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Item does not contain fulltext 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.

Contains fulltext : 178023.pdf (Publisher’s version ) (Closed access) 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.

Contains fulltext : 171319.pdf (Publisher’s version ) (Closed access) 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.

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disorder in developed countries with a global prevalence of approximately 25%. NAFLD represents a spectrum of disorders and starts with benign steatosis (NAFL, ≥5% hepatic steatosis (HS)), but may lead to nonalcoholic steatohepatitis (NASH), inflammation with hepatocyte injury with or without fibrosis, which may lead to cirrhosis. Qualitative scoring of liver biopsies still is the gold standard for staging steatosis however, they are invasive and complications such as bleeding and infection may occur. For this reason we developed and tested a computer aided ultrasound (CAUS) protocol for the non-invasive assessment of liver HS using quantitative ultrasound (QUS) B-mode images. CAUS showed to have high predictive values (area under the curve (AUC) up to 0.95) in cows and similar correlations value with HS in a human pilot study. The current study was conducted in order to assess the predictive values of CAUS in staging hepatic steatosis in-vivo.

Item does not contain fulltext 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. 01 mei 2012

Contains fulltext : 87739.pdf (Publisher’s version ) (Closed access) This simulation study is concerned with: 1) the feasibility of measuring rotation and 2) the assessment of the performance of strain estimation in shearing and rotating structures. The performance of 3 different radio frequency (RF) based methods is investigated. Linear array ultrasound data of a deforming block were simulated (axial shear strain = 2.0, 4.0, and 6.0%, vertical strain = 0.0, 1.0, and 2.0%). Furthermore, data of a rotating block were simulated over an angular range of 0.5 degrees to 10 degrees . Local displacements were estimated using a coarse-to-fine algorithm using 1-D and 2-D precompression kernels. A new estimation method was developed in which axial displacements were used to correct the search area for local axial motion. The study revealed that this so-called free-shape 2-D method outperformed the other 2 methods and produced more accurate displacement images. For higher axial shear strains, the variance of the axial strain and the axial shear strain reduced by a factor of 4 to 5. Rotations could be accurately measured up to 4.0 to 5.0 degrees . Again, the free-shape 2-D method yielded the most accurate results. After reconstruction of the rotation angle, the mean angles were slightly underestimated. The precision of the strain estimates decreased with increasing rotation angles. In conclusion, the proposed free-shape 2-D method enhances the measurement of (axial shear) strains and rotation. Experimental validation of the new method still has to be performed. 01 april 2010

Contains fulltext : 88176.pdf (Publisher’s version ) (Open Access) In this study, first we propose a biplane strain imaging method using a commercial ultrasound system, yielding estimation of the strain in three orthogonal directions. Secondly, an animal model of a child's heart was introduced that is suitable to simulate congenital heart disease and was used to test the method in vivo. The proposed approach can serve as a framework to monitor the development of cardiac hypertrophy and fibrosis. A 2D strain estimation technique using radio frequency (RF) ultrasound data was applied. Biplane image acquisition was performed at a relatively low frame rate (

Contains fulltext : 88821.pdf (Publisher’s version ) (Closed access) 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. 01 september 2010

The aim of this study was to assess the differentiation of histologically different types of choroidal melanomas by means of clinical and quantitative acoustic/texture parameters of echograms. Clinical parameters were graded by morphological, kinetic and quantitative statements about the A- and B-mode echograms by a skilled diagnostician. Acoustic/texture parameters were obtained by processing and analysing radio frequency, AM-demodulated and FM-demodulated echograms. The latter data were preprocessed to remove influence induced by beam diffraction and focusing. The best set of four clinical echographic parameters enabled a retrospective classification of spindle type melanomas vs. mixed + epithelioid type melanomas with an accuracy of 77% (area under the ROC-curve of 86%). The discriminant analysis performed with the best four acoustic/texture parameters (n = 30) yielded a sensitivity of 89%, a specificity of 92%, and an area under the ROC-curve which corresponds to a probability of correct classification of 96.6%. When using these data prospectively to classify tumours of unknown cell type (n = 21), this classification could be performed in 86% of cases.

The data on echographic routine diagnosis of intraocular tumours (prominence equal to, or larger than 2 mm) during the years 1976–1990 in the authors' department, were analyzed by multivariate statistical methods, using the final diagnosis either from pathology after enucleation or from the confirmed clinical diagnosis. The material consisted of melanomas (n = 325), metastases (n = 44), haemangiomas (n = 19) and other intraocular tumours (n = 16). The best set of echographic parameters in descending order of significance was: reflectivity (A-mode), choroidal excavation (B-mode), shape (B-mode), and regularity (A/B-mode). Echographic differentiation by computer analysis of data on the three main kinds of tumours (melanoma/metastasis/haemangioma) separate from all the remaining tumours was expressed by the correct fraction: melanoma 89%, metastasis 80% and haemangioma 97%. The clinical echographic classification for these cases was 89%, 93% and 99.5%, respectively. The simultaneous differentiation between the three classes was found to yield a correct fraction of 85% by computer statistics and 95% by routine echography. The results of the present study might be used for prospective classification through the use of the parameter ‘knowledge base’ contained in the statistical classification procedure.

Contains fulltext : 81914.pdf (Publisher’s version ) (Closed access) 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.

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 (SNRc) and contrast-to-noise ratio (CNRc). 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 SNRc and CNRc 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.

Objective: To investigate the feasibility of echographic imaging of healthy and reconstructed cleft lip and to estimate tissue dimensions and normalized echo level. Methods: Echographic images of the upper lip were made on three healthy subjects and two patients using a linear array transducer (7 to 11 MHz bandwidth) and a noncontact gel coupling. Tissue dimensions were measured using calipers. Echo levels were calibrated and were corrected for beam characteristics, gel path, and tissue attenuation using a tissue-mimicking phantom. Results: At the central position of the philtrum, mean thickness (SD) of lip loose connective tissue layer, orbicularis oris muscle, and dense connective layer was 4.0 (0.1) mm, 2.3 (0.7) mm, and 2.2 (0.7) mm, respectively, in healthy lip at rest; and 4.1 (0.9) mm, 3.8 (1.7) mm, and 2.6 (0.6) mm, respectively, in contracted lip. Mean (SD) echo level of muscle and dense connective tissue layer with respect to echo level of lip loose connective tissue layer was −19.3 (0.6) dB and −10.7 (4.0) dB, respectively, in relaxed condition and −20.7 (1.5) dB and −7.7 (2.3) dB, respectively, in contracted state. Color mode echo images were calculated, showing lip tissues in separate colors and highlighting details like discontinuity of the orbicularis oris muscle and presence of scar tissue. Conclusions: Quantitative assessment of thickness and echo level of various lip tissues is feasible after proper echographic equipment calibration. Diagnostic potentials of this method for noninvasive evaluation of cleft lip reconstruction outcome are promising.

Contains fulltext : 171983.pdf (Publisher’s version ) (Closed access) 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.

Contains fulltext : 49608.pdf (Publisher’s version ) (Closed access) AIM: To renew the echocardiographic reference values of heart dimensions in healthy children. METHODS AND RESULTS: Group 1 consisted of 587 children, of which 361 boys and 226 girls, age from birth to 18 years, body weight over 2500 g, who visited the Pediatric Cardiology outclinic during the period January 2000 till March 2004. All included children were diagnosed as normal, or as having innocent heart murmur. The second group was taken from an earlier study and comprised 160 children (77 boys and 83 girls). The echocardiographic measures were taken from conventional M-mode recording of the left ventricle (LV) parasternal long axis view. End diastolic septal (IVS) and LV posterior wall thickness (LVPW) and end diastolic as well as end systolic LV intracavity dimensions were retrospectively analyzed. The regression lines from all measured sizes are significantly different from those collected in the early eighties. Especially the thickness of the IVS is smaller. The regression lines are independent of gender. CONCLUSIONS: New reference values have been found which should replace the presently used ones. There is no difference between boys and girls. Why the muscular wall thicknesses are thinner than found 20 years ago needs to be further explored.

BACKGROUND: Tissue Doppler imaging (TDI) is a new non-invasive ultrasound technique that enables quantitative assessment of regional myocardial wall motion. A previous study of survivors of childhood malignancies demonstrated abnormalities of regional diastolic wall motion abnormalities many years after treatment with anthracyclines. The purpose of the present study was to investigate this phenomenon during and shortly after treatment. PROCEDURE: A total of 60 patients, age range 4.4-16.0 years, were included in this study: 43 early survivors, with a mean follow-up duration of 2.1 (range 0.3-5.2) years from end of anthracycline treatment, were evaluated retrospectively. Seventeen other patients were evaluated before, during, and 6 months after the end of anthracycline therapy. All patients received moderate cumulative doses of anthracyclines (range 120-450 mg/m2). Echocardiographic examination was performed using standardized conventional and TDI techniques. RESULTS: Of the early survivors, 26 (60%) demonstrated regional LV free wall motion abnormalities. In the prospective group, serial echocardiographic studies revealed three patients (18%) with regional abnormalities of LV free wall motion before starting chemotherapy, but 14 (82%) at the end of treatment. Six months later, however, the incidence decreased to 61% of the survivors. Subject and treatment characteristics, as well as LV wall diameters and fractional shortening were not significantly different for children with or without free wall motion abnormalities. Regional wall motion abnormalities were also seen in the interventricular septum, although this was less frequent. CONCLUSIONS: Regional diastolic wall motion abnormalities are common during and shortly after anthracyclines therapy but may be transient. The authors recommend simultaneous use of both conventional echocardiography & TDI for the monitoring of anthracycline-induced cardiotoxicity.

Objectives: in vitro assessment of the reproducibility and the optimal separation and position of the optodes in continuous wave (CW-) NIRS measurement of local inhomogeneities in absorption and/or scattering. Methods: a CW- NIRS system (OXYMON) was used with laser diodes at wavelengths of 767 nm, 845 nm, 905 nm, 945 nm and 975 nm. For practical considerations (dimensions of neonatal head) the measurements were performed on a cylindrical tissue-equivalent phantom (70 mm diameter of base material with µa = 0.01 mm-1 (800 nm) and µ's = 1.00 mm-1 (800 nm)), containing rods with 10 × absorption, or 10 × scattering, and 5 × both Monte Carlo simulations were carried out of a cylinder with transport scattering coefficient µ'e = 0.525 mm-1 and absorption coefficient µa = 0.075 mm-1 and two optode positions. Results: reproducibility of repeated measurements (n = 10) was ± 0.005 OD. Maximum OD in case of absorbing rod, and of absorbing + scattering rod was measured with optodes separated by 90° and rod position angle symmetrically (45°) in between. Minimum OD for these rods was obtained with optodes at 150° angle and rod position at 240° (i.e. relative to transmitting optode position at 0°). A second maximum OD was obtained at an optode angle 180° and rod position at 180°. Maximum OD (i.e. attenuation) for the scattering rod was at optode separation angle of 90° and rod at 0°. Minimum OD for this case was obtained with optode angle of 180° and rod positions around 80° and 280°. Maximum OD changes by absorbing rod were in the order of + 0.12 OD and -0.04 OD, respectively. Simulations at an optode separation angle of 90° showed a spatial sensitivity path enclosing the rod position at maximum absorption found experimentally. Conclusions: when considering the phantom as a realistic geometrical model for the neonatal head, it can be concluded that the optode position at 90° angle would be optimal for detecting an inhomogeneity at 15 mm depth, i.e. the location of the periventricular white matter. Since the rods are relatively strongly different from the base material the question remains to be answered whether local ischemia, which might lead to irreversible brain damage, can be detected by CW-NIRS.

Item does not contain fulltext Assessment of the performance of medical ultrasound equipment is generally based on the image quality in fundamental mode. Recent development of the so-called tissue harmonic imaging (THI) mode induces the need for assessment of differences in the quality of imaging in THI vs. fundamental imaging mode. Quality features to be tested are sensitivity (penetration depth), spatial resolution, contrast resolution, lesion signal-to-noise ratio, and tissue-to-clutter ratio (TCR). These features are explained and examples are shown. The main conclusion from a comparison of the results for the two imaging modes might be that when using THI improvement of TCR, in particular in the near field, is obtained at the expense of a loss in axial resolution. Furthermore, lesion detection is not significantly improved.

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.

The goal of this study was to develop a calibrated on-line technique to extract as much diagnostically-relevant information as possible from conventional video-format echograms. The final aim is to improve the diagnostic potentials of medical ultrasound. Video-output images were acquired by a frame grabber board incorporated in a multiprocessor workstation. Calibration images were obtained from a stable tissue-mimicking phantom with known acoustic characteristics. Using these images as reference, depth dependence of the gray level could fairly be corrected for the transducer performance characteristics, for the observer-dependent equipment settings and for attenuation in the examined tissues. Second-order statistical parameters still displayed some nonconsistent depth dependencies. The results obtained with two echoscanners for the same phantom were different; hence, an a posteriori normalization of clinical data with the phantom data is indicated. Prior to processing of clinical echograms, the anatomical reflections and echoless voids were removed automatically. The final step in the preprocessing concerned the compensation of the overall attenuation in the tissue. A ‘sliding window’ processing was then applied to a region of interest (ROI) in the ‘back-scan converted’ images. A number of first and second order statistical texture parameters and acoustical parameters were estimated in each window and assigned to the central pixel. This procedure results in a set of new ‘parametric’ images of the ROI, which can be inserted in the original echogram (gray value, color) or presented as a color overlay. A clinical example is presented for illustrating the potentials of the developed technique. Depending on the choice of the parameters, four full resolution calibrated parametric images can be calculated and simultaneously displayed within 5 to 20 seconds. In conclusion, an on-line technique has been developed to estimate acoustic and texture parameters with a reduced equipment dependence and to display acoustical and textural information that is present in conventional echograms.

Various sources of variability, such as speckle noise, depth dependence and inhomogeneous intervening tissue, are involved in B-mode images, even when using the same ultrasonic equipment with fixed settings. The behavior of these sources of variability was investigated by texture analysis of images obtained from simulations and from a tissue-mimicking phantom, a normal adult liver and a pediatric renal (Wilms') tumor. First-order statistics (MEAN and SNR) and second-order statistics from the co-occurrence matrix (ENT and COR) were calculated. In a phantom, the SNR and ENT show a clear depth dependence. In biological tissue, the variability is mainly caused by the speckle noise and inhomogeneous intervening tissue. In addition, almost the entire range of the COR feature is present in images of liver and tumor. Furthermore, all the features calculated in windows of 1 cm2 exhibit an overlap among the different media. With the second-order features, it is possible to discriminate 85% reliable (average) between the normal, adult, liver and the pediatric renal tumor above a window size of 9 cm2. The SNR can not discriminate between these tissues. The maximum resolution of 9 cm2 reveals a serious limitation of parametric imaging. Finally, the features reproduce well in the case of follow-up of an abdominal tumor during chemotherapy.

Computer texture analysis methods use texture features that are traditionally chosen from a large set of fixed features known in literature. These fixed features are often not specifically designed to the problem at hand, and as a result they may have low discriminative power, and/or may be correlated. Increasing the number of selected fixed features is statistically not a good solution in limited data environments such as medical imaging. For that reason, we developed an adaptive texture feature extraction method (ATFE) that extracts a small number of features that are tuned to the problem at hand. By using a feed-forward neural network, we ensure that even nonlinear relations are captured from the data. Using extensive, repeated synthetic ultrasonic images, we compared the performance of ATFE with the optimal feature set. We show that the ATFE method is capable of robust operation on small data sets with a performance close to that of the optimal feature set. Another experiment confirms that our ATFE is capable of capturing nonlinear relations from the dataset. We conclude that our method can improve performance in practical, limited dataset situations where an optimal fixed feature set can be hard to find.

Item does not contain fulltext 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 time already, as there are the 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.

Item does not contain fulltext 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.

The goal of this study was to investigate the potentials of cooccurrence matrix analysis for the characterization of echographic image texture. Echographic data were obtained by one-dimensional simulations. Various data sets were generated with different number densities of the randomly distributed scatterers and with different levels of structural scattering strength. Cooccurrence matrix parameters estimated for analysis were: angular second moment, contrast, correlation, entropy and kappa. The cooccurrence matrix analysis was tuned by varying its parameters: spatial displacement of the pixel pairs, number of gray levels and size of the window. The parameters reached a saturation level at a number density of 3-5 scatterers per resolution cell (-6 dB width). Similarly, when increasing the displacement, a limit value was reached at 4-20 samples, depending on the size of the resolution cell. Using the Mahalanobis distance as a measure of differentiating between two textures, a systematic inverse relation was observed between the size of the window and the number of gray levels used in the estimation of the cooccurrence matrix. The optimal parameters to differentiate textures without structure appeared to be entropy and angular second moment. A window size of 90 speckle cells and 64 gray levels is needed for this purpose. The effective speckle size was estimated from the mean number of maxima of the demodulated echo signals. Resolved structure results in a periodicity of parameter values with displacement. The periodicity can be calculated by changing the displacement d. Optimal parameters for detecting periodicity are contrast and correlation. Analysis of the correlation between parameters showed that entropy vs. angular second moment and contrast vs. correlation are highly correlated.

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.

Two iterative methods for the calculation of acoustic transmission through a rough interface between two media are compared. The methods employ a continuous version of the conjugate gradient technique. One method is based on plane-wave expansions and the other on boundary integral equations and Green’s functions. A preconditioner is presented which improves the convergence for spectra that include evanescent modes. The methods are compared with regard to computational efficiency, rate of convergence, and residual error. The sound field differences are determined for a focused ultrasound beam distorted by surfaces having a Gaussian roughness spectrum. The differences are evaluated from the root-mean-square differences on the rough surface and in the focal plane.

To investigate the discriminative power of pattern-reversal visual evoked potential characteristics (peak latencies and amplitude) and to test whether the addition of visual evoked potential amplitude can increase the power of the visual evoked potential in the diagnosis of multiple sclerosis, we retrospectively studied visual evoked potentials in 59 patients with definite multiple sclerosis and 126 control subjects. Two check sizes (17' and 10') were used. Females had significantly higher amplitudes and shorter latencies than males. N80 latency showed a gradual increase and P100 amplitude a decrease with age. P100 latency was stable between the ages of 20 and 55 years but was increased in childhood and the elderly. The significance of visual evoked potential peak latencies and amplitude in separating the two groups was investigated by means of a (multivariate) discriminant analysis. The visual evoked potential with a pattern of 10' could be measured in 58% of patients with multiple sclerosis. The exclusive use of the P100 amplitude in the discriminant analysis resulted in a percentage of correctly classified cases of 84%, whereas for P100 and N80 latency it was 85% and 90%, respectively. With the 17' pattern, the N80 latency yielded also a higher correct percentage than did the P100 latency. Although N80 latency is, to a greater extent than P100 latency, influenced by age, sex and size of stimulus pattern, when these influences are accounted for, the N80 latency is a more sensitive measure than P100 latency in the classification of multiple sclerosis. Combined use of latency and amplitude for discriminant analysis yielded no significant improvement of the percentage of correctly classified cases.

A computer aided ultrasound (CAUS) protocol was developed for the diagnosis and staging of hepatic steatosis. Calibration of the fixed imaging preset enables expression of the US parameters relative to the tissue mimicking phantom used and consequently a vendor independent comparison. The CAUS protocol was validated on high yielding dairy cows (n = 151), which severed as a reference model for human non-alcoholic fatty liver disease. The study showed high values for: area under the curve (AROC): 0.94; sensitivity: 87%; specificity: 83%. A pilot study in patients on Home Parenteral Nutrition (HPN, n = 14) and a more extensive study in an obese cohort (n = 116) was performed. Validation was performed by Magnetic Resonance Spectroscopy (MRS). Both studies showed that of all parameters, the residual attenuation coefficient (RAC, the depth dependent mean echo level corrected for beam profile and normal attenuation in liver tissue) has the highest correlation to the reference (MRS fat percentage). For the HPN co...

A rigorous iterative technique is described for calculating the acoustic wave reflection and transmission at an irregular interface between two different media. The method is based upon a plane-wave expansion technique in which the acoustic field equations and the radiation condition are satisfied analytically, while the boundary conditions at the interface are satisfied numerically. The latter is accomplished by an iterative minimization of the integrated squared error in the boundary conditions by a conjugate gradient technique, leading to a converging and relatively simple scheme. The plane interface result can be used as starting value. Although in principle the method is rigorous, numerical examples show that in practice there is a lower bound on the error in the boundary conditions which can be achieved. >

The aim of this study was to test the hypothesis that the Computer Aided UltraSound (CAUS) method developed by the authors [1-4] for the estimation of UltraSound Tissue Characteristics (UTC) parameters on transcutaneous (Transc) ultrasound (US) images can predict the liver fat content with similar accuracy and precision as with intraoperative (Intraop) US. A large animal study in post partum dairy cows (N=151) was performed to test these hypotheses. Five Transc B-Mode US liver image were acquired before surgery. During abomasal displacement surgery five Intraop US B-Mode liver images and a liver biopsy was taken. In liver tissue samples, triacylglycerol (TAG) content was measured by biochemical analysis. Firstly the equipment preset, which was kept fixed during whole study time, was carefully calibrated[5]. For the echo level calibration a TMP was used, and all UTC parameters were expressed relatively to those of the phantom. Prior to UTC parameters estimation several pre-processing steps were performed: Back-Scan Conversion (BSC); Look Up Table (LUT) correction; superficial tissue layers (Fat layer) attenuation correction and Automatic Gain Correction (AGC) were performed. Also several postprocessing steps were incorporated like: Automatic segmentation and residual attenuation correction were performed. Stepwise multiple linear regression analysis on a training set (N=76) was performed. In all cases the Residual Attenuation coefficient (ResAtt, R=0.81) was the only selected parameter. The results were tested on the residual cows (test set N=75) to predict the TAG content in the liver. Receiver Operating Characteristics (ROC) analysis then was applied to estimate the Area Under the Curve (AUC) and the sensitivity and specificity of the CAUS method. Equivalent high predictive values for AUC (95%), sensitivity(87%) and specificity (83%) for Intraop and Transc applications were found. Consequently, it can be concluded, applied Fat layer attenuation correction to Transc US images was performed adequately.

Item does not contain fulltext 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. 01 augustus 2012

Item does not contain fulltext PURPOSE: Congenital valvar aortic stenosis (VAS) causes a pressure overload to the left ventricle. In the clinical setting, the severity of stenosis is graded by the pressure drop over the stenotic valve (pressure gradient). This parameter is dependent on the hemodynamic status and does not provide information regarding myocardial performance. This study was undertaken to reveal the potential of two-dimensional strain echocardiography (2DSTE) for the detection of myocardial functional changes due to congenital VAS in children. MATERIALS AND METHODS: A total of 86 patients (aged from birth to 18 years) with various degrees of isolated congenital VAS were enrolled in this study. None of the patients had undergone any form of surgical or balloon intervention. 139 healthy children served as a control group. Two-dimensional cine-loop recordings of apical 4-chamber, mid-cavity short-axis and basal short-axis views were digitally stored for off-line analysis. Longitudinal, circumferential and radial peak systolic strain and strain rate values were determined as well as the time to peak systolic strain (T2P). Two-way analysis of variance was performed to assess the relationship between VAS severity and 2DSTE parameters. RESULTS: In all patients conventional echocardiographic findings did not indicate systolic left ventricular dysfunction. All strain parameters of the control group were significantly different from those of VAS patients. There was a statistically significant, inverse relationship between global peak systolic strain parameters in all three directions and the degree of VAS (p < 0.05). Local peak systolic strain (rate) in the interventricular septum was most affected. T 2P increased significantly with VAS severity (p < 0.05). The decline in LV longitudinal systolic performance preceded that in other directions. CONCLUSION: 2DSTE detects alterations in myocardial function in children diagnosed with congenital VAS, whose conventional echocardiographic findings did not indicate ventricular systolic dysfunction.

Two fast algorithms for interpolation of ultrasonic sector-scans were developed. Both algorithms are based on line-drawing algorithms and are free from multiplications in the innermost loops. The algorithms were compared to the following conventional interpolators: 2-D windowed sinc, bicubic spline, 4 × 4 point bicubic spline, bilinear, and nearest neighbor. The most accurate of the two new algorithms is about eight times faster than nearest neighbor interpolation. The quantitative errors are of the same order as the errors of the nearest neighbor interpolator. The subjective image quality is between nearest neighbor and bilinear interpolation.

The ultrasound velocity and frequency-dependent attenuation of human and porcine eye tissues (cornea, lens, retina, choroid, sclera, vitreous body) were measured in the frequency range from 17 to 23 MHz. The results for the ultrasound velocity were compared to values taken from the literature and appeared to be in the same range. A comparison made between the acoustic parameters of human and porcine eyes showed that the porcine eye can serve as an animal model for the human eye. A mathematical operation is proposed to extrapolate the attenuation to the lower frequencies that are commonly used in clinical equipment. Finally, a first attempt was made to investigate the age dependence of the acoustic parameters of human tissues: some tissues showed a significant age effect.

The correlation of several acoustic parameters with histological features was investigated in healthy White New Zealander rabbit liver (n = 10). Thin sections (10 microns) were studied by means of a light microscope in combination with a digital image processing system. Adjacent thick sections (250 microns) were studied by means of a custom-designed acoustic microscope. Markers of black silk suture material, that could be identified both optically and acoustically, enabled the spatial correlation of both imaging modalities. Acoustic images were reconstructed from the velocity of ultrasound, the attenuation at the central frequency (30 MHz), the attenuation spectral slope, the backscatter spectral slope and the backscatter at the central frequency. The measurements comprised the frequency range from 10 to 50 MHz, yielding a resolution of approximately 50 microns. From the thin sections (10 microns) the local histological composition was obtained by digital segmentation techniques. The features that were segmented are: the collagen rich fibrous tissue content, the area lumina, the area interstitial spaces, the number density of nuclei and the area parenchymal tissue. Correlation techniques revealed that the main feature responsible for attenuation is collagen. There was a fair correlation between area lumina and attenuation, but this was caused by a high correlation between the collagen that surrounds the lumina, and attenuation. No correlation was found between any histological feature and backscatter parameters or velocity.

With ultrasound strain imaging, the function of tissue and organs can be identified. The technique uses multiple images, acquired from tissue under different degrees of deformation. We developed techniques for cardiovascular applications.

Contains fulltext : 95767.pdf (Publisher’s version ) (Open Access) 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.

Item does not contain fulltext 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 (p0.80 (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.

Contains fulltext : 97460.pdf (Publisher’s version ) (Closed access) 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.