Eur Radiol (2011) 21:1797–1801 DOI 10.1007/s00330-011-2113-7

NEURO

Intravenous flat detector CT angiography for non-invasive visualisation of intracranial flow diverter: technical feasibility Tobias Struffert & Marc Saake & Sabine Ott & Tobias Engelhorn & Philipp Gölitz & Stephan Kloska & Marc Doelken & Arnd Doerfler

Received: 16 December 2010 / Revised: 3 February 2011 / Accepted: 16 February 2011 / Published online: 30 March 2011 # European Society of Radiology 2011

Abstract Objective To demonstrate the feasibility of intravenous Flat Detector CT Angiography (FD-CTA) for visualisation of intracranial Flow Diverting Devices. Flow Diverting Devices are used increasingly for treatment of intracranial aneurysms. A close follow up is necessary because it becomes obvious that a significant proportion of aneurysms treated with these devices remain patent. A minimally invasive method is highly desirable. Methods In two patients treated with flow diverters a Flat Detector CT (FD-CT) with intravenous contrast medium application was performed. Post-processing was performed using commercially available software. Results In both patients the lumen of the device and the lumen of the aneurysm could be clearly evaluated. Some beam hardening artefacts due to the marker wires of the device were obvious. Conclusion Flat Detector CT with intravenous contrast material application to evaluate flow-diverting devices seems to be feasible. Further studies are necessary to perform comparative evaluation of FD-CTA with angiography and other techniques like MRA or conventional CT angiography. Keywords Flat detector computed tomography . Flow diverter . Multislice CTA . Angiography . Classification

T. Struffert (*) : M. Saake : S. Ott : T. Engelhorn : P. Gölitz : S. Kloska : M. Doelken : A. Doerfler Department of Neuroradiology, University of Erlangen-Nuremberg, Schwabachanlage 6, 91054 Erlangen, Germany e-mail: [email protected]

Introduction Flow-diverting devices are used in increasing numbers for treatment of intracranial aneurysms. Despite the fact that sufficient studies providing information and guidelines concerning the outcome and the necessary follow-up are lacking it becomes obvious that a significant proportion of aneurysms treated with these devices remain patent. Some publications indicate that despite treatment an increase in volume or even a rupture of an aneurysm may occur. Additional late thrombosis of the device seems to be possible [1–4]. Therefore an effective follow-up seems to be mandatory. In most institutions digital subtraction angiography is used to perform follow-up imaging. This invasive method, however, has the disadvantage of a moderate to high cost and a low but serious complication rate [5]. Therefore, a non-invasive alternative method is highly desirable. Recently, a new method of visualising the lumen of intracranial stents used for treatment of intracranial atherosclerotic disease by Flat-Detector CT Angiography (FD-CTA) has been introduced [6]. Flat detectors have the physical features to provide an excellent visualisation of high contrast structures with superior spatial resolution in comparison to conventional multislice computed tomography (MSCT). In this new Flat-Detector CT (FD-CT) program an intravenous injection of contrast material is used to enhance the lumen of the stent. These first results of conventional intracranial stents are highly promising. The idea of obtaining FD-CT with intravenous contrast material on flow diverters is obvious, because they are similar in structure and size to conventional intracranial stents. If this new FD-CT program should be feasible in flow diverters, it may serve as a minimally invasive

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follow-up imaging technique. We report here on the feasibility of this new method in two patients treated with flow diverters.

Patients and methods Two patients treated recently with flow diverters for intracranial aneurysms, gave written informed consent to be investigated with this new method. After treatment in both patients a regular angiographic series (DSA), an intra-arterial 3-D rotational angiography (3-D DSA) and an intravenous FD-CT (FD-CTA) was obtained. Both DSA, 3-D DSA and FD-CTA were performed on a biplane flat-detector angiographic system (Axiom Artis dBA, Siemens AG, Healthcare Sector, Forchheim, Germany). Using standard angiographic methods a diagnostic catheter was used to obtain standard anterior-posterior and lateral projections. Additionally a 3D DSA was obtained by this catheter using a 5s_DSA program as provided by the manufacturer. After removal of the catheter and the introducer sheath a FD-CTA with intravenous contrast application was obtained. Here we used a 10s_DSA program as described before [6, 7]. Postprocessing of the 3-D DSA and the FD-CTA was performed using commercially available software (syngo XWP, DynaCT, InSpace 3D software, Siemens AG, Healthcare Sector, Forchheim, Germany). Briefly the 5 s-DSA and 10s_DSA program consist of a native mask run and a second fill run after contrast material injection. This feature allows dedicated post-processing with native and contrastenhanced images. The parameters of the 10s_DSA program indicate that the radiation dose is exactly identical to the 20sDR_H program that is used to perform a DynaCT of the brain. To limit the radiation dose, we used the shutters to restrict the investigation to the interesting region. It is well known that the radiation dose of the 20sDR_H program is slightly higher in comparison to a regular CT scan of the brain [8]. Concerning the 3-D DSA (5s_DSA program) we reconstructed subtracted images to demonstrate the arterial vascular structures and high resolution native images to visualise the device. Both these reconstructions are then fused and the vascular structures and the device can be analysed. This method is called Dual Volume reconstruction. We performed the identical reconstruction of the intravenous FD-CTA as described before [6, 7]. Here a Dual volume reconstruction is also possible and, additionally due to the adequate soft tissue resolution that is not possible in the 5s_DSA program, multiplanar reconstructions with and without contrast material to analyse the lumen of the device and the aneurysm were performed. A detailed description of the post-processing with all parameters has

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been published [6, 7]. We used 60 mL of contrast material (Imeron 400, Bracco Imaging, Konstanz, Germany) injected into a peripheral cubital vein at a rate of 5 mL/s using a power injector (MEDTRON, Saarbruecken, Germany) followed by a saline chaser (60 ml, injection rate 5 ml/s. To detect the inflow of contrast material to the arterial vascular structures we used a bolus watching method.

Case descriptions Case 1 A 72-year-old woman was admitted with the incidental finding of a wide neck aneurysm of the M1 segment of the middle cerebral artery (Figs. 1 and 2). The patient asked for a treatment option, because other members of her family had died due to aneurysm rupture. Treatment was performed using a Pipeline flow diverting device (PED, Chestnut Medical, Menlo Park, CA, USA) with a diameter of 2.75 and a length of 14 mm. Treatment was performed without any complications. The patient was transferred to the intensive care unit for observation and was discharged 3 days after treatment without any problems. Case 2 A 71-year-old woman was admitted with visual disturbances because of a large space-occupying carotid aneurysm (Figs. 3 and 4). Treatment was performed using a Silk flow diverting device (Balt Extrusion, Montmorency, France) with a diameter of 4 and a length of 25 mm. Treatment was performed without any complications. Because of the C shape of the implanted device curved multiplanar reconstructions were performed. We notice slight stenosis of the carotid artery at the neck of the aneurysm. The patient was also transferred to the intensive care unit for observation. The patient was discharged 3 days after treatment.

Results In both patients the acquisition of the DSA, 3-D DSA and especially intravenous FD-CTA was successful. In both patients the Dual Volume reconstructions of the FD-CTA resembled the quality of the 3-D DSA. In both the visualisation of the device indicated the correct positioning covering the neck of the aneurysms. Additionally, the MPR reconstructions with and without contrast material nicely demonstrated the lumen of the devices. We noticed some artefacts in the lumen of the Silk device possibly due to beam hardening of the marker wires. In the post-contrast reconstruction the perfused parts of the aneurysms are

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Fig. 1 In patient 1 a wide neck M1 segment aneurysm was treated (a). After treatment (b) the Pipeline device is hardly to see, but in native images it can be recognised (c, red arrows). In 3-D DSA the aneurysm can be analysed before (d) and after treatment (e, Dual Volume reconstruction). In FD-CT (f, Dual Volume reconstruction) the quality resembles the 3-D DSA image. The positioning of the device and the vascular structures including the opacified aneurysm is clearly visible

nicely visible. In case 2 sedimentation of contrast material due to multiple injections during the treatment was recognised.

Discussion We present here the first investigations on flow-diverting devices using FD-CTA with intravenous contrast material application. Our preliminary examples indicate that the lumen of the devices, the positioning and the aneurysms can be assessed by this new technique. Fig. 2 The multiplanar reconstructions (MPR) of the FD-CT pre- (c, d) and post (a, b) application of contrast medium nicely show the patency of the lumen of the device and the perfused lumen of the aneurysm

Flow-diverting devices are used in increasing numbers to treat intracranial aneurysms [9]. Although only a few publications with small numbers of patients have been published to date, it becomes obvious that the aneurysms may remain patent or serious complications may occur. There are reports of late thrombosis associated with the device. Other reports indicate that despite treatment an enlargement of the aneurysms and even a rupture may occur [1–4]. Another topic seems to be the periprocedural medication. Here different schemes have been described. Large studies to each of these aspects are lacking.

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Fig. 3 In patient 2 a large carotid aneurysm was treated with a Silk. Before (a) and after (b) treatment it seems that the inflow is not as intense as before. In lateral view (c) the positioning of the device in a C shape is visible (red arrows). In 3-D DSA before treatment (d) the carotid artery and the large aneurysm are nicely displayed. After treatment in 3-D DSA (e) the positioning and patency of the Silk is obvious. Due to limited inflow after treatment the volume of the aneurysm seems to be reduced. Additional in FD-CT Dual Volume reconstruction the device is clearly visible and the aneurysm also seems to be reduced in volume. Image Quality of (e) and (f) is comparable

It becomes obvious that a minimally invasive follow-up imaging technique is highly desirable to check the positioning of the device, the lumen of the flow diverter and to assess intra-aneurysmal thrombosis. Fig. 4 Due to the C shape a curved multiplanar reconstruction in coronal and in saggital orientation was performed. The native images (a, c) show some streak like artifacts due to beam hardening of the marker wire, but image quality is appropriate for evaluation. After contrast application (b, d) the enhancement of the aneurysm and of the lumen of the device clearly indicate patency of the silk and the aneurysm. In this patient a slight stenosis of the carotid artery at the neck of the aneurysm was known and is also visible in our reconstruction (red arrows). Please note contrast medium deposit within the aneurysm due to repeated intraarterial injections during treatment visible both in native (c) and contrast enhanced MPR reconstructions (black arrows)

The use of intravenous FD-CTA seems to have a lot of advantages. First, we can show that the lumen of the device can be visualised as in conventional stents. The Silk presents with some artefacts that appear to be due to beam

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hardening of the marker wire. The appearance of these artefacts is similar to those of the markers of the Wingspan stent (Wingspan; Boston Scientific/Target, Fremont, CA, USA), which have been described before [6]. In a comparison of the pre- and post-contrast images, an advantage of this FD-CT acquisition is to have both; they are easy to recognise. The Pipeline did not show any artefacts. Second, the lumen of the aneurysm pre- and post-contrast material injection can be evaluated. Here it should be possible to recognise enlargement or ongoing thrombosis or even complete occlusion of the aneurysm lumen. Third, the positioning of the device to check if the neck is covered by the device or not, is clearly visible. Finally, the method is a minimally invasive imaging technique. Only the risk of the contrast material application has to be taken into account. The amount of contrast material is within the same range as in conventional MSCT. The procedure requires about 5 min; the post-processing is done within 15–20 min. The examination can be done in an outpatient setting. At the moment there are two suggestions with regard to grading scales to describe aneurysms treated with flow diverters [10, 11]. The basis of the two classifications are in both DSA series. The impression of the occlusion has to be judged in both. This could be achieved using this FD-CT application. Additionally, the dynamic inflow pattern is evaluated. Of course the dynamics cannot be evaluated with this FD-CTA program. In future a cross-sectional imaging technique like FD-CTA should be used in further studies on flow diverters because the visualisation of the ongoing thrombosis and positioning of the device might be an important parameter in the assessment of the follow-up of flow diverters. Intravenous FD-CT is a promising new technique for visualising flow-diverting devices. Despite beam hardening artefacts of the marker wire of the Silk device assessment of the device lumen and of the aneurysm was possible in our patients. Though the patients were investigated under general aesthesia, we could achieve a good image quality. Any movement of the patient might decrease the image quality. Experience in regular stent devices indicates, that in patients with good compliance a sufficient image quality can be achieved without general aesthesia [6]. At the moment there are no results available concerning the visualisation of flow diverters by MRI or conventional MSCT. We have the impression that, as in conventional intracranial stents, that the superior spatial resolution of FD-CT allows the assessment of these devices. Further comparative studies are necessary to evaluate the possibilities of flow diverter visualisation using the different techniques.

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Conclusion We present here the first flow-diverting devices investigated with a minimally invasive FD-CT program after intravenous contrast material application. In comparison to DSA and 3-D DSA the evaluation of the devices seems to be feasible. The reconstructions clearly visualised the device lumen, the positioning and the perfused aneurysm. Therefore FD-CTA provides non-invasive visualisation of these devices and may be a non-invasive alternative tool to replace DSA for follow-up imaging. References 1. Fiorella D, Hsu D, Woo HH, Tarr RW, Nelson PK (2010) Very late thrombosis of a pipeline embolization device construct: case report. Neurosurgery Suppl 67:E313–E314 2. Lubicz B, Collignon L, Raphaeli G, Pruvo JP, Bruneau M, De Witte O et al (2010) Flow-diverter stent for the endovascular treatment of intracranial aneurysms: a prospective study in 29 patients with 34 aneurysms. Stroke 41:2247–2253 3. Kulcsár Z, Houdart E, Bonafé A, Parker G, Millar J, Goddard AJ et al (2011) Intra-aneurysmal thrombosis as a possible cause of delayed aneurysm rupture after flow-diversion treatment. AJNR Am J Neuroradiol 32:20–25 4. Turowski B, Macht S, Kulcsár Z, Hänggi D, Stummer W (2011) Early fatal hemorrhage after endovascular cerebral aneurysm treatment with a flow diverter (SILK-Stent): do we need to rethink our concepts? Neuroradiology 53:37–41 5. Willinsky RA, Taylor SM, TerBrugge K, Farb RI, Tomlinson G, Montanera W et al (2003) Neurologic complications of cerebral angiography: prospective analysis of 2,899 procedures and review of the literature. Radiology 227:522–528 6. Struffert T, Kloska S, Engelhorn T, Deuerling-Zheng Y, Ott S, Doelken M et al (2010) Optimized intravenous flat detector CT for non-invasive visualization of intracranial stents: first results. Eur Radiol 21:411–418 7. Struffert T, Deuerling-Zheng Y, Kloska S, Engelhorn T, Strother CM, Kalender WA et al (2010) Flat detector CT in the evaluation of brain parenchyma, intracranial vasculature, and cerebral blood volume: a pilot study in patients with acute symptoms of cerebral ischemia. AJNR Am J Neuroradiol 31:1462–1469 8. Kyriakou Y, Richter G, Dörfler A, Kalender WA (2008) Neuroradiologic applications with routine C-arm flat panel detector CT: evaluation of patient dose measurements. AJNR Am J Neuroradiol 29:1930–1936 9. Szikora I, Berentei Z, Kulcsar Z, Marosfoi M, Vajda ZS, Lee W et al (2010) Treatment of intracranial aneurysms by functional reconstruction of the parent artery: the Budapest experience with the pipeline embolization device. AJNR Am J Neuroradiol 31:1139–1147 10. Kamran M, Yarnold J, Grunwald IQ, Byrne JV (2010) Assessment of angiographic outcomes after flow diversion treatment of intracranial aneurysms: a new grading schema. Neuroradiology. doi:10.1007/ s00234-010-0767-5 11. O’Kelly CJ, Krings T, Fiorella D, Marotta TR (2010) A novel grading scale for the angiographic assessment of intracranial aneurysms treated using flow diverting stents. Interv Neuroradiol 16:133–137