Minimally Invasive Therapy & Allied Technologies
ISSN: 1364-5706 (Print) 1365-2931 (Online) Journal homepage: http://www.tandfonline.com/loi/imit20
Feasibility of electromagnetically guided transjugular intrahepatic portosystemic shunt procedure Peter Isfort, Tobias Penzkofer, Christoph Wilkmann, Hong-Sik Na, Christian Kotzlowski, Nobutake Ito, Joachim Georg Pfeffer, Stefan Bisplinghoff, Sabine Osterhues, Andreas Besting, Jorge Gooding, Thomas Schmitz-Rode, Christiane Kuhl, Andreas Horst Mahnken & Philipp Bruners To cite this article: Peter Isfort, Tobias Penzkofer, Christoph Wilkmann, Hong-Sik Na, Christian Kotzlowski, Nobutake Ito, Joachim Georg Pfeffer, Stefan Bisplinghoff, Sabine Osterhues, Andreas Besting, Jorge Gooding, Thomas Schmitz-Rode, Christiane Kuhl, Andreas Horst Mahnken & Philipp Bruners (2016): Feasibility of electromagnetically guided transjugular intrahepatic portosystemic shunt procedure, Minimally Invasive Therapy & Allied Technologies, DOI: 10.1080/13645706.2016.1214155 To link to this article: http://dx.doi.org/10.1080/13645706.2016.1214155
Published online: 09 Aug 2016.
Submit your article to this journal
Article views: 10
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=imit20 Download by: [Cornell University Library]
Date: 16 October 2016, At: 09:17
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES, 2016 http://dx.doi.org/10.1080/13645706.2016.1214155
ORIGINAL ARTICLE
Feasibility of electromagnetically guided transjugular intrahepatic portosystemic shunt procedure Peter Isforta, Tobias Penzkofera,b,c, Christoph Wilkmanna, Hong-Sik Naa, Christian Kotzlowskia, Nobutake Itod,e, Joachim Georg Pfeffera, Stefan Bisplinghoffh, Sabine Osterhuesf, Andreas Bestingg, Jorge Goodinge, Thomas Schmitz-Rodee, Christiane Kuhla, Andreas Horst Mahnkeni and Philipp Brunersa a Diagnostic and Interventional Radiology, RWTH Aachen University Hospital, Aachen, Germany; bSurgical Planning Laboratory, Brigham and Women's Hospital, Boston, MA, USA; cDiagnostic and Interventional Radiology, Charite Universit€atsmedizin Berlin, Berlin, Germany; dDepartment of Radiology, Keio University, Tokyo, Japan; eApplied Medical Engineering, RWTH Aachen University Hospital, Aachen, Germany; fVygon GmbH & Co. KG, Aachen, Germany; gSurgiTAIX AG, Herzogenrath, Germany; hMedical Engineering, RWTH Aachen University, Aachen, Germany; iDepartment of Diagnostic and Interventional Radiology, Philips University Hospital, Marburg, Germany
ABSTRACT
ARTICLE HISTORY
Objectives: To develop an electromagnetic navigation technology for transjugular intrahepatic portosystemic shunt (TIPS) creation and translate it from phantom to an in-vivo large animal setting. Material and methods: A custom-designed device for TIPS creation consisting of a stylet within a 5 French catheter as well as a software prototype were developed that allow real-time tip tracking of both stylet and catheter using an electromagnetic tracking system. Feasibility of navigated TIPSS creation was tested in a phantom by two interventional radiologists (A/B) followed by in-vivo testing evaluation in eight domestic pigs. Procedure duration and number of attempts needed for puncture of the portal vein were recorded. Results: In the phantom setting, intervention time to gain access to the portal vein (PV) was 144 ± 67 s (A) and 122 ± 51 s (B), respectively. In the in-vivo trials, TIPS could be successfully completed in five out of eight animals. Mean time for the complete TIPS was 245 ± 205 minutes with a notable learning curve towards the last animal. Conclusions: TIPS creation with the use of electromagnetic tracking technology proved to be feasible in-vitro as well as in-vivo. The system may be useful to facilitate challenging TIPSS procedures.
Received 14 March 2016 Accepted 8 June 2016 Published online 29 July 2016
Introduction In patients with liver cirrhosis, portal hypertension is a common problem that is associated with severe and often even life-threatening complications. These include therapy-refractory ascites and variceal bleeding (1). The outcome of acute variceal bleeding (VB) has dramatically improved over the last two decades, with mortality rates decreasing from over 40% in the 1980s down to about 15% in the year 2000 (2). This improvement is due to improved medical treatment, and, probably more important, to minimally invasive treatment methods such as endoscopic hemostasis and transjugular intrahepatic portosystemic shunt (TIPSS) placement. Developed in the early 1970s by R€ osch et al., an artificial portosystemic shunt between one of the hepatic veins and the portal vein is created. This is achieved by transjugular engaging the hepatic vein, followed by transhepatic puncture of a portal branch CONTACT P. Isfort
[email protected]
KEYWORDS
Image-guided procedures; interventional radiology; vascular intervention
with a bent needle. After balloon dilatation a stent or stent graft is placed to secure the transparenchymal passage (3). TIPS placement effectively achieves hemostasis in >90% of patients with acute variceal bleeding, and protects the patient from re-bleeding (4). In accordance with the results of randomized controlled trials, TIPS is today recommended as the treatment of choice in patients with variceal re-bleeding and/or refractory ascites in an acute and subacute setting (5–9). Further non-randomized studies also confirm the efficacy of TIPS in acute variceal bleeding, portal hypertensive gastropathy, bleeding gastric varices, refractory hepatic hydrothorax, hepatorenal syndrome (type 1 or type 2), Budd-Chiari syndrome, veno-occlusive disease and hepatopulmonary syndrome (10). Although TIPS is an effective therapy in many patients suffering from portal hypertension, it is mainly performed in specialized centers. One reason
Department of Diagnostic and Interventional Radiology, University Hospital RWTH Aachen, Germany
ß 2016 SMIT - Society for Minimally Invasive Therapy
2
P. ISFORT ET AL.
for this is the fact that severe complications caused by the transparenchymal puncture of the portal vein can yield lethal complications in patients with underlying liver disease who usually suffer from compromised coagulation function. Especially hemoperitoneum, due to extracapsular puncture of the hepatic artery, the inferior vena cava (IVC) or the aorta, may lead to a fatal outcome of the procedure (10). To avoid such complications, the crucial step of the TIPS procedure – i.e., the transhepatic portal vein puncture – is done under x-ray fluoroscopy control, with or without additional ultrasound. However, the ability of these methods to actually guide the puncture by locating the position of the needle tip with regard to the target, i.e., the portal vein branch, is poor. Fluoroscopy visualizes only radiopaque catheters/needles, but provides no direct 3D information about the anatomic structures in correlation to the needle tip. More importantly, only the hepatic veins can be opacified by contrast injection, whereas the portal vein remains invisible until after successful transhepatic puncture. Ultrasound provides only limited information of the needle position with respect to the portal vein; it provides only two-dimensional information, i.e., usually visualizes either portal vein or needle tip, or needs to use non-standard, oblique planes to visualize both structures within one section. Accordingly, there is a clear need to improve image guidance of this procedure. The ideal image guidance would provide visualization of the following aspects:
Levy et al. performed EMT-guided TIPS using a percutaneous transhepatic approach with a trackable straight puncture needle (18). A major drawback of this technique is the need for a transcapsular puncture. Therefore our aim was to transfer our experience with EMT from musculoskeletal and aortic interventions to the TIPS procedure and to use this technique in the standard transjugular approach (19–21).
Material and methods TIPS-device We developed a TIPS device that consists of a stainless steel stylet (diameter 0.9 mm; Figure 1 I-III(a)) with a flexible tip, a polypropylene catheter (diameter 1.65 mm; Figure 1 I-III(b)), an outer stainless steel cannula with a 30 bent tip (diameter 2.0 mm; Figure 1 I-III(c)) and a guiding catheter (Figure 1 I-III(d)). Coils with a diameter of 0.5 mm were integrated into the tips of the stylet and the guiding catheter for electromagnetic tracking. Furthermore, a 0.86 mm polyimide compound guidewire was developed with an integrated coil at the tip as well (Figure 1 IV). See also Figure 1 I-IV for details on the custom-made TIPS device.
3D visualization of the target structures, i.e., the hepatic veins and the portal vein, and of critical structures that need to be avoided, e.g., the liver capsule real-time time 3D visualization of the involved instruments and their movements starting point and end point of the transhepatic puncture. Electromagnetic tracking (EMT) is based on the detection of small metallic coils in a magnetic field by induction. In contrast to optical navigation, no direct line-of-sight between the tracked fiducials and the navigation system is needed, so direct tracking of the instrument tip and tracking of bendable instruments is possible (11). Over the past years, the size of EMT coils has significantly decreased. Coils as small as 0.3 mm in diameter are currently available. Accordingly, EMT seems to provide the necessary prerequisites for tracking of catheter-based vascular interventions (11–17).
Figure 1. Custom-made TIPS device I-III: A: 0.9 mm stainless steel stylet with integrated coil at stylet‘s tip; B: 1.65 mm polypropylene catheter; C: 2.0 mm stainless steel outer cannula with bent tip; D: 3.35 mm guiding catheter with integrated coil at the tip of the catheter. IV: Proprietary 0.86 mm polyimide compound guidewire with an integrated coil at the tip.
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES
3
Navigation system A state-of-the-art electromagnetic navigation system (Aurora, Northern Digital, Waterloo, Canada) was used as a platform for the EMT-guided TIPS procedure. Due to large metallic components in the angiography environment such as the c-arm or parts of the patient table, a significant distortion of the electromagnetic field can occur. This may lead to substantial errors of the detected device position. To dynamically detect and compensate such field distortions, an algorithm was implemented based on the continuous detection of sensors affixed at the animal’s thorax with a known geometry. Furthermore, due to patient or organ movement, and thus displacement of target structures during the respiratory cycle, motion-compensation was implemented using multiple miniature three-dimensional accelerometers. The sensors were affixed to the animal’s thorax prior to image acquisition in order to measure the inclination changes of the upper body at multiple positions. The system allows for visualization of the respiratory phase that matches the respiratory state of image acquisition best. Details on the electromagnetic tracking system, on the custom-designed and manufactured TIPS device, on respiratory motion compensation, and the proprietary software used in the in-vitro and in-vivo experiments have been published previously (20). In-vitro experiments As a first step, in-vitro experiments were performed in order to evaluate the technical feasibility of the EMT-guided TIPS procedure. For this purpose, a phantom was established consisting of custom-made silicon tubes representing the relevant vasculature (superior vena cava (SVC), hepatic veins (HV), portal vein (PV)), embedded in gel wax. Dimensions and geometry of the silicon tubes were derived from high resolution CT-datasets of ten consecutive patients who underwent TIPS-procedure at our institution within the last year. A flat detector CT (FDCT) (Artis Zeego, Siemens medical, Erlangen, Germany) of the phantom was acquired including the affixed reference plate serving as volume image dataset for the navigation system. After transfer of the reconstructed axial image data set (slice thickness: 1 mm; increment: 0.7 mm) to the navigation system and registration of the electromagnetic field and image volume, the transhepatic puncture was planned defining the exit of the liver vein as the start and the entry point into the portal vein
Figure 2. Experimental setting for the phantom study. I/II: A: Electromagnetic field generator; B: Instrument interface; C: Gelwax phantom – Arrow marks superior vena cava (SVC) with liver veins (HV); Arrowhead marks portal vein and its main branches. II: Setup of phantom study in angiography suite. The top opening of the phantom was closed during the trials to avoid optical bias.
branch as the endpoint. Both points were identified in the image dataset using the developed navigation software tool. Then navigated transhepatic punctures without additional image guidance were performed using the developed TIPS device. See also Figure 2 I-II for details on the experimental setting of the in-vitro study. For each puncture, the duration of the procedure was recorded. We defined insertion of the guidewire into the phantom as starting point; end point was successful placement of the guidewire through the liver vein into a portal vein branch after transhepatic puncture. The experiment was performed 40 times by each of two radiologists with three years (Radiologist A) and one year (Radiologist B) of experience in performing TIPS. Statistical analysis, i.e., comparison of the procedure times as defined above was performed using the t-test (MedCalc 13.2.2.0, Medcalc software, Ostend, Belgium). In-vivo experiments All animal experiments were performed in accordance with the local regulatory board (Ministry of
4
P. ISFORT ET AL.
Environment, Nature and Consumer Protection). EMT-guided TIPS procedures were performed in eight female domestic pigs with a mean weight of 60 kg. All interventions were done under general anesthesia after orotracheal intubation. A contrastenhanced FDCT (Artis Zeego, Siemens Medical, Germany) was acquired in the expiratory phase after injection of 60 ml iopromide (3 ml/s; 60 s delay) via a peripheral catheter placed in an ear vein. Thereafter, the right jugular vein was punctured under ultrasound guidance using an 18 G needle. A 10 F sheath was inserted over a hydrophilic guidewire. Next, the transhepatic puncture from the right or middle hepatic vein to a main portal vein branch was planned based on the acquired FDCT image set with the developed navigation software. Then the defined hepatic vein was cannulated using the proprietary EMT-guidewire in combination with a 5 F liver vein catheter. After opacification of the vein, the liver vein catheter was exchanged for the TIPS-device which was placed at the starting point of the transparenchymal passage. Transhepatic puncture was performed using real-time EMT guidance of the stylet without x-ray fluoroscopy control. Successful puncture of the target portal vein branch was verified by manual contrast injection. Thereafter, the proprietary guidewire was advanced through the portal vein into the superior mesenteric vein together with the polypropylene catheter. This was then exchanged for a stiff regular guidewire (Amplatz Super stiff guide wire, Boston Scientific, Natick, MA), followed by insertion of a long 8 F sheath and 8 mm TIPS endoprosthesis (Viatorr TIPS endoprosthesis, Gore, P€ utzbronn, Germany). The time between sheath placement in the right jugular vein and successful placement of the endoprosthesis was recorded. See also Figure 3(a–d) and Figure 4 for details on the in-vivo experiments.
Results In-vitro experiments All experiments were successful. The mean time between wire insertion in the SVC and successful wire placement in the PV/IMV was 144 ± 67 s (Radiologist A) and 122 ± 51 s (Radiologist B). No statistically significant difference was observed between the operators (p 0,05). See also Figure 5 for details on the results of the in-vitro experiments. In-vivo experiments EMT-guided TIPS could successfully be performed in five out of eight animals. One animal died due to
acute arrhythmia after passage of the TIPS device through the right atrium. In two animals TIPS could not be performed successfully because of an unfavourable anatomy of the liver vasculature. After multiple unsuccessful punctures animals were euthanized according to the animal experiment regulations. The mean time between sheath placement in the right jugular vein and successful placement of the TIPS endoprosthesis was 245 ± 205 minutes. The time varied between 85 and 590 minutes and showed a notable learning curve towards the last animals. See also Figure 6 for results of the in-vivo trials.
Discussion TIPS can be associated with life-threatening complications such as transcapsular puncture and intraperitoneal hemorrhage, which can be especially severe in the setting of ascites and deteriorated blood coagulation due to underlying liver disease. The risk for transcapsular puncture can be as high as 33% with significant intraperitoneal hemorrhage occurring in 1– 2% of cases (22). Compared to other image-guided procedures that involve transparenchymal punctures in the vicinity of large vessels or other structures at risk, that are usually performed under CT-guidance, image guidance of TIPS using x-ray fluoroscopy and additional ultrasound is rather poor. During transhepatic puncture only radiopaque parts of the TIPS-set are visualized and with ultrasound only parts of the needle tip can be depicted in two dimensions. Moreover, ultrasound guidance is often limited to an intercostal view because of air-filled bowel blocking the subcostal view. Given the current limitations of image guidance in TIPS there is a need for accurate 3D-imaging during TIPS in combination with real-time of the used devices. Kew et al. described in their study successful TIPS procedures under intravascular ultrasound (IVUS) guidance in three swine with the ultrasound system placed in the inferior vena cava (23). Nevertheless, IVUS allows only a limited two-dimensional visualization of the relevant parts of the liver. When compared to EMT-guidance it offers real-time imaging and in contrast to conventional ultrasound it is not affected by gas-filled organs like colon or the stomach. On the other hand, additional puncture of the femoral vein is necessary to advance the IVUS system in the inferior vena cava. Jomier et al. use a 3D/2D registration method with a preinterventionally acquired CT/MR dataset to create a vessel model. During the intervention angiograms in 90 angle using a biplanar
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES
5
Figure 3. TIPS procedure (A) Angiography of right hepatic vein (HV). (B) Portography after successful puncture of the portal vein. (C) Radiography after placement of stent graft. (D) Angiography after successful TIPS.
angiography unit were acquired and thereafter registered with the preinterventional vascular model. This technique was so far only validated in computer simulations (24). This interesting method does neither allow three-dimensional nor real-time imaging of the procedure and therefore does not seem to be very helpful to facilitate TIPS. In comparison to the previously proposed techniques EMT-guidance of TIPS allows for real-time 3Dvisualization of the TIPS-needle and the surrounding catheter in a preinterventionally acquired computed tomography (CT) or FDCT. To account for respiratory organ displacement and electromagnetic field
distortion by metallic objects (angiography table and other metallic material in the angiography suite) we were able to incorporate a respiratory monitoring system as well as field distortion compensation (25). In the in-vitro setting EMT-guided TIPS proved to be very feasible and allowed successful portal vein cannulation in all cases. For the transfer of this technique to the in-vivo situation several aspects have to be taken into account: Firstly due to respiratory organ displacement accurate visualization of the TIPS-set in relation to the preinterventionally acquired FDCT (expiratory phase) is only possible in the expiratory phase. Therefore, the respiration state was
6
P. ISFORT ET AL.
Figure 4. Software visualization screenshot of the software during intervention. During intervention two planes can be displayed simultaneously. Red crosshair marks the aim that was planned before using the software before starting the procedure. Blue crosshair marks the tip of the transjugular intrahepatic portosystemic shunt (TIPS) stylet and yellow crosshair marks the tip of outer guiding catheter.
Figure 5. Mean times needed for the trials of Radiologist A (blue; three years of experience in transjugular intrahepatic portosystemic shunt (TIPS)) and Radiologist B (red; one year experience in TIPS) in the phantom study including standard deviation. Time measured between wire insertion in the superior vena cava (SVC) and transhepatic wire placement in the portal vein (PV).
continuously monitored and the respiratory phase was displayed on the right side of the intervention screen so the interventionalist knew when EMT-guidance was accurate (25). Furthermore metallic objects such as the angiography table and other instruments potentially influence the accuracy of instrument detection.
To account for that a custom-designed field distortion compensation was implemented (25). Finally, the anatomy of the liver vasculature of swine differs markedly from the human anatomy. Due to the lobed character the swine liver has a very flexible position in the upper abdomen. Because of the lobed character
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES
7
Figure 6. Intervention time for in-vivo animal studies.
the extracapsular course of the PV is also longer and the intracapsular branches of the PV are smaller than in humans (26). Given the different anatomy swine are merely a good model for difficult TIPS cases. In this scenario TIPS could not be successfully performed in two cases. After multiple punctures the trials were terminated according to the animal experiment regulations. There are several limitations applying to our presented study. We did not monitor the number of punctures needed for successful PV cannulation in the in-vivo trials since it was not the goal of the study to investigate the difficulty of TIPS in swine but to evaluate the feasibility of EMT-guidance. Although not measured in this study EMT-guidance has the potential to reduce radiation exposure both to patient and interventionalist in TIPS since the critical and time-consuming part of the procedure is performed without the use of x-ray fluoroscopy. We performed only a limited number of experiments – but even in five successful experiments we were able to show that EMT-guided TIPS bears the potential to facilitate TIPS. During needle advancement a slight displacement of the liver occurred that may have altered the position of the liver compared to the preinterventionally acquired CT used for EMT-guidance. We did not feel it was a significant problem since the needle could be advanced quite smoothly, nevertheless the displacement could be more pronounced in cirrhotic livers – a scenario that was not taken into account in this experimental study. In conclusion EMT-guided TIPS could be successfully performed in-vitro and in-vivo. Furthermore it is
promising to facilitate TIPS in the clinical setting. Additional material refinement and more extensive studies are needed to fully translate the technique into clinical application.
Acknowledgements This work was carried out within the medtec-in.nrw project, supported by the state North Rhine-Westphalia and the European Union under the Ziel2 and EFRE programs.
Disclosure statement The authors declare that there is no conflict of interest to disclose.
References 1. 2.
3.
4.
5.
6.
Schuppan D, Afdhal NH. Liver cirrhosis. Lancet 2008;371:838–51. Carbonell N, Pauwels A, Serfaty L, Fourdan O, Levy VG, Poupon R. Improved survival after variceal bleeding in patients with cirrhosis over the past two decades. Hepatology 2004;40:652–9. Rosch J, Hanafee W, Snow H, Barenfus M, Gray R. Transjugular intrahepatic portacaval shunt. An experimental work. Am J Surg 1971;121:588–92. Colombato L. The role of transjugular intrahepatic portosystemic shunt (TIPS) in the management of portal hypertension. J Clin Gastroenterol 2007;41: S344–S51. D'Amico G, Pagliaro L, Bosch J. The treatment of portal hypertension: a meta-analytic review. Hepatology 1995;22:332–54. Gines P, Uriz J, Calahorra B, Garcia-Tsao G, Kamath PS, Del Arbol LR, et al. Transjugular intrahepatic portosystemic shunting versus paracentesis plus
8
P. ISFORT ET AL.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
albumin for refractory ascites in cirrhosis. Gastroenterology 2002;123:1839–47. Lebrec D, Giuily N, Hadengue A, Vilgrain V, Moreau R, Poynard T, et al. Transjugular intrahepatic portosystemic shunts: comparison with paracentesis in patients with cirrhosis and refractory ascites: a randomized trial. French group of clinicians and a group of biologists. J Hepatol 1996;25:135–44. Rossle M, Ochs A, Gulberg V, Siegerstetter V, Holl J, Deibert P, et al. A comparison of paracentesis and transjugular intrahepatic portosystemic shunting in patients with ascites. N Engl J Med 2000;342:1701–7. Garcia-Pagan JC, Caca K, Bureau C, Laleman W, Appenrodt B, Luca A, et al. Early use of TIPS in patients with cirrhosis and variceal bleeding. N Engl J Med 2010;362:2370–9. Boyer TD, Haskal ZJ, American Association for the Study of Liver D. The role of transjugular intrahepatic portosystemic shunt in the management of portal hypertension. Hepatology 2005;41:386–400. Wood BJ, Zhang H, Durrani A, Glossop N, Ranjan S, Lindisch D, et al. Navigation with electromagnetic tracking for interventional radiology procedures: a feasibility study. J Vasc Interv Radiol 2005;16: 493–505. Abi-Jaoudeh N, Glossop N, Dake M, Pritchard WF, Chiesa A, Dreher MR, et al. Electromagnetic navigation for thoracic aortic stent-graft deployment: a pilot study in swine. J Vasc Interv Radiol 2010;21:888–95. Barratt DC, Davies AH, Hughes AD, Thom SA, Humphries KN. Accuracy of an electromagnetic three-dimensional ultrasound system for carotid artery imaging. Ultrasound Med Biol 2001;27:1421–5. Bock M, Volz S, Zuhlsdorff S, Umathum R, Fink C, Hallscheidt P, et al. [Automatic slice tracking in interventional magnetic resonance imaging]. Z Med Phys 2003;13:177–82. Brost A, Wu W, Koch M, Wimmer A, Chen T, Liao R, et al. Combined cardiac and respiratory motion compensation for atrial fibrillation ablation procedures. Medical image computing and computerassisted intervention. MICCAI Int Conf Med Image Comput Computer-Assist Intervent 2011;14:540–7. de Lambert A, Esneault S, Lucas A, Haigron P, Cinquin P, Magne JL. Electromagnetic tracking for registration and navigation in endovascular aneurysm repair: a phantom study. Eur J Vasc Endovasc Surg 2012;43:684–9.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
Manstad-Hulaas F, Tangen GA, Gruionu LG, Aadahl P, Hernes TA. Three-dimensional endovascular navigation with electromagnetic tracking: ex vivo and in vivo accuracy. J Endovasc Ther 2011;18:230–40. Levy EB, Zhang H, Lindisch D, Wood BJ, Cleary K. Electromagnetic tracking-guided percutaneous intrahepatic portosystemic shunt creation in a swine model. J Vasc Interv Radiol 2007;18:303–7. Na HS, Penzkofer T, Isfort P, Wilkmann C, Mahnken AH, Kuhl CK, et al. In.nrw Hyther: electromagnetically navigated in situ fenestration of aortic stent grafts. Biomedizinische Technik/Biomedical Engineering 2012;57:92. doi: 10.1515/bmt-2012-4544. Penzkofer T, Bruners P, Isfort P, Schoth F, Gunther RW, Schmitz-Rode T, et al. Free-hand CT-based electromagnetically guided interventions: accuracy, efficiency and dose usage. Minim Invasive Ther Allied Technol 2011;20:226–33. Penzkofer T, Isfort P, Bruners P, Wiemann C, Kyriakou Y, Kalender WA, et al. Robot arm based flat panel CT-guided electromagnetic tracked spine interventions: phantom and animal model experiments. Eur Radiol 2010;20:2656–62. Boyer TD, Haskal ZJ. American association for the study of liver diseases practice guidelines: the role of transjugular intrahepatic portosystemic shunt creation in the management of portal hypertension. J Vasc Interv Radiol 2005;16:615–29. Kew J, Davies RP. Intravascular ultrasound guidance for transjugular intrahepatic portosystemic shunt procedure in a swine model. CVIR 2004;27:38–41. Jomier J, Bullitt E, Van Horn M, Pathak C, Aylward SR. 3D/2D model-to-image registration applied to TIPS surgery. Medical image computing and computer-assisted intervention. MICCAI Int Conf Med Image Comput Computer-Assist Intervent 2006;9: 662–9. Penzkofer T, Isfort P, Na HS, Wilkmann C, Osterhues S, Besting A, et al. Technical concepts for vascular electromagnetic navigated interventions: Aortic in situ fenestration and transjugular intrahepatic porto-systemic shunts. Biomedizinische Technik Biomed Eng 2014;59:153–63. Court FG, Wemyss-Holden SA, Morrison CP, Teague BD, Laws PE, Kew J, et al. Segmental nature of the porcine liver and its potential as a model for experimental partial hepatectomy. Br J Surg 2003;90:440–4.
ISSN: 1364-5706 (Print) 1365-2931 (Online) Journal homepage: http://www.tandfonline.com/loi/imit20
Feasibility of electromagnetically guided transjugular intrahepatic portosystemic shunt procedure Peter Isfort, Tobias Penzkofer, Christoph Wilkmann, Hong-Sik Na, Christian Kotzlowski, Nobutake Ito, Joachim Georg Pfeffer, Stefan Bisplinghoff, Sabine Osterhues, Andreas Besting, Jorge Gooding, Thomas Schmitz-Rode, Christiane Kuhl, Andreas Horst Mahnken & Philipp Bruners To cite this article: Peter Isfort, Tobias Penzkofer, Christoph Wilkmann, Hong-Sik Na, Christian Kotzlowski, Nobutake Ito, Joachim Georg Pfeffer, Stefan Bisplinghoff, Sabine Osterhues, Andreas Besting, Jorge Gooding, Thomas Schmitz-Rode, Christiane Kuhl, Andreas Horst Mahnken & Philipp Bruners (2016): Feasibility of electromagnetically guided transjugular intrahepatic portosystemic shunt procedure, Minimally Invasive Therapy & Allied Technologies, DOI: 10.1080/13645706.2016.1214155 To link to this article: http://dx.doi.org/10.1080/13645706.2016.1214155
Published online: 09 Aug 2016.
Submit your article to this journal
Article views: 10
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=imit20 Download by: [Cornell University Library]
Date: 16 October 2016, At: 09:17
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES, 2016 http://dx.doi.org/10.1080/13645706.2016.1214155
ORIGINAL ARTICLE
Feasibility of electromagnetically guided transjugular intrahepatic portosystemic shunt procedure Peter Isforta, Tobias Penzkofera,b,c, Christoph Wilkmanna, Hong-Sik Naa, Christian Kotzlowskia, Nobutake Itod,e, Joachim Georg Pfeffera, Stefan Bisplinghoffh, Sabine Osterhuesf, Andreas Bestingg, Jorge Goodinge, Thomas Schmitz-Rodee, Christiane Kuhla, Andreas Horst Mahnkeni and Philipp Brunersa a Diagnostic and Interventional Radiology, RWTH Aachen University Hospital, Aachen, Germany; bSurgical Planning Laboratory, Brigham and Women's Hospital, Boston, MA, USA; cDiagnostic and Interventional Radiology, Charite Universit€atsmedizin Berlin, Berlin, Germany; dDepartment of Radiology, Keio University, Tokyo, Japan; eApplied Medical Engineering, RWTH Aachen University Hospital, Aachen, Germany; fVygon GmbH & Co. KG, Aachen, Germany; gSurgiTAIX AG, Herzogenrath, Germany; hMedical Engineering, RWTH Aachen University, Aachen, Germany; iDepartment of Diagnostic and Interventional Radiology, Philips University Hospital, Marburg, Germany
ABSTRACT
ARTICLE HISTORY
Objectives: To develop an electromagnetic navigation technology for transjugular intrahepatic portosystemic shunt (TIPS) creation and translate it from phantom to an in-vivo large animal setting. Material and methods: A custom-designed device for TIPS creation consisting of a stylet within a 5 French catheter as well as a software prototype were developed that allow real-time tip tracking of both stylet and catheter using an electromagnetic tracking system. Feasibility of navigated TIPSS creation was tested in a phantom by two interventional radiologists (A/B) followed by in-vivo testing evaluation in eight domestic pigs. Procedure duration and number of attempts needed for puncture of the portal vein were recorded. Results: In the phantom setting, intervention time to gain access to the portal vein (PV) was 144 ± 67 s (A) and 122 ± 51 s (B), respectively. In the in-vivo trials, TIPS could be successfully completed in five out of eight animals. Mean time for the complete TIPS was 245 ± 205 minutes with a notable learning curve towards the last animal. Conclusions: TIPS creation with the use of electromagnetic tracking technology proved to be feasible in-vitro as well as in-vivo. The system may be useful to facilitate challenging TIPSS procedures.
Received 14 March 2016 Accepted 8 June 2016 Published online 29 July 2016
Introduction In patients with liver cirrhosis, portal hypertension is a common problem that is associated with severe and often even life-threatening complications. These include therapy-refractory ascites and variceal bleeding (1). The outcome of acute variceal bleeding (VB) has dramatically improved over the last two decades, with mortality rates decreasing from over 40% in the 1980s down to about 15% in the year 2000 (2). This improvement is due to improved medical treatment, and, probably more important, to minimally invasive treatment methods such as endoscopic hemostasis and transjugular intrahepatic portosystemic shunt (TIPSS) placement. Developed in the early 1970s by R€ osch et al., an artificial portosystemic shunt between one of the hepatic veins and the portal vein is created. This is achieved by transjugular engaging the hepatic vein, followed by transhepatic puncture of a portal branch CONTACT P. Isfort
[email protected]
KEYWORDS
Image-guided procedures; interventional radiology; vascular intervention
with a bent needle. After balloon dilatation a stent or stent graft is placed to secure the transparenchymal passage (3). TIPS placement effectively achieves hemostasis in >90% of patients with acute variceal bleeding, and protects the patient from re-bleeding (4). In accordance with the results of randomized controlled trials, TIPS is today recommended as the treatment of choice in patients with variceal re-bleeding and/or refractory ascites in an acute and subacute setting (5–9). Further non-randomized studies also confirm the efficacy of TIPS in acute variceal bleeding, portal hypertensive gastropathy, bleeding gastric varices, refractory hepatic hydrothorax, hepatorenal syndrome (type 1 or type 2), Budd-Chiari syndrome, veno-occlusive disease and hepatopulmonary syndrome (10). Although TIPS is an effective therapy in many patients suffering from portal hypertension, it is mainly performed in specialized centers. One reason
Department of Diagnostic and Interventional Radiology, University Hospital RWTH Aachen, Germany
ß 2016 SMIT - Society for Minimally Invasive Therapy
2
P. ISFORT ET AL.
for this is the fact that severe complications caused by the transparenchymal puncture of the portal vein can yield lethal complications in patients with underlying liver disease who usually suffer from compromised coagulation function. Especially hemoperitoneum, due to extracapsular puncture of the hepatic artery, the inferior vena cava (IVC) or the aorta, may lead to a fatal outcome of the procedure (10). To avoid such complications, the crucial step of the TIPS procedure – i.e., the transhepatic portal vein puncture – is done under x-ray fluoroscopy control, with or without additional ultrasound. However, the ability of these methods to actually guide the puncture by locating the position of the needle tip with regard to the target, i.e., the portal vein branch, is poor. Fluoroscopy visualizes only radiopaque catheters/needles, but provides no direct 3D information about the anatomic structures in correlation to the needle tip. More importantly, only the hepatic veins can be opacified by contrast injection, whereas the portal vein remains invisible until after successful transhepatic puncture. Ultrasound provides only limited information of the needle position with respect to the portal vein; it provides only two-dimensional information, i.e., usually visualizes either portal vein or needle tip, or needs to use non-standard, oblique planes to visualize both structures within one section. Accordingly, there is a clear need to improve image guidance of this procedure. The ideal image guidance would provide visualization of the following aspects:
Levy et al. performed EMT-guided TIPS using a percutaneous transhepatic approach with a trackable straight puncture needle (18). A major drawback of this technique is the need for a transcapsular puncture. Therefore our aim was to transfer our experience with EMT from musculoskeletal and aortic interventions to the TIPS procedure and to use this technique in the standard transjugular approach (19–21).
Material and methods TIPS-device We developed a TIPS device that consists of a stainless steel stylet (diameter 0.9 mm; Figure 1 I-III(a)) with a flexible tip, a polypropylene catheter (diameter 1.65 mm; Figure 1 I-III(b)), an outer stainless steel cannula with a 30 bent tip (diameter 2.0 mm; Figure 1 I-III(c)) and a guiding catheter (Figure 1 I-III(d)). Coils with a diameter of 0.5 mm were integrated into the tips of the stylet and the guiding catheter for electromagnetic tracking. Furthermore, a 0.86 mm polyimide compound guidewire was developed with an integrated coil at the tip as well (Figure 1 IV). See also Figure 1 I-IV for details on the custom-made TIPS device.
3D visualization of the target structures, i.e., the hepatic veins and the portal vein, and of critical structures that need to be avoided, e.g., the liver capsule real-time time 3D visualization of the involved instruments and their movements starting point and end point of the transhepatic puncture. Electromagnetic tracking (EMT) is based on the detection of small metallic coils in a magnetic field by induction. In contrast to optical navigation, no direct line-of-sight between the tracked fiducials and the navigation system is needed, so direct tracking of the instrument tip and tracking of bendable instruments is possible (11). Over the past years, the size of EMT coils has significantly decreased. Coils as small as 0.3 mm in diameter are currently available. Accordingly, EMT seems to provide the necessary prerequisites for tracking of catheter-based vascular interventions (11–17).
Figure 1. Custom-made TIPS device I-III: A: 0.9 mm stainless steel stylet with integrated coil at stylet‘s tip; B: 1.65 mm polypropylene catheter; C: 2.0 mm stainless steel outer cannula with bent tip; D: 3.35 mm guiding catheter with integrated coil at the tip of the catheter. IV: Proprietary 0.86 mm polyimide compound guidewire with an integrated coil at the tip.
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES
3
Navigation system A state-of-the-art electromagnetic navigation system (Aurora, Northern Digital, Waterloo, Canada) was used as a platform for the EMT-guided TIPS procedure. Due to large metallic components in the angiography environment such as the c-arm or parts of the patient table, a significant distortion of the electromagnetic field can occur. This may lead to substantial errors of the detected device position. To dynamically detect and compensate such field distortions, an algorithm was implemented based on the continuous detection of sensors affixed at the animal’s thorax with a known geometry. Furthermore, due to patient or organ movement, and thus displacement of target structures during the respiratory cycle, motion-compensation was implemented using multiple miniature three-dimensional accelerometers. The sensors were affixed to the animal’s thorax prior to image acquisition in order to measure the inclination changes of the upper body at multiple positions. The system allows for visualization of the respiratory phase that matches the respiratory state of image acquisition best. Details on the electromagnetic tracking system, on the custom-designed and manufactured TIPS device, on respiratory motion compensation, and the proprietary software used in the in-vitro and in-vivo experiments have been published previously (20). In-vitro experiments As a first step, in-vitro experiments were performed in order to evaluate the technical feasibility of the EMT-guided TIPS procedure. For this purpose, a phantom was established consisting of custom-made silicon tubes representing the relevant vasculature (superior vena cava (SVC), hepatic veins (HV), portal vein (PV)), embedded in gel wax. Dimensions and geometry of the silicon tubes were derived from high resolution CT-datasets of ten consecutive patients who underwent TIPS-procedure at our institution within the last year. A flat detector CT (FDCT) (Artis Zeego, Siemens medical, Erlangen, Germany) of the phantom was acquired including the affixed reference plate serving as volume image dataset for the navigation system. After transfer of the reconstructed axial image data set (slice thickness: 1 mm; increment: 0.7 mm) to the navigation system and registration of the electromagnetic field and image volume, the transhepatic puncture was planned defining the exit of the liver vein as the start and the entry point into the portal vein
Figure 2. Experimental setting for the phantom study. I/II: A: Electromagnetic field generator; B: Instrument interface; C: Gelwax phantom – Arrow marks superior vena cava (SVC) with liver veins (HV); Arrowhead marks portal vein and its main branches. II: Setup of phantom study in angiography suite. The top opening of the phantom was closed during the trials to avoid optical bias.
branch as the endpoint. Both points were identified in the image dataset using the developed navigation software tool. Then navigated transhepatic punctures without additional image guidance were performed using the developed TIPS device. See also Figure 2 I-II for details on the experimental setting of the in-vitro study. For each puncture, the duration of the procedure was recorded. We defined insertion of the guidewire into the phantom as starting point; end point was successful placement of the guidewire through the liver vein into a portal vein branch after transhepatic puncture. The experiment was performed 40 times by each of two radiologists with three years (Radiologist A) and one year (Radiologist B) of experience in performing TIPS. Statistical analysis, i.e., comparison of the procedure times as defined above was performed using the t-test (MedCalc 13.2.2.0, Medcalc software, Ostend, Belgium). In-vivo experiments All animal experiments were performed in accordance with the local regulatory board (Ministry of
4
P. ISFORT ET AL.
Environment, Nature and Consumer Protection). EMT-guided TIPS procedures were performed in eight female domestic pigs with a mean weight of 60 kg. All interventions were done under general anesthesia after orotracheal intubation. A contrastenhanced FDCT (Artis Zeego, Siemens Medical, Germany) was acquired in the expiratory phase after injection of 60 ml iopromide (3 ml/s; 60 s delay) via a peripheral catheter placed in an ear vein. Thereafter, the right jugular vein was punctured under ultrasound guidance using an 18 G needle. A 10 F sheath was inserted over a hydrophilic guidewire. Next, the transhepatic puncture from the right or middle hepatic vein to a main portal vein branch was planned based on the acquired FDCT image set with the developed navigation software. Then the defined hepatic vein was cannulated using the proprietary EMT-guidewire in combination with a 5 F liver vein catheter. After opacification of the vein, the liver vein catheter was exchanged for the TIPS-device which was placed at the starting point of the transparenchymal passage. Transhepatic puncture was performed using real-time EMT guidance of the stylet without x-ray fluoroscopy control. Successful puncture of the target portal vein branch was verified by manual contrast injection. Thereafter, the proprietary guidewire was advanced through the portal vein into the superior mesenteric vein together with the polypropylene catheter. This was then exchanged for a stiff regular guidewire (Amplatz Super stiff guide wire, Boston Scientific, Natick, MA), followed by insertion of a long 8 F sheath and 8 mm TIPS endoprosthesis (Viatorr TIPS endoprosthesis, Gore, P€ utzbronn, Germany). The time between sheath placement in the right jugular vein and successful placement of the endoprosthesis was recorded. See also Figure 3(a–d) and Figure 4 for details on the in-vivo experiments.
Results In-vitro experiments All experiments were successful. The mean time between wire insertion in the SVC and successful wire placement in the PV/IMV was 144 ± 67 s (Radiologist A) and 122 ± 51 s (Radiologist B). No statistically significant difference was observed between the operators (p 0,05). See also Figure 5 for details on the results of the in-vitro experiments. In-vivo experiments EMT-guided TIPS could successfully be performed in five out of eight animals. One animal died due to
acute arrhythmia after passage of the TIPS device through the right atrium. In two animals TIPS could not be performed successfully because of an unfavourable anatomy of the liver vasculature. After multiple unsuccessful punctures animals were euthanized according to the animal experiment regulations. The mean time between sheath placement in the right jugular vein and successful placement of the TIPS endoprosthesis was 245 ± 205 minutes. The time varied between 85 and 590 minutes and showed a notable learning curve towards the last animals. See also Figure 6 for results of the in-vivo trials.
Discussion TIPS can be associated with life-threatening complications such as transcapsular puncture and intraperitoneal hemorrhage, which can be especially severe in the setting of ascites and deteriorated blood coagulation due to underlying liver disease. The risk for transcapsular puncture can be as high as 33% with significant intraperitoneal hemorrhage occurring in 1– 2% of cases (22). Compared to other image-guided procedures that involve transparenchymal punctures in the vicinity of large vessels or other structures at risk, that are usually performed under CT-guidance, image guidance of TIPS using x-ray fluoroscopy and additional ultrasound is rather poor. During transhepatic puncture only radiopaque parts of the TIPS-set are visualized and with ultrasound only parts of the needle tip can be depicted in two dimensions. Moreover, ultrasound guidance is often limited to an intercostal view because of air-filled bowel blocking the subcostal view. Given the current limitations of image guidance in TIPS there is a need for accurate 3D-imaging during TIPS in combination with real-time of the used devices. Kew et al. described in their study successful TIPS procedures under intravascular ultrasound (IVUS) guidance in three swine with the ultrasound system placed in the inferior vena cava (23). Nevertheless, IVUS allows only a limited two-dimensional visualization of the relevant parts of the liver. When compared to EMT-guidance it offers real-time imaging and in contrast to conventional ultrasound it is not affected by gas-filled organs like colon or the stomach. On the other hand, additional puncture of the femoral vein is necessary to advance the IVUS system in the inferior vena cava. Jomier et al. use a 3D/2D registration method with a preinterventionally acquired CT/MR dataset to create a vessel model. During the intervention angiograms in 90 angle using a biplanar
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES
5
Figure 3. TIPS procedure (A) Angiography of right hepatic vein (HV). (B) Portography after successful puncture of the portal vein. (C) Radiography after placement of stent graft. (D) Angiography after successful TIPS.
angiography unit were acquired and thereafter registered with the preinterventional vascular model. This technique was so far only validated in computer simulations (24). This interesting method does neither allow three-dimensional nor real-time imaging of the procedure and therefore does not seem to be very helpful to facilitate TIPS. In comparison to the previously proposed techniques EMT-guidance of TIPS allows for real-time 3Dvisualization of the TIPS-needle and the surrounding catheter in a preinterventionally acquired computed tomography (CT) or FDCT. To account for respiratory organ displacement and electromagnetic field
distortion by metallic objects (angiography table and other metallic material in the angiography suite) we were able to incorporate a respiratory monitoring system as well as field distortion compensation (25). In the in-vitro setting EMT-guided TIPS proved to be very feasible and allowed successful portal vein cannulation in all cases. For the transfer of this technique to the in-vivo situation several aspects have to be taken into account: Firstly due to respiratory organ displacement accurate visualization of the TIPS-set in relation to the preinterventionally acquired FDCT (expiratory phase) is only possible in the expiratory phase. Therefore, the respiration state was
6
P. ISFORT ET AL.
Figure 4. Software visualization screenshot of the software during intervention. During intervention two planes can be displayed simultaneously. Red crosshair marks the aim that was planned before using the software before starting the procedure. Blue crosshair marks the tip of the transjugular intrahepatic portosystemic shunt (TIPS) stylet and yellow crosshair marks the tip of outer guiding catheter.
Figure 5. Mean times needed for the trials of Radiologist A (blue; three years of experience in transjugular intrahepatic portosystemic shunt (TIPS)) and Radiologist B (red; one year experience in TIPS) in the phantom study including standard deviation. Time measured between wire insertion in the superior vena cava (SVC) and transhepatic wire placement in the portal vein (PV).
continuously monitored and the respiratory phase was displayed on the right side of the intervention screen so the interventionalist knew when EMT-guidance was accurate (25). Furthermore metallic objects such as the angiography table and other instruments potentially influence the accuracy of instrument detection.
To account for that a custom-designed field distortion compensation was implemented (25). Finally, the anatomy of the liver vasculature of swine differs markedly from the human anatomy. Due to the lobed character the swine liver has a very flexible position in the upper abdomen. Because of the lobed character
MINIMALLY INVASIVE THERAPY & ALLIED TECHNOLOGIES
7
Figure 6. Intervention time for in-vivo animal studies.
the extracapsular course of the PV is also longer and the intracapsular branches of the PV are smaller than in humans (26). Given the different anatomy swine are merely a good model for difficult TIPS cases. In this scenario TIPS could not be successfully performed in two cases. After multiple punctures the trials were terminated according to the animal experiment regulations. There are several limitations applying to our presented study. We did not monitor the number of punctures needed for successful PV cannulation in the in-vivo trials since it was not the goal of the study to investigate the difficulty of TIPS in swine but to evaluate the feasibility of EMT-guidance. Although not measured in this study EMT-guidance has the potential to reduce radiation exposure both to patient and interventionalist in TIPS since the critical and time-consuming part of the procedure is performed without the use of x-ray fluoroscopy. We performed only a limited number of experiments – but even in five successful experiments we were able to show that EMT-guided TIPS bears the potential to facilitate TIPS. During needle advancement a slight displacement of the liver occurred that may have altered the position of the liver compared to the preinterventionally acquired CT used for EMT-guidance. We did not feel it was a significant problem since the needle could be advanced quite smoothly, nevertheless the displacement could be more pronounced in cirrhotic livers – a scenario that was not taken into account in this experimental study. In conclusion EMT-guided TIPS could be successfully performed in-vitro and in-vivo. Furthermore it is
promising to facilitate TIPS in the clinical setting. Additional material refinement and more extensive studies are needed to fully translate the technique into clinical application.
Acknowledgements This work was carried out within the medtec-in.nrw project, supported by the state North Rhine-Westphalia and the European Union under the Ziel2 and EFRE programs.
Disclosure statement The authors declare that there is no conflict of interest to disclose.
References 1. 2.
3.
4.
5.
6.
Schuppan D, Afdhal NH. Liver cirrhosis. Lancet 2008;371:838–51. Carbonell N, Pauwels A, Serfaty L, Fourdan O, Levy VG, Poupon R. Improved survival after variceal bleeding in patients with cirrhosis over the past two decades. Hepatology 2004;40:652–9. Rosch J, Hanafee W, Snow H, Barenfus M, Gray R. Transjugular intrahepatic portacaval shunt. An experimental work. Am J Surg 1971;121:588–92. Colombato L. The role of transjugular intrahepatic portosystemic shunt (TIPS) in the management of portal hypertension. J Clin Gastroenterol 2007;41: S344–S51. D'Amico G, Pagliaro L, Bosch J. The treatment of portal hypertension: a meta-analytic review. Hepatology 1995;22:332–54. Gines P, Uriz J, Calahorra B, Garcia-Tsao G, Kamath PS, Del Arbol LR, et al. Transjugular intrahepatic portosystemic shunting versus paracentesis plus
8
P. ISFORT ET AL.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
albumin for refractory ascites in cirrhosis. Gastroenterology 2002;123:1839–47. Lebrec D, Giuily N, Hadengue A, Vilgrain V, Moreau R, Poynard T, et al. Transjugular intrahepatic portosystemic shunts: comparison with paracentesis in patients with cirrhosis and refractory ascites: a randomized trial. French group of clinicians and a group of biologists. J Hepatol 1996;25:135–44. Rossle M, Ochs A, Gulberg V, Siegerstetter V, Holl J, Deibert P, et al. A comparison of paracentesis and transjugular intrahepatic portosystemic shunting in patients with ascites. N Engl J Med 2000;342:1701–7. Garcia-Pagan JC, Caca K, Bureau C, Laleman W, Appenrodt B, Luca A, et al. Early use of TIPS in patients with cirrhosis and variceal bleeding. N Engl J Med 2010;362:2370–9. Boyer TD, Haskal ZJ, American Association for the Study of Liver D. The role of transjugular intrahepatic portosystemic shunt in the management of portal hypertension. Hepatology 2005;41:386–400. Wood BJ, Zhang H, Durrani A, Glossop N, Ranjan S, Lindisch D, et al. Navigation with electromagnetic tracking for interventional radiology procedures: a feasibility study. J Vasc Interv Radiol 2005;16: 493–505. Abi-Jaoudeh N, Glossop N, Dake M, Pritchard WF, Chiesa A, Dreher MR, et al. Electromagnetic navigation for thoracic aortic stent-graft deployment: a pilot study in swine. J Vasc Interv Radiol 2010;21:888–95. Barratt DC, Davies AH, Hughes AD, Thom SA, Humphries KN. Accuracy of an electromagnetic three-dimensional ultrasound system for carotid artery imaging. Ultrasound Med Biol 2001;27:1421–5. Bock M, Volz S, Zuhlsdorff S, Umathum R, Fink C, Hallscheidt P, et al. [Automatic slice tracking in interventional magnetic resonance imaging]. Z Med Phys 2003;13:177–82. Brost A, Wu W, Koch M, Wimmer A, Chen T, Liao R, et al. Combined cardiac and respiratory motion compensation for atrial fibrillation ablation procedures. Medical image computing and computerassisted intervention. MICCAI Int Conf Med Image Comput Computer-Assist Intervent 2011;14:540–7. de Lambert A, Esneault S, Lucas A, Haigron P, Cinquin P, Magne JL. Electromagnetic tracking for registration and navigation in endovascular aneurysm repair: a phantom study. Eur J Vasc Endovasc Surg 2012;43:684–9.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
Manstad-Hulaas F, Tangen GA, Gruionu LG, Aadahl P, Hernes TA. Three-dimensional endovascular navigation with electromagnetic tracking: ex vivo and in vivo accuracy. J Endovasc Ther 2011;18:230–40. Levy EB, Zhang H, Lindisch D, Wood BJ, Cleary K. Electromagnetic tracking-guided percutaneous intrahepatic portosystemic shunt creation in a swine model. J Vasc Interv Radiol 2007;18:303–7. Na HS, Penzkofer T, Isfort P, Wilkmann C, Mahnken AH, Kuhl CK, et al. In.nrw Hyther: electromagnetically navigated in situ fenestration of aortic stent grafts. Biomedizinische Technik/Biomedical Engineering 2012;57:92. doi: 10.1515/bmt-2012-4544. Penzkofer T, Bruners P, Isfort P, Schoth F, Gunther RW, Schmitz-Rode T, et al. Free-hand CT-based electromagnetically guided interventions: accuracy, efficiency and dose usage. Minim Invasive Ther Allied Technol 2011;20:226–33. Penzkofer T, Isfort P, Bruners P, Wiemann C, Kyriakou Y, Kalender WA, et al. Robot arm based flat panel CT-guided electromagnetic tracked spine interventions: phantom and animal model experiments. Eur Radiol 2010;20:2656–62. Boyer TD, Haskal ZJ. American association for the study of liver diseases practice guidelines: the role of transjugular intrahepatic portosystemic shunt creation in the management of portal hypertension. J Vasc Interv Radiol 2005;16:615–29. Kew J, Davies RP. Intravascular ultrasound guidance for transjugular intrahepatic portosystemic shunt procedure in a swine model. CVIR 2004;27:38–41. Jomier J, Bullitt E, Van Horn M, Pathak C, Aylward SR. 3D/2D model-to-image registration applied to TIPS surgery. Medical image computing and computer-assisted intervention. MICCAI Int Conf Med Image Comput Computer-Assist Intervent 2006;9: 662–9. Penzkofer T, Isfort P, Na HS, Wilkmann C, Osterhues S, Besting A, et al. Technical concepts for vascular electromagnetic navigated interventions: Aortic in situ fenestration and transjugular intrahepatic porto-systemic shunts. Biomedizinische Technik Biomed Eng 2014;59:153–63. Court FG, Wemyss-Holden SA, Morrison CP, Teague BD, Laws PE, Kew J, et al. Segmental nature of the porcine liver and its potential as a model for experimental partial hepatectomy. Br J Surg 2003;90:440–4.
