraint in
the capsule. At the front of the camera is a short focal-length
lens (0.77mm/f 3.0 <110°» that is focused at the optical dome
and a few centimeters beyond, so that the bowel laying against
the optical dome would be in focus. This optical arrangement
allows the tissue to be in focus even if it is in a close contact
with the optical dome window, but also to remain in focus
over a few centimeters if the lumen opens. This CMOS imager
employs a wide-angle field of view which alone does not
significantly improve miss rates, but permits more efficient
examination of the large intestine. The selected image sensor
for the prototype is the 1/18" Color CMOS camera MO-B802-
105 (RF-LINKS, Toronto, Ontario, Canada).
operates at 3V, 18-19mA, its minimum required illumination
is 2Lux at fl.2, and number of effective pixels is 320x240
2) Video Transmitter:
There are several critical requirements for the transmitter in
the capsule endoscope, including size, power consumption and
data rate. The hardware needs to be robust in order to
withstand the knocks and bumps of normal human body
movement. The transmitter layout complements the other
electronic components, making the most out of the small space
inside the inner capsule. In order to transmit the diagnostic
real-time high-resolution image data at high speed and
because of the effect of human body tissue on antenna
propagation characteristics, the transmission frequency may
slightly shift during operation . Thus, a wide-bandwidth,
higher transmission frequency needs to be employed along
with a tunable receiver. With CMOS technology, the output
frequency typically increases as the physical size diminishes.
Among the industrial, scientific,
frequencies, 1.9 GHz is frequently used for transmission, and
and medical (ISM)
the smallest transmitters that are commercially available
operate in this range. The selected transmitter DX-5A (RF
LINKS, Toronto, Ontario, Canada) operates at 19S0MHz
(channel frequency), draws SmA from a 3V source, and its
power output is less than 1mW. This transmitter is ultra small
(4.Sx5.5x1.2mm), ultra low weight (O.lg), tunable in gain and
is capable of transmitting an NTSC signal. The frequency
stability of this RF transmitter is ± 250 KHz. It has hardwired
antenna. The capsule travels passively in the GI tract, and
therefore is randomly oriented. Thus, the direction of
transmission radiation is uncontrolled, and to detect the
transmitted signal independently of the transmitter position,
the antenna is required to emit an omni-directional radiation
3) External Video Receiver:
The external receiver records images received from the in
vivo sensing device into
simultaneously processes and displays images on a PC
display, while the sensing device is inside the patient's body.
This small receiver can monitor the 1900-2100 MHz video
bandwidth and the frequency is controlled in 0.25 MHz steps,
which is entirely sufficient for stable real time recording and
display of the results. In addition, the receiver has built-in a
special Automatic Frequency Tuning (AFT) control function
for best stability.
its digital memory, and
4) Illumination System:
The challenge in developing an illumination system for a
capsule endoscope is obtaining a uniform illumination  on
the observed object. Four white flat-top, wide-angle, surface
mount LEDs were utilized to minimize the space volume and
the current draw, while still providing adequate illumination to
cover a l70-degrees range. The Nichia NSSW156T LEDs
(NICHIA Corporation, Tokyo, Japan) were selected based on
their luminous intensity, viewing angle, and dimensions
(3.0x1.4xO.Smm). The experimental luminous intensity of a
single LED is above l30 mcd at a forward current of 1mA.
This provides sufficient illumination for the CMOS imager to
clearly view an image in the large intestine when the four
white LEDs are circumferentially positioned at the camera
side end of the capsule. To be effective, the illumination needs
to provide an adequate amount of uniform light and to come
from the correct angle, so as to avoid shadow effects.
5) Power Supply:
Since there are only certain types of batteries commercially
available that can fit in the limited space of the capsule, the
power supply needs to be designed very efficiently. The CR
1I3N battery (Duracell Canada Inc, Mississauga, Ontario,
Canada) provides enough continuous current to allow for
reliable operation of all electronics inside the capsule. The
operational voltage, continuous discharge current, and small
dimensions were deciding factors when selecting the power
supply. Another important parameter to consider was the
internal resistance since the battery must provide enough
continuous discharge current of 30mA for the electronics and
simultaneously. The lower the internal resistance, the less
restriction the battery encounters in delivering the needed
power spikes. Using a DC load test the internal resistance was
measured to be in range of 250 mOhms.
msec/SOmA pulses to trigger the micro-heater
The expandable material should be able to deform under
pressure but regain its original shape when the pressure is
removed. The expanded implement should also maintain its
consistency and not change state under the influence of water
or colonic fluids. The overall expansion time should be very
short «1 min). The materials that had the desired properties
were categorized according to the preferred mechanism of
expansion, osmosis (release of potential energy). Osmosis has
proven to be effective in several medical applications such as
stents that help relieve pathological obstruction of tubular
structures in vascular, urologic and GI systems, as well as in
self-expanding prostheses . The availability of stent
structures that can resist the peristaltic motion in the colon
without them moving is indicative that osmosis is the
preferred mechanism for the proposed apparatus . The
material used in this design are salt granules of hydrophyllic,
non-toxic, crosslinked polyacrylate polymer (Favor PAC,
Evonik Industries, Essen, Germany). These granules can
absorb several hundred times their weight in water, but cannot
dissolve because of their three-dimensional polymeric network
structure. The use of this super-absorbent polymer as an
expandable material for this device can be justified by its
ability to: be biocompatible; swell extensively; swell in a
relatively short period of time; exert a reasonable swelling
pressure on the walls of the lumen; and withstand the pressure
in the colon by remaining attached to the imaging component
while keeping its consistency. Thus, the expandable portion
consists of two components, the Favor PAC granules and a
custom-made, knitted PGA-based mesh. The Favor PAC
granules within this previously collapsed permeable PGA
mesh expand upon contact with fluids, serving as their
container. The faster the expansion, the faster the imaging
capsule would be stabilized in the colon, allowing quality
imaging of the organ as soon as the capsule enters the cecum.
The pressure exerted upon expansion on the walls of the colon
should not be harmful. The colon wall of the human body can
bear ""'7.71 pound-force/square inch .
IV. LABORATORY TESTING
Laboratory testing included comparing the image quality
between the stabilized and unstabilized capsules.
Methodologv: A transparent acrylic tube with a 4.5 cm
diameter, and 90 cm length, was sealed at one end, filled with
water/oil (approximately 1.5 1), and the capsule was let to fall
down its entire length. Agitation of the cylinder was delivered
manually, with a displacement of 12 cm from the centre of the
tube, at a frequency of approximately one back and forth
oscillation per second. A scaled paper grid was placed on the
floor below the center of the acrylic tube for the purpose of
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amplitude control while agitation of the tube was performed.
The stabilized capsule was dropped down the tube while
agitating it, with the intention of recording as lengthy trials as
possible. This was repeated with the unstabilized capsule,
using both water and canola oil as the medium in the tube to
reduce the speed at which the capsule fell, and to enable more
consistent video comparison. The improvement of video
stabilization was quantified using optical flow evaluation
provided by the software package Syntheyes Camera Tracker
(Andersson Technologies LLC, Malvern, PA, USA). Optical
tracking is used to monitor spatial and temporal changes in an
object during a video sequence, including its presence,
position, size, shape, etc. This is accomplished by solving the
temporal correspondence problem, which essentially boils
down to matching the target region in successive frames of a
sequence of images taken at closely-spaced time intervals
Tvpe of data collected: Estimated average pixel tracker motion
trajectory (optical flow), maximum tracker rate of change for
subsequent images, average radius movement of the capsule
endoscope relative to the centroid of the tube, average number
of tumbles for stabilized and unstabilized capsule endoscopes.
Observations: There were 10 video footages for both the
stabilized and the unstabilized cases. The centroid of the
cylinder was chosen as a tracking object. This is simply
because if the center of the capsule where the camera is
located (viewing angle 110°) is aligned within the center of
this tube, it is impossible to miss any important areas as the
capsule sweeps along the walls of the cylinder.
The average optical flow trajectory for the stabilized
capsule was measured to be 900.42±36.02 pixels whereas for
the unstabilized one it was in the range of 3214.58±48.20
pixels. This shows a major difference in average optical flow
trajectories and proves the stabilization concept. Additionally,
the stabilized capsule did not lose visual contact with the
centroid of the cylinder during the transit.
The maximum tracker rate of change for subsequent images
was measured to be 71.32±28.70 pixels/second for the
stabilized case while the unstabilized has shown 351.02±64.09
pixels/second. It can be clearly seen that the average pixel
movement for subsequent frames of a chosen tracked object
acquired for the stabilized capsule was much smaller than for
the unstabilized one. The stabilized capsule showed
significantly greater average improvement in the optical flow
tracking of its recorded video, versus the unstabilized capsule.
The average radius movement of the designed capsule
endoscope relative to the centroid of the cylinder was
69.72±24.26 pixels for the stabilized capsule and 90.54±42.71
pixels for the unstabilized capsule. This shows that on the
average, the centroid of the cylinder moved away much less
from the center of the camera for the stabilized capsule.
At no time in this testing the stabilized capsule tumbled
within the acrylic tube. The simple reason for this was that
both the combined length of the capsule and the stabilization
mechanism exceeded the diameter of the tube. Because the
connection between the two was rigid, the completed
assembly was unable to deform, and tumbling within the
acrylic tube became a geometric impossibility. Results from
this test evidently demonstrated the effectiveness of the
Progress in the design and implementation of self
stabilizing capsules for colon imaging was reported.
Challenges were discussed, and improvement in the optical
flow tracking of our new stabilized capsule design, compared
to an unstabilized one was shown. The proposed device can
be used in the screening of large-lumen organs and has the
ability to greatly improve GI diagnostics. Animal testing of
the proposed approach are ongoing.
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