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Assessment of transmitral and left atrial appendage flow rate from cardiac 4D-CT
Sophia Bäck1,2, Lilian Henriksson2,3, Ann F Bolger1,4
1Unit of Cardiovascular Sciences, Department of Health, Medicine and Caring Sciences, Linköping University, Linköping, Sweden.
Insights
A new algorithm accurately measures blood flow in the heart using 4D-CT scans. This technique aids in diagnosing conditions like diastolic dysfunction and assessing thrombus risk in atrial fibrillation.
Area of Science:
- Cardiovascular Imaging
- Medical Physics
- Biomedical Engineering
Background:
- 4D-CT provides high-quality cardiac anatomy but lacks validated methods for blood flow assessment.
- Assessing blood flow is crucial for diagnosing diastolic dysfunction (mitral valve flow) and atrial fibrillation (left atrial appendage flow).
- Existing techniques for extracting flow dynamics from 4D-CT are insufficient.
Purpose of the Study:
- To develop and validate a novel algorithm for measuring blood flow rates through the mitral valve (MV) and left atrial appendage (LAA) using 4D-CT.
- To compare the accuracy of the developed 4D-CT flow measurement technique against 4D flow MRI and short-axis MRI.
Main Methods:
- A motion tracking algorithm was developed, utilizing nonrigid deformation of the blood pool-myocardium surface.
- The left atrial appendage (LAA) was tracked separately to enhance accuracy.
- The algorithm's performance was evaluated in 9 patients by comparing 4D-CT derived flow data with 4D flow and short-axis MRI.
Main Results:
- The algorithm showed good agreement for the timing of diastolic peak flow across the mitral valve (bias <0.1 s).
- Ventricular stroke volume measurements from 4D-CT closely matched short-axis MRI (bias 3 ml).
- Peak left atrial appendage outflow rates demonstrated good agreement between 4D-CT and 4D flow MRI (bias -6 ml/s).
Conclusions:
- The developed algorithm accurately tracks dynamic cardiac geometries from 4D-CT data.
- The technique yields comparable flow rate measurements at the mitral valve and left atrial appendage to 4D flow MRI.
- This validated method enhances the utility of 4D-CT for assessing cardiac blood flow dynamics.
Background:
Cardiac time-resolved CT (4D-CT) acquisitions provide high quality anatomical images of the heart. However, some cardiac diseases require assessment of blood flow in the heart. Diastolic dysfunction, for instance, is diagnosed by measuring the flow through the mitral valve (MV), while in atrial fibrillation, the flow through the left atrial appendage (LAA) indicates the risk for thrombus formation. Accurate validated techniques to extract this information from 4D-CT have been lacking, however.
Methods:
To measure the flow rate though the MV and the LAA from 4D-CT, we developed a motion tracking algorithm that performs a nonrigid deformation of the surface separating the blood pool from the myocardium. To improve the tracking of the LAA, this region was deformed separately from the left atrium and left ventricle. We compared the CT based flow with 4D flow and short axis MRI data from the same individual in 9 patients.
Results:
For the mitral valve flow, good agreement was found for the time span between the early and late diastolic peak flow (bias: <0.1 s). The ventricular stroke volume is similar compared to short-axis MRI (bias 3 ml). There are larger differences in the diastolic peak flow rates, with a larger bias for the early flow rate than the late flow rate. The peak LAA outflow rate measured with both modalities matches well (bias: -6 ml/s).
Conclusions:
Overall, the developed algorithm provides accurate tracking of dynamic cardiac geometries resulting in similar flow rates at the MV and LAA compared to 4D flow MRI.
