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ROBOTICS continued
the PillCam and even high-resolution
endoscopy.”
The MGH imaging capsule uses opti-
cal frequency-domain imaging (OFDI)
technology developed at MGH: a near-
infrared laser beam sweeping from 1250
to 1380 nm is first sent to a beamsplitter,
where a small portion is captured by a
detector as the reference signal and the
rest is emitted as a focused, full-width
half-maximum, 30-µm-diameter beam
from an optical fiber tip (125 µm diam-
eter with 9 µm core) within the capsule
rotating at 20 Hz to illuminate an ap-
proximate 40 mm circumference sec-
tion of tissue surrounding the capsule.
The reflected signals from the tissue
(as a function of depth) are compared
to the reference signal and the differ-
ence is used to construct a microscop-
ic cross-section that is stacked together
with adjacent cross-sections as the cap-
sule moves to form a 3D image. Imaging
time for a 15 cm esophageal section with
30 µm (lateral) and 7 µm (axial) resolu-
tion takes only 58 seconds.
In addition to PillCam and the MGH
capsule, other commercially available
RCE devices include the EndoCapsule
from Olympus (Tokyo, Japan), the
MiRo capsule from IntroMedic (Seoul,
South Korea), and the OMOM capsule
from Jinshan Science and Technology
Group (Chongqing, China). 4 OMOM,
though slightly larger than PillCam at
27. 9 mm long and 13 mm in diame-
ter, offers an adjustable image format,
white-balance control, variable frame-
rate sampling frequency and illumina-
tion intensity, and automatic or man-
ual exposure.
Besides the ongoing imaging improve-
ments for RCEs, the InteliSite capsule
from Innovative Devices (Raleigh, NC),
the Enterion capsule from Phaeton
Research (Nottingham, England), and
the MAARS capsule from Matesy
(Jena, Germany) are also addressing
drug delivery and biopsy through var-
ious diffusion-based or spring-actuat-
ed methods. In their most recent work,
Vanderbilt University (Nashville, TN)
professors Robert J. Webster III and
Pietro Valdastri are attempting to over-
come one weakness of RCE compared
to traditional endoscopy, which is RCE’s
inability so far to “inflate” the gastro-
intestinal tract wirelessly—“wireless
insufflation”—to obtain better imag-
es of its normally folded surface. 5 To
date, their experiments with a capsule
that mixes potassium bicarbonate pow-
der with citric acid that escapes through
small holes in the 3D printed capsule
have been successful in generat-
ing the required carbon dioxide
to sufficiently insufflate a 5. 5 cm
diameter porcine colon.
Webster and Valdastri were
also part of a team from
Vanderbilt University and Scuola
Superiore Sant’Anna (Pisa, Italy)
that developed a truly robotic-looking imaging capsule with
physical appendages that was designed to crawl along the esophageal or gastrointestinal tract
(see Fig. 3). 6 Unfortunately, the
device development was short-lived: “Although the 12-legged
mechanics of our capsule—
comprised of more than 70 high-pre-cision components—enabled
high foot force [0.63 N average
propulsive force at each leg tip]
FIGURE 3. A “mesoscale legged locomotion”
design consisted of appendages to allow a robotic
capsule endoscope to traverse the esophageal
or gastrointestinal tract; unfortunately, it was not
successful and is being replaced by alternative
designs (Courtesy of Vanderbilt University and
Scuola Superiore Sant’Anna)
