Eur Radiol (2010) 20: 2000–2004DOI 10.1007/s00330-010-1739-1 INTERVENTIONAL

Philipp BrunersTobias PenzkoferPeter IsfortJochen PfefferThomas Schmitz-RodeRolf W. GüntherAndreas H. Mahnken

Received: 18 November 2009Accepted: 8 January 2010Published online: 24 February 2010# European Society of Radiology 2010

A trucut biopsy needle for bipolarradiofrequency ablation of needle tract:a proof-of-concept experiment

Abstract Objective: To develop atrucut biopsy needle featuring twoelectrodes that allow for bipolarradiofrequency (RF) coagulation ofthe puncture tract. Methods: Wemodified a 14-G trucut biopsy needleto contain two insulated electrodesand connected the device to an RFgenerator. Biopsies in ex vivo porcineliver and kidney were performed. Thepuncture tract was coagulated byusing different RF energy settings(5 W, 10 W, 20 W). Tissue specimenswere dissected along the puncturetract and the coagulation area wasmacroscopically evaluated. CT-guided in vivo liver and kidneybiopsies were performed in twodomestic pigs. Lengths of specimenswere measured. Post-biopsy contrast-enhanced CT examinations were per-formed to rule out biopsy-relatedbleeding. Animals were euthanised

and coagulation areas macroscopi-cally explored. Results: The meandiameters of the coagulated areaaround the ex vivo biopsy tract were4.2±1.1 mm (5 W), 6.0±2.0 mm(10 W) and 5.2±0.51 mm (20 W) inliver and 5.0±0.7 mm (5 W), 6.6±0.9(10 W) and 6.0±2.0 mm (20 W) inkidney. After biopsies CT revealed nobleeding. Mean maximum coagula-tion diameters were 10.1±4.6 mm(10 W) in liver and 6.0±2.5 mm(10 W) in kidney. Mean length of thespecimens was 12.2±4.4 mm in kid-ney and 11.1±3.6 mm in liver tissue.Conclusion: Bipolar RF biopsy is apromising tool for tract coagulationafter percutaneous biopsy.

Keywords Biopsy . Radiofrequencyablation . Trucut . Bleeding . Tumourcell seeding

Introduction

Abdominal percutaneous core biopsies under CT guidancewere shown to provide a sensitivity, specificity andaccuracy of 91.1%, 100% and 93.3%, respectively [1].Regarding the associated complication rate a large multi-centre study including 68,276 liver biopsies showed ahigher complication rate after biopsy with the trucut needlethan after biopsy with Menghini’s needle (0.3% vs. 0.1%)[2]. In a prospective study including 120 patients under-going liver biopsy with a 2-mm trucut needle, post-biopsyintrahepatic haematoma was found to occur in 18.2% ofcases [3]. Kim et al. found evidence that applyingradiofrequency current after liver biopsy reduces blood

loss in a canine model [4]. Furthermore seeding of tumourcells along the puncture tract following biopsy of malig-nant tumours is also a rare but severe complication [5]. Forpercutaneous biopsies of hepatocellular carcinoma (HCC)the rate of tumour cell seeding along the puncture tract wasfound in up to 5% of cases [6]. Use of radiofrequency (RF)ablation for the treatment of HCC coagulation of thepuncture tract is recommended to reduce the risk of tumourseeding [7].

Therefore, our aim was to develop a trucut biopsy needlefeaturing a fully integrated bipolar RF ablation electrodewithout the need for a neutral electrode for the post-biopsycoagulation of the puncture tract and to show the practic-ability of the device in an ex vivo and in vivo animal model.

P. Bruners . T. Penzkofer . P. Isfort .J. Pfeffer . T. Schmitz-RodeApplied Medical Engineering,Helmholtz Institute for BiomedicalEngineering,RWTH Aachen University,Aachen, Germany

P. Bruners (*) . T. Penzkofer .P. Isfort . R. W. Günther .A. H. MahnkenDepartment of Diagnostic Radiology,University Hospital,RWTH Aachen University,Pauwelsstrasse 30,52074 Aachen, Germanye-mail: bruners@rad.rwth-aachen.deTel.: +49-241-8088332Fax: +49-241-8082499

Materials and methods

Device specifications

Because trucut biopsy needles are widely used and effectiveinstruments only minimal modifications of the establisheddesign should be made. In particular the needle diametershould not be significantly increased. Because the aimwas tofully integrate the RF coagulation system into the biopsydevice, a bipolar concept was pursued without the need forlarge grounding pads. Accordingly both electrodes forbipolar RF coagulation as well as the required electric andthermal insulation should be integrated without changing theshape, function and handling of the device.

Design

The developed prototype is based upon a commerciallyavailable standard 14-gauge (G) trucut biopsy needle (Tru-Cut, Cardinal Health, IL, USA) with a length of 14 cm. Asthe standard biopsy needle consists of two electricity-conducting metallic components, namely the outer cannulaand the inner stylet, we decided to use these parts as theelectrodes. We electrically separated both components byusing polytetrafluorethylene (PTFE) insulation (thickness0.1 mm), which was fitted around the inner stylet except forthe distal notched part which worked as the first electrode(length 27 mm). Because the diameter of the inner stylet isexactly matched to the inner diameter of the cannula it wasnecessary tomill the surface of the stylet before the insulationwas attached. In order to prevent thermal damage to the skinat the entry site and to prevent the needle from sticking to thepuncture tract, the outer cannulawas also coatedwith a PTFEexcept for the distal part. Thus, the distal exposed part of theouter cannula with a length of 8 mm worked as the secondelectrode (Fig. 1). A conductor was fixed at the inner stylet aswell as at the outer cannula (Fig. 2). In addition, an interfacewas fitted to connect the device to a commercially availableRF generator (Celon AG Medical Instruments, Teltow,Germany).

Ex vivo testing

For ex vivo testing of the device a total of 30 punctures wereperformed in freshly excised porcine liver and kidneyspecimens by using different generator outputs (Table 1).During the puncture tract ablation, the applied energy,resistance and duration were monitored by a dedicatedsoftware tool (CelonPowerMonitor Version 2.6, Celon AGMedical Instruments, Teltow, Germany). After completeretraction of the device the diameter of the coagulatedpuncture tract was macroscopically evaluated by using acalliper. The results obtained in the ex vivo study were used tooptimise theRF energy setting used in the in vivo experiments.

In vivo testing

In vivo evaluation of the device was performed in a porcinemodel. Two domestic pigs weighing approximately 60 kgwere included in this study after approval from the officialcommittee on animal affairs. After administration of apremedication consisting of azaperone (Stresnil, Jansen-Cilag, Neuss, Germany) and ketamine (Ketamine 10%,Ceva Tiergesundheit, Düsseldorf, Germany) animals wereintubated and mechanically ventilated with an oxygen–airmixture containing 0.8 vol% isoflurane. For additionalanalgesia a fentanyl drip was inserted via a venous accessroute placed in an ear vein. In addition, 1 l of 0.9% salineinfusion was administered to prevent desiccation.

All biopsies were performed under CT guidance by usingdual-source CT (Somatom Definition, Siemens, Forchheim,Germany). For liver biopsies animals were placed on the CTtable in the supine position. After a non-enhanced spiral CTacquisition for biopsy planning (64 x 0.6 mm collimation,120 kV, 165 mAseff) the device was placed by usingsequential CT fluoroscopic controls. After successful place-ment a biopsy was taken. For this purpose the inner stylet

Fig. 1 Schematic of the biopsy needle concept showing theinsulation of the inner stylet (black arrow) and the insulation ofthe outer cannula (open arrow). Current runs between the exposedmetallic parts (curved arrows)

Fig. 2 The two parts of the prototype are coated with a PTFE layerfor electrical insulation

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with the specimen was removed while the outer cannula wasleft in place. All specimens were fixed in 10% bufferedformalin. Then the device was connected to the RF generator(CelonLabPower, Celon AG Medical Instruments, Teltow,Germany) and tract ablation was performed by employing agenerator output of 10W. Retraction speed of the device wasadjusted to the measured resistance which was continuouslymonitored and displayed by the software tool. Aftercompletion of the liver biopsies, dual-phase (arterial/venous)CT was performed after injection of 123 ml of iopromide(Ultravist 370, Bayer Schering Pharma, Berlin, Germany)(flow rate 3.3ml/s) followed by a saline chaser of 40ml (flowrate 2.5 ml/s) to evaluate the induced coagulation areassurrounding the puncture tracts and to rule out post-interventional bleeding.

Next the animals were moved into the prone position forbiopsies of both kidneys which were performed in ananalogous way.

Thereafter, animals were euthanised and the liver andboth kidneys were excised and macroscopically explored.Maximum diameters of the induced coagulation areas weremeasured by using a calliper. In addition, length of theharvested specimens was measured.

Results

Ex vivo study

As known from ex vivo RF ablation studies, coagulatedtissue was represented by a tan to charcoal area symme-trically surrounding the puncture tract (Fig. 3). In both liverand kidney specimens the tract ablation protocol employing10-W generator output resulted in the largest coagulationdiameter (liver, 6.0±2.0 mm; kidney, 6.6±0.9 mm) (Table 1).

In vivo study

As the ex vivo data showed the largest coagulationdiameter for the 10-W ablation protocol, this generatoroutput was also used for the in vivo experiments.

Post-interventional control CT revealed no signs ofany active bleeding following biopsies of liver andkidneys in both animals. As known from CT controlexaminations after RF ablations, coagulation areassurrounding the puncture tracts were characterised bya lack of contrast enhancement (Fig. 4). Correspondingto the boiling of interstitial fluid, gas bubbles were foundaround some of the coagulated areas being suggestive of amaximum temperature during RF ablation of greater than100°C.

The macroscopic evaluation of the coagulated puncturetracts showed a pale area surrounding a small cavity(Fig. 5). Mean coagulation diameters in kidneys (6.0±2.5 mm) were slightly smaller than in liver tissue (10.1±4.6 mm) (Table 2).

Mean length of the harvested specimens was 12.2±4.4 mm in kidney and 11.1±3.6 mm in liver tissue.

Discussion

So far, there have only been a few studies publishedreporting the development of devices for RF ablation ofpuncture tracts after image-guided biopsies. Laeseke et al.showed a decrease in blood loss due to RF coagulation ofthe puncture tract in an animal model by using a modified17-G introducer needle [8]. However, the authors onlyperformed punctures without taking biopsies using an opensurgical approach. Furthermore, a monopolar approachwas used requiring the placement of a dispersive pad toclose the electric circuit. Conversely, the device presentedin this study features a bipolar concept allowing the currentto run only between the two integrated electrodes. Thisconstruction may be beneficial due to the fact that skinburns at the dispersive pad are avoided. In addition, inmonopolar RF systems the current passes through the

Table 1 Results of the ex vivo experiments in liver and kidney byusing different generator outputs

Tissue Number Generatoroutput(W)

Durationof ablation(s)

Mean diameterof coagulation(mm)

Meanappliedenergy (kJ)

Liver 5 5 60 4.2±1.1 0.40±0.03Liver 5 10 60 6.0±2.0 0.90±0.08Liver 5 20 60 5.2±0.5 1.22±0.43Kidney 5 5 60 5.0±0.7 0.41±0.02Kidney 5 10 60 6.6±0.9 0.99±0.13Kidney 5 20 60 6.0±2.0 1.22±0.39

Fig. 3 The tan to charcoal area represents the coagulation of thetissue surrounding the puncture tract in ex vivo liver tissue

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tissue between the active electrode and the dispersive pad,which might lead to heating of the metallic implants or toan increase in body temperature depending on the energyapplied. Pritchard and coauthors also reported a modifiedintroducer needle for coagulation of puncture tracts [9].They used a 14-G introducer needle as a monopolar RFdevice allowing the coaxial use of a 16-G biopsy gun. Themodified introducer needle featured an outer insulationresulting in a total instrument diameter of approximately11 G. On the other hand, the prototype described in thisstudy integrates both functions, namely biopsy and coag-ulation, into one device with an outer diameter ofapproximately 13 G including insulation.

For RF ablation of malignant liver lesions neoplasticseeding along the puncture tract was reported to occur in0.2% to 12.5% of cases [10, 11]. In a large multicentrestudy published by Livraghi et al. in 2005, 1,314 patientssuffering from HCC were included and the authors

reported tumour cell seeding along the puncture tract in12 patients (0.9%) and previous biopsy was the only factorassociated with neoplastic seeding [12]. Considering thesefindings, the RF ablation of the puncture tract followingimage-guided biopsy of malignant lesions is reasonable.

Comparing the design of our prototype with commer-cially available needle-shaped RF probes, even a completeablation of small lesions appears to be feasible. Needle-shaped bipolar RF probes with an active tip length of 3 cmwere shown to generate coagulation areas with a diameterof approximately 21 mm in an ex vivo porcine model [13].But unlike the concept presented here, the bipolar RF probeused in our previous study [13] featured internal coolingwhich is known to allow the ablation of larger volumes.Nevertheless, the maximum achievable coagulation vol-ume should be evaluated in further experiments.

Our concept includes only minor changes to the designof a standard 14-G trucut needle, which is an establishedand widely used instrument for image-guided biopsies. Thetechnical changes made (insulation, electrical connection)were simple and did not influence the handling andfunction of the device. However, a further reduction of thedevice diameter should be the aim of further development.

This study suffers from several limitations. We did notinvestigate the quantitative reduction of blood loss by RFablation of the puncture tract. In addition, relevant bleedingafter biopsy due to injury of large vessels cannot be treatedwith the developed device but may require other interven-

Fig. 5 After coagulation of the puncture tract a pale coagulationzone is found in the in vivo kidney model

Table 2 Results of the in vivo puncture tract ablations after biopsiesin porcine liver and kidneys by using a generator output of 10 W

Tissue Number Generatoroutput(W)

Meanduration ofablation (s)

Mean diameterof coagulation(mm)

Meanappliedenergy (kJ)

Liver 16 10 109±77 10.1±4.6 0.84±0.61Kidney 10 10 124±61 6.0±2.5 1.00±0.50

Fig. 4 CT control examinationsshowed a lack of contrast en-hancement (white arrows) aftertract coagulation in porcinekidney (left) and liver (right)

2003

tions like selective embolization. Furthermore, the hypoth-esis of a reduced risk of tumour cell seeding was not proven.

In conclusion the construction of a trucut biopsy needlefeaturing a fully integrated bipolar RF ablation electrodefor coagulation of the puncture tract following image-

guided biopsy is technically feasible without changing theshape, function and handling of the device. Further in vivotests are necessary to determine the achievable reduction ofblood loss and tumour cell seeding after image-guidedbiopsy.

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