用深度集成混合密度网络量化扩散MRI参数不确定性,提升结果可信度。
A Comprehensive Framework for Uncertainty Quantification of Voxel-wise Supervised Models in IVIM MRI
- 采用深度集成混合密度网络,分解预测误差为随机与认知两类不确定性。
- 在模拟与真实数据上,对扩散系数和灌注分数的预测更准确且分布更锐利。
- 适用于生理模型拟合,尤其适合需要可靠性评估的医学影像分析场景。
从扩散加权MRI中准确估计体素内不相干运动(IVIM)参数仍具挑战性,主要源于反问题病态及对噪声高度敏感,尤其在灌注分量。本文提出一种基于深度集成混合密度网络(MDN)的概率深度学习框架,可同时估计总预测不确定性并分解为随机性(AU)与认知性(EU)成分。在合成数据上进行监督训练,并在模拟数据与一个体内数据集上评估性能。通过校准曲线、输出分布锐度及连续排名概率评分(CRPS)验证不确定性可靠性。结果显示,MDN在扩散系数D和分数f上的预测分布更具校准性且更锐利,而伪扩散系数D*存在轻微过自信。鲁棒变异系数(RCV)表明,与单高斯模型相比,MDN在体内数据上对D*的估计更平滑。尽管训练数据覆盖正常生理范围,体内数据仍显示较高的认知不确定性,揭示实际采集条件与训练假设的不匹配,凸显纳入认知不确定性的必要性。本研究构建了一个全面的IVIM拟合不确定性量化框架,能识别并解释不可靠估计。该方法亦可通过结构与仿真调整,推广至其他物理模型拟合。
原文摘要 · Abstract (English)
Accurate estimation of intravoxel incoherent motion (IVIM) parameters from diffusion-weighted MRI remains challenging due to the ill-posed nature of the inverse problem and high sensitivity to noise, particularly in the perfusion compartment. In this work, we propose a probabilistic deep learning framework based on Deep Ensembles (DE) of Mixture Density Networks (MDNs), enabling estimation of total predictive uncertainty and decomposition into aleatoric (AU) and epistemic (EU) components. The method was benchmarked against non probabilistic neural networks, a Bayesian fitting approach and a probabilistic network with single Gaussian parametrization. Supervised training was performed on synthetic data, and evaluation was conducted on both simulated and an in vivo dataset. The reliability of the quantified uncertainties was assessed using calibration curves, output distribution sharpness, and the Continuous Ranked Probability Score (CRPS). MDNs produced more calibrated and sharper predictive distributions for the diffusion coefficient D and fraction f parameters, although slight overconfidence was observed in pseudo-diffusion coefficient D*. The Robust Coefficient of Variation (RCV) indicated smoother in vivo estimates for D* with MDNs compared to Gaussian model. Despite the training data covering the expected physiological range, elevated EU in vivo suggests a mismatch with real acquisition conditions, highlighting the importance of incorporating EU, which was allowed by DE. Overall, we present a comprehensive framework for IVIM fitting with uncertainty quantification, which enables the identification and interpretation of unreliable estimates. The proposed approach can also be adopted for fitting other physical models through appropriate architectural and simulation adjustments.
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