ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Fig 1: Image of experimental system
showing camera pair.
a: b:
Fig 2: a- example of a single unit of the stent,
b- method used to calculate unit angle (equation 1).
During stent expansion pairs of images were obtained at each pressure value. Following
stent expansion the stereo image pairs were used, along with camera calibration data, to
determine the 3D coordinates (x, y, z) of two points on selected stent struts (Fig. 2).
These points provided the 3D orientation of the struts at each stage of stent expansion.
The orientation of neighbouring stent struts was used to provide a measure of the
expansion of a strut unit, as illustrated in figure 2a. The angle (β) between the direction
vectors along each strut was calculated as follows:
where u and w are vectors along each strut direction and cosβ is angle between vectors
(figure 2b).
Using the same method as Kiousus et al, the extent of dog-boning (DB) was determined
as follows:
where Ddistal is the distal diameter and Dcentral the central diameter. The extent of dogboning
was also calculated using the proximal diameter for comparison.
RESULTS
Figure 3 demonstrates a typical stent response, along with the definition of the strut
orientations used to quantify inter-strut angle. Three images taken during the inflation
of the 4 mm diameter stent are presented in figure 4. These images clearly show
significant dog-boning at the proximal end of the stent at a balloon pressure of 3.75
atmospheres.
Figure 5 presents the variation in dog-boning ratio with balloon pressure, as defined in
equation 2, for both the proximal and distal ends of each stent. Figure 6 shows the
change in inter-strut angle for selected stent units at the proximal and distal ends of the
stent. The error bars in figure 6 represent the estimated error in angle from comparison
between optical methods and micro-CT reconstruction of stent geometry from a
(1)
(2)