Noninvasive Staging of Hepatic Steatosis Using Calibrated 2D US with Liver Biopsy as the Reference Standard.

Background Accumulation of lipid in the liver (ie, hepatic steatosis) is the basis of nonalcoholic fatty liver disease (NAFLD). Asymptomatic steatosis can lead to nonalcoholic steatohepatitis and downstream complications. Purpose To assess the diagnostic performance of calibrated US (CAUS) as a method for detection and staging of hepatic steatosis in comparison with liver biopsy. Materials and Methods Two-dimensional US images in 223 consecutive patients who underwent US-guided liver biopsy from May 2012 to February 2016 were retrospectively analyzed by two observers using CAUS. CAUS semiautomatically estimates echo-level and texture parameters, with particular interest in the residual attenuation coefficient (RAC), which is the remaining steatosis-driven attenuation obtained after correction of the beam profile. Data were correlated with patient characteristics and histologically determined steatosis grades and fibrosis stages. The data were equally divided into training and test sets to independently train and test logistic regression models for detection (>5% fat) and staging (>33% and >66% fat) of hepatic steatosis by using area under the receiver operating characteristic curve (AUC) analysis. Results A total of 195 patients (mean age, 50 years ± 13 [SD]; 110 men) were included and divided into a training set (n = 97 [50%]) and a test set (n = 98 [50%]). The average CAUS interobserver correlation coefficient was 0.95 (R range, 0.87-0.99). The best correlation with steatosis was found for the RAC parameter (R = 0.78, P < .01), while no correlation was found for fibrosis (R = 0.14, P = .054). Steatosis detection using RAC showed an AUC of 0.97 (95% CI: 0.94, 1.00), and the multivariable AUC was found to be 0.97 (95% CI: 0.95, 1.00). The predictive performance for moderate and severe hepatic steatosis using RAC was 0.93 (95% CI: 0.88, 0.98) and 0.93 (95% CI: 0.87, 0.98), respectively. Conclusion The calibrated US parameter residual attenuation coefficient detects and stages steatosis accurately with limited interobserver variability, and performance is not hampered by the presence of fibrosis. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Grant in this issue.

Three-Dimensional Model-Based Segmentation in Echocardiography Using High Temporal Tissue and Blood Flow Information.

Accurate 3-D surface segmentation is a challenging task in echocardiography because of the relatively low image quality. We introduce a new method for 3-D segmentation of the endocardium involving temporal decorrelation of echo signals originating from tissue and blood using radiofrequency (RF) signals acquired in 3-D Doppler mode. Temporal features were extracted in 3-D Doppler mode, where a sequence of RF lines is recorded for each image line. Each set of RF lines is highly correlated because of the high pulse repetition frequency. However, for high blood flow, the RF signals will decorrelate over time in contrast to the endocardium, which will remain relatively highly correlated over time. These decorrelation features permit differentiation between myocardial tissue and blood flow. We describe an implementation of a 3-D segmentation model in which temporal information is used as external constraint. The model was validated in a phantom and in vivo in healthy volunteers (n = 5). The phantom study revealed that the model successfully segmented the artificial blood lumen even for low flow velocity and illustrated the sensitivity of the segmentations to flow rate. In healthy volunteers, high Dice similarity indices indicate that 3-D segmentation of the endocardial border in vivo is feasible.

Automated Assessment of Right Ventricular Volumes and Function Using Three-Dimensional Transesophageal Echocardiography.

Assessment of right ventricular (RV) function is known to be of diagnostic value in patients with RV dysfunction. Because of its complex anatomic shape, automated determination of the RV volume is difficult and strong reliance on geometric assumptions is not desired. A method for automated RV assessment was developed using three-dimensional (3-D) echocardiography without relying on a priori knowledge of the cardiac anatomy. A 3-D adaptive filtering technique that optimizes the discrimination between blood and myocardium was applied to facilitate endocardial border detection. Filtered image data were incorporated in a segmentation model to automatically detect the endocardial RV border. End-systolic and end-diastolic RV volumes, as well as ejection fraction, were computed from the automatically segmented endocardial surfaces and compared against reference volumes manually delineated by two expert cardiologists. The results reported good performance in terms of correlation and agreement with the results from the reference volumes.

Quantitative Ultrasound for Staging of Hepatic Steatosis in Patients on Home Parenteral Nutrition Validated with Magnetic Resonance Spectroscopy: A Feasibility Study.

Patients on home parenteral nutrition are at risk for developing liver dysfunction, which is due partly to the accumulation of lipids in the liver (steatosis) and may progress to end-stage liver disease with overt liver failure. Therefore, a timely diagnosis with easy access to repeated assessment of the degree of liver steatosis is of great importance. A pilot study was performed in 14 patients on long-term home parenteral nutrition using the computer-aided ultrasound method. Ultrasound radio frequency data were acquired using a phased array transducer and were converted into conventional B-mode images. All patients were subjected to proton magnetic resonance spectroscopy measurement of liver fat content for reference. Computer-aided ultrasound parameters similar to those in a previous validation study in cows revealed significant correlations with fat content measured by magnetic resonance spectroscopy. The most significant parameters were the residual attenuation coefficient (R = 0.95, p < 0.001) and the lateral speckle size (R = 0.77, p = 0.021). These findings indicate the potential usefulness of computer-aided ultrasound for staging of hepatic steatosis.

Enhancing the performance of lateral shear strain estimation by using 2-D strain imaging.

Radio-frequency (RF) ultrasound can be used to estimate deformation of biological tissue. Decorrelation of sequentially acquired ultrasound signals resulting from the deformation imposes a limitation on the precision (elastographic signal-to-noise ratio; SNRe) of estimating these deformations; this is presented as the lateral shear strain filter. In this paper, we explore the effect of a 2-D-window-based strain estimation approach on the lateral shear strain filter and propose an extension of the 1-D theoretical lateral shear strain filter to 2-D. We compared the performance of the 2-D approach in simulated ultrasound data and a tissue-mimicking phantom with that of the 2-D lateral shear strain filter. In simulations, the 2-D-window-based approach shows an effect in the axial direction similar to the 2-D prediction. In simulations and experiments, increasing the window size in the lateral direction shows an increase in the maximum SNRe of the lateral shear strain filter. Increasing the lateral overlap has no effect on the estimation of lateral shear strain. These results were confirmed in the tissue-mimicking phantom experiments. When compared with the 2-D lateral shear strain filter, the results obtained with the 2-D-window-based approach showed an enhanced performance by incorporating the lateral window size in the lateral shear strain estimation, which was consistent with the proposed theory.

Cardiological Ultrasound Imaging.

This review paper is intended for the interested outsider of the field of echocardiography and it presents a short introduction into the numerous ultrasound (US) methods and techniques for anatomical and functional diagnosis of the heart. The basic techniques are generally used for some times already, as there are one dimensional (1D) M(otion) mode, the real time 2D B(rightness) mode technique and the various Doppler measurement techniques and imaging modes. The M-mode technique shows the movements of the tissue in a 1D B-mode display vs. time. The 2D B-mode images are showing the heart contractions and dilations in real time, thus making this technique the basic tool for detecting anatomical disturbances and myocardial (localized) abnormal functioning. Improved image quality is achieved by Second Harmonic Imaging and myocardial perfusion can be quantified using Contrast Agent Imaging. Doppler techniques were introduced in the fifties of last century and used for blood flow velocity measurement. Continuous wave (CW) Doppler has the advantage of allowing measurement of high velocities, as may occur in vascular or valvular stenosis and insufficiency. The exact location of the major Doppler signal received cannot be estimated making this technique ambiguous in some clinical problems. Single gated Pulse Wave (PW) Doppler velocity measurement delivers exact location of the measurement position by using an interactively positioned time (=depth) gate in which the velocity is being measured. The disadvantage of this technique is the relatively low maximum velocity that can be measured. Multigate PW Doppler techniques can be used for the assessment of a velocity profile over the vessel cross section. A more sophisticated use of this technique is the combination with 2D B-mode imaging in the color Doppler mode, called "color flow mapping", in which the multigate Doppler signal is color coded and shown in 2D format overlayed in the conventional 2D B mode image. In the past two decades, technique to quantify myocardial function were developed: Tissue Doppler Imaging (TDI), Strain Rate and Strain Imaging. The temporal resolution of ultrasound imaging can be further improved by Plane Wave Imaging, and Synthetic Aperture Imaging. The recent introduction of 2D matrix transducers extended the real time imaging potential by allowing 3D imaging and sophisticated segmentation techniques for the estimation of quantitative functional parameters, as for instance cardiac output.

New developments in paediatric cardiac functional ultrasound imaging.

Ultrasound imaging can be used to estimate the morphology as well as the motion and deformation of tissues. If the interrogated tissue is actively deforming, this deformation is directly related to its function and quantification of this deformation is normally referred as 'strain imaging'. Tissue can also be deformed by applying an internal or external force and the resulting, induced deformation is a function of the mechanical tissue characteristics. In combination with the load applied, these strain maps can be used to estimate or reconstruct the mechanical properties of tissue. This technique was named 'elastography' by Ophir et al. in 1991. Elastography can be used for atherosclerotic plaque characterisation, while the contractility of the heart or skeletal muscles can be assessed with strain imaging. Rather than using the conventional video format (DICOM) image information, radio frequency (RF)-based ultrasound methods enable estimation of the deformation at higher resolution and with higher precision than commercial methods using Doppler (tissue Doppler imaging) or video image data (2D speckle tracking methods). However, the improvement in accuracy is mainly achieved when measuring strain along the ultrasound beam direction, so it has to be considered a 1D technique. Recently, this method has been extended to multiple directions and precision further improved by using spatial compounding of data acquired at multiple beam steered angles. Using similar techniques, the blood velocity and flow can be determined. RF-based techniques are also beneficial for automated segmentation of the ventricular cavities. In this paper, new developments in different techniques of quantifying cardiac function by strain imaging, automated segmentation, and methods of performing blood flow imaging are reviewed and their application in paediatric cardiology is discussed.

Transcutaneous vs. intraoperative quantitative ultrasound for staging bovine hepatic steatosis.

The aim of this study was to test the hypothesis that quantitative analysis of transcutaneous (Transc) ultrasound (US) images can predict the liver fat content with similar accuracy and precision as using intraoperative (Intraop) US. The second goal was to investigate if a tissue mimicking phantom (TMP) might be used as reference for automatic gain compensation (AGC) vs. depth instead of using the data of a set of cows without hepatic alterations. A study was performed in post partum dairy cows (N = 151), as an animal model of human nonalcoholic fatty liver disease (NAFLD), to test these hypotheses. Five Transc and five Intraop US liver images were acquired in each animal and a liver biopsy was taken. In liver tissue samples, triacylglycerol (TAG) content was measured by biochemical analysis and hepatic alterations, other than hepatic steatosis, were excluded by clinical examination. Several preprocessing steps were performed before the ultrasound tissue characteristics (UTC) parameters of B-mode images were derived. Stepwise multiple linear regression analysis was performed on a training set (N = 76) and the results were used on the test group (N = 75) to predict the TAG content in the liver. In all cases, the residual attenuation coefficient (ResAtt) was the only selected parameter. Receiver operating characteristics (ROC) analysis was applied to assess the performance and area under the curve (AUC) of predicting TAG and to compare the sensitivity and specificity of the methods used. High ROC values for AUC (95%), sensitivity (87%) and specificity (83%) for both Intraop and Transc applications with control group as well as with phantom-based AGC were obtained. Consequently, it can be concluded that Transc results are equivalent to Intraop results. Furthermore, equivalent ROC values, when using TMP AGC, indicates the potential use of TMP-based corrections instead of normal group-based corrections. The high predictive values indicate that noninvasive quantitative US has a great potential for staging and screening on hepatic steatosis in cows.

Persistent reduction in left ventricular strain using two-dimensional speckle-tracking echocardiography after balloon valvuloplasty in children with congenital valvular aortic stenosis.

BACKGROUND: The aim of this study was to investige serial changes of myocardial deformation using two-dimensional speckle-tracking echocardiographic (2DSTE) imaging in children undergoing balloon valvuloplasty for congenital valvular aortic stenosis (VAS). METHODS: Thirty-seven children with isolated congenital VAS were enrolled in this study prospectively. Patients underwent echocardiographic evaluation at three instances: before balloon valvuloplasty, 6 months after intervention, and 3 years after intervention. Longitudinal, circumferential, and radial peak systolic strain values were determined, as well as systolic strain rate and the time to peak global systolic strain. Linear mixed statistical models were used to assess changes in 2DSTE parameters after balloon intervention. Using one-way analysis of variance, 2DSTE results at 3-year follow-up were compared with 2DSTE measurements in 74 healthy age-matched children and 76 children with uncorrected VAS whose severity of stenosis corresponded to residual stenosis of study subjects at 3-year follow-up. RESULTS: Global peak strain and strain rate measurements in all three directions were decreased before intervention compared with healthy children. Global peak strain and strain rate measurements increased significantly (P < .001) several months after balloon valvuloplasty and continued to increase at 3-year follow-up. However, at 3-year follow-up, global peak strain and strain rate in the longitudinal and circumferential directions were significantly lower (P < .001) compared with both control groups. Measurements of time to peak global systolic strain were significantly shorter at early follow-up compared with measurements before intervention (P < .05). CONCLUSIONS: Shortly after balloon valvuloplasty for severe congenital VAS, there is an improvement in systolic myocardial deformation. However, 2DSTE parameters do not return to normal at 3-year follow-up. These abnormalities in systolic deformation cannot be fully attributed to residual stenosis or aortic regurgitation.

Ultrasound image analysis offers the opportunity to predict plasma progesterone concentrations in the estrous cycle in cows: a feasibility study.

In recent years, several attempts have been made to evaluate the activity of a corpus luteum by determining its sonographic echo texture. In all of these studies the values of the echo texture parameters depended on the type and settings of the ultrasound machine. Therefore, the aim of the study was to investigate if a quantitative analysis of ultrasound (US) images of the corpus luteum (CL) after calibration of the ultrasound machine enables the assessment of the peripheral plasma progesterone (P4) level. Ten Holstein Friesian cows were examined daily at Days 4 to 8, 10 to 16, and -5 to -1 (Day 1=ovulation) of the estrous cycle. B-mode sonography of the corpora lutea was performed and blood samples were taken for plasma P4 analysis. US images were calibrated and analyzed using a software package (CAUS) developed by the authors. In addition to the area of the CL (Total Area, TotA; Tissue Area interactive, TisAi; Tissue Area Automatic, TisAa), the following US parameters were calculated from the gray level histogram and from the size of the speckles: Mean, Standard Deviation (SD) and Signal-to-Noise Ratio (SNR=Mean/SD) of echo levels, Residual Attenuation (ResAtt), Axial and Lateral speckle size (Ax and Lat, respectively). The inter-individual variability of the P4 level was expressed by the coefficient of variability (CV), averaged over all days. It appeared that the CV of the absolute P4 was high (0.65) and the P4 relative to that at Day 4 and at Day 16 was of comparable magnitude. Correlations of US parameters with P4 were highest for the P4 relative to Day 16 (P4_rel_D16). This relative P4 measure was then used for further analysis. The correlations of P4_rel_D16 with TotA, TisAa (CL area after automatic segmentation of tissue) and ResAtt were found the highest (R=0.68, 0.74, and -0.42, respectively). Multiple linear regression analysis, incorporating all US parameters revealed the formula: P4_rel_D16(pred)=-0.315+0.225TisAa-0.023ResAtt, and a goodness of fit: R(2)=0.59 (p<0.001). This formula was then used to "predict" for each image the P4_rel_D16 from the estimated US parameters. A high correlation of the predicted with the measured P4_rel_D16 was found: R=0.77. Classification of images using the predicted P4_rel_D16 to be in the range >0.80 (corresponding to 0.95 times the average_P4_rel_D16 measured during the "static" phase of the luteal cycle) by ROC analysis was correctly made in 88% of cases. In conclusion the quantitative analysis of calibrated ultrasound images may yield a good prediction of cyclic changes of P4 levels and has potential for predicting the phase in the estrous cycle of a cow.

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.

Correlation based 3-D segmentation of the left ventricle in pediatric echocardiographic images using radio-frequency data.

Clinical diagnosis of heart disease might be substantially supported by automated segmentation of the endocardial surface in three-dimensional (3-D) echographic images. Because of the poor echogenicity contrast between blood and myocardial tissue in some regions and the inherent speckle noise, automated analysis of these images is challenging. A priori knowledge on the shape of the heart cannot always be relied on, e.g., in children with congenital heart disease, segmentation should be based on the echo features solely. The objective of this study was to investigate the merit of using temporal cross-correlation of radio-frequency (RF) data for automated segmentation of 3-D echocardiographic images. Maximum temporal cross-correlation (MCC) values were determined locally from the RF-data using an iterative 3-D technique. MCC values as well as a combination of MCC values and adaptive filtered, demodulated RF-data were used as an additional, external force in a deformable model approach to segment the endocardial surface and were tested against manually segmented surfaces. Results on 3-D full volume images (Philips, iE33) of 10 healthy children demonstrate that MCC values derived from the RF signal yield a useful parameter to distinguish between blood and myocardium in regions with low echogenicity contrast and incorporation of MCC improves the segmentation results significantly. Further investigation of the MCC over the whole cardiac cycle is required to exploit the full benefit of it for automated segmentation.

Interactive vs. automatic ultrasound image segmentation methods for staging hepatic lipidosis.

The aim of this study was to test the hypothesis that automatic segmentation of vessels in ultrasound (US) images can produce similar or better results in grading fatty livers than interactive segmentation. A study was performed in postpartum dairy cows (N=151), as an animal model of human fatty liver disease, to test this hypothesis. Five transcutaneous and five intraoperative US liver images were acquired in each animal and a liverbiopsy was taken. In liver tissue samples, triacylglycerol (TAG) was measured by biochemical analysis and hepatic diseases other than hepatic lipidosis were excluded by histopathologic examination. Ultrasonic tissue characterization (UTC) parameters--Mean echo level, standard deviation (SD) of echo level, signal-to-noise ratio (SNR), residual attenuation coefficient (ResAtt) and axial and lateral speckle size--were derived using a computer-aided US (CAUS) protocol and software package. First, the liver tissue was interactively segmented by two observers. With increasing fat content, fewer hepatic vessels were visible in the ultrasound images and, therefore, a smaller proportion of the liver needed to be excluded from these images. Automatic-segmentation algorithms were implemented and it was investigated whether better results could be achieved than with the subjective and time-consuming interactive-segmentation procedure. The automatic-segmentation algorithms were based on both fixed and adaptive thresholding techniques in combination with a 'speckle'-shaped moving-window exclusion technique. All data were analyzed with and without postprocessing as contained in CAUS and with different automated-segmentation techniques. This enabled us to study the effect of the applied postprocessing steps on single and multiple linear regressions ofthe various UTC parameters with TAG. Improved correlations for all US parameters were found by using automatic-segmentation techniques. Stepwise multiple linear-regression formulas where derived and used to predict TAG level in the liver. Receiver-operating-characteristics (ROC) analysis was applied to assess the performance and area under the curve (AUC) of predicting TAG and to compare the sensitivity and specificity of the methods. Best speckle-size estimates and overall performance (R2 = 0.71, AUC = 0.94) were achieved by using an SNR-based adaptive automatic-segmentation method (used TAG threshold: 50 mg/g liver wet weight). Automatic segmentation is thus feasible and profitable.

Dynamic imaging of skeletal muscle contraction in three orthogonal directions.

In this study, a multidimensional strain estimation method using biplane ultrasound is presented to assess local relative deformation (i.e., local strain) in three orthogonal directions in skeletal muscles during induced and voluntary contractions. The method was tested in the musculus biceps brachii of five healthy subjects for three different types of muscle contraction: 1) excitation of the muscle with a single electrical pulse via the musculocutaneous nerve, resulting in a so-called "twitch" contraction; 2) a train of five pulses at 10 Hz and 20 Hz, respectively, to obtain a submaximum tetanic contraction; and 3) voluntary contractions at 30, 60, and 100% of maximum contraction force. Results show that biplane ultrasound strain imaging is feasible. The method yielded adequate performance using the radio frequency data in tracking the tissue motion and enabled the measurement of local deformation in both the vertical direction (orthogonal to the arm) and in the horizontal directions (parallel and perpendicular to direction of the arm) in two orthogonal cross sections of the muscle. The twitch experiments appeared to be reproducible in all three directions, and high strains in vertical (25 to 30%) and horizontal (-20% to -10%) directions were measured. Visual inspection of both the ultrasound data, as well as the strain data, revealed a relaxation that was significantly slower than the force decay. The pulse train experiments nicely illustrated the performance of our technique: 1) similar patterns of force and strain waveforms were found; and 2) each stimulation frequency yielded a different strain pattern, e.g., peak vertical strain was 40% during 10-Hz stimulation and 60% during 20-Hz stimulation. The voluntary contraction patterns were found to be both practically feasible and reproducible, which will enable muscles and more natural contraction patterns to be examined without the need of electrical stimulation.

Performance of two dimensional displacement and strain estimation techniques using a phased array transducer.

The goal of this study was to investigate the applicability of conventional 2-D displacement and strain imaging techniques to phased array radiofrequency (RF) data. Furthermore, the possible advantages of aligning and stretching techniques for the reduction of decorrelation artefacts was examined. Data from both realistic simulations and phantoms were used in this study. Recently, the used processing concepts were successfully applied to linear array data. However, their applicability to sector scan data is not trivial because of the polar grid. Homogeneous and inhomogeneous tissue phantoms were simulated at a range of strains (0 to 5%) using Field II((c)). The inhomogeneous phantom, a commonly used tumor/lesion model, was also constructed using gelatin/agar solutions. A coarse-to-fine displacement algorithm was applied, using aligning and stretching to enhance re-correlation. Vertical and horizontal strains were reconstructed from the axial and lateral displacements. Results revealed that the error on displacement estimates was lower when using 2-D data windows rather than 1-D windows. For regions at large depths and large insonification angles, the allowed lateral window size was limited. Still, 1-D windows resulted in larger errors. The re-correlation techniques resulted in a significant increase in the elastographic signal-to-noise ratio (SNRe) and elastographic contrast-to-noise ratio (CNRe) of the vertical and horizontal strain components. An increase of the SNRe of 5-20 dB was observed over a range of strains (0.5 to 5.0%). In the inhomogeneous phantom, a vertical SNRe of 27.7 dB and a horizontal SNRe of 16.7 dB were measured in the background. The vertical and horizontal CNRe were 35 dB and 23.1 dB, respectively. For the experimental data, lower SNRe (vertical: 19.1 dB; horizontal: 11.4 dB) and CNRe (vertical: 33.3 dB; horizontal: 12.5 dB) were found. In conclusion, 2-D window matching of sector scan data is feasible and outperforms 1-D window matching. Furthermore, the use of re-correlation techniques enhances both precision and contrast of strain images.

Comparison of one-dimensional and two-dimensional least-squares strain estimators for phased array displacement data.

In this study, the performances of one-dimensional and two-dimensional least-squares strain estimators (LSQSE) are compared. Furthermore, the effects of kernel size are examined using simulated raw frequency data of a widely-adapted hard lesion/soft tissue model. The performances of both methods are assessed in terms of root-mean-squared errors (RMSE), elastographic signal-to-noise ratio (SNRe) and contrast-to-noise ratio (CNRe). RMSE analysis revealed that the 2D LSQSE yields better results for phased array data, especially for larger insonification angles. Using a 2D LSQSE enabled the processing of unfiltered displacement data, in particular for the lateral/horizontal strain components. The SNRe and CNRe analysis showed an improvement in precision and almost no loss in contrast using 2D LSQSE. However, the RMSE images for different kernel sizes revealed that the optimal 2D kernel size depends on the region-of-interest and showed that the LSQ kernel size should be limited to avoid loss in resolution.

Performance evaluation of methods for two-dimensional displacement and strain estimation using ultrasound radio frequency data.

In elastography, several methods for 2-D strain imaging have been introduced, based on both raw frequency (RF) data and speckle-tracking. Although the precision and lesion detectability of axial strain imaging in terms of elastographic signal-to-noise ratio (SNRe) and elastographic contrast-to-noise ratio (CNRe) have been reported extensively, analysis of lateral precision is still lacking. In this paper, the performance of different 2-D correlation RF- and envelope-based strain estimation methods was evaluated using simulation data and phantom experiments. Besides window size and interpolation methods for subsample displacement estimation, the influence of recorrelation techniques was examined. Precision and contrast of the measured displacements and strains were assessed using the difference between modeled and measured displacements, SNRe and CNRe. In general, a 2-D coarse-to-fine displacement estimation method is favored, using envelope data for window sizes exceeding the theoretical upper bound for strain estimation. Using 2-D windows of RF data resulted in better displacement estimates for both the axial and lateral direction than 1-D RF-based or envelope-based techniques. Obtaining subsample lateral displacement estimates by fitting a predefined shape through the cross-correlation function (CCF) yielded results similar to those obtained with up-sampling of RF data in the lateral direction. Using a CCF model was favored because of the decreased computation time. Local aligning and stretching of the windows (recorrelation) resulted in an increase of 2-17 and 6-7 dB in SNRe for axial and lateral strain estimates, respectively, over a range of strains (0.5 to 5.0%). For a simulated inhomogeneous phantom (2.0% applied strain), the measured axial and lateral SNRes were 29.2 and 20.2 dB, whereas the CNRes were 50.2 dB and 31.5 dB, respectively. For the experimental data, lower SNRe (axial: 28.5 dB; lateral: 17.5 dB) and CNRe (axial: 39.3 dB; lateral: 31 dB) were found. In conclusion, a coarse-to-fine approach is favored using RF data on a fine scale. The use of 2D parabolic interpolation is favored to obtain subsample displacement estimates. Recorrelation techniques, such as local aligning and stretching, increase SNRe and CNRe in both directions.

Quantitative assessment of oral orbicular muscle deformation after cleft lip reconstruction: an ultrasound elastography study.

Reconstruction of a cleft lip leads inevitably to scar tissue formation. Scar tissue within the restored oral orbicular muscle might be assessed by quantification of the local contractility of this muscle. Furthermore, information about the contraction capability of the oral orbicular muscle is crucial for planning the revision surgery of an individual patient. We used ultrasound elastography to determine the local deformation (strain) of the upper lip and to differentiate contracting muscle from passive scar tissue. Raw ultrasound data (radio-frequency format; rf-) were acquired, while the lips were brought from normal state into a pout condition and back in normal state, in three patients and three normal individuals. During this movement, the oral orbicular muscle contracts and, consequently, thickens in contrast to scar tissue that will not contract, or even expand. An iterative coarse-to-fine strain estimation method was used to calculate the local tissue strain. Analysis of the raw ultrasound data allows estimation of tissue strain with a high precision. The minimum strain that can be assessed reproducibly is 0.1%. In normal individuals, strain of the orbicular oral muscle was in the order of 20%. Also, a uniform strain distribution in the oral orbicular muscle was found. However, in patients deviating values were found in the region of the reconstruction and the muscle tissue surrounding that. In two patients with a successful reconstruction, strain was reduced by 6% in the reconstructed region with respect to the normal parts of the muscle (from 22% to 16% and from 25% to 19%). In a patient with severe aesthetical and functional disability, strain decreased from 30% in the normal region to 5% in the reconstructed region. With ultrasound elastography, the strain of the oral orbicular muscle can be quantified. In healthy subjects, the strain profiles and maximum strain values in all parts of the muscle were similar. The maximum strain of the muscle during pout was 20% +/- 1%. In surgically repaired cleft lips, decreased deformation was observed.

3D cardiac segmentation using temporal correlation of radio frequency ultrasound data.

Semi-automatic segmentation of the myocardium in 3D echographic images may substantially support clinical diagnosis of heart disease. Particularly in children with congenital heart disease, segmentation should be based on the echo features solely since a priori knowledge on the shape of the heart cannot be used. Segmentation of echocardiographic images is challenging because of the poor echogenicity contrast between blood and the myocardium in some regions and the inherent speckle noise from randomly backscattered echoes. Phase information present in the radio frequency (rf) ultrasound data might yield useful, additional features in these regions. A semi-3D technique was used to determine maximum temporal cross-correlation values locally from the rf data. To segment the endocardial surface, maximum cross-correlation values were used as additional external force in a deformable model approach and were tested against and combined with adaptive filtered, demodulated rf data. The method was tested on full volume images (Philips, iE33) of four healthy children and evaluated by comparison with contours obtained from manual segmentation.