Capsule endoscopy of the future: What's on the horizon?

Capsule endoscopes have evolved from passively moving diagnostic devices to actively moving systems with potential therapeutic capability. In this review, we will discuss the state of the art, define the current shortcomings of capsule endoscopy, and address research areas that aim to overcome said shortcomings. Developments in capsule mobility schemes are emphasized in this text, with magnetic actuation being the most promising endeavor. Research groups are working to integrate sensor data and fuse it with robotic control to outperform today's standard invasive procedures, but in a less intrusive manner. With recent advances in areas such as mobility, drug delivery, and therapeutics, we foresee a translation of interventional capsule technology from the bench-top to the clinical setting within the next 10 years

Autonomous Retroflexion of a Magnetic Flexible Endoscope

Retroflexion during colonoscopy is typically only practiced in the wider proximal and distal ends of the large intestine owing to the stiff nature of the colonoscope. This inability to examine the proximal side of the majority of colon folds contributes to today's suboptimal colorectal cancer detection rates. We have developed an algorithm for autonomous retroflexion of a flexible endoscope that is actuated magnetically from the tip. The magnetic wrench applied on the tip of the endoscope is optimized in real time with data from pose detection to compute motions of the actuating magnet. This is the first example of a completely autonomous maneuver by a magnetic endoscope for exploration of the gastrointestinal tract. The proposed approach was validated in plastic tubes of various diameters with a success rate of 98.8% for separation distances up to 50 mm. Additionally, a set of trials was conducted in an excised porcine colon observing a success rate of 100% with a mean time of 19.7 s. In terms of clinical safety, the maximum stress that is applied on the colon wall with our methodology is an order of magnitude below what would damage tissue

Laparoscopic Camera Based on an Orthogonal Magnet Arrangement

In this letter, we present for the first time a magnetic anchoring-actuation link with an auto-flip feature. This orthogonal magnetic arrangement relies on the placement of two permanent magnets such that their magnetic moments are respectfully orthogonal. Though the arrangement may have many applications, in this study we integrate it in a small factor magnetic camera for minimally invasive procedures. Upon insertion through a trocar incision, the 5.5 mm diameter and 35 mm length magnetic camera is coupled with an external robotic controller and displaced from the port thus preventing clutter of the surgical workspace. The device allows for manual lateral translation as well as robotically controlled tilt and pan, resulting in four degrees of freedom. The auto-flip feature prevents the need for image adjustment in software as the camera tilts through its hemispherical workspace. A static model that relates an input external control tilt and output camera tilt has been developed and validated. Favorable results during bench and canine cadaver evaluation suggest promise for the proposed magnetic camera to improve the state of art in minimally invasive surgical procedures

Sensorless Estimation of the Planar Distal Shape of a Tip-Actuated Endoscope

Traditional endoscopes consist of a flexible body and a steerable tip with therapeutic capability. Although prior endoscopes have relied on operator pushing for actuation, recent robotic concepts have relied on the application of a tip force for guidance. In such case, the body of the endoscope can be passive and compliant; however, the body can have significant effect on mechanics of motion and may require modeling. As the endoscope body's shape is often unknown, we have developed an estimation method to recover the approximate distal shape, local to the endoscope's tip, where the tip position and orientation are the only sensed parameters in the system. We leverage a planar dynamic model and extended Kalman filter to obtain a constant-curvature shape estimate of a magnetically guided endoscope. We validated this estimator in both dynamic simulations and on a physical platform. We then used this estimate in a feed-forward control scheme and demonstrated improved trajectory following. This methodology can enable the use of inverse-dynamic control for the tip-based actuation of an endoscope, without the need for shape sensing

Sensitivity Ellipsoids for Force Control of Magnetic Robots With Localization Uncertainty

The navigation of magnetic medical robots typically relies on localizing an actuated, intracorporeal, ferromagnetic body and back-computing a necessary field and gradient that would result in a desired wrench on the device. Uncertainty in this localization degrades the precision of force transmission. Reducing applied force uncertainty may enhance tasks such as in vivo navigation of miniature robots, actuation of magnetically guided catheters, tissue palpation, as well as simply ensuring a bound on forces applied on sensitive tissue. In this paper, we analyze the effects of localization noise on force uncertainty by using sensitivity ellipsoids of the magnetic force Jacobian and introduce an algorithm for uncertainty reduction. We validate the algorithm in both a simulation study and in a physical experiment. In simulation, we observe reductions in estimated force uncertainty by factors of up to 2.8 and 3.1 when using one and two actuating magnets, respectively. On a physical platform, we demonstrate a force uncertainty reduction by a factor of up to 2.5 as measured using an external sensor. Being the first consideration of force uncertainty resulting from noisy localization, this paper provides a strategy for investigators to minimize uncertainty in magnetic force transmission

Towards Recovering a Lost Degree of Freedom in Magnet-Driven Robotic Capsule Endoscopy

Flexible endoscopy, a procedure during which an operator pushes a semi-rigid endoscope through a patient’s gastrointestinal tract, has been the gold-standard screening method for colon cancer screening (colonoscopy) for over 50 years. Owing to the large amounts of tissue stress that result from the need for transmitting a force to the tip of the endoscope while the device wraps through the bowel, implementing a front-actuated endoscopy system has been a popular area of research [1]. The pursuit of such a concept was accelerated by the advent of ingestible capsule endoscopes, which, since then, have been augmented by researchers to include therapeutic capabilities, modalities for maneuverability, amongst other diagnostic functions [2]. One of the more common approaches investigated has been the use of magnetic fields to apply forces and torques to steer the tip of an endoscope [3]. Recent efforts in magnetic actuation have resulted in the use of robot manipulators with permanent magnets at their end effectors that are used to manipulate endoscopes with embedded permanent magnets. Recently, we implemented closed loop control of a tethered magnetic capsule by using real-time magnetic localization and the linearization of a magnetic wrench applied to the capsule by the actuating magnet [4]. This control was implemented in 2 degrees-of-freedom (DoF) in position (in the horizontal plane) and 2 DoF in orientation (panning and tilting). One DoF in position is lost owing to the tethered capsule being actuated in air and thus lacking a restoring force to counter the high field gradient. The 3rd orientation DoF is lost owing to the axial symmetry of the permanent magnet in the capsule; this prevents the application of torque in the axial direction and thus controlled roll and introduces a singularity in the capsule’s actuation. Although another dipole could be used to eliminate this singularity, this would complicate both the actuation and localization methods. In this manuscript, we consider the consequences of the embedded magnet (EM) being radially offset from the center of the capsule while being manipulated by an external actuating magnet (AM).We have developed a tethered capsule endoscope that contains a cylindrical EM (11.11 mm in length and diameter) with a residual flux density of 1.48 T that is offset by 1.85 mm from the center of the capsule; a distance that is less than 10% of the capsule diameter. Our investigation into the topic results from repeated observation of the capsule’s preference to align such that the internal magnet is closest to the actuating magnet (AM). The AM is a cylindrical magnet (101.6 mm in length and diameter) with a residual flux density of 1.48 T that is mounted at the end effector of a 6 DoF manipulator, as seen in Figure 1. In this manuscript, we evaluate the torqueing effects of the presence of this magnet offset with the goal of determining whether the torque effect is negligible, or impacts capsule motion and thus can potentially be used for the benefit of endoscope manipulation. A concept schematic of this effect is shown in Figure 2. A discussion of how to use this torque is beyond the scope of this manuscript. To the authors’ knowledge, the use of such concept in permanent-magnet based control has not been investigated