Hooi Fong Ming, Nagle Anna, Subramanian Swetha, Douglas Mast T
Department of Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio 45267-0586.
J Acoust Soc Am. 2015 Feb;137(2):585-97. doi: 10.1121/1.4906580.
Echo decorrelation imaging, a method for mapping ablation-induced ultrasound echo changes, is analyzed. Local echo decorrelation is shown to approximate the decoherence spectrum of tissue reflectivity. Effects of the ultrasound measurement system, echo signal windowing, electronic noise, and tissue motion on echo decorrelation images are determined theoretically, leading to a method for reduction of motion and noise artifacts. Theoretical analysis is validated by simulations and experiments. Simulated decoherence of the scattering medium was recovered with root-mean-square error less than 10% with accuracy dependent on the correlation window size. Motion-induced decorrelation measured in an ex vivo pubovisceral muscle model showed similar trends to theoretical motion-induced decorrelation for a 2.1 MHz curvilinear array with decorrelation approaching unity for 3-4 mm elevational displacement or 1-1.6 mm range displacement. For in vivo imaging of porcine liver by a 7 MHz linear array, theoretical decorrelation computed using image-based motion estimates correlated significantly with measured decorrelation (r = 0.931, N = 10). Echo decorrelation artifacts incurred during in vivo radiofrequency ablation in the same porcine liver were effectively compensated based on the theoretical echo decorrelation model and measured pre-treatment decorrelation. These results demonstrate the potential of echo decorrelation imaging for quantification of heat-induced changes to the scattering tissue medium during thermal ablation.
对回波去相关成像（一种用于绘制消融引起的超声回波变化的方法）进行了分析。结果表明，局部回波去相关近似于组织反射率的去相干谱。从理论上确定了超声测量系统、回波信号加窗、电子噪声和组织运动对回波去相关图像的影响，从而得出一种减少运动和噪声伪像的方法。理论分析通过模拟和实验得到验证。散射介质的模拟去相干恢复时的均方根误差小于10%，其精度取决于相关窗口大小。在离体耻骨内脏肌模型中测量的运动诱导去相关显示出与2.1 MHz曲线阵列的理论运动诱导去相关相似的趋势，对于3 - 4 mm的仰角位移或1 - 1.6 mm的距离位移，去相关接近1。对于用7 MHz线性阵列对猪肝进行体内成像，使用基于图像的运动估计计算的理论去相关与测量的去相关显著相关（r = 0.931，N = 10）。基于理论回波去相关模型和测量的预处理去相关，有效补偿了在同一猪肝体内进行射频消融期间产生的回波去相关伪像。这些结果证明了回波去相关成像在量化热消融过程中热诱导的散射组织介质变化方面的潜力。
