Flow Dynamics in the Aortic Arch and Its Effect on the Arterial Input Function in Cardiac Computed Tomography

Area of Science:

• Cardiovascular Imaging
• Medical Physics
• Computational Fluid Dynamics

Background:

• The arterial input function (AIF), represented by the time-density curve (TDC) of contrast at the coronary ostia, is crucial for contrast-enhanced computed tomography angiography (CTA).
• Accurate measurement of AIF is essential for quantitative analysis, including estimating coronary flow rate and detecting myocardial ischemia.

Purpose of the Study:

• To investigate contrast mixing and dispersion within a patient-specific aorta model.
• To compare TDCs at the coronary ostium and descending aorta.
• To validate the use of descending aorta TDCs as a surrogate for the AIF in CTA.

Main Methods:

• Computational fluid dynamics (CFD) simulations were performed on a patient-specific aortic model derived from CTA data.
• Hemodynamics and contrast dispersion were analyzed.
• TDCs were compared at different aortic locations, focusing on the coronary ostia and descending aorta.

Main Results:

• Simulations revealed complex, pulsatile flow patterns driving contrast mixing and dispersion in the aortic arch.
• Despite the anatomical distance, TDCs at the coronary ostia and descending aorta exhibited similar rise-times and up-slopes.
• A minor time lag of 0.19 seconds was observed between the TDCs at these two locations.

Conclusions:

• The time-density curve in the descending aorta serves as an accurate analog for the arterial input function.
• Current clinical practices using descending aorta TDCs as a surrogate for AIF in quantitative CTA are validated.
• This finding supports the continued use of descending aorta TDCs for estimating coronary flow rate and myocardial ischemia.