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Flip angle optimization for dynamic contrast-enhanced MRI-studies with spoiled gradient echo pulse sequences
D De Naeyer1, J Verhulst, W Ceelen
1Department of Civil Engineering, Institute of Biomedical Technology (IBiTech), Ghent University, Belgium, De Pintelaan 185, B-9000 Ghent, Belgium. dieter.denaeyer@Ugent.be
Abstract:
Spoiled gradient echo pulse (SPGRE) sequences are commonly used in dynamic contrast-enhanced MRI (DCE-MRI) studies to measure the contrast agent concentration in a tissue of interest over time. However, due to improper tuning of the SPGRE parameters, concentration uncertainty can be very high, even at high signal-to-noise ratio in the MR measurement. In this work, an optimization procedure is proposed for selecting the optimal value of the SPGRE-flip angle FA(opt), given the expected concentration range. The optimization condition ensures that every concentration in the assumed range has the lowest possible uncertainty. By decoupling the R(1)- and R*(2)-effects caused by the presence of the contrast agent, a contour plot has been generated from which FA(opt) can be read off for any study design. Investigation of ten recent DCE-MRI studies showed that improper flip angle selection unnecessarily increases the concentration uncertainty, up to 742% and 72% on average for the typical physiological concentration ranges of 0-2 mM in tumour tissue and 0-10 mM in blood, respectively. Simulations show that the reduced noise levels on the concentration curves, observed at the optimal flip angle, effectively increase the precision of the kinetic parameters estimates (up to 82% for K(trans), 82% for ν(e) and 92% for ν(p) in the case of an individually measured arterial input function (AIF), up to 53% for K(trans), 59% for ν(e) and 67% for ν(p) in the case of a standard AIF). In vivo experiments confirm the potential of flip angle optimization to increase the reproducibility of the kinetic parameter estimates.
Insights
Optimizing the spoiled gradient echo pulse (SPGRE) flip angle in dynamic contrast-enhanced MRI (DCE-MRI) significantly reduces concentration uncertainty. This optimization enhances the precision of kinetic parameter estimates, improving reproducibility in DCE-MRI studies.
Area of Science:
- Medical Imaging
- Biophysics
- Radiology
Background:
- Spoiled gradient echo pulse (SPGRE) sequences are crucial for dynamic contrast-enhanced MRI (DCE-MRI) to quantify contrast agent concentration.
- Improper SPGRE parameter tuning leads to high concentration uncertainty, even with high signal-to-noise ratios.
Purpose of the Study:
- To propose an optimization procedure for selecting the optimal SPGRE flip angle (FA(opt)) to minimize concentration uncertainty within a given range.
- To decouple R(1) and R*(2) effects for a more accurate assessment of contrast agent concentration.
Main Methods:
- Developed an optimization procedure to determine the optimal flip angle (FA(opt)) based on the expected concentration range.
- Generated contour plots by decoupling R(1) and R*(2) effects to identify FA(opt) for various study designs.
- Analyzed ten recent DCE-MRI studies and performed simulations and in vivo experiments.
Main Results:
- Improper flip angle selection in DCE-MRI studies increased concentration uncertainty by up to 742% (tumor tissue) and 72% (blood).
- Optimal flip angle use reduced noise, increasing precision of kinetic parameters (K(trans), ν(e), ν(p)) by up to 92%.
- In vivo experiments confirmed improved reproducibility of kinetic parameter estimates with flip angle optimization.
Conclusions:
- Flip angle optimization is essential for accurate and reproducible DCE-MRI studies.
- The proposed method provides a practical approach to minimize concentration uncertainty and enhance kinetic parameter estimation precision.
- This optimization has significant implications for improving the reliability of DCE-MRI in clinical and research settings.
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