A Basic Model for IVUS Image Simulation - Biomedical Image Analysis - page 13

Figure 1.10: An ultrasound pulse P 1 that has width d 1 frontally affects a linear
scatterer array placed at a distance d oi .
transducers be smaller so that the resolution is increased, but this diminishes
their capacity to explore greater tissues depth. For the IVUS techniques, the res-
olution plays a very important role since most of the structures to be visualized
directly depend on these parameters.
1.4.1.1 Axial Resolution
Axial resolution is the capacity of an ultrasound technique to separate the spa-
tial position of two consecutive scatterers through its corresponding echoes
[13, 14, 16]. In Fig. 1.10 an ultrasound pulse P 1 that has a width d 1 frontally af-
fects a linear scatterer array at a distance d oi . Each one of the echoes forms a
“train” of pulses temporally distanced according to the equation t oi = 2 | R i | / c ,
R i being the i th relative emitter/scatterer distance and c is the pulse propaga-
tion speed. The progressive distance reduction of the linear scatterers, given by
( a 1 ,..., a 4 ) (Fig. 1.10) and ( b 1 ,..., b 4 ) (Fig. 1.11), reduces the time interval be-
tween the maximums of the “trains” pulses. There exists a critical distance width
d t at which the pulses that arrive at the receiver are superposed, therefore, not
being able to discriminate or separate individually the echoes produced by each
scatterer. In Fig. 1.11 one can observe that the resolution can be improved by