IVUS Image Processing Methodologies

IVUS Image Processing Methodologies

Antonis A. Sakellarios (University of Ioannina, Greece), Christos V. Bourantas (Castle Hill Hospital, UK), Lambros S. Athanasiou (University of Ioannina, Greece), Dimitrios I. Fotiadis (University of Ioannina, Greece ) and Lampros K. Michalis (University of Ioannina, Greece)
DOI: 10.4018/978-1-61350-095-8.ch003
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Intravascular Ultrasound (IVUS) is an invasive imaging technique that allows detailed visualization of the arterial lumen and outer vessel wall and permits characterization of the type of the plaque and quantification of its burden. Traditionally IVUS processing was performed manually. However, it became apparent that manual segmentation is time consuming, and the obtained results depend on the experience of the operators. To overcome these limitations and enhance the role of IVUS in clinical practice and research, several (semi-) automated methods have been developed that expedite detection of the regions of interest and/or characterization of the type of the plaque. In this chapter we review the available IVUS processing techniques and present the developed commercial solutions for IVUS segmentation and plaque characterization.
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Apart from the regions of interest (lumen, media-adventitia and stent border) and the plaque [which depending on its echogenisity can be classified as echolucent/soft (lipid rich) plaque, intermediate (fibrous) plaque, echo dense (calcific) plaque and mixed if it includes more than one acoustic subtypes] (Mintz et al. 2001) various artefacts are often seen in IVUS images which should be taken into consideration during the segmentation process (Figure 1). Some of these depend on the type of the catheter (mechanical or solid state) used, while others can be detected in all IVUS sequences. For example, the non-uniform rotational artefacts can be seen only in mechanical IVUS imaging and are due to asymmetric friction which leads the transducer to lag during one part of the rotation and whip through the other part of its 360o rotation resulting in geometrical distortion of the image. On the other hand the ring down artefact, the shadowing artefact, the reverberations and the blood speckles are seen in both mechanical and solid state IVUS imaging. The ring down artefact is due to signal disorganization and appears as a bright halo of variable thickness around the catheter while the shadowing artefact occurs when a structure with a marked difference in acoustic impedance (e.g. calcific plaque) blocks the transmission of the ultrasound beyond that point resulting in a shadow behind the echoreflective structure, which follows the ultrasound signal. The reverberations are artefacts caused by secondary false echoes of the same structure and are more common in strong echoreflectors such as calcium, stent or the guidewire. Finally, the blood speckles are spots that are moving with a characteristic pattern and are due to the reflection of the signal by the red blood cells (Nissen et al. 1998). From the above it is obvious that there is a variety of artefacts which renders the automated segmentation of the IVUS images a challenging process.

Figure 1.

Structures and artefacts seen in IVUS images

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