Renal Transplant Elasticity Ultrasound Imaging: Correlation Between Normalized Strain and Renal Cortical Fibrosis

After transplantation, over a widely variable time course, the cortex of the transplanted kidney becomes stiffer as interstitial fibrosis develops and renal function declines. Elasticity ultrasound imaging (EUI) has been used to assess biomechanical properties of tissue that change in hardness as a result of pathologic damage. We prospectively assessed the hardness of the renal cortex in renal transplant allograft patients using a normalized ultrasound strain procedure measuring quasi-static deformation, which was correlated with the grade of renal cortical fibrosis. To determine cortical strain, we used 2-D speckle-tracking software (EchoInsight, Epsilon Imaging, Ann Arbor, MI, USA) to perform offline analysis of stored ultrasound loops capturing deformation of renal cortex and its adjacent soft tissue produced by pressure applied using the scanning transducer. Normalized strain is defined as the mean developed strain in the renal cortex divided by the overall mean strain measured in the soft tissues from the abdominal wall to pelvic muscles. Using the Banff scoring criteria for renal cortical fibrosis as the gold standard, we classified 20 renal transplant allograft biopsy tissue samples into two groups: group 1 (n = 10) with mild (<25%) renal cortical fibrosis and group 2 (n = 10) with moderate (26%–50%) renal cortical fibrosis. An unpaired two-tailed t-test was used to determine the statistical difference in strains between patients with mild and those with moderate renal cortical fibrosis. Receiver operating characteristic curve analysis was performed to assess the accuracy of developed strain and normalized strain in predicting moderate renal cortical fibrosis. The reference strain did not significantly differ between the two groups (p = 0.10). However, the developed renal cortical strain in group 1 with mild fibrosis was higher than that in group 2 with moderate fibrosis (p = 0.025). The normalized strain in group 1 was also higher than that in group 2 (p = 0.0014). The areas under receiver operating characteristic curves for developed strain and normalized strain were 0.78 and 0.95, respectively. The optimal cutoff for distinguishing moderate renal cortical fibrosis was −0.08 for developed strain (sensitivity = 0.50, specificity = 1.0) and 2.5 for normalized strain (sensitivity = 0.80, specificity = 1.0). In summary, renal cortex strain is strongly correlated with grade of renal cortical fibrosis. Normalized strain is superior to developed strain in distinguishing moderate from mild renal cortical fibrosis. We conclude that free-hand real-time strain EUI may be useful in assessing the progression of cortical fibrosis in renal transplant allografts. Further prospective study using this method is warranted.     

Liver Stiffness Measurements by Means of Supersonic Shear Imaging in Patients Without Known Liver Pathology

We used supersonic shear imaging to determine the liver stiffness (LS) values of 82 patients without known liver pathology and studied the factors that influence these measurements. Five LS measurements were made in each subject, and the median value, expressed in kilopascals, was calculated. Reliable LS measurements were obtained in 84.5% of patients. Higher body mass index and older age were associated with failure to obtain reliable measurements. The mean value of LS measurements determined by SSI in our cohort of patients without known liver pathology was 6 ± 1.4 kPa. The mean LS measurements determined by SSI for men were significantly higher than those for women; body mass index did not significantly influence SSI measurements. Thus, 6 kPa is the mean SSI value in patients without known liver pathology, with higher values being obtained in men.     

超声弹性成像技术评估肝纤维化的临床价值

超声弹性成像技术已用于临床多种疾病的诊断与鉴别诊断,针对肝纤维化的定性及定量研究也已取得一定进展。本文就三种弹性成像技术:实时弹性成像、Fibroscan仪成像及脉冲声辐射力弹性成像在肝纤维化评估中的应用及新进展综述如下。     

Direct mean strain estimation for elastography using nearest-neighbor weighted least-squares approach in the frequency domain

Ultrasound elastography is emerging with enormous potential as a medical imaging modality for effective discrimination of pathological changes in soft tissue. It maps the tissue elasticity or strain due to a mechanical deformation applied to it. The strain image most often calculated from the derivative of the local displacement field is highly noisy because of the de-correlation effect mainly due to unstable free-hand scanning and/or irregular tissue motion; consequently, improving the SNR of the strain image is still a challenging problem in this area. In this paper, a novel approach using the nearest-neighbor weighted least-squares is presented for direct estimation of the ‘mean’ axial strain for high quality strain imaging. Like other time/frequency domain reported schemes, the proposed method exploits the fact that the post-compression rf echo signal is a time-scaled and shifted replica of the pre-compression rf echo signal. However, the elegance of our technique is that it directly computes the mean strain without explicitly using any post filter and/or previous local displacement/strain estimates as is usually done in the conventional approaches. It is implemented in the short-time Fourier transform domain through a nearest-neighbor weighted least-squares-based Fourier spectrum equalization technique. As the local tissue strain is expected to maintain continuity with its neighbors, we show here that the mean strain at the interrogative window can be directly computed from the common stretching factor that minimizes a cost function derived from the exponentially weighted windowed pre- and post-compression rf echo segments in both the lateral and axial directions. The performance of our algorithm is verified for up to 8% applied strain using simulation and experimental phantom data and the results reveal that the SNR of the strain image can be significantly improved compared to other reported algorithms in the literature. The efficacy of the algorithm is also tested with in vivo breast data known to have malignant or benign masses from histology.     

超声弹性成像观察肝脏凝固灶:体外实验

目的 运用实验手段探讨超声弹性成像(EI)在肝脏凝固灶中的应用.方法 选取新鲜离体猪肝,通过无水乙醇注射和微波消融两种方法产生不同形态的凝固灶,观察实验前、后的EI图,利用虚拟声触诊定量(VTQ)技术测定作用区的剪切波传播速度.实验结束后切开标本记录实际凝固灶形态、范围.结果 无水乙醇注射和微波消融均可使局部肝组织发生凝固性坏死,EI图上表现为红色硬变区,且不随时间延长而衰减,较常规二维超声更接近凝固灶形态,但与实际仍有一定差异.作用区的剪切波速度较实验前明显增高(P＜0.01),也表明凝固性坏死的肝组织硬度增加.结论 EI可从力学角度提供凝固灶信息,应用简捷、无创,是常规超声的有益补充.     

超声弹性成像在涎腺局灶性病变诊断中的初步应用

目的 探讨超声弹性成像技术在腮腺和颌下腺局灶性病变诊断中的临床应用价值.方法 对30例患者共30个腮腺或颌下腺局灶性病变行实时超声弹性成像检查,根据病灶软硬度不同进行评分,并与术后病理进行相关分析.结果 超声弹性图中良性病变以1～3分多见,而恶性病变以4～5分多见,两组病变的弹性评分情况比较差异具有统计学意义(P＜0.01).以≥4分作为判断恶性病变的标准,其敏感度为72.73％,特异度为84.21％,准确率为80.00％.结论 超声弹性成像可为腮腺和颌下腺局灶性病变良恶性病变的鉴别诊断提供有价值的信息.     

子宫颈占位性病变的经阴道实时弹性成像表现

目的 探讨子宫颈占位性病变的实时超声弹性成像表现.方法 分析20例官颈良性占位性病变、40例官颈癌以及20例正常宫颈超声弹性成像表现,分别采用改良弹性评分标准对其进行弹性评分和应变率比值测定,并与病理结果作对比.结果 正常宫颈弹性图像评分100％为1分;官颈良性占位性病变弹性图像评分95％≤2分,官颈良性占位性病变的弹性应变率比值为0.75±0.32;宫颈癌弹性评分90％≥3分,官颈癌应变率比值3.31±1.47.良恶性占位性病变弹性评分间差异有统计学意义(P＜0.001),良恶性占位性病变弹性应变率比值间差异有统计学意义(P＜0.001).结论 不同性质的官颈占位性病变弹性图像具有较明显的特征性表现.     

超声弹性成像技术在甲状腺结节中的临床应用价值

目的探讨超声弹性成像技术在甲状腺结节诊断中的临床应用价值。方法对经手术病理证实的127例甲状腺结节患者（158个结节）的术前常规超声、超声弹性成像特征进行回顾性分析,并与病理结果进行对照。结果本组158个甲状腺结节,病理证实良性结节127个,其中弹性分级0～11级者109个（85．8％）,弹性分级Ⅲ-Ⅳ级者18个（14．2％）;31个恶性结节中有4个（12．9％）弹性分级为0～Ⅱ级,27个（87．1％）结节为Ⅲ～Ⅳ级。超声弹性成像诊断甲状腺结节良恶性的敏感性和特异性分别为87．1％和85．8％,明显高于常规超声检查的67．7％和81．1％（P〈0．05）。结论超声弹性成像技术可显著提高超声对甲状腺良恶性结节的鉴别诊断能力。     

超声实时弹性成像整体应变率与局部应变率诊断乳腺病灶的比较

目的 比较超声实时弹性成像整体应变率(ESR)、局部应变率(LSR)对乳腺良恶性病灶的诊断价值。 方法 对113例患者共145个乳腺病灶(良性组:85个,恶性组:60个)分别行LSR、ESR两种应变率测量。以病理诊断为金标准,构建ROC曲线,分别获得两种方法鉴别乳腺病灶良恶性的最佳临界点,比较其诊断效率。 结果 构建ROC曲线后,ESR ROC曲线下面积(AUC)为0.90±0.03,最佳临界点为3.16,其敏感度、特异度、准确率分别为88.33%(53/60)、88.24%(75/85)、88.28%(128/145)。LSR的AUC为0.97±0.02,最佳临界点为31.15,其敏感度、特异度、准确率分别为96.67%(58/60)、94.12%(80/85)、95.17%(138/145)。LSR对乳腺病灶良恶性的诊断价值及准确率均优于ESR(P＜0.05)。 结论 ESR和LSR对乳腺病灶良恶性的鉴别诊断具有较大价值,LSR优于ESR。     

经阴道超声弹性成像对宫颈癌诊断的临床应用初探

目的 探讨实时经阴道超声弹性成像在宫颈病变诊断中的临床应用价值.方法 分析124例宫颈病变患者的超声弹性图像,所有病例均经手术或组织活检病理证实.计算病变区与周围组织的弹性应变比值(strain ratio),以病理结果为金标准进行良恶性病变比较,采用ROC曲线分析strain ratio在诊断宫颈病变中的最佳截断值.结果 良性病变的弹性图像以绿色渲染为主,平均strain ratio值为2.71±1.56;恶性病变者渲染为蓝色,平均strain ratio为8.32±4.11,二者差异有统计学意义(P＜0.01).ROC 曲线显示当选取strain ratio为4.99时,曲线下面积最大达0.912,特异性和灵敏性分别为80.7％和89.6％.结论 实时超声弹性成像为宫颈病变良、恶性的鉴别诊断提供了一种新的无创检查方法.