Measurement of Corneal Elasticity with an Acoustic Radiation Force Elasticity Microscope

To investigate the role of collagen structure in corneal biomechanics, measurement of localized corneal elasticity with minimal destruction to the tissue is necessary. We adopted the recently developed acoustic radiation force elastic microscopy (ARFEM) technique to measure localize biomechanical properties of the human cornea. In ARFEM, a low-frequency, high-intensity acoustic force is used to displace a femtosecond laser-generated microbubble, while high-frequency, low-intensity ultrasound is used to monitor the position of the microbubble within the cornea. Two ex vivo human corneas from a single donor were dehydrated to physiologic thickness, embedded in gelatin and then evaluated using the ARFEM technique. In the direction perpendicular to the corneal surface, ARFEM measurements provided elasticity values of E = 1.39 ± 0.28 kPa for the central anterior cornea and E = 0.71 ± 0.21 kPa for the central posterior cornea in pilot studies. The increased value of corneal elasticity in the anterior cornea correlates with the higher density of interweaving lamellae in this region.     

Volumetric Elasticity Imaging with a 2-D CMUT Array

This article reports the use of a two-dimensional (2-D) capacitive micro-machined ultrasound transducer (CMUT) to acquire radio-frequency (RF) echo data from relatively large volumes of a simple ultrasound phantom to compare three-dimensional (3-D) elasticity imaging methods. Typical 2-D motion tracking for elasticity image formation was compared with three different methods of 3-D motion tracking, with sum-squared difference (SSD) used as the similarity measure. Differences among the algorithms were the degree to which they tracked elevational motion: not at all (2-D search), planar search, combination of multiple planes and plane independent guided search. The cross-correlation between the predeformation and motion-compensated postdeformation RF echo fields was used to quantify motion tracking accuracy. The lesion contrast-to-noise ratio was used to quantify image quality. Tracking accuracy and strain image quality generally improved with increased tracking sophistication. When used as input for a 3-D modulus reconstruction, high quality 3-D displacement estimates yielded accurate and low noise modulus reconstruction. (E-mail: tgfisher@wisc.edu)     

A 3-D Region-Growing Motion-Tracking Method for Ultrasound Elasticity Imaging

A 3-D region-growing motion-tracking (RGMT) method for ultrasound elasticity imaging is described. This 3-D RGMT method first estimates the displacements at a sparse subset of points, called seeds; uses an objective measure to determine, among those seeds, which displacement estimates to trust; and then performs RGMT in three dimensions to estimate displacements for the remaining points in the field. During the growing process in three dimensions, the displacement estimate at one grid point is employed to guide the displacement estimation of its neighboring points using a 3-D small search region. To test this algorithm, volumetric ultrasound radiofrequency echo data were acquired from one phantom and five in vivo human breasts. Displacement estimates obtained with the 3-D RGMT method were compared with a published 2-D RGMT method via motion-compensated cross-correlation (MCCC) of pre- and post-deformation radiofrequency echo signals. For data from experiments with the phantom, the MCCC values in the entire tracking region of interest averaged approximately 0.95, and the contrast-to-noise ratios averaged 4.6 for both tracking methods. For all five patients, the average MCCC values within the region of interest obtained with the 3-D RGMT were consistently higher than those obtained with the 2-D RGMT method. These results indicate that the 3-D RGMT algorithm is able to track displacements with increased accuracy and generate higher-quality 3-D elasticity images than the 2-D RGMT method.     

Detecting Regional Stiffness Changes in Aortic Aneurysmal Geometries Using Pressure-Normalized Strain

Transabdominal ultrasound elasticity imaging could improve the assessment of rupture risk for abdominal aortic aneurysms by providing information on the mechanical properties and stress or strain states of vessel walls. We implemented a non-rigid image registration method to visualize the pressure-normalized strain within vascular tissues and adapted it to measure total strain over an entire cardiac cycle. We validated the algorithm's performance with both simulated ultrasound images with known principal strains and anatomically accurate heterogeneous polyvinyl alcohol cryogel vessel phantoms. Patient images of abdominal aortic aneurysm were also used to illustrate the clinical feasibility of our imaging algorithm and the potential value of pressure-normalized strain as a clinical metric. Our results indicated that pressure-normalized strain could be used to identify spatial variations in vessel tissue stiffness. The results of this investigation were sufficiently encouraging to warrant a clinical study measuring abdominal aortic pressure-normalized strain in a patient population with aneurysmal disease.     

超声应变率显像技术估测犬的右心室长轴收缩功能

目的探讨超声应变率显像技术对犬的右心室长轴收缩功能的评估价值。方法采集7只犬心尖四腔心切面右室游离壁在5种不同心肌收缩力状态下的组织多普勒超声图像,同步记录右室等容收缩期最大压力上升速率(maxdp/dt),并作为金指标。QLAB分析软件分别测量长轴方向右室游离壁基底段、中段收缩期平均峰值速度(V)、平均峰值应变率(SR)和平均峰值应变(S),并与右室maxdp/dt作直线相关分析。结果应用多巴酚丁胺(dobutamine)后右室游离壁基底段、中段收缩期V、SR、S增加,应用艾司络尔(esmolol)上述各指标明显下降。与maxdp/dt相关分析表明,右室游离壁基底段和中段收缩期V、SR和S与dp/dt显著相关,但以SR最显著。结论超声应变率显像技术可定量估测右室长轴收缩功能,右室游离壁基底段、中段收缩期SR是无创性估测右室长轴收缩功能的良好指标。     

Correlation of Cognitive Function with Ultrasound Strain Indices in Carotid Plaque

Instability in carotid vulnerable plaque can generate cerebral micro-emboli, which may be related to both stroke and eventual cognitive abnormality. Strain imaging to detect plaque vulnerability based on regions with large strain fluctuations, with arterial pulsation, may be able to determine the risk of cognitive impairment. Plaque instability may be characterized by increased strain variations over a cardiac cycle. Radiofrequency signals for ultrasound strain imaging were acquired from the carotid arteries of 24 human patients using a Siemens Antares with a VFX 13-5 linear array transducer. These patients underwent standardized cognitive assessment (Repeatable Battery for the Assessment of Neuropsychological Status [RBANS]). Plaque regions were segmented by a radiologist at end-diastole using the Medical Imaging Interaction Toolkit. A hierarchical block-matching motion tracking algorithm was used to estimate the cumulated axial, lateral and shear strains within the imaging plane. The maximum, minimum and peak-to-peak strain indices in the plaque computed from the mean cumulated strain over a small region of interest in the plaque with large deformations were obtained. The maximum and peak-to-peak mean cumulated strain indices over the entire plaque region were also computed. All strain indices were then correlated with RBANS Total performance. Overall cognitive performance (RBANS Total) was negatively associated with values of the maximum strain and the peak-to-peak for axial and lateral strains, respectively. There was no significant correlation between the RBANS Total score and shear strain and strain indices averaged over the entire identified plaque for this group of patients. However, correlation of maximum lateral strain was higher for symptomatic patients (r = −0.650, p = 0.006) than for asymptomatic patients (r = −0.115, p = 0.803). On the other hand, correlation of maximum axial strain averaged over the entire plaque region was significantly higher for asymptomatic patients (r = −0.817, p = 0.016) than for symptomatic patients (r = −0.224, p = 0.402). The results reveal a direct relationship between the maximum axial and lateral strain indices in carotid plaque and cognitive impairment.     

高血压病患者升主动脉弹性的应变率评价

目的 探讨应变率（SR）评价高血压病患者升主动脉弹性的可行性。方法 正常对照组、高血压病组各50例,对升主动脉均进行Peterson’s弹性指数（Ep）、Young’s弹性指数（Es）、僵硬度、膨胀性测定,以及应变（ε）、SR分析,并对高血压病组进行上述4项弹性指标与ε、SR间的相关性分析。结果 SR与Ep、Es、僵硬度、膨胀性均有明显的相关性。结论 SR可作为评价高血压病患者升主动脉弹性的新方法。     

Three-Dimensional Cardiac Strain Imaging in Healthy Children Using RF-Data

In this study, a new radio-frequency (RF)-based, three-dimensional (3-D) strain imaging technique is introduced and applied to 3-D full volume ultrasound data of the heart of healthy children. Continuing advances in performance of transducers for 3-D ultrasound imaging have boosted research on 3-D strain imaging. In general, speckle tracking techniques are used for strain imaging. RF-based strain imaging has the potential to yield better performance than speckle- based methods because of the availability of phase information but such a system output is commercially not available. Furthermore, the relatively low frame rate of 3-D ultrasound data has limited broad application of RF-based cardiac strain imaging. In this study, the previously reported two-dimensional (2-D) strain methodology was extended to the third dimension. Three-dimensional RF-data were acquired in 13 healthy children, in the age range of 6-15 years, at a relatively low frame rate of 38-51 Hz. A 3-D, free-shape, coarse-to-fine displacement and strain estimation algorithm was applied to the RF-data. The heart was segmented using 3-D ellipsoid fitting. Strain was estimated in the radial (R), circumferential (C) and longitudinal directions (L). Our preliminary results reveal the applicability of the 3-D strain estimation technique on full volume 3-D RF-data. The technique enabled 3-D strain imaging of all three strain components. The average strains for all children were in the lateral wall R = 37 ± 10% (infero-lateral) and R = 32% ± 10% (antero-lateral), C = −9% ± 4% (antero-lateral) and C = −9% ± 4% (infero-lateral), L = −18% ± 6 % (antero-lateral) and L = −15% ± 4% (infero-lateral). In the septum, strains were found to be R = 24% ± 10% (antero-septal) and R = 13% ± 5% (infero-septal), C = −13% ± 5% (antero-septal) and −13% ± 5% (infero-septal) and L = −13% ± 3% (antero-septal) and L = −16% ± 5% (infero-septal). Strain in the anterior and inferior walls seemed underestimated, probably caused by the low (in-plane) resolution and poor image quality. The field-of-view as well as image quality were not always sufficient to image the entire left ventricle. It is concluded that 3-D strain imaging using RF-data is feasible, but validation with other modalities and with conventional 3-D speckle tracking techniques will be necessary.     

Tissue Motion and Strain in the Human Brain Assessed by Intraoperative Ultrasound in Glioma Patients

The objective of the study was to investigate tissue motion and strain imposed by cardiovascular pulsation in pathologic and normal brain parenchyma, as quantified from in vivo ultrasound data. Ultrasound acquired during surgery of 16 patients with glial tumors was retrospectively processed and analyzed. The tissue velocity was quantified at depths of 1 cm, 2 cm and 3 cm from brain cortex to investigate spatial dependency with depth. Comparison of strain and velocity in tumor and adjacent normal parenchyma was performed by selecting two regions-of-interest in the hyperechoic tumor and two regions in the low-echogenic areas interpreted as mainly normal tissue with some degree of tumor cell infiltration. The absolute maximum tissue velocity is seen to increase with increasing depths in 14 of 16 cases (87.5%). The maximum tissue velocities in the four regions close to the ultrasound visible tumor border are not statistically different (p = 0.163 to p = 0.975). The strain magnitudes are significantly higher in the regions with expected normal brain parenchyma than in regions with expected glial tumor tissue, both for the two regions being closest to the tumor border (p = 0.0004) and for the two regions further away from the tumor border (p = 0.0009). We conclude that the velocity of the brain parenchyma imposed by arterial pulsation during a cardiac cycle is generally increasing with increasing depth from cortex. The maximum velocity appears to be similar in regions with expected normal brain and tumor tissue, thus, does not seem to be affected by pathology. Strain magnitude is, however, a suitable parameter for discrimination of glial tumor and normal brain parenchyma. (E-mail: Tormod.Selbekk@sintef.no)     

弹性成像5分评分法与应变率比值法鉴别诊断肝脏良恶性病变

目的 比较弹性成像5分评分法与应变率比值法对肝脏良恶性病变的鉴别诊断价值。 方法 对165例患者(共183个肝脏局灶性病变)进行肝脏弹性成像检查,分别对病灶进行弹性评分及应变率比值测定。以病理结果作为金标准,构建ROC曲线并计算曲线下面积,分别计算弹性评分法和应变率比值用于鉴别诊断肝脏良恶性肿瘤的敏感度、特异度、准确率、阳性预测值和阴性预测值;比较两种方法对肝脏局灶性病变的诊断效能。 结果 采用应变率比值鉴别诊断肝脏良恶性病灶时,曲线下面积为0.85;采用弹性评分时,曲线下面积为0.82,二者差异无统计学意义(P=0.14)。应变率比值诊断肝脏良恶性肿瘤的敏感度、特异度、准确率、阳性预测值及阴性预测值分别为71.26%(62/87)、91.67%(88/96)、81.97%(150/183)、88.57%(62/70)、77.88%(88/113);弹性评分诊断肝脏恶性肿瘤的敏感度、特异度、准确率、阳性预测值及阴性预测值分别为88.51%(77/87)、60.42%(58/96)、73.77%(135/183)、66.96%(77/115)、85.29%(58/88)。应变率比值法的特异度高于弹性评分法(P<0.05),但其敏感度较低(P<0.05),二者准确率差异无统计学意义(P>0.05),二者诊断能力的差异主要体现在弹性评分为3分的病灶中。 结论 应用弹性成像鉴别诊断肝脏局灶性病变的良恶性时,应变率比值法及弹性评分法各有优缺点,在临床应用中应结合具体情况选择合理方法。     

A Generalized Speckle Tracking Algorithm for Ultrasonic Strain Imaging Using Dynamic Programming

This study developed an improved motion estimation algorithm for ultrasonic strain imaging that employs a dynamic programming technique. In this article, we model the motion estimation task as an optimization problem. Since tissue motion under external mechanical stimuli often should be reasonably continuous, a set of cost functions combining correlation and various levels of motion continuity constraint were used to regularize the motion estimation. To solve the optimization problem with a reasonable computational load, a dynamic programming technique that does not require iterations was used to obtain displacement vectors in integer precision. Then, a subsample estimation algorithm was used to calculate local displacements in fractional precision. Two implementation schemes were investigated with in vivo ultrasound echo data sets. We found that the proposed algorithm provides more accurate displacement estimates than our previous algorithm for in vivo clinical data. In particular, the new algorithm is capable of tracking motion in more complex anatomy and increases strain image consistency in a sequence of images. Preliminary results also suggest that a significantly longer sequence of high contrast strain images could be obtained with the new algorithm compared with the previous algorithm. The new algorithm can also tolerate larger motion discontinuities (e.g., cavity in an anthropomorphic uterine phantom). (E-mail: jjiang2@wisc.edu)     

超声弹性分级与应变率比值鉴别诊断甲状腺微小结节

目的 评价超声弹性成像分级与弹性应变率比值法对直径≤1 cm甲状腺微小结节的诊断价值。方法 对手术病理证实的55例患者的72个直径≤1 cm甲状腺结节的超声弹性图像进行分析,弹性分级分为4级,计算甲状腺组织与结节的弹性应变率比值。分别绘制弹性分级法及弹性应变率比值法的ROC曲线,评价其诊断价值。结果 甲状腺良、恶性结节的超声弹性分级及弹性应变率比值差异均有统计学意义(P<0.001)。超声弹性分级及弹性应变率比值判断甲状腺占位性病灶的ROC曲线下面积分别为0.851、0.890(P=0.124)。甲状腺良、恶性小结节弹性应变率比值诊断界值为2.85。结论 超声弹性分级法同弹性应变率比值法均能够有效地鉴别诊断甲状腺微小结节的性质。     

Ex Vivo and In Vivo Assessment of the Non-linearity of Elasticity Properties of Breast Tissues for Quantitative Strain Elastography

The aim of this study was to reveal the background to the image variations in strain elastography (strain imaging [SI]) depending on the manner of manipulation (compression magnitude) during elasticity image (EI) acquisition. Thirty patients with 33 breast lesions who had undergone surgery followed by SI assessment in vivo were analyzed. An analytical approach to tissue elasticity based on the stress-elastic modulus (Young's modulus) relationship was adopted. Young's moduli were directly measured ex vivo in surgical specimens ranging from 2.60 kPa (fat) to 16.08 kPa (invasive carcinoma) under the weak-stress condition (<0.2–0.4 kPa, which corresponds to the appropriate “light touch” technique in SI investigation. The contrast (ratio) of lesion to fat in elasticity ex vivo gradually decreased as the stress applied increased (around 1.0 kPa) on the background of significant non-linearity of the breast tissue. Our results indicate that the differences in non-linearity in elasticity between the different tissues within the breast under minimal stress conditions are closely related to the variation in EI quality. The significance of the “pre-load compression” concept in tissue elasticity evaluation is recognized. Non-linearity of elasticity is an essential attribute of living subjects and could provide useful information having a considerable impact on clinical diagnosis in quantitative ultrasound elastography.     

Ultrasound-Mediated Microbubble Enhancement of Radiation Therapy Studied Using Three-Dimensional High-Frequency Power Doppler Ultrasound

Tumor responses to high-dose (>8 Gy) radiation therapy are tightly connected to endothelial cell death. In the study described here, we investigated whether ultrasound-activated microbubbles can locally enhance tumor response to radiation treatments of 2 and 8 Gy by mechanically perturbing the endothelial lining of tumors. We evaluated vascular changes resulting from combined microbubble and radiation treatments using high-frequency 3-D power Doppler ultrasound in a breast cancer xenograft model. We compared treatment effects and monitored vasculature damage 3 hours, 24 hours and 7 days after treatment delivery. Mice treated with 2 Gy radiation and ultrasound-activated microbubbles exhibited a decrease in vascular index to 48 ± 10% at 24 hours, whereas vascular indices of mice treated with 2 Gy radiation alone or microbubbles alone were relatively unchanged at 95 ± 14% and 78 ± 14%, respectively. These results suggest that ultrasound-activated microbubbles enhance the effects of 2 Gy radiation through a synergistic mechanism, resulting in alterations of tumor blood flow. This novel therapy may potentiate lower radiation doses to preferentially target endothelial cells, thus reducing effects on neighboring normal tissue and increasing the efficacy of cancer treatments.     

应变率显像对左室不同层次心肌舒张早期应变率的研究

目的应用应变率成像评价正常人与高血压患者舒张早期左室不同层次心肌的应变率差异。方法高血压组22例,正常对照组28例,行常规二维超声心动图检查后,采集左室乳头肌短轴二维组织多普勒图像,应用QLab软件中将应变率取样容积分段的方法,脱机分析该切面左室后壁心肌舒张早期心内膜下、心外膜下心肌应变率（SRendo、SRepi）峰值及平均应变率（SRmean）峰值。结果正常人心肌舒张早期存在应变率阶差,心内膜下心肌应变率显著高于心外膜下心肌（P〈0.001）;与正常组比较,高血压组SRendo、SRmean显著降低,差异有统计学意义（P〈0.001）,而SRepi无统计学差异（P=0.58）。结论通过将应变率取样容积分层的方法可以检测出不同层次心肌应变率的差别,从而为进一步了解局部心肌的生理运动和病理改变提供了一种简便、无创、准确、重复性较好的研究方法。     

超声血管回声跟踪技术评价NO对兔股动脉血管弹性的调节

目的应用超声血管回声跟踪（ET）技术评价一氧化氮（NO）对兔股动脉血管弹性的调节。方法ET技术检测12只正常兔股动脉注入L-单甲基精氨酸（L-NMMA）、乙酰胆碱（ACH）、ACH＋L-NMMA、硝酸甘油（GTN）、GTN＋L-NMMA后股动脉弹性。结果注入L-NMMA后兔股动脉弹性较静息时降低（P〈0.05）,注入ACH、GTN、GTN＋L-NMMA后兔股动脉弹性较静息时增高（P〈0.05）,ACH与L-NMMA一并注入后,其弹性与静息时无统计学差异（P〉0.05）。结论静息状态下和激发状态下（即注入ACH和GTN后）NO可对兔股动脉的扩张性进行调节。     

Layer-Specific Radiofrequency Ultrasound-Based Strain Analysis in a Porcine Model of Ischemic Cardiomyopathy Validated by a Geometric Model

Local layer-specific myocardial deformation after myocardial infarction (MI) has not been studied extensively although the sub-endocardium is more vulnerable to ischemia and interstitial fibrosis deposition. Radiofrequency (RF) ultrasound-based analysis could provide superior layer-specific radial strain estimation compared with clinically available deformation imaging techniques. In this study, we used RF-based myocardial deformation measurements to investigate layer-specific differences between healthy and damaged myocardium in a porcine model of chronic MI. RF data were acquired epicardially in healthy (n = 21) and infarcted (n = 5) regions of a porcine chronic MI model 12 wk post-MI. Radial and longitudinal strains were estimated in the sub-endocardial, mid-wall and sub-epicardial layers of the left ventricle. Collagen content was quantified in three layers of healthy and infarcted regions in five pigs. An analytical geometric model of the left ventricle was used to theoretically underpin the radial deformation estimated in different myocardial layers. Means ± standard errors of the peak radial and longitudinal strain estimates of the sub-endocardial, mid-wall and sub-epicardial layers of the healthy and infarcted tissue were: 82.7 ± 5.2% versus 39.9 ± 10.8% (p = 0.002), 63.6 ± 3.3% versus 38.8 ± 7.7% (p = 0.004) and 34.3 ± 3.0% versus 35.1 ± 5.2% (p = 0.9), respectively. The radial strain gradient between the sub-endocardium and the sub-epicardium had decreased 12 wk after MI, and histologic examination revealed the greatest increases in collagen in the sub-endocardial and mid-wall layers. Comparable normal peak radial strain values were found by geometric modeling when input values were derived from the in vivo measurements and literature. In conclusion, the estimated strain values are realistic and indicate that sub-endocardial radial strain in healthy tissue can amount to 80%. This high value can be explained by the cardiac geometry, as was illustrated by geometric modeling. After MI, strain values were decreased and collagen content was increased in the sub-endocardial and mid-wall layers. Layer-specific peak radial strain can be assessed by RF strain estimation and clearly differs between healthy and infarcted tissue. Although the relationship between tissue stiffness and tissue strain is not strictly local, this novel technique provides a valuable way to assess layer-specific regional cardiac function in a variety of myocardial diseases.     

超声二维应变成像评价高血压病患者颈总动脉弹性的研究

目的 应用超声二维应变成像检测高血压病患者颈总动脉整体圆周应变(CS)、应变率(CSr)和硬度参数(β),探讨其评价颈总动脉弹性的临床应用价值.方法 选择33例高血压病患者(高血压病组)和32例正常人(对照组),在颈总动脉二维短轴图像测量收缩期峰值CS和CSr.分别根据M型超声和二维应变成像计算动脉硬度参数(β1和β2),并将两者与脉压(PP)进行相关性分析.结果 高血压病组颈总动脉CS和CSr均小于对照组,β1和β2 则明显增大 (P<0.05) .β1和β2均与PP显著相关(r=0.49和r=0.64,P<0.001).结论 超声二维应变成像可作为评价高血压病患者颈总动脉弹性的新方法.     

Comparison of Two Different Ultrasound Devices Using Strain Elastography Technology in the Diagnosis of Breast Lesions Related to the Histologic Results

This study was conducted to provide evidence that elastograms of two different devices and different manufacturers using the same technical approach provide the same diagnoses. A total of 110 breast lesions were prospectively analysed by two experts in ultrasound, using the strain elastography function from two different manufacturers (Hitachi HI-RTE, Hitachi Medical Systems, Wiesbaden, Germany; and Siemens eSie Touch, Siemens Medical Systems, Erlangen, Germany). Results were compared with the histopathologic results. Applying the Bowker test of symmetry, no statistically significant difference between the two elastography functions of these two devices was found (p?=?0.120). The Cohen's kappa of k?=?0.591 showed moderate strength of agreement between the two elastograms. The two examiners yielded moderate strength of agreement analysing the elastograms (Hitachi HI-RTE, k?=?0.478; Siemens eSie Touch, k?=?0.441). In conclusion, evidence is provided that elastograms of the same lesion generated by two different ultrasound devices equipped with a strain elastography function do not significantly differ.     

Ultrasound Strain Zero-Crossing Elasticity Measurement in Assessment of Renal Allograft Cortical Hardness: A Preliminary Observation

To determine whether ultrasound strain zero-crossing elasticity measurement can be used to discriminate moderate cortical fibrosis or inflammation in renal allografts, we prospectively assessed cortical hardness with quasi-static ultrasound elastography in 38 renal transplant patients who underwent kidney biopsy from January 2013 to June 2013. With the Banff score criteria for renal cortical fibrosis as gold standard, 38 subjects were divided into two groups: group 1 (n = 18) with ≤25% cortical fibrosis and group 2 (n = 20) with >26% cortical fibrosis. We then divided this population again into group 3 (n = 20) with ≤ 25% inflammation and group 4 (n = 18) with >26% inflammation based on the Banff score for renal parenchyma inflammation. To estimate renal cortical hardness in both population divisions, we propose an ultrasound strain relative zero-crossing elasticity measurement (ZC) method. In this technique, the relative return to baseline, that is zero strain, of strain in the renal cortex is compared with that of strain in reference soft tissue (between the abdominal wall and pelvic muscles). Using the ZC point on the reference strain decompression slope as standard, we determined when cortical strain crossed zero during decompression. ZC was negative when cortical strain did not return or returned after the reference, whereas ZC was positive when cortical strain returned ahead of the reference. Fisher's exact test was used to examine the significance of differences in ZC between groups 1 and 2 and between groups 3 and 4. The accuracy of ZC in determining moderate cortical fibrosis and moderate inflammation was examined by receiver operating characteristic analysis. The intra-class correlation coefficient and analysis of variance were used to test inter-rater reliability and reproducibility. ZC had good inter-observer agreement (ICC = 0.912) and reproducibility (p = 0.979). ZCs were negative in 18 of 18 cases in group 1 and positive in 19 of 20 cases in group 2 (p ? 0.001), and were positive in 18 of 20 cases in group 3 and negative in 17 of 18 cases in group 4 (p ? 0.001). The area under the receiver operating characteristic curve was 0.992 ± 0.010 for fibrosis and 0.988 ± 0.021 for inflammation. ZC had 100% sensitivity and 95% specificity when zero strain was used as the cutoff value to determine moderate cortical fibrosis and 94% sensitivity and 90% specificity for inflammation. ZC is a new strain marker that could be straightforward to interpret and perform, making it a potentially practical approach for monitoring progression of cortical fibrosis or inflammation in renal allografts.