The study evaluates four physically motivated constraints in the estimation of the proton density fat fraction (PDFF). Least squares approaches were developed for constraining the parameters in PDFF quantification based on the physics of magnetic resonance imaging. These were smooth fieldmap, smooth initial phase, nonnegative proton density and moderate R2∗ values. The constraints were evaluated in terms of their influence on the bias and standard deviation of the estimated parameters using numerical simulations and in vivo data acquired at 0.35 T. Results show that unconstrained least squares estimation is noisy and biased and that constraints can be effective at reducing both the standard deviation and bias.

中文翻译：

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限制估计质子密度脂肪分数。

该研究评估了在估算质子密度脂肪分数（PDFF）时的四个物理动机约束。基于磁共振成像的物理原理，开发了最小二乘方法来约束PDFF量化中的参数。这些是平滑的场图，平滑的初始相位，非负质子密度和适度的R2 *值。使用数值模拟和在0.35 T下获得的体内数据，根据约束条件对估计参数的偏差和标准偏差的影响，对约束条件进行了评估。结果表明，无约束最小二乘估计是有噪声且有偏差的，并且约束条件可以有效地降低标准偏差和偏差。