Name: Monitoring the Wall Mechanics During Stent Deployment in a Vessel (Video) | JoVE Journal
Uploaded: 2012-05-08T12:00:00.000+00:00
Duration: 8 min 28 s
Description: Learn to monitor stent-induced strain distribution in mock arteries using the non-contact Aramis optical measurement system. This method provides detailed insights for improving cardiovascular stent design.

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This study was supported in part by the NASA Nebraska Space Grant and National Science Foundation under grant No. 0926880.

1. Preparation of the Latex Vessel
<ol>
	<li>Fix both ends of the latex vessel to barbed hose connections, which are fastened on a sturdy workbench.</li>
	<li>Measure the area of interest on latex vessel to determine the field of view. The area of interest for a stent test should be centered between the barbed hose connectors and include approximately one inch on each side of the stent in order to observe the strains outside the stented area.</li>
	<li>Record the distance from the outside edge of one barbed hose connector to the center location between the connectors, which is also the approximate center of the latex vessel. Translate the distance onto the catheter by measuring from the center of the stent up the catheter. Then mark the catheter with a marker.</li>
	<li>Remove the latex vessel from the barbed hose connectors.</li>
	<li>Prepare the latex vessel by spraying the area of interest with a stochastic pattern of white and black spray paint or marking the area of interest with random dots using permanent marker. For smaller samples and finer stochastic pattern is required.</li>
</ol>
2. In vitro Test System and Calibration of ARAMIS System
<ol>
	<li>Select the calibration panel that is slightly larger than the area of interest measured in step 1.</li>
	<li>Place the calibration panel between the barbed hose connectors at the area of interest and ensure that the area of interest is well lit.</li>
	<li>Adjust the distance between two cameras, the distance from the sample, and the camera height based on the calibration panel selected. Each calibration panel is different; therefore the ARAMIS user manual will have to be consulted to determine these distances.</li>
	<li>Open a new project in ARAMIS by selecting "File", then "New Project". Next click on the "Sensor" tab and select "Calibration", then "Full Calibration".</li>
	<li>The ARAMIS software will now walk the user through the steps to calibrate the cameras.</li>
	<li>With the lens aperture fully open, focus the camera on the calibration panel by loosening the set screw on the camera and rotating the lens. Once focused, retighten the set screw and close the aperture.</li>
	<li>Take the first image of the calibration process. Displace or rotate the calibration panel according to the demonstration on the computer, until the image is focused on the computer screen. Take the second image. Repeat this process for the remainder of the calibration images.</li>
	<li>Once all of the calibration images are taken, the ARAMIS imaging analysis software will calculate the calibration settings. The calibration process should be repeated if the calibration deviation is greater than 0.04. Any adjustments made to the focus of the camera or the distance between cameras will render the calibration process void.</li>
	<li>Remove the calibration panel and place the painted latex vessel back onto the barbed hose connectors.</li>
</ol>
3. Pretest to Avoid Excessive Background Noise
<ol>
	<li>Determine the number of frames per second that is desired for the test. Increased frames per second will produce more uniform strain results.</li>
	<li>Adjust the shutter speed to less than 1 frame per second and so that no red is displayed on the image.</li>
	<li>Take 5 images.</li>
	<li>Add start points on the image series and compute the test.</li>
	<li>While holding "ctrl", click on the center of sample to observe the background noise. If the pretest noise is above 75 microstrain the calibration process must be redone.</li>
</ol>
4. Stent Deployment
<ol>
	<li>Select the amount of images desired to take during the test. 200 images will suffice for the stent expansion.</li>
	<li>Gradually insert the catheter into the latex vessel, and using the marker indicator on the catheter to guide the stent insertion until it reaches the central location.</li>
	<li>Begin taking images with ARAMIS.</li>
	<li>For the balloon-expandable stent, gradually increase the balloon pressure to expand stent until the balloon is fully expanded; then gradually decrease the pressure of balloon to zero and the balloon is deflated and withdrawn along with the catheter.</li>
	<li>For the self -expanding stent, gradually remove the sheath until the stent is fully expanded; then gradually retract the catheter.</li>
</ol>
5. Images Analysis
<ol>
	<li>Strain history of a specific point on the vessel
	<ol>
		<li>Create a stage point by holding the "ctrl" key and clicking on the area of interest.</li>
		<li>Select the type of strain that is desired, i.e. strain in the X, Y, XY, major strain, minor strain, or Mises strain.</li>
		<li>The plot in the lower right corner will display the strain at the point selected over the duration of the test.</li>
	</ol>
	</li>
	<li>Spatial strain along a specific path of the vessel
	<ol>
		<li>Create a multistage point line by clicking on the "sections" tab, then "create section". Select a line on the image parallel to the X axis at Y equals zero. This will create a number of stage points in a line.</li>
		<li>After the multistage line is created the plot in the lower corner will display a series of lines on one plot. Each line represents the strain at one instance in time along the length of the section.</li>
	</ol>
	</li>
	<li>Creating a best fit cylinder to analyze expansion rate and radius of the vessel
	<ol>
		<li>In the upper tool bar select "primitives", then "best fit cylinder".</li>
		<li>Select a small section of the image using the "select through surface" tool on the right tool bar.</li>
		<li>The ARAMIS software will generate a three dimensional best fit cylinder.</li>
		<li>The images can then be cycled through to observe how the diameter of the latex vessel is varying.</li>
	</ol>
	</li>
	<li>Evaluating the distance between two points
	<ol>
		<li>Under the "analysis" tab click on "point to point distance".</li>
		<li>Select a length on the image that is desired for analysis by selecting two points.</li>
		<li>The images can then be cycled through to observe the change in distance between the two points over time.</li>
	</ol>
	</li>
</ol>
6. Representative Results
The stent struts expand the vessel wall outwards, strains will generally be higher around stent location. Figure 1 is an example of strain mapping during the recoil process of balloon-expandable stent, as well as major strain history at one specific point. The black dots in Figure 1 are reference points, which were used by the high-speed cameras to capture and track the displacements of these reference points on the conduit. Based on the recorded movement of reference points, the software will then be used to calculate the strains of the conduit or any other targeted object. Major strain, also referred to as the maximum principal strain, is calculated as follows:
<img alt="Strain transformation equation, material stress-strain analysis, mathematical formula." src="/files/ftp_upload/3945/3945eq1.jpg" data-altupdatedat="1787630408000" data-alt="Equation 1">
It is clear that the implanted stent led to non-uniform strain distribution on the vessel surface. This could be explained by the recoil loading from ends-constrained latex conduit and the mesh structure of stent. This strain field corresponds to the initial stage of stent recoil, as identified by the red cross marker in the bottom image of Figure 1. The major strain-history curve of a specific point 10 demonstrated distinguishable stages of stent implantation. The balloon expansion occurs from approximately 10 to 12 seconds and stent recoil following the deflation of the balloon occurs between 12 and 14 seconds.
<img alt="Static equilibrium analysis; strain distribution diagram and graph; tensile stress experiment." src="/files/ftp_upload/3945/3945fig1.jpg" data-altupdatedat="1787630408000" data-alt="Figure 1"> 
Figure 1. Experimental setup (top); non-uniform strain distribution on the stented conduit surface (middle); the major strain history at the point 10 (bottom).

<ol><li>Fischman, D. L., Leon, M. B., Baim, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+randomized+comparison+of+coronary-stent+placement+and+balloon+angioplasty+in+the+treatment+of+coronary+artery+disease.+Stent+Restenosis+Study+Investigators%5BTitle%5D)+AND+%22N.+Engl.+J.+Med%22%5BJournal%5D)">A randomized comparison of coronary-stent placement and balloon angioplasty in the treatment of coronary artery disease. Stent Restenosis Study Investigators.</a> N. Engl. J. Med. 331, 496-501 (1994).</li>
<li>Abul Hasan Muhammad Bashar, T. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mechanical+Properties+of+Various+Z-Stent+Designs%3A+An+Endovascular+Stent-Grafting+Perspective%5BTitle%5D)+AND+%22Artificial+Organs%22%5BJournal%5D)">Mechanical Properties of Various Z-Stent Designs: An Endovascular Stent-Grafting Perspective.</a> Artificial Organs. 27, 714-721 (2003).</li>
<li>Nuutinen, J. uha-P. ekka <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mechanical+properties+and+in+vitro+degradation+of+bioabsorbable+self-expanding+braided+stents%5BTitle%5D)+AND+%22Journal+of+Biomaterials+Science+--+Polymer+Edition%22%5BJournal%5D)">Mechanical properties and in vitro degradation of bioabsorbable self-expanding braided stents.</a> Journal of Biomaterials Science -- Polymer Edition. , 255-266 (2003).</li>
<li>C. Schulz, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Coronary+stent+symmetry+and+vascular+injury+determine+experimental+restenosis%5BTitle%5D)+AND+%22Heart%22%5BJournal%5D)">Coronary stent symmetry and vascular injury determine experimental restenosis.</a> Heart. 83, 462-467 (2000).</li>
<li>Jiménez, J. M., Davies, P. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Hemodynamically+Driven+Stent+Strut+Design%5BTitle%5D)+AND+%22Annals+of+Biomedical+Engineering%22%5BJournal%5D)">Hemodynamically Driven Stent Strut Design.</a> Annals of Biomedical Engineering. 1483, (2009).</li>
<li>Johnston, C. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Mechanical+Properties+of+Endovascular+Stents%3A+An+In+Vitro+Assessment%5BTitle%5D)+AND+%22Cardiovascular+Engineering%3A+An+International+Journal%22%5BJournal%5D)">The Mechanical Properties of Endovascular Stents: An In Vitro Assessment.</a> Cardiovascular Engineering: An International Journal. 10, 128-135 (2010).</li>
<li>Mejia, J. uan <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Evaluation+of+the+effect+of+stent+strut+profile+on+shear+stress+distribution+using+statistical+moments%5BTitle%5D)+AND+%22Biomedical+Engineering+Online%22%5BJournal%5D)">Evaluation of the effect of stent strut profile on shear stress distribution using statistical moments.</a> Biomedical Engineering Online. , 1-10 (2009).</li>
<li><a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=%22ARAMIS+User+Manual%22">ARAMIS User Manual</a>. , GOM mbH. Braunschweig, Germany. (2009).</li>
<li>GOM mbH. (n.d.). New ARAMIS/PONTOS 12M and HS sensors available. , GOM: Optical Measuring Techniques. Available from: 
		
	 <a target="_blank" href="http://www.gom.com/news/history/single/article/new-aramispontos-12m-and-hs-sensors-available.html">http://www.gom.com/news/history/single/article/new-aramispontos-12m-and-hs-sensors-available.html</a> (2011).</li>
<li>Chesler, N. C., Thompson-Figueroa, J., Millburne, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Measurements+of+Mouse+Pulmonary+Biomechanics%5BTitle%5D)+AND+%22Journal+of+Biomechanical+Engineering%22%5BJournal%5D)">Measurements of Mouse Pulmonary Biomechanics.</a> Journal of Biomechanical Engineering. 126, 309-314 (2004).</li>
<li>de Korte, C. L., Sierevogel, M. J., Mastik, F., Strijder, C., Schaar, J. A., Velema, E., Pasterkamp, G., Serruys, P. W., van der Steen, A. F. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Identification+of+Atherosclerotic+Plaque+Components+With+Intravascular+Ultrasound+Elastography+In+Vivo+A+Yucatan+Pig+Study%5BTitle%5D)+AND+%22Circulation%22%5BJournal%5D)">Identification of Atherosclerotic Plaque Components With Intravascular Ultrasound Elastography In Vivo A Yucatan Pig Study.</a> Circulation. 105, 1627-1630 (2002).</li>
</ol>

No conflicts of interest declared.

The stereo optical surface strain measurement system is used to measure the local strains over the deforming surface for both the in- and out-of-plane motions without contacting the specimen. This system uses two high-speed optical cameras to take pictures of a random contrasting pattern putting on the surface to construct accurate measurements of motions of each point, with a high accuracy of resolving surface strains.
It should be noted that the required contrasting pattern need adheres to ...

<table><tbody><tr><td>ARAMIS Camera System</td><td>GOM: Optical Measuring Techniques</td><td></td><td></td></tr><tr><td>PALMAZ Genesis TRANSHEPATIC BILIARY STENT</td><td>Cordis Corporation</td><td>PG5910B</td><td>Balloon-expandable stent</td></tr><tr><td>Z-MED Balloon Dilatation Catheter</td><td>B. Braun Medical Inc.</td><td>PDZ336</td><td>Balloon dilatation catheter</td></tr></tbody></table>

monitoring the wall mechanics during stent deployment in a vessel

Monitoring the Wall Mechanics During Stent Deployment in a Vessel

Clinical trials have reported different restenosis rates for various stent designs1. It is speculated that stent-induced strain concentrations on the arterial wall lead to tissue injury, which initiates restenosis2-7. This hypothesis needs further investigations including better quantifications of non-uniform strain distribution on the artery following stent implantation. A non-contact surface strain measurement method for the stented artery is presented in this work. ARAMIS stereo optical surface strain measurement system uses two optical high speed cameras to capture the motion of each reference point, and resolve three dimensional strains over the deforming surface8,9. As a mesh stent is deployed into a latex vessel with a random contrasting pattern sprayed or drawn on its outer surface, the surface strain is recorded at every instant of the deformation. The calculated strain distributions can then be used to understand the local lesion response, validate the computational models, and formulate hypotheses for further in vivo study.

Stent-induced arterial strain distributions are characterized using an optical surface strain measurement system. This visualization technique is used to gain insights into the impact of stent implantation on the host vessel.

Clinical trials have reported different restenosis rates for various stent designs1. It is speculated that stent-induced strain concentrations on the ...

This experiment uses non-contact strain measuring equipment to monitor and capture the stent induced non-uniform strain on a mock artery. First, prepare a mock vessel for the stent expansion environments. After calibrating the aramis software system, expand the stent and capture the deformation of the mock vessel.Results from analyses of the stent induced strain along one axial path of mock vessel. Show that the stent induced strain distribution on mock vessel is non-uniform. The primary advantage of the Aramis camera system versus other methods of strain measurements such as strain gauges, are that the ARAMIS camera system allows for non-contact strain measurement.This protocol will demonstrate how to calibrate the aramis system along with analysis of the sample Here. This method offers insights into a stream distribution due to stand expansion. It can also be applied to other systems like a string on a head during the shock wave or on a string on steel bar on tension.First, fix both ends of the latex vessel to barbed hose connections that have fastened on a sturdy workbench. For a stent test center the area of interest between the barbed hose connectors and include approximately one inch on each side of the stent. In order to observe the strains outside the stented area, measure the area of interest on the latex vessel to determine the field of view.Next, record the distance from the outside edge of one barbed hose connector to the center location between the connectors. Translate the distance onto the catheter by measuring from the center of the stent up the catheter. Then mark the catheter with a marker.Now remove the latex vessel from the barbed hose connectors. Prepare the latex vessel by spraying the area of interest with a stochastic pattern of white and black spray paint or marking the area of interest with random dots. Using a permanent marker, select a calibration panel that is slightly larger than the area of interest.Then place the calibration panel between the barbed hose connectors at the area of interest. Ensure that the area of interest is well lit. Now, adjust the distance between the two cameras, the distance from the sample and the camera height to open a new project in Aramis select file and then new project.Next, click on the sensor tab and select calibration. Then full calibration for the RMS software to step through calibration of the cameras with, with the lens aperture fully open, focus the camera on the calibration panel by loosening the set screw on the camera and rotating the lens. Once focused, re-tighten the set screw and close the aperture.Take the first image of the calibration process. Displace the calibration panel according to the demonstration on the computer until the image is focused on the computer screen. Then take the second image.Repeat this process for the remainder of the calibration images. Once all of the calibration images are taken, the RM S imaging analysis software will calculate the calibration settings. If the calibration deviation is less than 0.04, remove the calibration panel and place the painted latex vessel back onto the barb hose.Connectors, given that increased frames per second will produce more uniform strain results. Determine the number of frames per second for the test. Also adjust the shutter speed to less than one frame per second.To minimize red on the image, take five images, then add start points on the image series and compute the test while holding control. Click on the center of the sample to observe the background noise. If the pretest noise is above 75 micros drain.Repeat the calibration process. Prepare for stent deployment by selecting the number of images desired to take during the test. 200 images will suffice for the stent expansion.Proceed to gradually insert the catheter into the latex vessel. Use the marker indicator on the catheter to guide the stent insertion until it reaches the central location. Begin taking images with AAMI for the balloon expandable stent.Gradually increase the balloon pressure to expand the stent until the balloon is fully expanded. Then gradually decrease the pressure of the balloon to zero, to deflate the balloon to withdraw along with the catheter for the self-expanding stent. Gradually remove the sheath until the stent is fully expanded.Then gradually retract the catheter to calculate strain history of a specific point on the vessel. First, create a stage point by holding the control key and clicking on the area of interest. Then select strain type to plot the strain at the point selected over the duration of the test for spatial strain along a specific path of the vessel.Create a multi-stage point line by clicking on the sections tab and then create section. Select a line on the image parallel to the X axis at y equals zero. This will create a number of stage points in a line and display a series of lines on one plot.Each line represents the strain at one instance in time along the length of the section. To analyze expansion rate and radius of the vessel, create a best fit cylinder in the upper toolbar, select primitives, then best fit cylinder. Using the select through surface tool, identify a small section of the image for the A is software to generate a three dimensional best fit cylinder cycle through these fit cylinder images to observe variation of the diameter of the latex vessel.To evaluate the distance between two points under the analysis tab, click on point to point distance. Then select two points to indicate the length on the image that is desired for analysis. Proceed to cycle through the images to observe the change in distance between the two points over time.This experiment demonstrates strain mapping during the recoil process of a balloon expandable stent, as well as major strain history. At one specific point, while the stent struts expand the vessel wall outwards, the high speed cameras captured and tracked displacement of the black reference points on the conduit. Based on the recorded movement of reference points, the software calculated the strains of the conduit or any other targeted object.Clearly, the implanted stent led to non-uniform strain distribution on the vessel surface. Furthermore, the major strain history curve of a specific point 10 demonstrated distinguishable stages of stent implantation. The balloon expansion occurs from approximately 10 to 12 seconds, and stent recoil following the deflation of the balloon occurs between 12 and 14 seconds.Last mastered. This technique can be performed in two hours. Remember to complete the calibration process correctly.

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Learn to monitor stent-induced strain distribution in mock arteries using the non-contact Aramis optical measurement system. This method provides detailed insights for improving cardiovascular stent design.

Monitoring the Wall Mechanics During Stent Deployment in a Vessel

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