Quantitative assessment of colorectal morphology: Implications for robotic colonoscopy

Experimental Measurements of the Length of the Human Colon: A Systematic Review and Meta-Analysis

PURPOSE

Knowledge of the length of the colon is relevant to understanding physiological and pathological function. It also has implications for diagnostic and clinical interventions, as well as for the design of delayed-release drug formulations and drug disposition modeling.

METHODS

Over the years, a range of different experimental methods have been employed to assess colon length. These methods vary from direct measurements on cadavers and during intraoperative procedures to measurements obtained from endoscopic and medical imaging techniques. However, no systematic review or meta-analysis of these findings has yet been carried out. In this systematic review, we identified 31 published experimental studies that measured the length of the human colon and/or its segments.

RESULTS

We synthesized the available data, comprising colon length measurements from 5741 adults and 337 children and young people, in a meta-analysis. The data contribute to our understanding of colon morphology and may have implications for clinical practice, particularly for colonoscopy and preoperative planning of surgical resections. Additionally, this review provides potential insights into anatomical correlates of functional diseases, such as constipation.

CONCLUSIONS

This review highlights that non-invasive, non-destructive diagnostic imaging techniques, such as magnetic resonance imaging (MRI), can provide more physiologically relevant measurements of colon length. However, there is a need for more standardized measurement protocols and for additional pediatric data.

The adult large bowel: describing environment morphology for effective biomedical device development

An understanding of the biological environment, and in particular the physical morphology, is crucial for those developing medical devices and software applications. It not only informs appropriate design inputs, but provides the opportunity to evaluate outputs via virtual or synthetic models before investing in costly clinical investigations. The large bowel is a pertinent example, having a major demand for effective technological solutions to clinical unmet needs. Despite numerous efforts in this area, there remains a paucity of accurate and reliable data in literature. This work reviews what is available, including both processed datasets and raw medical images, before providing a comprehensive quantitative description of the environment for biomedical engineers in this and related regions of the body. Computed tomography images from 75 patients, and a blend of different mathematical and computational methods, are used to calculate and define several crucial metrics, including: a typical adult size (abdominal girth) and abdominal shape, location (or depth) of the bowel inside the abdomen, large bowel length, lumen diameter, flexure number and characteristics, volume and anatomical tortuosity. These metrics are reviewed and defined by both gender and body posture, as well as-wherever possible-being spilt into the various anatomical regions of the large bowel. The resulting data can be used to describe a realistic 'average' adult large bowel environment and so drive both design specifications and high fidelity test environments.

MorphGI: A Self-Propelling Soft Robotic Endoscope Through Morphing Shape

Colonoscopy is currently the best method for detecting bowel cancer, but fundamental design and construction have not changed significantly in decades. Conventional colonoscope (CC) is difficult to maneuver and can lead to pain with a risk of damaging the bowel due to its rigidity. We present the MorphGI, a robotic endoscope system that is self-propelling and made of soft material, thus easy to operate and inherently safe to patient. After verifying kinematic control of the distal bending segment, the system was evaluated in: a benchtop colon simulator, using multiple colon configurations; a colon simulator with force sensors; and surgically removed pig colon tissue. In the colon simulator, the MorphGI completed a colonoscopy in an average of 10.84 min. The MorphGI showed an average of 77% and 62% reduction in peak forces compared to a CC in high- and low-stiffness modes, respectively. Self-propulsion was demonstrated in the excised tissue test but not in the live pig test, due to anatomical differences between pig and human colons. This work demonstrates the core features of MorphGI.

A Tension Sensor Array for Cable-Driven Surgical Robots

Tendon-sheath structures are commonly utilized to drive surgical robots due to their compact size, flexibility, and straightforward controllability. However, long-distance cable tension estimation poses a significant challenge due to its frictional characteristics affected by complicated factors. This paper proposes a miniature tension sensor array for an endoscopic cable-driven parallel robot, aiming to integrate sensors into the distal end of long and flexible surgical instruments to sense cable tension and alleviate friction between the tendon and sheath. The sensor array, mounted at the distal end of the robot, boasts the advantages of a small size (16 mm outer diameter) and reduced frictional impact. A force compensation strategy was presented and verified on a platform with a single cable and subsequently implemented on the robot. The robot demonstrated good performance in a series of palpation tests, exhibiting a 0.173 N average error in force estimation and a 0.213 N root-mean-square error. In blind tests, all ten participants were able to differentiate between silicone pads with varying hardness through force feedback provided by a haptic device.

Morphometric analysis and tortuosity typing of the large intestine segments on computed tomography colonography with artificial intelligence

Background

Morphological properties such as length and tortuosity of the large intestine segments play important roles, especially in interventional procedures like colonoscopy.

Objective

Using computed tomography (CT) colonoscopy images, this study aimed to examine the morphological features of the colon's anatomical sections and investigate the relationship of these sections with each other or with age groups. The shapes of the transverse colon were analyzed using artificial intelligence.

Methods

The study was conducted as a two- and three-dimensional examination of CT colonography images of people between 40 and 80 years old, which were obtained retrospectively. An artificial intelligence algorithm (YOLOv8) was used for shape detection on 3D colon images.

Results

160 people with a mean age of 89 men and 71 women included in the study were 57.79±8.55 and 56.55±6.60, respectively, and there was no statistically significant difference (p= 0.24). The total colon length was 166.11±25.07 cm for men and 158.73±21.92 cm for women, with no significant difference between groups (p=0.12). As a result of the training of the model Precision, Recall, and Mean Average Precision (mAP) were found to be 0.8578, 0.7940, and 0.9142, respectively.

Conclusion

The study highlights the importance of understanding the type and morphology of the large intestine for accurate interpretation of CT colonography results and effective clinical management of patients with suspected large intestine abnormalities. Furthermore, this study showed that 88.57% of the images in the test data set were detected correctly and that AI can play an important role in colon typing.

"Flexures and bends of the large intestine: Current terminology and a suggestion to simplify it"

There are a number of inconsistencies in the description of the bends of the colon down to the anus. This is historically based on the fact that anatomists saw the colon in its position in the abdominal cavity down to the pelvis and thus from the "outside" and also described it in this way. This view is still useful in clinical practice today (e.g. for the abdominal surgeons). For the greater part of clinicians, however, the view has shifted due to modern endoscopy. This allows examiners to see the terminal section of the intestine and the colon from the "inside". To accommodate both "ways of looking" in terms of modern medicine, we have been guided by today's clinical needs, and here we attempt to reconcile these with the historically evolved anatomical terms to create a nomenclature that meets all the needs of students, anatomists and clinicians looking at the large intestine from the inside and outside. With this in mind, we propose to speak of colic flexures (right colic flexure = RCF = hepatic flexure, flexura coli sinistra; left colic flexure = LCF = splenic flexure, flexura coli dextra; descending-sigmoid flexure = DSF; sigmoid-rectum flexure = SRF) for the colon (colon). For the rectum (rectum), we suggest the term bend (superior, intermediate and inferior) when viewed in the frontal plane, the term curvature (sacral curvature; anorectal curvature = perineal curvature) when viewed in the sagittal plane.

Acute colonic flexures: the basis for developing an artificial intelligence-based tool for predicting the course of colonoscopy

Tortuosity of the colon is an important parameter for predicting the course of colonoscopy. Computed tomography scans of the abdominal cavity were performed in 224 (94 female, 130 male) adult subjects. The number of acute (angle not exceeding 90°) bends between adjacent colonic segments was noted and analyzed. Data were analyzed for correlation with gender, age, height and weight. An artificial intelligence algorithm was proposed to predict the course of colonoscopy. We determined the number of acute flexions in females to be 9.74 ± 2.5 (min-max: 4-15) and in males to be 8.7 ± 2.75 (min-max: 4-20). In addition, more acute flexions were found in women than in men and in older women (after 60 years) and men (after 80 years) than in younger ones. We found the greatest variability in the number of acute flexures in the sigmoid colon (0-9), but no correlation was found between the number of acute flexures and age, gender, height or BMI. In the transverse colon, older and female subjects had more flexures than younger and male subjects, respectively. Older subjects had more acute flexures in the descending colon than younger subjects. There are opportunities to use the number of acute flexures (4-7, 8-12, more than 12 flexures) to classify patients into appropriate risk categories for future incomplete colonoscopy. On this basis, we predicted troublesome colonoscopies in 14.9% female and in 6.1% male subjects.

A Soft Robotic Balloon Endoscope for Airway Procedures

Soft robots can provide advantages for medical interventions given their low cost and their ability to change shape and safely apply forces to tissue. This article explores the potential for their use for endoscopically-guided balloon dilation procedures in the airways. A scalable robot design based on balloon catheter technology is proposed, which is composed of five balloons together with a tip-mounted camera and LED. Its design parameters are optimized with respect to the clinical requirements associated with balloon dilation procedures in the trachea and bronchi. Possessing a lumen to allow for respiration and powered by the pressure and vacuum sources found in a clinical procedure room, the robot is teleoperated through the airways using a game controller and real-time video from the tip-mounted camera. The robot design includes proximal and distal bracing balloons that expand radially to produce traction forces. The distal bracing balloon is also used to perform balloon dilation. Three actuation balloons, located between the bracing balloons, produce elongation and bending of the robot body to enable locomotion and turning. An analysis of the actuation balloons, which incorporate helical coils to prevent radial collapse, provides design formulas by relating geometric parameters to such performance criteria as maximum change in actuator length and maximum robot bending angle. Experimental evaluation of a prototype robot inside rigid plastic tubes and ex vivo porcine airways is used to demonstrate the potential of the approach.

Robotic Autonomy for Magnetic Endoscope Biopsy

Magnetically actuated endoscopes are currently transitioning in to clinical use for procedures such as colonoscopy, presenting numerous benefits over their conventional counterparts. Intelligent and easy-to-use control strategies are an essential part of their clinical effectiveness due to the un-intuitive nature of magnetic field interaction. However, work on developing intelligent control for these devices has mainly been focused on general purpose endoscope navigation. In this work, we investigate the use of autonomous robotic control for magnetic colonoscope intervention via biopsy, another major component of clinical viability. We have developed control strategies with varying levels of robotic autonomy, including semi-autonomous routines for identifying and performing targeted biopsy, as well as random quadrant biopsy. We present and compare the performance of these approaches to magnetic endoscope biopsy against the use of a standard flexible endoscope on bench-top using a colonoscopy training simulator and silicone colon model. The semi-autonomous routines for targeted and random quadrant biopsy were shown to reduce user workload with comparable times to using a standard flexible endoscope.

A Novel Inchworm-Inspired Soft Robotic Colonoscope Based on a Rubber Bellows

Colorectal cancer is a serious threat to human health. Colonoscopy is the most effective procedure for the inspection of colorectal cancer. However, traditional colonoscopy may cause pain, which can lead to the patient’s fear of colonoscopy. The use of active-motion colonoscopy robots is expected to replace traditional colonoscopy procedures for colorectal cancer screening, without causing pain to patients. This paper proposes an inchworm-like soft colonoscopy robot based on a rubber spring. The motion mechanism of the robot consists of two anchoring units and an elongation unit. The elongation unit of the robot is driven by 3 cables during contraction and by its inherent elasticity during extension. The balloon is selected as the anchoring mechanism of the robot. It has soft contact with the colon and will not damage the colon wall, which means no discomfort is caused. The elastic force test of the rubber spring shows that the elongation unit of the robot has sufficient restorative force to drive the robot to move forward and backward. The influence of the balloon’s expansion size on the dexterity of the robot head is analyzed, and the functions of the balloons are expounded. The balloon can not only assist the robot in its locomotion but also assist the robot to perform a better inspection. The robot can move successfully in a horizontal, straight, and inclined isolated pig colon, showing great clinical application potential.

Endorobots for Colonoscopy: Design Challenges and Available Technologies

Colorectal cancer (CRC) is the second most common cause of cancer death worldwide, after lung cancer (Sung et al., 2021). Early stage detection is key to increase the survival rate. Colonoscopy remains to be the gold standard procedure due to its dual capability to optically inspect the entire colonic mucosa and to perform interventional procedures at the same time. However, this causes pain and discomfort, whereby it requires sedation or anaesthesia of the patient. It is a difficult procedure to perform that can cause damage to the colonic wall in some cases. Development of new technologies aims to overcome the current limitations on colonoscopy by using advancements in endorobotics research. The design of these advanced medical devices is challenging because of the limited space of the lumen, the contorted shape, and the long tract of the large bowel. The force applied to the colonic wall needs to be controlled to avoid collateral effects such as injuries to the colonic mucosa and pain during the procedure. This article discusses the current challenges in the colonoscopy procedure, the available locomotion technologies for endorobots used in colonoscopy at a prototype level and the commercial products available.

EXPERIMENTAL ASSESSMENT OF INTACT COLON DEFORMATION UNDER LOCAL FORCES APPLIED BY MAGNETIC CAPSULE ENDOSCOPES

Magnetically guided capsule endoscopy is a promising technology for clinical application. A platform that simulates the magnetic capsule endoscope system is built to study the deformation process of the colon when its lumen suffers local forces. Force-displacement curves of the porcine large intestine under various experiment conditions, including different loading positions (haustra or taeniae coli), loading directions, colon inner pressures and specimen lengths, were measured to analyze the mechanical behavior of the intact large intestine during interactions with magnetic capsule endoscopes. In the practical application of the magnetic capsule endoscope, these data are imperative to optimize the control scheme and reduce operation risks. Based on our experiments, the taeniae coli of the intact large intestine show higher linear stiffness than the haustra, and inflation reduces the linear stiffness of the colon. Magnetic capsule with small edge radii can more easily damage or even perforate the colon. Based on our test results, we suggest that the force applied to the colon should be limited to below 17[Formula: see text]N when the capsule is actuated forward along the colon and limited to below 10[Formula: see text]N when the capsule is vertical to the colon during lesion screening.

Soft Robotics in Minimally Invasive Surgery

Soft robotic devices have desirable traits for applications in minimally invasive surgery (MIS), but many interdisciplinary challenges remain unsolved. To understand current technologies, we carried out a keyword search using the Web of Science and Scopus databases, applied inclusion and exclusion criteria, and compared several characteristics of the soft robotic devices for MIS in the resulting articles. There was low diversity in the device designs and a wide-ranging level of detail regarding their capabilities. We propose a standardized comparison methodology to characterize soft robotics for various MIS applications, which will aid designers producing the next generation of devices.

A Soft Pneumatic Inchworm Double balloon (SPID) for colonoscopy

The design of a smart robot for colonoscopy is challenging because of the limited available space, slippery internal surfaces, and tortuous 3D shape of the human colon. Locomotion forces applied by an endoscopic robot may damage the colonic wall and/or cause pain and discomfort to patients. This study reports a Soft Pneumatic Inchworm Double balloon (SPID) mini-robot for colonoscopy consisting of two balloons connected by a 3 degrees of freedom soft pneumatic actuator. SPID has an external diameter of 18 mm, a total length of 60 mm, and weighs 10 g. The balloons provide anchorage into the colonic wall for a bio-inspired inchworm locomotion. The proposed design reduces the pressure applied to the colonic wall and consequently pain and discomfort during the procedure. The mini-robot has been tested in a deformable plastic colon phantom of similar shape and dimensions to the human anatomy, exhibiting efficient locomotion by its ability to deform and negotiate flexures and bends. The mini-robot is made of elastomer and constructed from 3D printed components, hence with low production costs essential for a disposable device.

The large intestine from fetal period to adulthood and its impact on the course of colonoscopy

The human large intestine in the living adult has a total length of about 1300 mm, ranging from 1100 to 2108 mm. The development of the gut continues after birth, up to the age 4-5. The large intestine ascends at the beginning in the right abdominal quadrant, then it traverses the abdominal cavity, and finally it descends to the anus. The left and right colic flexures are the basic flexions between the transverse, ascending and descending colon, respectively. Additionally, there are secondary bendings between intestinal segments. The angles between the neighbouring parts can vary between examined subjects. Most of the angulations can be found in the transverse (range 2-9) and sigmoid colon (range 1-9), making them the most troublesome parts to pass with a colonoscope. Colonoscopy (usually performed in the left lateral or supine position) is one of the most important examination of the large intestine mucus membrane. During this procedure the endoscope is passed through the colon into the cecum or terminal ilium. The individual anatomical features (tortuosity, supernumerary loops and elongation) may slow down or interfere with the progress of the scope. We summarize current knowledge on the human large intestine from the fetal period to adulthood and carve out some aspects that are currently less known to colonoscopists.

Magnetic Levitation for Soft-Tethered Capsule Colonoscopy Actuated With a Single Permanent Magnet: A Dynamic Control Approach

The present letter investigates a novel control approach for magnetically driven soft-tethered capsules for colonoscopy-a potentially painless approach for colon inspection. The focus of this work is on a class of devices composed of a magnetic capsule endoscope actuated by a single external permanent magnet. Actuation is achieved by manipulating the external magnet with a serial manipulator, which in turn produces forces and torques on the internal magnetic capsule. We propose a control strategy which, counteracting gravity, achieves levitation of the capsule. This technique, based on a nonlinear backstepping approach, is able to limit contact with the colon walls, reducing friction, avoiding contact with internal folds, and facilitating the inspection of nonplanar cavities. The approach is validated on an experimental setup, which embodies a general scenario faced in colonoscopy. The experiments show that we can attain 19.5% of contact with the colon wall, compared to the almost 100% of previously proposed approaches. Moreover, we show that the control can be used to navigate the capsule through a more realistic environment-a colon phantom-with reasonable completion time.

A Soft Retraction System for Surgery Based on Ferromagnetic Materials and Granular Jamming

In recent years, minimally invasive surgery (MIS) has gained wider acceptance among surgeons. MIS requires high skills for the operators, mainly due to its intrinsic technical limitations. Tissue manipulation and retraction remain the most challenging tasks; more specifically liver, stomach, and intestine are the organs mostly involved in retraction tasks for abdominal procedures. The literature reports an increasing interest toward dedicated solutions for abdominal tissue retraction tasks. To overcome the limitations of commercial systems and research prototypes, the aim of this study is the design, the realization, and the validation of a retraction system that is simple, reliable, easy to use, safe, and broadly compatible with MIS. The proposed retractor has two main components: (1) a soft central part with variable stiffness obtained by exploiting the granular jamming phenomenon for assuring, at the same time, safe introduction into the abdominal cavity and stable retraction and (2) two iron cylinders located at the two extremities of the device for anchoring the retractor to the abdominal wall by using the magnetic attraction force between these components and two external permanent magnets. System design has been performed by deeply investigating granular jamming principle and ferromagnetic properties of iron elements. Ex vivo and in vivo assessment has been carried out with the final aim to identify the most appropriate design of each retractor component and to demonstrate the advantages of using a soft system with variable stiffness during a retraction task.

Enhanced Real-Time Pose Estimation for Closed-Loop Robotic Manipulation of Magnetically Actuated Capsule Endoscopes

Pose estimation methods for robotically guided magnetic actuation of capsule endoscopes have recently enabled trajectory following and automation of repetitive endoscopic maneuvers. However, these methods face significant challenges in their path to clinical adoption including the presence of regions of magnetic field singularity, where the accuracy of the system degrades, and the need for accurate initialization of the capsule's pose. In particular, the singularity problem exists for any pose estimation method that utilizes a single source of magnetic field if the method does not rely on the motion of the magnet to obtain multiple measurements from different vantage points. We analyze the workspace of such pose estimation methods with the use of the point-dipole magnetic field model and show that singular regions exist in areas where the capsule is nominally located during magnetic actuation. Since the dipole model can approximate most magnetic field sources, the problem discussed herein pertains to a wider set of pose estimation techniques. We then propose a novel hybrid approach employing static and time-varying magnetic field sources and show that this system has no regions of singularity. The proposed system was experimentally validated for accuracy, workspace size, update rate and performance in regions of magnetic singularity. The system performed as well or better than prior pose estimation methods without requiring accurate initialization and was robust to magnetic singularity. Experimental demonstration of closed-loop control of a tethered magnetic device utilizing the developed pose estimation technique is provided to ascertain its suitability for robotically guided capsule endoscopy. Hence, advances in closed-loop control and intelligent automation of magnetically actuated capsule endoscopes can be further pursued toward clinical realization by employing this pose estimation system.

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.

Design and preliminary evaluation of a self-steering, pneumatically driven colonoscopy robot

Colonoscopy is a diagnostic procedure to detect pre-cancerous polyps and tumours in the colon, and is performed by inserting a long tube equipped with a camera and biopsy tools. Despite the medical benefits, patients undergoing this procedure often complain about the associated pain and discomfort. This discomfort is mostly due to the rough handling of the tube and the creation of loops during the insertion. The overall goal of this work is to minimise the invasiveness of traditional colonoscopy. In pursuit of this goal, this work presents the development of a semi-autonomous colonoscopic robot with minimally invasive locomotion. The proposed robotic approach allows physicians to concentrate mainly on the diagnosis rather than the mechanics of the procedure. In this paper, an innovative locomotion approach for robotic colonoscopy is addressed. Our locomotion approach takes advantage of longitudinal expansion of a latex tube to propel the robot's tip along the colon. This soft and compliant propulsion mechanism, in contrast to minimally invasive mechanisms used in, for example, inchworm-like robots, has shown promising potential. In the preliminary ex vivo experiments, the robot successfully advanced 1.5 metres inside an excised curvilinear porcine colon with average speed of 28 mm/s, and was capable of traversing bends up to 150 degrees. The robot creates less than 6 N of normal force at its tip when it is pressurised with 90 kPa. This maximum force generates pressure of 44.17 mmHg at the tip, which is significantly lower than safe intraluminal human colonic pressure of 80 mmHg. The robot design inherently prevents loop formation in the colon, which is recognised as the main cause of post procedural pain in patients. Overall, the robot has shown great promise in an ex vivo experimental setup. The design of an autonomous control system and in vivo experiments are left as future work.

Nonholonomic Closed-loop Velocity Control of a Soft-tethered Magnetic Capsule Endoscope

In this paper, we demonstrate velocity-level closed-loop control of a tethered magnetic capsule endoscope that is actuated via serial manipulator with a permanent magnet at its end-effector. Closed-loop control (2 degrees-of-freedom in position, and 2 in orientation) is made possible with the use of a real-time magnetic localization algorithm that utilizes the actuating magnetic field and thus does not require additional hardware. Velocity control is implemented to create smooth motion that is clinically necessary for colorectal cancer diagnostics. Our control algorithm generates a spline that passes through a set of input points that roughly defines the shape of the desired trajectory. The velocity controller acts in the tangential direction to the path, while a secondary position controller enforces a nonholonomic constraint on capsule motion. A soft nonholonomic constraint is naturally imposed by the lumen while we enforce a strict constraint for both more accurate estimation of tether disturbance and hypothesized intuitiveness for a clinician's teleoperation. An integrating disturbance force estimation control term is introduced to predict the disturbance of the tether. This paper presents the theoretical formulations and experimental validation of our methodology. Results show the system's ability to achieve a repeatable velocity step response with low steady-state error as well as ability of the tethered capsule to maneuver around a bend.