  Morphology of cardiovascular tissue is influenced by the unsteady behavior of
the blood flow and vice versa. Therefore, the pathogenesis of several
cardiovascular diseases is directly affected by the blood-flow dynamics.
Understanding flow behavior is of vital importance to understand the
cardiovascular system and potentially harbors a considerable value for both
diagnosis and risk assessment. The analysis of hemodynamic characteristics
involves qualitative and quantitative inspection of the blood-flow field.
Visualization plays an important role in the qualitative exploration, as well
as the definition of relevant quantitative measures and its validation. There
are two main approaches to obtain information about the blood flow: simulation
by computational fluid dynamics, and in-vivo measurements. Although research on
blood flow simulation has been performed for decades, many open problems remain
concerning accuracy and patient-specific solutions. Possibilities for real
measurement of blood flow have recently increased considerably by new
developments in magnetic resonance imaging which enable the acquisition of 3D
quantitative measurements of blood-flow velocity fields. This chapter presents
the visualization challenges for both simulation and real measurements of
unsteady blood-flow fields.
