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This short movie shows the dynamic reconstruction of the blood flow of a healthy human heart. It is based exclusively on real medical data gathered by an MRI scanner. The colored virtual particle traces visualize the blood flow, similar to ink spreading in water. The movements of the particles represent the blood flow of a patient’s heart during a single heartbeat and illustrate the speed and direction of the flow. During particle acceleration, the color changes from blue to orange. Sophisticated volume rendering shows the anatomy of the pumping heart. Scientists from Fraunhofer MEVIS created the movie using MeVisLab, a software package for developing medical image processing assistance systems for physicians.

Understanding Blood Flow in the Heart

The hearts depicted below demonstrate the differences in blood flow with a healthy three-leaflet aortic valve (left) and with a defective two-leaflet valve (right, bicuspid aortic valve).

The Beauty of Blood Flow Analysis.
The Beauty of Blood Flow Analysis.

The valves, located at the ellipsoids in the image, work like mechanical outlets and cause the blood to flow in only one direction. A bicuspid aortic valve is the most common congenital leaflet defect. During fetal development in the womb, two of the leaflets of the valve fuse. This causes turbulence when the left ventricle ejects blood. The turbulence gradually destructs the leaflets, causing them to harden and stiffen. Ultimately, this leads to calcification accompanied by a constriction of the surface of the open valve. The resulting high blood flow turbulence (shown in the heart on the right) leads to power loss caused by friction and viscous dissipation and alters shear wall stress. Such losses can cause breathlessness and an increase in the energy required for blood circulation. Therapeutic approaches include replacing or reconstructing the aortic valve. The aestheticized visualizations shown above provide contextual information, such as the transparent outline of the heart, and help to brief a patient on their current condition, to train students, or to explain heart diseases to the public. However, a visualization that supports a physician during diagnosis has to be limited to specific flow characteristics to avoid distractions. Scientists mathematically derive various flow characteristics from the movement of blood over time, shown in the figure below:

Different blood flow characteristics.
Representation of different aspects of blood flow in the aorta, such as (a) connectivity with the brain, (b) distribution to different branches, (c) pressure, and (d) vorticity. Copyright: Fraunhofer MEVIS

Blood cells that flow from the heart directly to the brain are visually emphasized in orange (a), depicting connectivity with the brain. This gives hints about how much oxygen reaches the brain or whether a thrombus that has formed in the heart could reach the brain and causes a stroke.  Particles coloured in blue, yellow, or purple (b) deliver information about the overall distribution of the blood leaving the heart according to the vascular branch into which they flow. The relative blood pressure is calculated from the speed of the particles. As in a traffic jam, the blood cells decelerate, seen here as higher pressure zones depicted in orange (c). In some cases, blood cells temporarily swirl at a certain location before they are further distributed. If this happens too often at too many locations, kinetic energy is lost and the instable flow stresses the vascular wall. Clinicians assess the anatomical or functional changes that led to the vortex formation by analyzing the particles in brown (d), and thereby choose a suitable treatment option.

The anatomical and flow information is derived from a 4D phase-contrast MRI dataset, which includes 3D visualization and measurement of blood flow and temporal resolution. These measurements were also used to produce the short movie.

The Future of Flow Visualizations for Diagnoses

New imaging methods for flow visualizations as shown are integrated into software assistants to help doctors determine how the blood flow changes due to heart diseases without using a catheter. They help calculate how the blood pressure and shear forces on the wall of the blood vessels change for patients with heart valve problems. Additional patient-specific numerical flow simulations could help estimate the benefits provided by a new heart valve before an intervention.

Helping the Public Understand Science

Fraunhofer MEVIS is committed to raising awareness about how computerization influences health care and to inspiring the young to consider career pathways in science by showing new ideas, approaches, and possibilities that emerge from innovative R&D.
https://www.mevis.fraunhofer.de/en/press-and-scicom/science-communication.html

For more about cardiac image analysis, visit:
https://www.mevis.fraunhofer.de/en/solutionpages/solutions-for-cardiac-imaging.html

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