Grand challenges in magnetic capsule endoscopy

Wireless capsule endoscopy (WCE) was introduced at the beginning of this century [1] as a technological revolution for comfortable, safe and easy explorations of the GI tract with a swallowable capsule-sized miniaturized camera [1–5]. The different endoscopic capsules available on the market nowadays [5] have opened up a new era for the diagnosis of small intestine diseases, where WCE currently shows its greatest potential [5]. In the other areas of the GI tube equally accessible to both WCE and probe endoscopy, the latter retains a superior diagnostic performance [2–5]. The major limitation of WCE is that the capsule movement is passive and random, as it is driven by visceral peristalsis and gravity. Owing to the lack of a controllable motion, the capsule cannot stop, tilt, turn or change direction, as would be required for detailed and localized inspections. This drawback is prone to limit the diagnostic efficacy. In addition, WCE does not allow for biopsies, local drug delivery, as well as air insufflation to distend the bowels. These limitations raise formidable challenges to make this technology truly alternative, rather than complementary, to probe endoscopy. These challenges are separately discussed below. The first grand challenge deals with robotic magnetic maneuvering. To provide WCE with controllable motion, a variety of solutions has been proposed, such as legged locomotion [6,7], paddling [8], inchworm or earthworm-like crawling [9–12] and swimming [13–15]. Despite the interest raised by such approaches [5], the state of the art reveals that none of them looks as promising as the use of an external magnetic field to steer a magnetically responsive capsule. Indeed, magnetic driving has become an area of intense research [16–25]. Even the two principal producers of endoscopic capsules (Given Imaging and Olympus) are currently experimenting with magnetic driving. Indeed, their most advanced prototype capsules have internal magnets and allow for image visualizations in real time, as required by magnetic manoeuvring [5,18,21–23,25]. The idea of magnetic driving is based on the interaction of two magnetic fields: one generated inside the capsule and another outside of it (external control system). The external field exerts a controllable torque and force on the capsule to actively guide it. The most effective and convenient configuration is such that a permanent magnet is used inside the capsule, while the external field is generated with electromagnetic coils. This allows for miniaturization and energy efficiency in the capsule and force control and high energy density in the external driving system. Magnetic driving has become highly ‘popular’ because of its simplicity and effectiveness; in contrast with any attempt to provide the capsule with internal mechanisms for autonomous locomotion, magnetic driving overcomes the inadequacy of conventional motor technologies to fit on board the capsule suitable amounts of Grand challenges in magnetic capsule endoscopy