Vasconcelos Luiz, Kijanka Piotr, Grande Joseph P, Oliveira Rebeca, Amador Carolina, Aristizabal Sara, Sanger Nicholas M, Rule Andrew D, Atwell Thomas D, Urban Matthew W
Department of Radiology, Mayo Clinic, Rochester, MN, USA.
Department of Robotics and Mechatronics, AGH University of Krakow, Krakow, Poland.
Comput Methods Programs Biomed. 2024 Mar;245:108035. doi: 10.1016/j.cmpb.2024.108035. Epub 2024 Jan 15.
Biopsy stands as the gold standard for kidney transplant assessment, yet its invasive nature restricts frequent use. Shear wave elastography (SWE) is emerging as a promising alternative for kidney transplant monitoring. A parametric study involving 12 biopsy data sets categorized by standard biopsy scores (3 with normal histology, 3 with interstitial inflammation (i), 3 with interstitial fibrosis (ci), and 3 with tubular atrophy (ct)), was conducted to evaluate the interdependence between microstructural variations triggered by chronic allograft rejection and corresponding alterations in SWE measurements.
Heterogeneous shear wave motion simulations from segmented kidney cortex sections were performed employing the staggered-grid finite difference (SGFD) method. The SGFD method allows the mechanical properties to be defined on a pixel-basis for shear wave motion simulation. Segmentation techniques enabled the isolation of four histological constituents: glomeruli, tubules, interstitium, and fluid. Baseline ex vivo Kelvin-Voigt mechanical properties for each constituent were drawn from established literature. The parametric evaluation was then performed by altering the baseline values individually. Shear wave velocity dispersion curves were measured with the generalized Stockwell transform in conjunction with slant frequency-wavenumber analysis (GST-SFK) algorithm. By fitting the curve within the 100-400 Hz range to the Kelvin-Voigt model, the rheological parameters, shear elasticity (µ) and viscosity (µ), were estimated. A time-to-peak algorithm was used to estimate the group velocity. The resultant in silico models emulated the heterogeneity of kidney cortex within the shear wave speed (SWS) reconstructions.
The presence of inflammation showed considerable spatial composition disparities compared to normal cases, featuring a 23 % increase in interstitial area and a 19 % increase in glomerular area. Concomitantly, there was a reduction of 12 % and 47 % in tubular and fluid areas, respectively. Consequently, mechanical changes induced by inflammation predominate in terms of rheological differentiation, evidenced by increased elasticity and viscosity. Mild tubular atrophy showed significant elevation in group velocity and µ. Conversely, mild and moderate fibrosis exhibited negligible alterations across all parameters, compatible with relatively limited morphological impact.
This proposed model holds promise in enabling patient-specific simulations of the kidney cortex, thus facilitating exploration into how pathologies altering cortical morphology correlates to modifications in SWE-derived rheological measurements. We demonstrated that inflammation caused substantial changes in measured mechanical properties.
活检是肾移植评估的金标准，但其侵入性限制了其频繁使用。剪切波弹性成像（SWE）正成为肾移植监测的一种有前景的替代方法。进行了一项参数研究，涉及12个活检数据集，这些数据集按标准活检评分分类（3个组织学正常，3个有间质炎症（i），3个有间质纤维化（ci），3个有肾小管萎缩（ct）），以评估慢性同种异体移植排斥引发的微观结构变化与SWE测量中相应改变之间的相互依存关系。
采用交错网格有限差分（SGFD）方法对分割后的肾皮质切片进行非均匀剪切波运动模拟。SGFD方法允许在像素基础上定义剪切波运动模拟的力学性能。分割技术能够分离出四种组织学成分：肾小球、肾小管、间质和液体。每个成分的离体基线开尔文 - 沃伊特力学性能取自已发表的文献。然后通过单独改变基线值进行参数评估。使用广义斯托克韦尔变换结合倾斜频率 - 波数分析（GST - SFK）算法测量剪切波速度色散曲线。通过将100 - 400 Hz范围内的曲线拟合到开尔文 - 沃伊特模型，估计流变学参数，剪切弹性（µ）和粘度（µ）。使用峰值时间算法估计群速度。所得的计算机模拟模型在剪切波速度（SWS）重建中模拟了肾皮质的异质性。
与正常情况相比，炎症的存在显示出相当大的空间组成差异，间质面积增加23%，肾小球面积增加19%。同时，肾小管和液体面积分别减少12%和47%。因此，炎症引起的力学变化在流变学差异方面占主导地位，表现为弹性和粘度增加。轻度肾小管萎缩显示群速度和µ显著升高。相反，轻度和中度纤维化在所有参数上的变化可忽略不计，与相对有限的形态学影响相符。
该模型有望实现肾皮质的患者特异性模拟，从而有助于探索改变皮质形态的病理状况与SWE衍生的流变学测量变化之间的关系。我们证明炎症会导致测量的力学性能发生重大变化。
