Conventional and compound scanning of the carotid artery

Plaque in the carotid artery is typically formed at the bifurcation in the neck, but in contrast to most other vessels in the body, rather than the reduction in lumen diameter it is risk of embolization of small blood vessels in the brain, i.e. the risk of stroke, that is the primary cause for concem.

The carotid artery can be visualized with extra-vascular ultrasound and the main parameters of this scanning situation is considered in this chapter, including aspects of the degradation due to the medium between transducer and plaque. The ultrasound images are affected by variations in gray scale value due to speckle and angle-dependence and due to intervening anisotropic tissue.

Spatial compound imaging is introduced and it is shown with in vitro and in vivo examples how the speckle can be reduced this way. Error sources and potential problems are discussed. For the in vitro investigations, it is shown how the tissue types in the plaque can be determined by scanning the plaque casted into an agar block and subsequently cutting this block at given calibration marker locations.

Both anatomical and histological images can then be obtained at the same scan plane as that of the ultrasound image. Finally, future techniques for classification ofplaque tissue with extra-vascular ultrasound is discussed.