Localization Strategies for Robotic Endoscopic Capsules: A Review

本文是WCE定位领域最新的一篇review，非常有价值。

内窥镜胶囊机器人的定位策略：一个回顾
Localization Strategies for Robotic Endoscopic Capsules: A Review [1]
Paper Link
Authors: Federico Bianchi, etc.
2019，Expert Review of Medical Devices

1. 介绍（节选）Introduction (Excerpt)

当前，商业上可获得的内窥镜技术不能够完全应付为了在无症状阶段根除结肠癌的大规模筛查的有效性的缺失。在另一方面，WCE技术的革命性方法，和它对病人的潜在的好处，使得它成为一个对工程师和医师来说都重要的研究和开发的领域。研究团队已经提出创新性的理论，研究和增加的模块来提高检查，诊断和治疗能力，比如：（i）高效率无线能量传输；（ii）可控的主动运动；(iii) 精确的定位，等等。胶囊定位在WCE内窥镜中扮演了重要的角色，虽然最好的胶囊表现是通过一个在所有模块和功能中的最优平衡来获得的。确实，对胶囊位置和姿态的精确认知-被定义为它的位姿-当它运行在消化道中，并抓取图像时，这样的认知表示一种宝贵的信息，能够被医师利用用来更好地：(i) 定位内部病态； (ii) 进行接下来的诊断和干预（比如说给药）；(iii) 主动运动WCE的辅助导航；和 (iv) 在无线充电情况下进行无线能量传输。
Nowadays, the commercially available endoscopic technologies are not able to completely cope with the lack of effectiveness of mass screening campaigns for eradicating CRC in a symptomless state. On the other hand, the revolutionary approach of WCE technology, and its potential benefits for patients, make it an important field of research and development for engineers and physicians. Research teams have proposed innovative methods, studies and additional modules to improve screening, diagnostic, and therapeutic capabilities, such as (i) high-efficiency wireless powering; (ii) controllable active locomotion; (iii) accurate localization, etc. Capsule localization plays a key role in WCE endoscopy, although the best performance can be obtained through an optimum trade-off between all modules and functionalities. Indeed, accurate knowledge of the position and orientation of the capsule - defined as its pose - when it moves along the GI tract and captures images represents an invaluable information that can be exploited by physicians to better: (i) localize internal pathologies; (ii) perform follow-up diagnosis and intervention (such as drug delivery); (iii) assist navigation of active locomotion WCEs; and (iv) perform power transmission in case of wireless battery charging.

因此，因为它的重要性，一些解决方案，从磁场到超声和计算机视觉技术的使用，已经被调查。一份关于最新最近的定位策略的重要的回顾可能对于考虑进入这一具有挑战性的领域或在这一领域进一步发展的研究者来说是一个有用的工具。
Therefore, due to its importance, several solutions, ranging from the use magnetic fields to ultrasounds and computer-vision technologies, have been investigated. A critical review on the state-of-art of recent localization strategies may represent a useful tool for researchers who are considering entering or further progressing in this challenging field.

这篇回顾文章由三个主要的部分组织，三部分关注于：(i) 基于磁场的定位策略；(ii) 基于电磁波的定位策略；和 (iii) 其他方式的定位策略，比如超声波。
The review paper is organized into three main sections focused on: (i) magnetic fields-based localization strategies; (ii) electromagnetic wave-based localization strategies; and (iii) other types of localization strategies, such as ultrasound.

2. 基于磁场的定位策略 （节选） Magnetic field-based localization strategies (Excerpt)

在过去的几十年里，用于医疗目的的磁场使用已经极大地抓住了众多学术界和工业界团队的注意力，这些团队有兴趣在人类身体内部定位，锚定或导航医疗设备。这些团队被磁场的内在优势所激励，比如贯穿人体的低衰减和基于磁性的传感器能力去检测目标却没有视线的限制，与基于视觉的传感器技术相反。然而，最大的挑战性问题之一是在定位系统和连续铁磁模块之间的可能的干扰，比如手术工具，但是运动模块自身，在胶囊的主动驱动情况下，也是通过高强度永磁或电磁铁源获得的。对于这个原因，这个部分已被组织以使用和不使用高强度，磁驱动模块为条件来详细描述磁定位理论。
Over the past decade, the use of magnetic fields for medical purposes has significantly captured the attention of numerous academic and industrial groups interested to localize, anchor and navigate medical devices inside the human body. These groups were motivated by the intrinsic advantages of magnetic fields, such as low attenuation through the human body and capability of the magnetic-based sensor technologies to detect targets without the limitation of . a line-of-sight, contrarily to visual-based sensor technologies. However, one of the most challenging problems is the possible interferences between the localization system and contiguous ferromagnetic modules, such as surgical tools, but also the locomotion module itself, in case the capsule’s active propulsion is obtained by high-intensity permanent and electromagnetic sources. For this reason, this section has been organized to detail magnetic localization methodologies in the condition with and without the use of high-intensity, magnetically driven actuation modules.

2.1. 无磁驱动情况下的磁定位理论 Magnetic localization methodologies without magnetic-based actuation

一个磁追踪系统的典型部件有一个或多个磁源（发射器），和一个或多个传感器模块（接收器）。因此，基于发射器和接收器之间的相对位置，两个用于胶囊机器人定位的主要方法被定义。第一个方法包含定位胶囊内的磁源和病人体外的传感器模块，而第二个方法包含定位胶囊内的传感器和病人体外的磁源。
The typical components of a magnetic tracking system are one or more magnetic sources (transmitters), and one or more sensor modules (receivers). Therefore, based on the relative position between transmitters and receivers, two main approaches are defined for robotic capsule localization. The first approach consists in positioning the magnetic sources inside the capsule and the sensing modules outside the patient’s body, while the second approach consists in positioning the sensing module inside the capsule and the magnetic sources outside the patient’s body.

2.1.1 磁源在胶囊内部，传感模块在胶囊外部 Magnetic source inside, sensing module outside the capsule

（2005年，胡老师首先提出了用外部传感器阵列测量胶囊内的磁铁的磁场分布，从而利用磁极子模型反解出胶囊的5-D pose，求解优化算法是非线性算法 [2] Paper Link。同年，胡老师改进了原始算法，提出了线性算法，大大加快了求解速度，可以达到对胶囊pose的实时定位 [3] Paper Link。2008年，胡老师将非线性算法的准确性的优点和线性算法的快速性的有点结合起来，最终获得了$2mm$和$1.6^{\circ }$的5-D pose 精度 [4] Paper Link。因为以上只有一块传感器阵列，有效的定位距离大约只有$120mm$，这对于应用是不够的，至少需要$300mm$，2010年，胡老师提出了传感器立方体阵列 [5] Paper Link，在$0.5m\times 0.5m\times 0.5m$的空间内定位误差为$1.82mm$和$1.62^{\circ }$。2014年，宋老师利用Biot-Savart法则计算了磁环的磁场模型，从而解出了6-D pose [6] Paper Link。2016年，胡老师提出了可穿戴的定位装置，用来定位体内胶囊磁体，通过将两块磁铁贴在人体表面，提出了对胶囊内磁铁的运动补偿，补偿后，胶囊磁铁达到了$3.82mm$和$2.2^{\circ }$的精度 [7] Paper Link。）

总结一下，适用于无磁驱动WCE且有胶囊外传感器模块的磁定位策略的最显而易见的解决方案已经从2005开始被香港中文大学开发并改进。系统的最新配置集成了一个内部永磁铁在WCE内部，和一个可穿戴霍尔效应传感器阵列在病人外。6自由度定位策略演示了定位和姿态的平均误差分别低于5毫米和3°。请注意，在所有的分析工作中，定位系统的精度随着外部传感器数量的变多而变高。
In summary, the most notable solution of magnetic localization strategy suitable with not magnetically driven WCE with sensing module outside the capsule has been developed and improved since 2005 by the Chinese University of Hong Kong. The latest configuration of the system integrates an internal permanent magnet into the WCE, and a wearable array of Hall-effector sensors placed outside the patient. The 6-DoFs localization strategy demonstrated an average error under 5 mm and 3° for position and orientation, respectively. It be noted that in all the analyzed works, it has been shown that the accuracy of the localization system increases with the number of external sensors.

2.2. 有磁驱动情况下的磁定位理论 Magnetic Localization methodologies with magnetic-based actuation

值得一提的是，在本节中所有定位策略都嵌入传感模块到内窥镜胶囊中。
It is worth mentioning that all the localization strategies presented in this section embed the sensing module inside the endoscopic capsule.

正如之前提到的，一些研究被施行确保对一个CE的基于磁性的运动和定位，通常利用两个或多个放置在病人体外的磁源和一个或多个放置在内窥镜胶囊内部的磁源的磁交互。显然地，用于运动和定位目的的磁源的使用可能导致对定位系统不期望的干扰，因为可能不能够区分用于运动目的的磁源或者被强生成的磁场影响，导致传感器饱和。
As previously mentioned, several studies were performed for ensuring both magnetic-based locomotion and localization of a CE, generally by exploiting the magnetic interaction between two or more magnetic sources placed outside the patient’s body and one or more placed inside the endoscopic capsule. Obviously, the use of magnetic sources for both locomotion and localization purposes may result in undesired interferences with the localization system, since it could be unable to distinguish the magnetic source used for locomotion purposes or being affected by strong generated magnetic field, leading to sensors saturation.

总结一下，在基于静态磁场驱动情况下的主动运动胶囊的最显而易见的解决方案被利兹大学开发了。系统的最新配置是展示了一个混合解决方案，使用一个EPM和一个电磁铁，有一个机器臂的末端执行器举起，来实时引导和定位一个主动软线胶囊。它能够展现在位置和姿态的平均误差分别为$5mm$和$6^{\circ }$的一个6自由度定位 [8] Paper Link。
在另一方面，在基于旋转磁场驱动的情况下，最卓越的解决方案是由犹他大学自2013年开发的。与Taddese的主要不同在于螺旋型的胶囊通过施加一个角旋转到一个RPM被驱动。对位置和姿态类似的结果（$8.5mm$，$7.1^{\circ }$）被报告 [9] Paper Link。请注意，在两种情况中，霍尔传感器和/或惯性传感器都被嵌入胶囊内部作为感知单元。
In summary, the most notable solution for active-locomotion capsules in case of static magnetic field-based actuation was developed by the University of Leeds. The latest configuration of the system presents a hybrid solution that integrated an EPM and an electromagnet, held by the end-effector of a robot, to guide and localize in real time an active soft-tether capsule. It was able to perform a 6-DoF localization with an average error in position and orientation under 5 mm and 6°, respectively [8] Paper Link.
On the other hand, in case of alternating magnetic field-based actuation, the most remarkable solution was developed since 2013 by University of Utah. The main difference with Taddese et.al. is that the spiral-shape capsule is propelled applying an angular rotation to an RPM. Similar results ($8.5mm$, $7.1^{\circ }$) were reported both for position and orientation [9] Paper Link. It should be noted that in both cases Hall-effector and/or inertial sensors are embedded inside the capsule as sensing units.

3. 其他部分略去

[1]: Bianchi, Federico, et al. “Localization strategies for robotic endoscopic capsules: a review.” Expert review of medical devices 16.5 (2019): 381-403.
[2]: Hu, Chao, Max Q-H. Meng, and Mrinal Mandal. “Efficient magnetic localization and orientation technique for capsule endoscopy.” International Journal of Information Acquisition 2.01 (2005): 23-36.
[3]: Hu, Chao, MQ-H. Meng, and Mrinal Mandal. “Efficient linear algorithm for magnetic localization and orientation in capsule endoscopy.” 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference. IEEE, 2006.
[4]: Hu, Chao, et al. “An improved magnetic localization and orientation algorithm for wireless capsule endoscope.” 2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE, 2008.
[5]: Hu, Chao, et al. “A cubic 3-axis magnetic sensor array for wirelessly tracking magnet position and orientation.” IEEE Sensors Journal 10.5 (2010): 903-913.
[6]: Song, Shuang, et al. “6-D magnetic localization and orientation method for an annular magnet based on a closed-form analytical model.” IEEE Transactions on Magnetics 50.9 (2014): 1-11.
[7]: Hu, Chao, et al. “Locating intra-body capsule object by three-magnet sensing system.” IEEE Sensors Journal 16.13 (2016): 5167-5176.
[8]: Taddese, Addisu Z., et al. “Enhanced real-time pose estimation for closed-loop robotic manipulation of magnetically actuated capsule endoscopes.” The International journal of robotics research 37.8 (2018): 890-911.
[9]: Popek, Katie M., Tucker Hermans, and Jake J. Abbott. “First demonstration of simultaneous localization and propulsion of a magnetic capsule in a lumen using a single rotating magnet.” 2017 IEEE International Conference on Robotics and Automation (ICRA). IEEE, 2017.