Design and Fabrication of Ultrasound Phantoms to Identify the Actuator of Arterial Wall Longitudinal Movement

Abstract (Swedish)

Trots att ett decennium har gått sedan artärernas longitudinella rörelse visades in vivo är bakgrunden till denna multifasiska rörelse fortfarande inte fastställd. Att trycket skulle kunna driva rörelsen har ledigt avfärdats. Resonemanget har varit att eftersom trycket verkar vinkelrätt mot väggen kan det endast påverka den radiella töjningen.
I följande arbete har vi visat i en förenklad teoretisk modell samt i fantom-modeller att trycket kan orsaka en longitudinell rörelse hos kärlfantomer med vissa specifika geometrier.
En kombination av traditionella och nyskapande tekniker användes för att skapa de sammansatta fantomerna. Fantomerna gjordes i två delar och PVA användes till båda. Ett system för att koppla samman fantomen med en pump utvecklades. Fantomerna designades så att en eventuell tryckdriven rörelse kunde isoleras.

Resultatet visade att geometrin påverkade storleken av den longitudinella rörelsen. En jämförelse av rörelsens omfattning mellan tre olika fantomer visade att rörelsen var minst för den fantom där trycket inte skulle kunna orsaka en stor framåtrörelse enligt teorin. Geometrin för denna fantom var en cylinder med konstant diameter och förlängningen uppmättes till 0.186 mm med en standardavvikelse på 0.057. De andra geometrierna hade en minskande diameter, den ena gradvis, den andra abrupt. Förlängningen var 3.258 ± 0.077 respektive 5.375 ± 0.392 mm.

Rörelsemönstret längst med en av fantomerna är också en stark indikation på att större delen av rörelsen härrör från den position där trycket skulle ha störst påverkan.
Detta tyder på att trycket verkligen kan driva en framåtriktad rörelse av kärlväggen.

Abstract

Although a decade has passed since the longitudinal movement of arteries was shown in vivo, the cause for this multiphasic movement has not yet been established. Pressure as a force driving the forward motion has been repeatedly dismissed on the grounds that pressure acts perpendicular to the wall and therefore solely in the radial direction.
In this work we have shown in a simplified theoretical model and phantom models that pressure can cause a longitudinal movement of vessel phantoms of some specific geometries.
The compound phantoms were produced using a combination of traditional and innovatory techniques. The phantoms were in two parts and PVA was used for both. A system to connect the phantom inlet to a pump was also developed. The phantoms where designed such that any movement due to pressure could be isolated.

The result showed that the geometry and position influenced the longitudinal movement. A comparison of the magnitude of the movements of three different phantoms showed that the movement was smallest in the phantom where pressure could not generate a large forward movement according to the theory. The geometry of this particular phantom was a cylinder of constant diameter, and the lengthening was measured to 0.186 mm with a standard deviation of 0.057.
The other geometries involved a decrease of the diameter, one gradual and another abrupt. The lengthening was 3.258 ± 0.077 and 5.375 ± 0.392 mm respectively.

The movement pattern along the length of one of the phantoms strongly indicate that the largest part of the movement originates where pressure would have the greatest influence.
This implies that the pressure can drive the forward motion of the vessel wall.

Popular Abstract

The Moving Artery Phantom

Illnesses related to the heart and blood vessels are a common cause of death in the world. A relatively new discovery is that the arterial wall moves back and forth along with the blood flow. To understand if this motion is related to these illnesses, researchers like to know its origin. We have designed and fabricated phantoms to be used in investigating if varying the pressure of the flow can give rise to this motion.

Many people suffer and die from illnesses related to the heart and blood vessels. To understand whom is in the risk group researchers try to learn all about these organs. Arteries are the blood vessels transporting blood from the heart out to the body. The arteries are elastic and they move when the heart is pumping.
The arteries widen due to the incoming blood, but the arterial wall also moves along the blood flow back and forth. This second movement has only been known for a little more than a decade. The reason for the movement is not yet known.
We want to see if varying the pressure can give rise to a motion. The pressure acts at a 90 degrees angle to the wall, widening the vessel by pushing it out. But if the vessels diameter becomes narrower the pressure could act along the direction of flow. We want to investigate if the pressure can drive the motion.
Inside the human body there are so many variables that can affect the motion of the vessels. It is impossible to design a test that investigates how just one of all of these parameters affect it. Therefore we have designed and fabricated models, also called phantoms to investigate the movement in a much simpler system.
The phantom is fabricated in two parts. One part is representing the moving artery and the second part the surrounding tissue. These two elastic, slightly slimy, parts are assembled under water and viewed with an ultrasound equipment. Ultrasound is a high frequency sound and an image is created from the echoes. It is frequently used in medical diagnosis, for example on babies before they are born.
To cast the phantom we use 3D-printed molds. The printer prints from the bottom up, one layer at the time. Each print is drawn in a computer program, and it takes approximately three hours from the printer starting until the plastic part is in our hands.
We compare three different geometries. One straight, one with an abrupt diameter change, making the phantom vessel narrower and one with a more gradual diameter change, also making the vessel narrower.
The assembled phantoms are connected to a tube from the pump. The pump is taking the place of the heart, but instead of using blood we pump water into the phantom. The pressure is varied. By using the ultrasound equipment the movement of the vessel phantom could be seen and later analyzed.
The results show that the straight vessel did not move much along the vessel wall but both of the vessels with changing diameter move!

• author: Widerström, Alice and Sjöstrand, Sandra
• supervisor: Magnus Cinthio; Hans W Persson
• organization: Department of Biomedical Engineering
• course: BMEM01 20151
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Cardiovascular, Longitudinal, Phantom, Ultrasound, Artery
• language: English
• additional info: 2015-08
• id: 7359329
• date added to LUP: 2015-06-22 13:19:23
• date last changed: 2016-01-01 04:06:56