advantages relative to IVUS. Intravascular optical
coherence tomography uses the same concept of
imaging, only it uses light instead of ultrasound
waves. The underlying concept of OCT is similar to
that of ultrasound; by measuring the delay time of
optical echoes reflected or back scattered from sub-surface structures in tissues, we can obtain structural
information as a function of depth within the tissue
(Tearney et al. 2012).
In IVOCT, we obtain cross-sectional images by
inserting a flexible imaging probe (catheter) into the
blood vessel to be imaged. The catheter has an opti-
cal fiber coupled to a lens and microprism. The
microprism reflects the OCT beam perpendicular to
the catheter’s longitudinal direction and captures the
light that is back scattered from that tissue (the
reflected beam is referred to as an A-Line, figure 2a).
The probe is then rotated and pulled back. This pull-
back creates a two-dimensional image (referred to as
polar or r-θ image) by assembling successive A-lines
next to each other resulting in an image shown in fig-
ure 2b. This image is then transformed to Cartesian
coordinates to produce the image shown in figure 2c.
A typical pullback contains 271 images covering 54
mm and an image contains 504 A-lines.
Different tissues have different qualities that influence the back reflectance. The longer the distance
traveled, the longer the delay in returning to a detec-
Figure 1. Intravascular Ultrasound Image.