Current State of Robotics in Interventional Radiology

As a relatively new specialty with a minimally invasive nature, the field of interventional radiology is rapidly growing. Although the application of robotic systems in this field shows great promise, such as with increased precision, accuracy, and safety, as well as reduced radiation dose and potential for teleoperated procedures, the progression of these technologies has been slow. This is partly due to the complex equipment with complicated setup procedures, the disruption to theatre flow, the high costs, as well as some device limitations, such as lack of haptic feedback. To further assess these robotic technologies, more evidence of their performance and cost-effectiveness is needed before their widespread adoption within the field. In this review, we summarise the current progress of robotic systems that have been investigated for use in vascular and non-vascular interventions.


Introduction
Interventional radiology (IR) is one of the most innovative and creative disciplines, with a steady stream of developments in imaging techniques, catheters and devices as well as treatment procedures. Nevertheless, IR has been lagging behind other specialities when it comes to robotics. The DaVinci robot was first used for laparoscopic cholecystectomy in Belgium in 1997 [1] and has been widely used since 1999, especially in visceral surgery, urology and ophthalmology. Orthopaedic surgeons have been implanting robotic-assisted endoprostheses since 2000 [2]. Much later, angiographic robots were invented initially for use in cardiology, and subsequently transitioned into the field of IR [3][4][5].
In the field of IR, the robotic catheterisation systems aim to improve 1) the precision and safety of the operation and 2) the access and comfort of the patient, while 3) minimising operator skill variability and 4) reducing radiation exposure to both patients and clinicians. In addition, given the teleoperated nature of these systems, their benefits can be made accessible to patients in rural and underserved populations. Similarly, the application of robotics to nonvascular IR procedures provides the opportunity to improve the precision of percutaneous procedures with enhanced adherence to the predefined target path. In this paper, we will explore the current robotic advancements in endovascular and non-vascular IR procedures.

Robotic Endovascular Procedures
Over the past two decades, several commercial and research platforms have been developed to assist interventionalists in peripheral vascular (PVI), neurovascular (NVI) and percutaneous coronary interventions (PCI) [3,[6][7][8][9][10][11][12][13]. A summary of the key characteristics of these robotic systems is listed in Table 1 and a summary of the clinical studies undertaken using these robots is found in Table 2.

Sensei and Magellan
Sensei (Hansen Medical, Mountain View, CA, USA) was one of the first commercially available robotic system that obtained the US Food and Drug Administration (FDA) approval in 2007 to be used in cardiac mapping and ablative procedures [14]. This system enabled robotic control of a steerable guide catheter remotely using 3 degrees of freedom (DOF) joystick [15,16]. Although Sensei provided better catheter stability in comparison with manual procedures and was successfully used for cardiac ablation and endovascular aneurysm repairs, mechanical issues related to the system profile and applicability were reported using this system [17]. The next generation of the robotic platform from Hansen Medical was the Magellan robotic system, which received its FDA 510(k) clearance back in 2012, and allowed interventional radiologists to remotely control the shape and movement of the distal co-axial tip of 6Fr, 9Fr, and 10Fr robotic catheters and the robotic manipulation of standard off-the-shelf guidewires. The robot is able to control the movements of 0.035 00 and 0.018 00 wires, and the operator is able to advance, retract, rotate in 360 degrees and park the wire by using buttons in the robot control station. The pioneering robotic system has shown its efficacy and safety in several peripheral arterial interventions such as aortic stent grafting, fenestrated endovascular aneurysm repair (FEVAR) and embolisation techniques [18,19]. Through several individual cases and in small, selected case series, this system has demonstrated certain benefits, such as reduced vessel wall damage and embolic events with better control of vessel centreline navigation, improved stability while navigating tortuous anatomy, enhanced cannulation success of target vessels, improved movement economy and reduced radiation doses to operators [4,[18][19][20][21][22][23][24]. However, the main limitations of the Magellan were the high installation and running costs, as well as the inability to integrate all therapeutic devices.

CorPath GRX
In contrast to the discontinued Magellan, the FDA-approved and CE-marked CorPath GRX (Corindus, Siemens Healthineers, Waltham, MA, USA) facilitates the control of third-party guiding catheters, guidewires, and therapeutic balloon/stent catheters. The GRX platform, the successor of the CorPath 200, includes additional advanced procedural automation movements (FDA-cleared 2018 and 2020) such as rotate on retract (RoR) [25] wiggle, spin, dotter and constant speed. The main applications of the GRX systems are for use in PCIs and NVIs. Nonetheless, the applications of this system in other procedures have also been explored, such as for percutaneous renal stent implantation in five patients [26]. In 2020, the CorPath GRX robotic system was used in a stent-assisted coiling procedure of a basilar artery aneurysm [27]. A prospective, multicentre single-arm trial, recently presented in a congress [28], has evaluated the procedural technical success and the incidence of intra-and peri-procedural complications using the CorPath GRX in 113 patients with at least one unruptured cerebral aneurysm requiring endovascular coil and/or stent-assisted coiling embolisation [28,29]. Robot-assisted embolisation success rate without the need to convert to manual operation was 94.7%. In order to complete the procedure, five subjects underwent conversion to manual operation [28]. The results of this trial are yet to be published.
Whereas the Magellan robotic platform uses dedicated robotic catheters of 6Fr, 9Fr, and 10Fr, the CorPath GRX   system uses commercially available 5-7Fr guiding catheters, which is partially responsible for making the CorPath GRX system more cost-effective in comparison. Using the CorPath GRX, the operator is able to use the joystick in the control station to advance and retract off-the-shelf catheters. The platform is currently able to accommodate 0.014 00 wires. Although the initial cost of acquisition of the Magellan system, estimated at around $600 K, is similar to the GRX system with figures ranging between $480-650 K, the cost of each disposable Magellan robotic catheter is $1500 compared to $400-750 for the single-use cassette of the GRX system [11,30]. While there is no direct comparative study between CorPath GRX and Magellan systems, it is the view of the author who has had experience with both devices (MH), that the technical abilities of CorPath GRX, such as navigation, stability and applicability across a range of anatomical variations are likely inferior to its predecessor. This is related mainly to the inherent feature of CorPath GRX which uses standard offthe-shelf catheters with no added mechanical features.

R-One
Another robotic platform which offers a similar solution to the GRX is the R-One robotic PCI system (Robocath, Rouen, France) that received CE marking in 2019. The R-One allows interventionalists to manipulate off-the-shelf guidewires and stent/balloon catheters (excluding a guiding catheter). The R-One was used in the R-Evolution clinical trial in a non-randomised, prospective single-arm clinical trial [31]. Sixty-two patients requiring stent implantation were enrolled across six European centres. The findings of this clinical trial identified that the technical success rate for this system is [ 95% with a 100% clinical success rate.
No device-related complications were observed post-procedure, and the robotic assistance allowed an average of 84.5% reduction in radiation dose to the physician. Total manual conversion was required in three patients [31].

Niobe ES
Niobe ES (Stereotaxis Inc., MO, USA) is a commercially available magnetically driven robotic platform that implements magnetic fields to navigate and relocate custom-made magnetic catheters in 3 DOF. The magnetic catheter is made up of soft material to avoid excessive contact force and reduces the risk of cardiac perforation [17]. The main drawbacks of Niobe are related to its need for costume designed catheters, relatively long set-up time of roughly 30 min, and the need for a large space to place the device [14]. In 2020, Stereotaxis introduced Genesis, an updated version of the Niobe system, which incorporates a novel design with a reduced robot size, weight, and faster and more flexible magnet movement [32].

Amigo
The Amigo Remote Catheter System (Catheter Precision, Inc., Mount Olive, NJ, USA) was designed with the goal of providing a simple and less expensive solution for remote catheter manipulation in cardiac electrophysiology procedures [33]. The Amigo benefits from a handheld remote device as the control panel and compatibility with off-theshelf ablation catheters. As a result of being designed specifically for cardiac electrophysiological treatments, this system has limited potential clinical application in PCI or PVI [34]. The safety and performance of the Amigo robotic system has been evaluated in a number of previous studies [35][36][37][38] that have been explained in further detail in Table 2. In parallel to the ongoing commercialisation efforts, a plethora of work has been reported in literature [6,12]. Most recently, the ongoing research endeavours in developing magnetic resonance (MR) safe and MR conditional robotic platforms for MR-guided endovascular interventions [39]. Generally speaking, MRI offers unprecedented opportunities to combine diagnosis, therapy and early evaluation of therapy in a single endovascular intervention [40]. Researchers overcome the material constraints (i.e. inability to use ferromagnetic materials) of the highly magnetic MRI environment by replacing the commonly used electric motors with non-ferromagnetic ultrasonic motors [41] and plastic stepper motors [42,43]. These versatile systems can help mitigate the challenges of performing manual MR-guided interventions by: (a) providing accessibility to patients inside the MRI bore (especially paediatric patients) and (b) reducing the physicians' exposure to the uncomfortable acoustic noise, which may lead to hearing impairment [44]. Moreover, companies such as MaRVis Interventional GmbH (Krün, Germany), Nano4imaging (Düsseldorf, Germany) and EPFlex (Dettingen an der Erms, Germany) are complementing these advancements in robotics through their leading developments in the field of MR compatible instrumentation (i.e. MR safe and MR conditional guidewires) which could potentially pave the way for the broader adoption of MRguidance in endovascular interventions.

Robotic Non-vascular Systems
Interventional radiologists have successfully used various imaging modalities to guide their path to target and monitor their treatment outcome in a vast number of non-vascular interventions. The application of robotic systems in these CT-and MRI-guided procedures could aid in improving accuracy, precision and safety. In addition, it could reduce the high radiation exposure of CT scans to the physician and other healthcare staff. In this section, we will review some of the advancements in robotic CT-and MRIguided systems in non-vascular IR procedures. A summary of the key characteristics of these robotic systems is listed in Table 3 and a summary of the clinical studies undertaken using these robots is found in Table 4.

AcuBot
One of the first CT-compatible robotic systems was the AcuBot (URobotics Laboratory, The Johns Hopkins University, Georgetown, USA) [45]. The FDA-approved AcuBot was built on the previous PAKY-RCM robotic system and was improved with the addition of several new components including a passive S-arm and an XYZ Cartesian stage [45]. The robot has 6 DOF designed for decoupled positioning, orientation, and instrument insertion [45]. This robotic system has been tested in a cadaveric study for nerve and facet blocks, with an average placement accuracy of 1.44 ± 0.66 mm (mean ± SD) [46]. A recent gel phantom study compared the Acubot with a computer-assisted optical navigation system in the performance of percutaneous ablative targeting in gel phantom [47]. The mean translational offset from the predefined targets was 1.2 mm (range 0.39-2.82 mm) for the AcuBot system and 5.8 mm (range 1.8-11.9 mm) for the navigation system. The AcuBot was also faster to reach target with an average of 37 s (range 15-75), compared to 108 s (range 45-315) for the navigation system [47].

B-Rob II
The B-Rob II robotic system (Austrian Research Group ARC, Seibersdorf Research, Austria), the successor of the B-Rob I, has 7 DOF and has been designed for both CTand Ultrasound (US)-guided biopsy sampling. This secondgeneration robot was designed with the aim of creating a flexible setup design that was better suited for clinical practice, with easier integration with other systems while reducing technical complexity and costs. The accuracy of robotic needle placement of the B-Rob II system was evaluated using a gelatin phantom with 21 biopsies performed [48]. The average needle placement accuracy was 1.8 ± 1.1 mm (mean ± SD), and the average procedure time was 2 min 21 s [48]. More recently, this robotic system was used to assist post-mortem CT-guided biopsies for foetus and infants; however, it provided limited additional diagnostic value [49]. The authors explained that biopsy sampling failure mostly involved organs with reduced soft tissue contrast on CT, such as the spleen, and that evaluation of these organs in foetuses with low abdominal and subcutaneous fat is generally difficult.
iSYS1 The iSYS1 robot system (iSYS Medizintechnik GmbH, Kitzbuehel, Austria) is the successor of B-Rob II system. The iSYS1 robot received its CE mark and FDA approval in 2013 and 2014, respectively, and has since been used in pre-clinical and clinical settings [50][51][52][53]. The robot is compatible with cone beam CT (CBCT) as well as CT/ fluoroscopy. The robot has a four axial robotic positioning unit, which consists of a 2 DOF translational workspace measuring 40 9 40 mm and another 2 DOF angulation of ± 32 degree of the needle [54,55]. In a phantom study, the iSYS1 robot successfully performed 40 needle target punctures, with 20 targets in single and 20 in double oblique trajectories. Overall, the mean length of the target path was 8.5 cm (range 4.2-13.5 cm) from the phantom surface. For all procedures, the average duration was 3 min 59 s with an overall needle tip deviation of 1.1 mm (range 0-4.5 mm) from the predefined path [50]. Another study utilised the iSYS1 robotic system for CT-guided punctures of targets placed in a torso phantom [51]. The mean difference between the depth of the planned needle trajectories with the actual needle placements was 1.3 ± 1.2 mm. The authors also reported the mean Euclidean distance between the target and the actual needle tip as 2.3 ± 0.9 mm, and concluded that accurate needle placement near small targets was feasible with the iSYS1 robotic system [51].

Zerobot
The Zerobot (designed by Okayama University; manufactured by Medicalnet Okayama) is another remote-controlled robot designed for CT-guided procedures requiring needle insertion, such as ablation, biopsy, and drainage [56]. The Zerobot has an operation interface that can manipulate the robot with 6 DOF. Following an experiment through which the robot yielded accurate and safe results in phantom and animal experiments [57], the robot was used in needle orientation and insertion under CT guidance using four different ablation needle types in six swine,  Evaluation of MR-guided robotic-assisted percutaneous facet joint treatment 100% procedures completed Some minor side effects: hyperhidrosis (n = 1), prolonged menstruation (n = 1) No major adverse events aiming for targets in the liver, kidney, lung, and hip muscle [58]. It was found that the overall mean accuracy of all needles for all targets was 2.8 ± 1.0 mm (mean ± SD).

Robio EX
The Robio EX (Perfint Healthcare Pvt. Ltd, Florence, USA) is another CE-marked robotic system that is compatible with CT and positron emission tomography (PET)-CT. The Robio EX's robotic arm has 5 DOF movement with two linear motions for positioning of the guide and two angular motions to modify the needle to the appropriate angular entry [59]. This robotic system was designed for thoracic and abdominal interventions, including biopsy, drainage, and tumour ablation. It also includes a breath hold management system in order to secure targets that may move due to respiratory effort. One main disadvantage of the Robio EX is that it is situated on its stand which fixed to the floor, and as such the needle must be decoupled every time the CT table is moved.

EPIONE
The EPIONE robotic system (Quantum Surgical, Montpellier, France), both CE marked, and FDA cleared, is another robotic system used in CT-guided percutaneous needle insertion. The EPIONE robotic system has 6 DOF and is comprised of five components: the mobile arm (1) which has attached to it the needle guide (2), an infra-red camera (3) acting as the navigation cart, a workstation (4), and patient reference (5) which is adhesively attached to the patient's skin and allows tracking of patient's respiratory cycle [60]. This robotic system has been safely used in CT-guided percutaneous needle placement for targeting of previously implanted fiducials in the liver of ten swine [61]. Similarly, the robot was used in CT-guided percutaneous needle insertion targeting a total of eight fiducial targets placed in the kidneys of two swine. All needle insertions successfully reached the target on the first attempt with no need for readjustment; however, there were two subcapsular haematomas which did not progress to retroperitoneal effusions [62]. In a recent prospective study, the EPIONE robotic system was used for roboticassisted thermal ablation of liver tumours [60].

INNOMOTION
MRI has slowly become a popular choice of imaging modality in interventional procedures mainly due to the excellent soft tissue contrast resolution, the lack of ionising radiation, and the ability for multimodality sensing such as blood flow, motion, deformation, strain, and temperature [63]. However, as previously mentioned, it has major disadvantages including cost, the limited bore space, and the constraints on compatible instruments [64].

Discussion and Conclusion
Recent advances in robotic platforms and technologies have resulted in improvements in robotic-assisted endovascular and non-vascular procedures. Robotic systems in IR can address one of the few downsides of this field, which is the exposure to ionising radiation to both patients and healthcare staff (Fig. 1). In addition, other potential benefits that have been claimed using robotic systems in IR include increased accuracy and precision, reduced operation time, and reduced numbers of readjustments needed to reach target. Ultimately, with further advancements in remotely controlled robotic systems, robotic-assisted IR may lead to improved access to healthcare, especially in rural areas. In combination with surgical simulators, robotic systems can be used as a potential training tool in the future that will allow highly accurate training scenarios with minimised radiation exposure. Similarly, the use of robotic systems may lead to minimisation of user-variability in future interventions. However, there are still a number of drawbacks that need to be addressed to allow widespread adoption of this technology in the field of IR. Some of these limitations include the high cost of these robots, the inability to integrate some robotic systems with other surgical devices and/or instruments, the interference to workflow in the IR suite, and the lack of haptic feedback. The application of artificial intelligence (AI) to robotic surgery has shown some promise in improving surgical parameters, such as improved haptic feedback systems and surgical guidance, as well as better prediction of operative time and post-op outcomes [76]. Thereby, the integration of AI with robotic systems in IR may address some of the current pitfalls of these systems.
In conclusion, robotic guided interventions are continuously developing with established safety records and promising efficacy prospects. While the balance between efficacy and cost implications needs to be considered, interventional radiologists should be continuously engaged and lead the robotic development in the field of vascular and oncology interventions to maximise the benefits to patients and operators.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the Fig. 1 A Current, routine IR procedures during which the physician is exposed to ionising X-ray radiations, which may lead to a sizeable risk of cancer. The physician is also wearing a heavy lead apron, which makes the physician more prone to orthopaedic injuries. B Physician is remotely operating a robotic platform. The physician is no longer exposed to ionising radiations and no longer needs to wear the lead apron. The robotic platform may also improve the precision, stability, and comfort of endovascular procedures. C Physician is remotely operating a robotic platform inside an MRI scanner instead of using X-ray guidance. MRI does not have any ionising radiation, which makes it a safe option for patients, especially the paediatric population. MRI can also provide better visualisation of soft tissue and offers unparalleled 3D evaluations of pathology and function across the body source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons. org/licenses/by/4.0/.