Biomedical Engineering Reference
In-Depth Information
devices. At the end, being aware which parameters and in which grade influence
to image formation is of unquestionable importance for all persons involved in
comprehension of IVUS data and taking final decision for diagnosis and inter-
vention of vessel lesions. In this chapter, we discuss a simple simulation model
for the formation of 2D IVUS data that explains the complete process of data
generation as a result of the interaction between ultrasound signals and vessel
morphological structures.
1.2.1 A Basic IVUS Image Model
Correct image processing needs an understanding of image formation, gray-level
meaning, artifact causes, the averaging, and the motion of the dynamics struc-
tures effects in the image. The generation of simulated IVUS images investigates
four important aspects: (a) The generation, processing, and visualization of the
data in the format that doctors use, (b) the exploration of some of the artifacts
generated by the averaging of the beams, (c) the smoothing and treatment of the
images to generate sufficient data for the validation of image processing algo-
rithms, and (d) comparison of data generated by the image formation model with
the real data. IVUS images can be obtained in a simulated form, from a simple
physical model based on the transmission and reception of high-frequency sound
waves, when these radially penetrate a simulated arterial structure (Fig. 1.4).
We assume that for this model the waves are emitted by a transducer located
at the center of the artery and that these waves propagate radially through the
blood and the arterial structures (intima, media, and adventitia), being reflected
progressively by them. The reflected waves or echoes that return are received
by the transducer, which now behaves as a receiver. The time interval between
the emission and the reception of the waves is directly related to the distance
between the source and the reflector (Fig. 1.5). The echo amplitude, which is
a function of time, is transformed on gray scale and later to penetration depth,
so the radial coordinate is determined. If we place a rotatory transducer, make
a registry of the corresponding echoes for each angular position of the trans-
ducer, and combine all the lines obtained from different positions, we will be
able to obtain a simulated 2D image of the structure under study. The 3D IVUS
simulated images can be generated as a sequence of n-planes generated inde-
pendently, taking into account the arterial deformation caused by the blood
pulsatile pressure.
