Biomedical Engineering Reference
In-Depth Information
1.2 Present Limitations of the IVUS Technique
and the Need for a Generation Model of
IVUS Data
The main function of the IVUS technique is to serve as a guide in the interven-
tional procedures, allowing us to measure the cross section of the artery. The
precision in the measurements of distance is subject to the following potential
sources of error [9]:
(a)
Incorrect identification of the surface and the sections to be measured.
Although the vessel and the interface defining the wall vessel have suffi-
ciently good acoustics in most of the cases, in several cases the identifi-
cation of the surface and differentiating tissues can be difficult. Improv-
ing the radial resolution could improve the detection of contours, which
would reduce the errors. These errors can in some cases be systematic
and lead to an overestimation of the dimensions. This could get consid-
erably worse if the irregularities of the vessels are very pronounced.
(b)
Assumption that the sound speed is constant in the arterial structure.
The second kind of problem related to the assumption of constant speed
of the sound of 1540 m/sec is systematic and small (of the order of 1-2%),
which brings as a consequence the propagation of the error in the location
of each one of the structures under study.
(c)
Artifacts caused by inhomogeneities in the rotation of the catheter and
pronounced reverberations generated by very acute irregularities of
the vessel.
The appearance of some artifacts such as the inhomogeneities
in the rotation of the catheter influences the quality of the image. The
absence of beams, when the catheter stops momentarily, brings as a
consequence a propagation of errors in the tangential direction of the
image.
(d)
Presence of zones of acoustic shade, which prevents access to certain
regions of interest
(ROIs). The presence of zones of acoustic shade is inti-
mately related to the presence of calcification or regions of high acoustic
impedance. The shades prevent some structures from being evaluated
from the distribution of the gray levels.
