Preliminary in vitro angiographic comparison of the flow diversion behavior of Evolve and Pipeline devices

Background and purposeFlow diverters are increasingly used to treat a broad category of cerebral aneurysms. We conducted an in vitro study to angiographically compare the flow diversion effect of Surpass Evolve from Stryker Neurovascular with the Pipeline Shield Embolization Device from Medtronic Neurovascular.MethodsThree copies each of three carotid aneurysm geometries were manufactured from silicone. Evolve and Pipeline flow diverters were deployed in one copy of each geometry; the third copy was used as Control. High-speed angiography was acquired under pulsatile flow in each replica, contrast concentration-time curves within the aneurysms were recorded, and the curves were quantified with six parameters. The parameters were statistically evaluated to compare the flow diversion effect of both devices.ResultsThe Evolve showed greater flow diversion trends in almost all intra-geometry comparisons than the Pipeline. When aggregated over the three geometries, the Evolve was statistically significantly better than the Pipeline in four of the six parameters, and about the same or better (not statistically significant) than the Pipeline in the other two parameters.ConclusionsThe Evolve device demonstrated greater in vitro flow diversion effects than Pipeline. Comparative efficacy of the devices will need to be adjudicated based on clinical outcomes.</jats:sec

Mixing of Angiographic Contrast With Blood During Injections in the Cerebral Circulation

In the past, various techniques such as indicator dilution, transit time, parametric imaging, or first-pass distribution have been used to estimate blood flow rates during angiographic contrast injections. We have previously employed the method of modeling contrast concentration curves to assess changes in flow exchange between parent cerebral vessels and cerebral aneurysms due to endovascular treatment by flow divertors [1]. There has been concern, however, that contrast injected under such situations may remain as a separate slug or stream flowing with blood or that contrast may settle from blood in the direction of gravity due to its higher density [2,3]. According to this argument, therefore, the analysis of the transport of angiographic contrast visualized under X-ray cannot be used to represent the transport of blood.</jats:p

Experimental Investigation on the Dispersive Transport of Angiographic Contrast Injected Antegradely Into Flow in a Tube

In catheter-based angiography contrast is injected through a catheter into flowing arterial blood to attenuate the X-ray beam such that physicians can view vascular luminal morphology for diagnosis of vascular pathology [1]. Since real time angiography became available the transport of contrast could be visualized and numerous attempts have been made to relate the visualized transport of contrast to blood flow or blood velocity. Since the dispersion of contrast is a complex process and thorough understanding of contrast mixing with the flowing blood is missing, many physicians and researchers alike implicitly assume that mixing of contrast and blood is either instantaneously completed or that mixing does not take place at all during the short visualization period. In the former case many erroneously assume that the visualization of contrast transport directly reflect blood flow characteristics. Yet others attributed homogeneous mixing to turbulence even when the Reynolds number was as low as 77 [2]. In the latter case some reports suggested that since the two do not mix, the contrast, which is denser than blood, will tend to accumulate at low parts of the arterial system due to the gravity. The stereotypical concept is that under laminar flow conditions homogeneous mixing will take a long time and consequently a long distance. The fact that the angiographic contrast is a liquid tracer injected forcefully into the blood, generating an ejector effect is ignored. The velocity mismatch between the injected contrast and the flowing blood plays a major role in laminar mixing of the contrast. In this paper, we report our experimental investigation that was designed to find out how far distal to the catheter tip will the injected contrast reach homogeneous mixing with a blood analog fluid as evident by no further changes in the contrast density profiles measured downstream of the catheter tip.</jats:p

An in vitro study of pressure increases during contrast injections in diagnostic cerebral angiography

Background During diagnostic cerebral angiography, the contrast bolus injected into a vessel can cause substantial changes in baseline pressures and flows. One potential, and serious complication is the re-rupture of aneurysms due to these injections. The goals of this in vitro study were to evaluate the effect of injection conditions on intraneurysmal pressure changes during angiography. Methods A silicone replica of a complete circle of Willis model with ophthalmic, anterior communicating, and basilar tip aneurysms was connected to a physiologically accurate flow pump. Contrast injections were performed under different conditions (carotid or vertebral vessel imaging, catheter diameter, injection rate, injection time, and arterial blood flow rate) and the pressure in each aneurysm was recorded before and during each injection. The effect of injection conditions on percentage increase in aneurysm pressures was statistically assessed. Additionally, the effect of the distance between the aneurysm and the catheter-tip on aneurysmal pressures was assessed. Results Mean intraneurysmal pressures during injection (84.5 ± 10.8 mmHg) were significantly higher than pre-injection pressures (80.4 ± 10.6 mmHg, p &lt; 0.0001). Only 3 of the 5 conditions – carotid injections, higher injection rates, and smaller catheter diameters – significantly increased intraneurysmal pressures. The catheter-tip distance showed no correlation to pressure increases. Conclusions Increasing contrast injection rates and decreasing catheter diameters are correlated to intraneurysmal pressure increases during angiography irrespective of the distance to the catheter tip. Future in vivo studies are required to confirm these findings and determine whether the amplitude of pressure increases with commonly used injection rates can be clinically detrimental. </jats:sec

Phototherapy Enhanced Exclusion of Aneurysms From the Cerebral Circulation

Accumulated experience using flow diverters in humans suggests that complete cure of the aneurysm is usually a protracted process that can last up to twelve months [1]. While it is well established that a properly designed flow diverter serves as a scaffold for neointimal proliferation, the process of its formation over the aneurysm neck is delayed until the aneurysm cavity itself is occluded by a thrombus, negating flow of fresh blood through the neck, and thus allowing the neointimal formation to bridge the aneurysm neck. The notion that induction of some injury to the luminal surface of the aneurysmal tissue, particularly to the endothelium, may result in a healing response that is faster than just placing a flow diverter and waiting for thrombus formation within the aneurysm has been tried in the past using various experimental models. Some of the injuries to the aneurysm tissue that have been tried in the past include mechanical scraping, thermal heating and UV irradiation. All these attempts, while showing that hastening the thrombus formation is feasible, have not resulted in any success due to the fact that the processes that were tried suffered from lack of proper control to be implemented in actual aneurysmal tissue that is weakened and diseased a priori.</jats:p