Konstantinos Triantafyllou, MD, PhD, FEBGH
Assistant Professor of Gastroenterology
Chrysoula Malli, MD
Hepatogastroenterology Unit, Second Department of Internal Medicine – Propaedeutic Research Institute and Diabetes Center, Medical School,
National and Kapodistrian University of Athens, ‘‘Attikon” University General Hospital
Advances in wireless technology offer innovative solutions for diagnostic and –potentially- therapeutic endoscopy. The development of capsule endoscopy allows the investigation of the gastrointestinal tract overcoming the limits of traditional instruments, more comfortably and less stressfully for the patient.
Nowadays, a variety of wireless endoscopes are available for the examination of the small and large bowel, of the lower esophagus, and (if magnetically guided) even of the stomach. However, we have not reached yet the ultimate targets of this technology: mini-robots for pan-endoscopy and interventional endoscopy. The major obstacles to achieving these goals are limited battery power, lack of capsule control and guidance through the digestive tract, accurate localization of the ingested device, enhancement of image quality, and development of biopsy and drug delivery systems.
Energy, energy, energy: the prerequisite to achieve the aforementioned goals. Today, the deliverable power supply to the capsules is about 25mW and it is estimated that future mini-robots will require more than 550mW to fulfill our expectations. Therefore, we must either increase power supply or develop new technology that requires minimum energy to perform the required tasks.
Many innovative solutions are under investigation ex-vivo to overcome the limited battery life of the commercially available capsules. Among them, the wireless power transmission technology that transfers power from a transmitter (outside of the body) to a receiver (within the capsule) in the form of electromagnetic waves based on inductive coupling is the most promising solution for the delivery of safe, stable, and sufficient energy. 1 While a portable transmitter has recently been developed, 2 issues such as misalignment between the transmitter and receiver magnetic fields and efficient power transmission through biological tissues need to be solved and successful testing in humans is pending. On the other hand, taking advantage of nanotechnology medicine, new miniature devices incorporated in capsules and new technologies like the field programmable gate array (FPGA) and the application-specific circuit (ASCI) are expected to consume less energy. Indeed, an ASCI based prototype micro-robot has been shown to consume less energy than the commercially available capsules. 3
The mobility, localization, and orientation of wireless capsules in the digestive tract are unpredictable and largely undetectable (the latter two), so far. The active locomotion systems under development are divided in those with internal (within the capsule), external, and mixed actuators. 4 Within the first group, friction force based mechanisms (worm-like, paddle/legged, crawler mobility) predominate; however, high energy requirements, “hostile” shape for the intestine, and capture of the majority of the endoscope space make their use questionable.
The future of the active locomotion of the wireless robot seems to be the magnet. External locomotion actuators take advantage of an external magnetic field coupled with a permanent magnet within the capsule to propel the device. 4 Perhaps a hybrid locomotion system that combines internal and external actuators may eventually prevail. 5 Currently research focuses on the development of a safe, low power consuming system that will offer proper endoscope velocity and ability to move backward - forwards and to stop under real time control. 4
Exact localization of the capsule endoscope in the digestive tract is of imperative importance for the accurate localization of the detected lesions and potential therapy application in real-time. The existing capsule route 2-D tracking softwares are inaccurate and their use is limited in clinical practice. Magnetic field strength-based and electromagnetic wave-based methods are currently under investigation to resolve the issue of device localization; the former giving promising results. However, none of these methods can provide information regarding the distance that the robot has traveled from a landmark (e.g. pylorus) to the detected lesion. 6 A device like OdoCapsule that incorporates a micro-motor system, consisting of three miniature legs, torsion springs, and wheels, promises accurate measurement of the distance from the duodenal bulb to areas with pathological findings. 7
Another challenge for active capsule endoscopes is to incorporate mechanisms that allow tissue sampling. Several prototypes have been tested ex vivo, but their clinical utility is limited by unprecise targeting, difficulty navigating to the target, and obtaining single sample capacity. Recently, the combination of a magnetically actuated soft capsule robot that has abilities for advanced functions (e.g. localized drug delivery) with self-folding microgrippers –which have already been used in vivo to obtain biopsy in pig’s bile duct- offers the next “sweet dream” option for accurate active biopsy capsule operation –albeit with many limitations. 8
The ultimate challenge for the future endoscopy robot is active drug delivery. The major problem to overcome is limited capsule space, where two principal mechanisms should be incorporated: an anchoring system to guide capsule positioning and a drug release mechanism to control the dose and the frequency of the released drug by remote actuation. Researchers have suggested mechanical systems using micro motors embedded in the capsule and a specific “legged” mechanism to attach the wall of the gastrointestinal tract. Magnetically actuated mechanisms have been tested to control the active drug release; however, a lot of work has to be done yet. 9 Part of this work has been incorporated in two European projects: the NEMO (Nano-based capsule Endoscopy with Molecular imaging and Optical biopsy) and the VECTOR (Versatile Endoscopic Capsule for gastrointestinal TumOr Recognition and therapy) design intending to create new capsules with therapeutic and diagnostic capabilities. 10
Regarding higher image resolution, the closest to our expectations prototype is a low energy ASCI model that supports light and autofluorescence imaging at 24 frames/sec, 400 x 400 (almost double the existing) image resolution, and an efficient image compressing module. The device has successfully been tested in pigs, however attenuation of the signal transmitted through biological tissues has still to be addressed. 3
In 1966 the original “Fantastic Voyage” movie was released. Today, Guillermo del Toro is in talks to remake the film where the miniaturized scientist will reach and treat the trauma of the scientist’s brain. Is the ideal future micro-robot still faraway 11 and how long is far? During the last five years major technological achievements have been accomplished in the field of endoscopic micro-robots, promising that the future of endoscopy is wireless, indeed!