减少谐波成像中基于参考频率的超声衰减估计的谱振荡以提升鲁棒性
Reducing Spectral Oscillations for Robust Reference Frequency-Based Ultrasound Attenuation Estimation in Harmonic Imaging
AI总结：
该研究针对参考频率法（RFM）超声衰减估计中频率功率比衰减曲线的振荡问题，提出多频率多扫描角度的发射方案，通过平均曲线提升线性度与准确性，在体模和患者研究中均优于传统方法，临床潜力更佳。
AI中文摘要：
超声衰减系数估计（ACE）已成为用于非侵入性评估肝脂肪变性的定量成像生物标志物。一种基于谱归一化的与系统无关的技术，即参考频率法（RFM），此前已被提出，用于在无需校准良好的参考体模的情况下估计ACE。此外，结合谐波成像可显著抑制混响信号。在之前的临床研究中，RFM已与MRI-PDFF实现高相关性，显示出其临床应用潜力。然而，RFM的一个主要挑战是频率功率比衰减曲线（FPDCs）中存在振荡，这会扭曲用于估计衰减系数的线性拟合，进而降低ACE的准确性。这些振荡源于背散射回波之间的相长干涉和相消干涉，导致测量的功率谱出现振荡波动，并传递到FPDCs中。我们提出一种结合多个频率和扫描角度的发射方案，以减轻FPDCs中的振荡。对这些FPDCs进行平均可抑制干涉诱导的振荡，同时保留与衰减相关的衰减趋势，从而提高线性度和ACE结果的准确性。在使用校准体模（0.5和0.76 dB/cm/MHz）的体外实验中，所提方法可提高FPDC线性度和ACE准确性，实现R²为0.99，衰减系数估计值为0.51和0.77 dB/cm/MHz；而传统RFM的R²为0.89，估计值为0.56和0.70 dB/cm/MHz。所提方法在试点患者研究（n=15）中也表现出更优性能，与MRI-PDFF的相关性更强（R=0.89 vs. 0.83），同时降低了测量间变异性，表明其鲁棒性得到提升且具有临床潜力。
英文摘要：
Ultrasound attenuation coefficient estimation (ACE) has emerged as a quantitative imaging biomarker for noninvasive assessment of hepatic steatosis. A system-independent technique based on spectral normalization, known as the reference frequency method (RFM), was previously proposed to estimate ACE without requiring a well-calibrated reference phantom. Furthermore, incorporating harmonic imaging can significantly suppress reverberation signals. In previous clinical study, RFM has achieved high correlation with MRI-PDFF, demonstrating its potential for clinical application. However, a major challenge of RFM is the presence of oscillations in the frequency power-ratio decay curves (FPDCs), which can distort the linear fitting used to estimate the attenuation coefficient and consequently degrade ACE accuracy. These oscillations arise from constructive and destructive interference among backscattered echoes, resulting in oscillatory fluctuations in the measured power spectrum that propagate into the FPDCs. We propose a transmission scheme combining multiple frequencies and steering angles to mitigate oscillations in the FPDCs. Averaging these FPDCs suppresses the interference-induced oscillations while preserving the attenuation-dependent decay trend, thereby improving linearity and the accuracy of ACE results. In in-vitro experiments using calibrated phantoms (0.5 and 0.76 dB/cm/MHz) demonstrated that the proposed method improved FPDC linearity and ACE accuracy, achieving an R2 of 0.99 and attenuation coefficient estimates of 0.51 and 0.77 dB/cm/MHz, versus an R2 of 0.89 and estimates of 0.56 and 0.70 dB/cm/MHz for conventional RFM. The proposed method also demonstrated superior performance in a pilot patient study (n=15), achieving a stronger correlation with MRI-PDFF (R = 0.89 vs. 0.83) while reducing inter-measurement variability, indicating improved robustness and clinical potential.
