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CFD- and Bernoulli-based pressure drop estimates: A comparison using patient anatomies from heart and aortic valve
Jürgen Weese1, Angela Lungu2, Jochen Peters1
1Philips Research Laboratories, Röntgenstrasse 24-26, D-22335, Hamburg, Germany.
Insights
This study reveals that the effective orifice area (EOA) in aortic valve stenosis can be larger than the projected aortic valve area (AVA) for certain cases. Advanced CT imaging and CFD simulations provide new insights into aortic valve stenosis quantification.
Area of Science:
- Cardiovascular Imaging and Fluid Dynamics
- Medical Image Analysis
- Computational Fluid Dynamics
Background:
- Aortic valve stenosis (AVS) is a critical condition characterized by aortic valve (AV) narrowing, impeding blood flow.
- Quantification of AVS typically involves geometric orifice area (AVA) and pressure drop (PD), often related via the Bernoulli equation to effective orifice area (EOA).
- Understanding the relationship between AVA and EOA is crucial for accurate AVS assessment.
Purpose of the Study:
- To investigate the relationship between the geometric aortic valve area (AVA) and the effective orifice area (EOA) in patients with aortic valve stenosis.
- To utilize patient-specific anatomies from cardiac CT angiography and computational fluid dynamics (CFD) simulations for this investigation.
- To compare different methods of AVA calculation and their correlation with EOA.
Main Methods:
- Developed a shape-constrained deformable model for segmenting the aortic valve (AV), ascending aorta (AA), and left ventricle (LV) from cardiac CT images.
- Determined planimetric AVA from the minimum cross-sectional opening and projected AVA from leaflet rims.
- Performed steady-state CFD simulations on patient anatomies to calculate pressure drop (PD) and subsequently EOA using the Bernoulli equation.
Main Results:
- Analyzed 22 patient cases with varying degrees of aortic valve calcification, yielding AVAs from 1-4.5 cm² and ejection fractions (EFs) of 20-75%.
- Projected AVA values were consistently smaller than planimetric AVA values, though highly correlated (R² = 0.995).
- EOA values derived from CFD-based PD showed strong correlation with both AVA measurements (R² = 0.97), with EOA approximately 10% smaller than planimetric AVA. Notably, for EOA < 2.0 cm², EOA was up to 15% larger than projected AVA.
Conclusions:
- The developed segmentation algorithm enabled detailed AV modeling for 22 patients.
- The crown-like 3D structure of the AV results in planimetric AVA exceeding projected AVA.
- The finding that projected AVA can be smaller than EOA for EOA < 2.0 cm² contradicts previous studies, attributed to the more detailed AV models used herein.
Purpose:
An aortic valve stenosis is an abnormal narrowing of the aortic valve (AV). It impedes blood flow and is often quantified by the geometric orifice area of the AV (AVA) and the pressure drop (PD). Using the Bernoulli equation, a relation between the PD and the effective orifice area (EOA) represented by the area of the vena contracta (VC) downstream of the AV can be derived. We investigate the relation between the AVA and the EOA using patient anatomies derived from cardiac computed tomography (CT) angiography images and computational fluid dynamic (CFD) simulations.
Methods:
We developed a shape-constrained deformable model for segmenting the AV, the ascending aorta (AA), and the left ventricle (LV) in cardiac CT images. In particular, we designed a structured AV mesh model, trained the model on CT scans, and integrated it with an available model for heart segmentation. The planimetric AVA was determined from the cross-sectional slice with minimum AV opening area. In addition, the AVA was determined as the nonobstructed area along the AV axis by projecting the AV leaflet rims on a plane perpendicular to the AV axis. The flow rate was derived from the LV volume change. Steady-state CFD simulations were performed on the patient anatomies resulting from segmentation.
Results:
Heart and valve segmentation was used to retrospectively analyze 22 cardiac CT angiography image sequences of patients with noncalcified and (partially) severely calcified tricuspid AVs. Resulting AVAs were in the range of 1-4.5 cm2 and ejection fractions (EFs) between 20 and 75%. AVA values computed by projection were smaller than those computed by planimetry, and both were strongly correlated (R2 = 0.995). EOA values computed via the Bernoulli equation from CFD-based PD results were strongly correlated with both AVA values (R2 = 0.97). EOA values were ∼10% smaller than planimetric AVA values. For EOA values < 2.0 cm2 , the EOA was up to ∼15% larger than the projected AVA.
Conclusions:
The presented segmentation algorithm allowed to construct detailed AV models for 22 patient cases. Because of the crown-like 3D structure of the AV, the planimetric AVA is larger than the projected AVA formed by the free edges of the AV leaflets. The AVA formed by the free edges of the AV leaflets was smaller than the EOA for EOA values <2.0cm2. This contradiction with respect to previous studies that reported the EOA to be always smaller or equal to the geometric AVA is explained by the more detailed AV models used within this study.
