Strain Images Research Articles

Anthropomorphic Phantoms for Assessment of Strain Imaging Methods Involving Saline-Infused Sonohysterography

Two anthropomorphic uterine phantoms were developed that allow assessment and comparison of strain imaging systems adapted for use with saline-infused sonohysterography (SIS). Tissue-mimicking (TM) materials consist of dispersions of safflower oil in gelatin. TM fibroids are stiffer than the TM myometrium/cervix, and TM polyps are softer. The first uterine phantom has 3-mm-diameter TM fibroids distributed randomly in TM myometrium. The second uterine phantom has a 5-mm and 8-mm spherical TM fibroid, in addition to a 5-mm spherical and a 12.5-mm-long (medicine capsule–shaped) TM endometrial polyp protruding into the endometrial cavity; also, a 10-mm spherical TM fibroid projects from the serosal surface. Strain images using the first phantom show the stiffer 3-mm TM fibroids in the myometrium. Results from the second uterine phantom show that, as expected, parts of inclusions projecting into the uterine cavity will appear very stiff, whether they are stiff or soft. Results from both phantoms show that although there is a five-fold difference in the Young's moduli values, there is not a significant difference in the strain in the transition from the TM myometrium to the TM fat. These phantoms allow for realistic comparison and evolution of SIS strain imaging techniques and can aid clinical personnel to develop skills for SIS strain imaging. (E-mail: mahobson@gmail.com)

Ultrasound-Based Elastography: A Novel Approach to Assess Radio Frequency Ablation of Liver Masses Performed With Expandable Ablation Probes

The purpose of this study was to evaluate the technical feasibility of ultrasound-based elastography as a tool for assessing the size and shape of the coagulation necrosis caused by radio frequency ablation (RFA) probes using expandable electrodes ex vivo as well as in a patient with a liver metastasis. A commercially available expandable RFA probe was used to create a 3-cm ablation in a piece of bovine liver. The ablation probe was used in situ to induce tissue deformation for elastography before and after ablation. Ultrasonic radio frequency data were processed to generate elasticity strain images. The appearance of the ablation zone was compared with magnetic resonance imaging and a gross section specimen. One patient with malignant metastatic disease to the liver and a clinical indication for RFA was investigated for the feasibility of percutaneous elastography of RFA using the same technique. Sonographic strain images were compared with the appearance of the nonenhancing ablation zone on contrast-enhanced computed tomography. Ex vivo, the ablation zone on ultrasound-based elastography was represented by an area of increased stiffness and was well demarcated from the nonablated surrounding tissue. The size and shape of the ablated zone on the strain image correlated well with the gross specimen and the magnetic resonance imaging appearance. Strain images obtained from the patient showed results similar to those of the ex vivo experiment and correlated well with the nonenhancing area of ablation on contrast-enhanced computed tomography. Ultrasound-based elastography may be a promising tool for displaying the ablation zone created by expandable RFA probes.

SU‐EE‐A4‐06: Estimation of the Optimal Maximum Beam Angle and Angular Increment for Normal and Shear Strain Estimation

Purpose: In current ultrasound elastography, only the axial component of the displacement vector is estimated and used to produce strain images. Previously we had proposed a method to estimate both the axial and lateral components of a displacement vector using radiofrequency echo signal data acquired along multiple angular insonification directions of the ultrasound beam. In this study, we present error propagation through the least square fitting process for optimization of the angular increment and maximum beam steered angle. Method and Materials: Ultrasound simulations are performed to corroborate theoretical predictions of the optimal values for the maximum beam angle and angular increment. Beam steering characteristics of the linear array were simulated by selecting appropriate time delays for each element which determines the focal point and steering angle for the beam. A uniformly elastic phantom was simulated by modeling a random distribution of 50 μm polystyrene beads with an average concentration of 9.7/mm3 in a medium (to simulate Rayleigh scattering). After computing RF signals for each insonification angle, the phantom was deformed by a uniaxial compression (1% of the phantom height). The displacement of each scatterer in the phantom was calculated using the Finite Element Analysis (FEA) software ANSYS. The new scatterer positions were used for calculating the post compression echo signals at each insonification angle. Results: The theoretical prediction matches well with numerical simulations. For typical system parameters, the optimal maximum beam angle is around 10‐deg for axial strain estimation, and around 15‐deg for lateral strain estimation. The optimal angular increment is around 4∼6 deg, which indicates that only 5∼7 beam angles are required for this strain tensor estimation technique. Conclusion: The theory presented in this study is useful for choosing optimal parameters for the angular data acquisition process for strain tensor estimation.

Radio‐frequency ablation electrode displacement elastography: A phantom study

This article describes the evaluation of a novel method of tissue displacement for use in the elastographic visualization of radio-frequency (rf) ablation-induced lesions. The method involves use of the radio-frequency ablation electrode as a displacement device, which provides localized compression in the region of interest. This displacement mechanism offers the advantage of easy in vivo implementation since problems such as excessive lateral and elevational displacements present when using external compression are reduced with this approach. The method was tested on a single-inclusion tissue-mimicking phantom containing a radio-frequency ablation electrode rigidly attached to the inclusion center. Full-frame rf echo signals were acquired from the phantom before and after electrode displacements ranging from 0.05 to 0.2 mm. One-dimensional cross-correlation analysis between pre- and postcompression signals was used to measure tissue displacements, and strains were determined by computing the gradient of the displacement. The strain contrast, contrast-to-noise ratio, and signal-to-noise ratio were estimated from the resulting strain images. Comparisons are drawn between the elastographically measured dimensions and those known a priori for the single-inclusion phantom. Electrode displacement elastography was found to slightly underestimate the inclusion dimensions. The method was also tested on a second tissue-mimicking phantom and on in vitro rf-ablated lesions in canine liver tissue. The results validate previous in vivo findings that electrode displacement elastography is an effective method for monitoring rf ablation.

Ultrasound Image Sequence Registration and its Application for Thyroid Nodular Disease

Ultrasound elastography is a promising technique that can assist in diagnosis of thyroid cancer. However, the tissue movements generated by the freehand compression are complex and difficult to estimate. Therefore, the aim of this study was to propose a motion estimation technique adapted to our application. First, a parametric deformable block matching is introduced and shown to provide better results than classical block matching. Afterwards, the extension of this method to motion estimation with image sequences is presented. Moreover, motion analysis using a technique of compression orientation detection led us to introduce a new parameter based on the angle of estimated motion vectors. The accuracy of our methods was tested on simulated and in-vivo ultrasound images. The in-vivo data sets correspond to thyroid gland images acquired using freehand tissue compression by ultrasound probe of a clinical ultrasound scanner modified for research. Thus, we show how our method improves the contrast between the healthy part of the thyroid and the malignant tumor by a factor of 3 compared to ultrasound images and by a factor of 2 compared to classical strain images.

Tissue Doppler strain-mapping in the assessment of the extent of chronic myocardial infarction: validation using magnetic resonance imaging

The distribution of myocardial strain values can be visualized by colour-coded strain images. We examined for the first time if this strain-mapping function can be used to study the extent of prior myocardial infarction. Echocardiography and cardiac magnetic resonance imaging with delayed contrast enhancement were performed in 26 patients with chronic myocardial infarction. Two-dimensional strain images of the left ventricle were obtained in all standard apical views. Myocardial segments (n = 416) were assigned a score ranging from one to four based on the strain-coded colour of the segment, with higher scores representing worse myocardial function. Strain-mapping scores and quantitative strain values averaged, respectively, 1.3 +/- 0.6 and -16.4 +/- 7.6% in segments without infarction, 1.7 +/- 1.0 and -15.0 +/- 8.6% in non-transmural infarctions, and 2.8 +/- 1.2 and -6.5 +/- 8.6% in transmural infarctions. Strain-mapping had a sensitivity of 60% and a specificity of 95% in detecting segments with transmural myocardial infarction. Corresponding values for echocardiographic wall motion analysis were 50 and 96%. Strain-mapping was possible in 80% of the segments and inter-observer agreement was substantial (kappa = 0.63). Strain-mapping is a clinically applicable method for the assessment of regional myocardial function in post-myocardial infarction patients. Strain-mapping has reasonable feasibility and is more sensitive in detecting infarction damage than routine wall motion analysis.

Direct three-dimensional myocardial strain tensor quantification and tracking using zHARP

Images of myocardial strain can be used to diagnose heart disease, plan and monitor treatment, and to learn about cardiac structure and function. Three-dimensional (3D) strain is typically quantified using many magnetic resonance (MR) images obtained in two or three orthogonal planes. Problems with this approach include long scan times, image misregistration, and through-plane motion. This article presents a novel method for calculating cardiac 3D strain using a stack of two or more images acquired in only one orientation. The zHARP pulse sequence encodes in-plane motion using MR tagging and out-of-plane motion using phase encoding, and has been previously shown to be capable of computing 3D displacement within a single image plane. Here, data from two adjacent image planes are combined to yield a 3D strain tensor at each pixel; stacks of zHARP images can be used to derive stacked arrays of 3D strain tensors without imaging multiple orientations and without numerical interpolation. The performance and accuracy of the method is demonstrated in vitro on a phantom and in vivo in four healthy adult human subjects.

Elasticity reconstruction from displacement and confidence measures of a multi-compressed ultrasound RF sequence

Ultrasound elasticity imaging shows promise as a new way for early detection of cancers by assessing the elastic characteristics of soft tissue. So far the commonly used approach involves solving the so-called inverse elasticity problem of recovering elastic parameters from displacement measurements. We propose a finite-elementbased nonlinear scheme to estimate the elasticity distribution of soft tissue from multi-compressed ultrasound radio frequency (RF) data. An experimental ultrasound workstation has been developed to acquire multi-compressed data. A composite probe was employed as the compression plate. The contact forces and torques were acquired at the same time as imaging. Axial displacements under different static loads are estimated from the RF data before and after deformation using a cross-correlation technique. The confidence of displacement estimates is employed as a weighting factor in solving the objective function describing the inverse elasticity reconstruction problem. A novel splitand- merge strategy is employed over the image sequence in which strain images are used to provide a priori knowledge of the relative stiffness distribution of the tissue to constrain the inverse problem solution. The experimental study has allowed us to investigate the performance of our approach in the controlled environment of simulated and phantom data. For a simulated single inclusion model with 5% axial displacement estimation error, the L2-error between the target and the reconstructed Young's modulus was found to be about 1%. In vivo validation of the proposed method has been carried out and some preliminary results are presented.

2-D Locally Regularized Tissue Strain Estimation From Radio-Frequency Ultrasound Images: Theoretical Developments and Results on Experimental Data

In this paper, a 2-D locally regularized strain estimation method for imaging deformation of soft biological tissues from radio-frequency (RF) ultrasound (US) data is introduced. Contrary to most 2-D techniques that model the compression-induced local displacement as a 2-D shift, our algorithm also considers a local scaling factor in the axial direction. This direction-dependent model of tissue motion and deformation is induced by the highly anisotropic resolution of RF US images. Optimal parameters are computed through the constrained maximization of a similarity criterion defined as the normalized correlation coefficient. Its value at the solution is then used as an indicator of estimation reliability, the probability of correct estimation increasing with the correlation value. In case of correlation loss, the estimation integrates an additional constraint, imposing local continuity within displacement and strain fields. Using local scaling factors and regularization increase the method's robustness with regard to decorrelation noise, resulting in a wider range of precise measurements. Results on simulated US data from a mechanically homogeneous medium subjected to successive uniaxial loadings demonstrate that our method is theoretically able to accurately estimate strains up to 17%. Experimental strain images of phantom and cut specimens of bovine liver clearly show the harder inclusions.

Shear strain imaging using shear deformations

In this article we investigate the generation of shear strain elastograms induced using a lateral shear deformation. Ultrasound simulation and experimental results demonstrate that the shear strain elastograms obtained under shear deformation exhibit significant differences between bound and unbound inclusions in phantoms, when compared to shear strain images induced upon an axial compression. A theoretical model that estimates the decorrelation between pre- and postdeformation radio frequency signals, as a function of extent of shear deformation, is also developed. Signal-to-noise ratios of shear strain elastograms obtained at different shear angles are investigated theoretically and verified using ultrasound simulations on a uniformly elastic phantom. For the simulation and experiment, a two-dimensinal block-matching-based algorithm is used to estimate the axial and lateral displacement. Shear strains are obtained from the displacement vectors using a least-squares strain estimator. Our results indicate that the signal-to-noise ratio (SNR) of shear strain images increases to reach a maximum and saturates, and then decreases with increasing shear angle. Using typical system parameters, the maximum achievable SNR for shear strain elastography is around 8 (18 dB), which is comparable to conventional axial strain elastography induced by axial compression. Shear strain elastograms obtained experimentally using single inclusion tissue-mimicking phantoms with both bound and unbound inclusions (mimicking cancerous masses and benign fibroadenomas, respectively) demonstrate the characteristic differences in the depiction of these inclusions on the shear strain elastograms.

Left Atrial Dyssynchrony in Patients With Nonobstructive Hypertrophic Cardiomyopathy Evaluated by Myocardial Strain Imaging

Background. The present study was conducted to examine left atrial (LA) dyssynchrony, determined by echocardiographic myocardial strain imaging, in patients with hypertrophic cardiomyopathy (HCM). Methods. We studied 26 patients with HCM (20 men and 6 women, age, 66±7 years) and 25 normal subjects (controls). Tissue Doppler-based strain images were recorded in the apical 2-, 4-chamber, and long-axis views. The LA strain curve was obtained with the region of interest placed at the 5 LA segments, namely, the atrial septum, lateral wall, inferior wall, anterior wall, and posterior wall. We measured standard deviation (SD) of the time-periods between aortic valve opening and maximal strain (reservoir dyssynchrony index) and SD of the time-periods between mitral valve opening and minimal strain (emptying dyssynchrony index).Results. Compared with controls, patients with HCM had greater indexes of reservoir (40±23 ms vs. 23±8 ms, p=0.001) and emptying (37±17 ms vs. 28±11 ms, p=0.02) dyssynchrony. Reservoir dyssynchrony (index >39 ms) was detectable in 11 patients, and emptying dyssynchrony (index >50 ms) was detectable in 5 patients. Patients with reservoir dyssynchrony had a greater LV mass index than those without (182±45 g/m2 vs. 142±32 g/m2, p=0.01), whereas patients with emptying dyssynchrony had greater LA minimal volume (39±12 ml/m2 vs. 26±10 ml/m2 p=0.02) and lower LA emptying fraction than those without (27±3% vs. 39±11%, p=0.02).Conclusions. LA dyssynchrony can be present throughout the cardiac cycle in patients with HCM. LA dyssynchrony is more common in the reservoir phase and may be attributed to significant myocardial involvement.

Similar Degree in Mechanical Left Ventricular Dyssynchrony Between Right Ventricular Outflow Tract and Right Ventricular Apical Pacing: A Strain Doppler Imaging Study

Background and Objectives: Long-term right ventricular (RV) apex pacing has been associated with left ventricular (LV) systolic dysfunction. However, pacing in the RV outflow tract (RVOT) is associated with a narrower QRS duration and may have a more normal LV activation in comparison to RV apical (RVA) pacing. We hypothesized that RVOT pacing is associated with less mechanical dyssynchrony compared to RVA pacing and that it also more closely resembles mechanical activation in normal controls with a narrow QRS. Subjects and Methods: We studied 9 patients with RV pacing, 9 with left bundle branch block (LBBB), and 15 normal controls with a narrow QRS. In the RV pacing group, we paced from the RVA and RVOT. At the end of each pacing train, we obtained echocardiographic images in the apical 4- and 2-chamber views and obtained the following parameters: the compression/expansion crossover point (CEP) for myocardial strain and the time from QRS onset to the CEP in the strain image. The degree of dyssynchrony was evaluated using the dispersion and standard deviation of CEP times in 12 segments of the LV. Results: Significant dyssynchrony was observed in the RVOT pacing group compared to the group with normal QRS. No significant difference was observed in LV mechanical dyssynchrony among the RVOT pacing, RVA pacing, and LBBB groups. Conclusion: RVOT pacing is associated with significant LV dyssynchrony. Although the RVOT has been recommended as an alternative site for pacing, this approach may have adverse effects on long-term LV function. (Korean Circ J 2008;38:590-595)

Imaging and Estimation of Tissue Elasticity by Ultrasound

Ultrasound (US) elasticity imaging is an extension of the ancient art of palpation and of earlier US methods for viewing tissue stiffness such as echopalpation. Elasticity images consist of either an image of strain in response to force or an image of estimated elastic modulus. There are 3 main types of US elasticity imaging: elastography that tracks tissue movement during compression to obtain an estimate of strain, sonoelastography that uses color Doppler to generate an image of tissue movement in response to external vibrations, and tracking of shear wave propagation through tissue to obtain the elastic modulus. Other modalities may be used for elasticity imaging, the most powerful being magnetic resonance elastography. With 4 commercial US scanners already offering elastography and more to follow, US-based methods may be the most widely used for the near future. Elasticity imaging is possible for nearly every tissue. Breast mass elastography has potential for enhancing the specificity of US and mammography for cancer detection. Lesions in the thyroid, prostate gland, pancreas, and lymph nodes have been successfully imaged using elastography. Evaluation of diffuse disease including cirrhosis and transplant rejection is also possible using both imaging and nonimaging methods. Vascular imaging including myocardium, blood vessel wall, plaque, and venous thrombi has also shown great potential. Elasticity imaging may also be important in assessing the progress of ablation therapy. Recent work in assessing porous materials using elastography suggests that the technique may be useful in monitoring the severity of lymphedema.

Angular strain estimation method for elastography

In the conventional cross-correlation-based strain estimation, there is a trade-off between the interpolation accuracy and the computational requirement. On the other hand, the autocorrelation-based method does not need interpolation, but it cannot estimate the wide range of displacements for elastography. We have developed a new strain estimator, called the angular strain estimation method, which does not need any interpolation and can estimate strain without restricting the range of displacements. The new method estimates strain utilizing complex correlation between correlated ultrasound signals from pre-and post-compression frames. From simulation and experiments, we found that the angular strain estimation method improves the accuracy and strain image quality compared to the conventional strain estimator using cross correlation with interpolation. Furthermore, it is computationally efficient and can be readily incorporated in ultrasound machines for rea -time elastography.

Improving B mode ultrasound evaluation of breast lesions with real-time ultrasound elastography—A clinical approach

Ultrasound elastography using the extended combined auto-correlation method of tissue elasticity allows for real-time strain image visualisation using a free-hand probe with concurrent conventional B mode imaging. Four hundred and fifteen consecutive women with 550 breast lesions confirmed on B mode ultrasound were assessed with elastography using the elasticity score. There were 119 malignant and 431 benign lesions. The elastography sensitivity was 78.0%, specificity was 98.5% and overall accuracy was 93.8%. The median score for malignancy was 5 and that for benign lesions was 2. There was good correlation with B mode BIRADS category. 98.6% of lesions with an elasticity score of 2 or below (95%CI=96.8–99.4) were benign. BIRADS 3 lesions with an elasticity score of 2 or below may be re-classified as BIRADS 2 lesions. We found that 15.3% of BIRADS 2 and 3 lesions with an elasticity score of 3 were malignant. Real-time ultrasound elastography is user-friendly with a high accuracy rate, thereby improving B mode ultrasound assessment.

Ultrasonic measurements of breast viscoelasticity

In vivo measurements of the viscoelastic properties of breast tissue are described. Ultrasonic echo frames were recorded from volunteers at 5 fps while applying a uniaxial compressive force (1-20 N) within a 1 s ramp time and holding the force constant for up to 200 s. A time series of strain images was formed from the echo data, spatially averaged viscous creep curves were computed, and viscoelastic strain parameters were estimated by fitting creep curves to a second-order Voigt model. The useful strain bandwidth from this quasi-static ramp stimulus was 10(-2) < or = omega < or = 10(0) rad/s (0.0016-0.16 Hz). The stress-strain curves for normal glandular tissues are linear when the surface force applied is between 2 and 5 N. In this range, the creep response was characteristic of biphasic viscoelastic polymers, settling to a constant strain (arrheodictic) after 100 s. The average model-based retardance time constants for the viscoelastic response were 3.2 +/- 0.8 and 42.0 +/- 28 s. Also, the viscoelastic strain amplitude was approximately equal to that of the elastic strain. Above 5 N of applied force, however, the response of glandular tissue became increasingly nonlinear and rheodictic, i.e., tissue creep never reached a plateau. Contrasting in vivo breast measurements with those in gelatin hydrogels, preliminary ideas regarding the mechanisms for viscoelastic contrast are emerging.

Differentiating Benign from Malignant Solid Breast Masses with US Strain Imaging

To prospectively evaluate the sensitivity and specificity of ultrasonographic (US) strain imaging for distinguishing between benign and malignant solid breast masses, with biopsy results as the reference standard. The study was institutional review board approved and HIPAA compliant. Informed consent was obtained from all participating patients. US strain imaging of 403 breast masses was performed. The 50 malignant and 48 benign lesions (in patients aged 19-83 years; mean age, 49 years +/- 17 [standard deviation]) with the highest quality were selected for the reader study. Three observers blinded to the pathologic outcomes first described the B-mode image findings by using US Breast Imaging Reporting and Data System descriptors and derived a probability of malignancy. They then updated the probability by assessing strain images. Receiver operating characteristic (ROC) curves were constructed by using these probabilities. Areas under the ROC curve, sensitivities, and specificities were calculated and compared. Interobserver variability and the correlation between automated and subjective image quality assessment were analyzed. The average area under the ROC curve for all three readers after US strain imaging (0.903) was greater than that after B-mode US alone (0.876, P = .014). With use of a 2% probability of malignancy threshold, strain imaging-as compared with B-mode US alone-had improved average specificity (0.257 vs 0.132, P < .001) and high sensitivity (0.993 vs 0.987, P > .99). Significant interobserver variability was observed (P < .001). The ability to assess strain image quality appeared to correlate with the highest observer performance. US strain imaging can facilitate improved classification of benign and malignant breast masses. However, interobserver variability and image quality influence observer performance.

Elasticity Imaging Using Conventional and High-Frame Rate Ultrasound Imaging: Experimental Study

High-frame rate ultrasound imaging is necessary to track fast deformation in ultrasound elasticity imaging, but the image quality may be degraded. Previously, we investigated the performance of strain imaging using numerical models of conventional and ultrafast ultrasound imaging techniques. In this paper, we performed experimental studies to quantitatively evaluate the strain images and elasticity maps obtained using conventional and high frame rate ultrasound imaging methods. The experiments were carried out using point target and tissue mimicking phantoms. The experimental results were compared with the results of numerical simulation. Our experimental studies confirm that the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and axial/lateral resolution of the displacement and strain images acquired using high-frame rate ultrasound imaging are slightly lower but comparable with those obtained using conventional imaging. Furthermore, the quality of elasticity images also exhibits similar trends. Thus, high-frame rate ultrasound imaging can be used reliably for static elasticity imaging to capture the internal tissue motion if the frame rate is critical.

Estimation of Displacement Location for Enhanced Strain Imaging

Ultrasonic strain imaging usually begins with displacement estimates computed using finite-length sections of RF ultrasound signals. Amplitude variations in the ultrasound are known to perturb the location at which the displacement estimate is valid. If this goes uncorrected, it is a significant source of estimation noise, which is amplified when displacement fields are converted into strain images. We present a study of this effect based on theoretical analysis and practical experiments. A correction method based on the analysis is tested on phase zero and correlation coefficient strain imaging, and compared to the amplitude compression techniques of earlier studies. We also test adaptive strain estimation to provide a benchmark, but the performance of our new method matches or surpasses this benchmark under normal scanning conditions. Furthermore, the new correction is suitable for real time applications owing to its extreme computational simplicity.

In Vitro Uterine Strain Imaging

Uterine abnormalities, such as leiomyomas, endometrial polyps, and adenomyosis, are often clinically associated with irregular uterine bleeding. These abnormalities can have similar B-mode characteristics but require different treatment. The objective of this study was to develop diagnostic techniques based on ultrasound strain imaging that would allow in vivo visualization and characterization of endometrial and myometrial uterine abnormalities, enabling physicians to improve diagnosis and treatment. Ultrasound strain imaging was performed on 29 uteri removed via elective hysterectomy. An ultrasound system with a linear array transducer was used to obtain radio frequency echo data during manual freehand compressions of the tissue. Radio frequency data were post-processed with a 2-dimensional block-matching algorithm to generate strain images. In the uteri involved in this study, there were 19 leiomyomas, 1 case of adenomyosis, and 3 endometrial polyps observed on strain imaging. Leiomyomas appeared stiffer than the surrounding normal myometrium in strain images and were characterized by a slipping artifact at their boundary. Endometrial polyps appeared softer than the normal surrounding myometrium. The average strain contrast in small leiomyomas (<1.5 cm) compared to the myometrium was 1.75 +/- 1.14; the strain contrast was 2.50 +/- 1.15 in large leiomyomas and 0.40 +/- 0.05 in endometrial polyps. Leiomyoma strain contrast results were consistent with modulus contrast values from mechanical testing results. Ultrasound strain imaging can differentiate between endometrial polyps and leiomyomas. More data are necessary to validate these results and to ascertain whether other uterine abnormalities can also be differentiated.