Johan Thijssen - Academia.edu (original) (raw)

Papers by Johan Thijssen

2008 IEEE Ultrasonics Symposium, 2008

Automatic segmentation of the endocardial surface in three-dimensional (3D) echocardiographic ima... more Automatic segmentation of the endocardial surface in three-dimensional (3D) echocardiographic images is an important tool to assess left ventricular (LV) geometry and cardiac output (CO). The presence of speckle noise as well as the nonisotropic characteristics of the myocardium impose strong demands on the segmentation algorithm. In the analysis of normal heart geometries of standardized (apical) views, it is advantageous to incorporate a priori knowledge about the shape and appearance of the heart. In contrast, when analyzing abnormal heart geometries, for example in children with congenital malformations, this a priori knowledge about the shape and anatomy of the LV might induce erroneous segmentation results. This study describes a fully automated segmentation method for the analysis of non-standard echocardiographic images, without making strong assumptions on the shape and appearance of the heart. The method was validated in vivo in a piglet model. Real-time 3D echocardiographic image sequences of five piglets were acquired in radiofrequency (rf) format. These ECG-gated full volume images were acquired intra-operatively in a non-standard view. Cardiac blood flow was measured simultaneously by an ultrasound transit time flow probe positioned around the common pulmonary artery. Three-dimensional adaptive filtering using the characteristics of speckle was performed on the demodulated rf data to reduce the influence of speckle noise and to optimize the distinction between blood and myocardium. A gradient-based 3D deformable simplex mesh was then used to segment the endocardial surface. A gradient and a speed force were included as external forces of the model. To balance data fitting and mesh regularity, one fixed set of weighting parameters of internal, gradient and speed 0031-9155/09/071951+12$30.00 © 2009 Institute of Physics and Engineering in Medicine Printed in the UK 1951 1952 M M Nillesen et al

Proceedings of the Ieee Ultrasonics Symposium, Nov 3, 1996

fields aberrated in P plane located at M arbitrary distance from an Abmocr-A method is presented ... more fields aberrated in P plane located at M arbitrary distance from an Abmocr-A method is presented toor iterative correction of wave array transducer. The signals received from the transducer are p m the transducer sienals as if the transducer bad been located directly cesed by an inverse extrapolator in such a way that the output yields nt the position of the aberrator. For subsequent transmission cycles, the =me inverse extrapolator is applied to delta pulses at time instants incorporating the time-reversnl estimated aberration profile. The method can be applied lo scattering and absorptive media, i.e. in developed. 11 is shown that correction algorithms intended for con-medicalconditions.Thecompensationofdistributedaberrstionisnlso aberrations: our conclusions with respeci to the position of the equiv-centrated aberrations can be used lo reduce effects due to distributed dent concentrated aberrator differ from results reported in the literalure. The method is demonstrated on realistic simulations of solid lesions, and cysts (voids) disturbed by interveningaberratingmedia.

Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 1996

Abstruct-The Conjugate Gradient Rayleigh method for the calculation of acoustic reflection and tr... more Abstruct-The Conjugate Gradient Rayleigh method for the calculation of acoustic reflection and transmission at a rough interface between two media was experimentally verified. The method is based on a continuous version of the conjugate gradient technique and plane-wave expansions. We measured the beam profiles of a nonfocused linear array transducer distorted by propagation through an aberrating interface. The directivity of the hydrophone was compensated for by means of spatial deconvolution. Sinusoidal, cylindrical aberrators were made of a water-based gelatine material. The measurements were compared with 2-and 3-D simulations. The measured and simulated beam profiles are in good agreement, as shown by the root-mean-square difference.

Physiol Meas, 2003

This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infr... more This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infrared spectroscopy (NIRS) and a continuous wave NIR laser Doppler flow system (LDF) to measure changes in the blood oxygenation, blood concentration and blood flow velocity in the brain. A piglet was used as animal model. A controlled change in the arterial CO2 pressure (PaCO2) was applied for achieving changes in the listed cerebrovascular parameters. The time courses of blood concentration parameters (NIRS) and RMS blood flow velocity (LDF) were found to correspond closely with those of carotid blood flow and arterial carbon dioxide pressure (PaCO2). This result shows the additional value of LDF when combined with NIRS, preferably in one instrument. Development of pulsed LDF for regional blood flow measurement is indicated.

In a clinical pilot study radiofrequency echograms were acquired during routine echography of int... more In a clinical pilot study radiofrequency echograms were acquired during routine echography of intraocular tumours. The data acquisition was performed with an "add-on" device, which was developed at our laboratory. The acquired data were pre-processed to remove the effects due to equipment performance and beam characteristics. The analysis was performed in the frequency domain (acoustospectrography) and acoustic tissue parameters like the attentuation coefficient and backscatter cross section estimated. In addition the gray level statistics of B-mode images were analysed. A set of parameters was thus obtained which was subjected to a discriminant analysis, based on a classification of the tumours by histology (i.e. after removal of the eyes). The results show a significant discriminability between different tumours and even between histological types of the same tumour (choroidal melanoma).

The information about the condition of parenchymal tissues is obscured by the performance charact... more The information about the condition of parenchymal tissues is obscured by the performance characteristics of echographic equipment. The authors investigated by realistic 3-D simulations the so-called beam diffraction effects on two echographic imaging modalities: amplitude modulated (AM) and phase derivative (PD) echograms. Furthermore the modification of the image texture by attenuation was quantified. In order to assess the potentials of statistical analysis of texture for medical diagnostics the effects caused by varying the density of scattering particles in a homogeneous medium were studied. It is concluded, that unless beam diffraction effects are either prevented, or adequately corrected for, quantitative texture analysis is not meaningful. In addition, the data have to be corrected for the non-linear and time dependent amplifier characteristics. Data-acquisition and preprocessing equipment performing these tasks has been developed at the authors' laboratory.

2006 IEEE Ultrasonics Symposium, 2006

A fully automated segmentation of the endocardial surface was developed by integrating spatio-tem... more A fully automated segmentation of the endocardial surface was developed by integrating spatio-temporal information of D ultrasound image sequences. 3D echocardiographic image sequences of the left ventricle of five healthy children were obtained in transthoracic short/long axis view. 2D and 3D (adaptive) filtering was used to reduce speckle noise and optimize the distinction between blood and myocardium, while preserving sharpness of edges between various structures. Four different filters (2D adaptive mean, 2D and 3D adaptive mean squares filter and 2D local entropy) were tested. The filter kernel was related to speckle size to yield statistically robust data. Filter quality was measured by comparing overlap percentages of histograms of manually segmented blood and myocardial regions. ROC curves of manually segmented blood regions were determined to compare effects of the different filters. A deformable contour algorithm was used, after automatic thresholding, to yield a closed contour of the endocardial border in each elevational plane. Each contour was optimized using contours of surrounding spatio-temporal planes as limiting condition to ensure spatio-temporal. The combination of adaptive filtering using image statistics and deformable contours has potential to segment the endocardial surface in 3D

Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2010

Ultrasound in medicine & biology, Jan 19, 2015

Patients on home parenteral nutrition are at risk for developing liver dysfunction, which is due ... more 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 =...

Ultrasound in medicine & biology, Jan 26, 2015

Assessment of right ventricular (RV) function is known to be of diagnostic value in patients with... more 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 agreeme...

IFMBE Proceedings, 2009

ABSTRACT Semi-automatic segmentation of the heart muscle in three-dimensional (3D) echographic im... more ABSTRACT Semi-automatic segmentation of the heart muscle in three-dimensional (3D) echographic images may substantially support clinical diagnosis of (congenital) heart disease. It may serve as an important preprocessing step for automated cardiac strain imaging and could be used for cardiac output measurement. Echocardiographic image sequences of the left ventricle of one healthy subject and one piglet were obtained in radiofrequency (rf) format, directly after beamforming, in Full Volume mode. 3D Adaptive Mean Squares (AMS) filtering was performed on the demodulated rf-data to optimize the distinction between blood and myocardium. A 3D deformable simplex mesh was then used to segment the endocardial surface. A gradient and a speed force were included as external forces of the model. Initial results show that segmentation of the endocardial surface using 3D deformable simplex meshes in combination with adaptive filtering is feasible. Cardiac output (CO) measurements in the piglet model, based on this segmentation technique were promising. The method can be applied to non-standard heart geometries without having to impose strong shape constraints.

Animal reproduction science

In recent years, several attempts have been made to evaluate the activity of a corpus luteum by d... more 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 calcula...

Proceedings of IEEE Ultrasonics Symposium ULTSYM-94, 1994

Two iterative methods for the calculation of acoustic reflection and transmission at a rough inte... more Two iterative methods for the calculation of acoustic reflection and transmission at a rough interface between two media are compared. The methods are based on a continuous version of the conjugate gradient technique. One method is based on plane-wave expansions while the other method is based on boundary integral equations and Green's functions. The methods are compared with regard to

Medical Imaging 2006: Ultrasonic Imaging and Signal Processing, 2006

2012 IEEE International Ultrasonics Symposium, 2012

ABSTRACT The aim of this study was to test the hypothesis that the Computer Aided UltraSound (CAU... more ABSTRACT 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 Trans- US images was performed adequately.

IFMBE Proceedings, 2009

Fatty liver (steatosis) occurs in obese patients, among others, and is related to the development... more Fatty liver (steatosis) occurs in obese patients, among others, and is related to the development of diabetes type-2. Timely diagnosis of steatosis is therefore of great importance. Steatosis is also the most common liver disease of high-yielding dairy cattle during early lactation. This makes it a suitable animal model for studying liver steatosis. Furthermore, reference of derived ultrasound parameters against a "gold standard" is possible in cattle by taking a liver biopsy for the assessment of fat concentration. The authors undertook this pilot study to investigate the hypothesis that quantitative, computer-aided Bmode ultrasound enables the noninvasive detection of hepatic steatosis. Echographic images were obtained postpartum from dairy cows (n = 12) in transcutaneous and direct (intraoperative) applications using a convex array transducer at 4.2 MHz. During surgery, a biopsy was taken from the caudate lobe to assess the liver fat content (fat score). A custom-designed software package for computer-aided ultrasound diagnosis (CAUS) was developed. After linearizing the post-processing look-up-table (LUT), the image gray levels were transferred into echo levels in decibels relative to the mean echo level in a tissue-mimicking phantom. The quantitative comparison of transcutaneous and intraoperative images enabled the correction for the attenuation effect of skin and subcutaneous fat layer on the mean echo level in the liver, as well as for the effects of the beam formation and attenuation of liver tissue on the echo level vs. depth. The residual attenuation coefficient (dB/cm) in fatty liver vs. normal liver was estimated and compensated for. Finally, echo level was estimated relative to the phantom used for calibration, and echo texture was characterized by the mean axial and lateral speckle size within the regions of interest. In the no fat/low fat group (n = 5) skin plus fat layer attenuation was 3.4 dB/cm. A correlation of skin layer thickness vs. fat score of r = 0:48 was found. The mean transcutaneous liver tissue echo level correlated well with fat score: r = 0:80. A residual liver attenuation coefficient of 0.76 dB/cm and 1.19 dB/cm was found in medium and high fat liver, respectively. In transcutaneous images, correlation of residual attenuation coefficient with fat score was r = 0:69. Axial and lateral speckle sizes were on the order of 0.2 and 1.0 cm, respectively, and no correlation was found with liver fat content. Results for transcutaneous and intraoperative images were similar. The authors conclude that this pilot study shows the feasibility Manuscript

International Symposium on Signals, Circuits and Systems, 2005. ISSCS 2005., 2005

This paper presents a fully automated method for endocardial and epicardial contour estimation fr... more This paper presents a fully automated method for endocardial and epicardial contour estimation from sequences of echocardiographic images using a short axis view of the left ventricle. The segmentation is performed by maximum likelihood estimation, separating the Rayleigh modes that model the regions of interest (inside endocardium, between endocardium and epicardium, or outside epicardium). The presented method leads to a

European journal of echocardiography : the journal of the Working Group on Echocardiography of the European Society of Cardiology, 2006

To renew the echocardiographic reference values of heart dimensions in healthy children. Group 1 ... more To renew the echocardiographic reference values of heart dimensions in healthy children. 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...

Ultrasound in medicine & biology, 1994

The image quality of two ultrasonic imaging techniques was studied: conventional echography and t... more The image quality of two ultrasonic imaging techniques was studied: conventional echography and the recently introduced elastography. The image quality was assessed by estimating the detectability of disc-shaped lesions of various sizes and contrast levels. The study was designed to verify the hypothesis that elastograms could show lesions at a higher subjective and objective level of detectability than echograms of the same object contrast. This hypothesis was adopted because homogeneous elastograms can present a higher point signal-to-noise ratio than uniform echograms. Both elastograms and echograms were generated by two-dimensional (2D) simulations. The subjective assessment was performed by psychophysical experiments using the staircase up-down method. The threshold contrast of detection for both modalities was determined at different diameters of the disc-shaped lesion. These values were used to construct the contrast-detail curves for both techniques. For identical object con...

2008 IEEE Ultrasonics Symposium, 2008

Automatic segmentation of the endocardial surface in three-dimensional (3D) echocardiographic ima... more Automatic segmentation of the endocardial surface in three-dimensional (3D) echocardiographic images is an important tool to assess left ventricular (LV) geometry and cardiac output (CO). The presence of speckle noise as well as the nonisotropic characteristics of the myocardium impose strong demands on the segmentation algorithm. In the analysis of normal heart geometries of standardized (apical) views, it is advantageous to incorporate a priori knowledge about the shape and appearance of the heart. In contrast, when analyzing abnormal heart geometries, for example in children with congenital malformations, this a priori knowledge about the shape and anatomy of the LV might induce erroneous segmentation results. This study describes a fully automated segmentation method for the analysis of non-standard echocardiographic images, without making strong assumptions on the shape and appearance of the heart. The method was validated in vivo in a piglet model. Real-time 3D echocardiographic image sequences of five piglets were acquired in radiofrequency (rf) format. These ECG-gated full volume images were acquired intra-operatively in a non-standard view. Cardiac blood flow was measured simultaneously by an ultrasound transit time flow probe positioned around the common pulmonary artery. Three-dimensional adaptive filtering using the characteristics of speckle was performed on the demodulated rf data to reduce the influence of speckle noise and to optimize the distinction between blood and myocardium. A gradient-based 3D deformable simplex mesh was then used to segment the endocardial surface. A gradient and a speed force were included as external forces of the model. To balance data fitting and mesh regularity, one fixed set of weighting parameters of internal, gradient and speed 0031-9155/09/071951+12$30.00 © 2009 Institute of Physics and Engineering in Medicine Printed in the UK 1951 1952 M M Nillesen et al

Proceedings of the Ieee Ultrasonics Symposium, Nov 3, 1996

fields aberrated in P plane located at M arbitrary distance from an Abmocr-A method is presented ... more fields aberrated in P plane located at M arbitrary distance from an Abmocr-A method is presented toor iterative correction of wave array transducer. The signals received from the transducer are p m the transducer sienals as if the transducer bad been located directly cesed by an inverse extrapolator in such a way that the output yields nt the position of the aberrator. For subsequent transmission cycles, the =me inverse extrapolator is applied to delta pulses at time instants incorporating the time-reversnl estimated aberration profile. The method can be applied lo scattering and absorptive media, i.e. in developed. 11 is shown that correction algorithms intended for con-medicalconditions.Thecompensationofdistributedaberrstionisnlso aberrations: our conclusions with respeci to the position of the equiv-centrated aberrations can be used lo reduce effects due to distributed dent concentrated aberrator differ from results reported in the literalure. The method is demonstrated on realistic simulations of solid lesions, and cysts (voids) disturbed by interveningaberratingmedia.

Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 1996

Abstruct-The Conjugate Gradient Rayleigh method for the calculation of acoustic reflection and tr... more Abstruct-The Conjugate Gradient Rayleigh method for the calculation of acoustic reflection and transmission at a rough interface between two media was experimentally verified. The method is based on a continuous version of the conjugate gradient technique and plane-wave expansions. We measured the beam profiles of a nonfocused linear array transducer distorted by propagation through an aberrating interface. The directivity of the hydrophone was compensated for by means of spatial deconvolution. Sinusoidal, cylindrical aberrators were made of a water-based gelatine material. The measurements were compared with 2-and 3-D simulations. The measured and simulated beam profiles are in good agreement, as shown by the root-mean-square difference.

Physiol Meas, 2003

This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infr... more This paper describes the simultaneous use of two, noninvasive, near-infrared techniques near-infrared spectroscopy (NIRS) and a continuous wave NIR laser Doppler flow system (LDF) to measure changes in the blood oxygenation, blood concentration and blood flow velocity in the brain. A piglet was used as animal model. A controlled change in the arterial CO2 pressure (PaCO2) was applied for achieving changes in the listed cerebrovascular parameters. The time courses of blood concentration parameters (NIRS) and RMS blood flow velocity (LDF) were found to correspond closely with those of carotid blood flow and arterial carbon dioxide pressure (PaCO2). This result shows the additional value of LDF when combined with NIRS, preferably in one instrument. Development of pulsed LDF for regional blood flow measurement is indicated.

In a clinical pilot study radiofrequency echograms were acquired during routine echography of int... more In a clinical pilot study radiofrequency echograms were acquired during routine echography of intraocular tumours. The data acquisition was performed with an "add-on" device, which was developed at our laboratory. The acquired data were pre-processed to remove the effects due to equipment performance and beam characteristics. The analysis was performed in the frequency domain (acoustospectrography) and acoustic tissue parameters like the attentuation coefficient and backscatter cross section estimated. In addition the gray level statistics of B-mode images were analysed. A set of parameters was thus obtained which was subjected to a discriminant analysis, based on a classification of the tumours by histology (i.e. after removal of the eyes). The results show a significant discriminability between different tumours and even between histological types of the same tumour (choroidal melanoma).

The information about the condition of parenchymal tissues is obscured by the performance charact... more The information about the condition of parenchymal tissues is obscured by the performance characteristics of echographic equipment. The authors investigated by realistic 3-D simulations the so-called beam diffraction effects on two echographic imaging modalities: amplitude modulated (AM) and phase derivative (PD) echograms. Furthermore the modification of the image texture by attenuation was quantified. In order to assess the potentials of statistical analysis of texture for medical diagnostics the effects caused by varying the density of scattering particles in a homogeneous medium were studied. It is concluded, that unless beam diffraction effects are either prevented, or adequately corrected for, quantitative texture analysis is not meaningful. In addition, the data have to be corrected for the non-linear and time dependent amplifier characteristics. Data-acquisition and preprocessing equipment performing these tasks has been developed at the authors' laboratory.

2006 IEEE Ultrasonics Symposium, 2006

A fully automated segmentation of the endocardial surface was developed by integrating spatio-tem... more A fully automated segmentation of the endocardial surface was developed by integrating spatio-temporal information of D ultrasound image sequences. 3D echocardiographic image sequences of the left ventricle of five healthy children were obtained in transthoracic short/long axis view. 2D and 3D (adaptive) filtering was used to reduce speckle noise and optimize the distinction between blood and myocardium, while preserving sharpness of edges between various structures. Four different filters (2D adaptive mean, 2D and 3D adaptive mean squares filter and 2D local entropy) were tested. The filter kernel was related to speckle size to yield statistically robust data. Filter quality was measured by comparing overlap percentages of histograms of manually segmented blood and myocardial regions. ROC curves of manually segmented blood regions were determined to compare effects of the different filters. A deformable contour algorithm was used, after automatic thresholding, to yield a closed contour of the endocardial border in each elevational plane. Each contour was optimized using contours of surrounding spatio-temporal planes as limiting condition to ensure spatio-temporal. The combination of adaptive filtering using image statistics and deformable contours has potential to segment the endocardial surface in 3D

Ieee Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2010

Ultrasound in medicine & biology, Jan 19, 2015

Patients on home parenteral nutrition are at risk for developing liver dysfunction, which is due ... more 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 =...

Ultrasound in medicine & biology, Jan 26, 2015

Assessment of right ventricular (RV) function is known to be of diagnostic value in patients with... more 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 agreeme...

IFMBE Proceedings, 2009

ABSTRACT Semi-automatic segmentation of the heart muscle in three-dimensional (3D) echographic im... more ABSTRACT Semi-automatic segmentation of the heart muscle in three-dimensional (3D) echographic images may substantially support clinical diagnosis of (congenital) heart disease. It may serve as an important preprocessing step for automated cardiac strain imaging and could be used for cardiac output measurement. Echocardiographic image sequences of the left ventricle of one healthy subject and one piglet were obtained in radiofrequency (rf) format, directly after beamforming, in Full Volume mode. 3D Adaptive Mean Squares (AMS) filtering was performed on the demodulated rf-data to optimize the distinction between blood and myocardium. A 3D deformable simplex mesh was then used to segment the endocardial surface. A gradient and a speed force were included as external forces of the model. Initial results show that segmentation of the endocardial surface using 3D deformable simplex meshes in combination with adaptive filtering is feasible. Cardiac output (CO) measurements in the piglet model, based on this segmentation technique were promising. The method can be applied to non-standard heart geometries without having to impose strong shape constraints.

Animal reproduction science

In recent years, several attempts have been made to evaluate the activity of a corpus luteum by d... more 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 calcula...

Proceedings of IEEE Ultrasonics Symposium ULTSYM-94, 1994

Two iterative methods for the calculation of acoustic reflection and transmission at a rough inte... more Two iterative methods for the calculation of acoustic reflection and transmission at a rough interface between two media are compared. The methods are based on a continuous version of the conjugate gradient technique. One method is based on plane-wave expansions while the other method is based on boundary integral equations and Green's functions. The methods are compared with regard to

Medical Imaging 2006: Ultrasonic Imaging and Signal Processing, 2006

2012 IEEE International Ultrasonics Symposium, 2012

ABSTRACT The aim of this study was to test the hypothesis that the Computer Aided UltraSound (CAU... more ABSTRACT 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 Trans- US images was performed adequately.

IFMBE Proceedings, 2009

Fatty liver (steatosis) occurs in obese patients, among others, and is related to the development... more Fatty liver (steatosis) occurs in obese patients, among others, and is related to the development of diabetes type-2. Timely diagnosis of steatosis is therefore of great importance. Steatosis is also the most common liver disease of high-yielding dairy cattle during early lactation. This makes it a suitable animal model for studying liver steatosis. Furthermore, reference of derived ultrasound parameters against a "gold standard" is possible in cattle by taking a liver biopsy for the assessment of fat concentration. The authors undertook this pilot study to investigate the hypothesis that quantitative, computer-aided Bmode ultrasound enables the noninvasive detection of hepatic steatosis. Echographic images were obtained postpartum from dairy cows (n = 12) in transcutaneous and direct (intraoperative) applications using a convex array transducer at 4.2 MHz. During surgery, a biopsy was taken from the caudate lobe to assess the liver fat content (fat score). A custom-designed software package for computer-aided ultrasound diagnosis (CAUS) was developed. After linearizing the post-processing look-up-table (LUT), the image gray levels were transferred into echo levels in decibels relative to the mean echo level in a tissue-mimicking phantom. The quantitative comparison of transcutaneous and intraoperative images enabled the correction for the attenuation effect of skin and subcutaneous fat layer on the mean echo level in the liver, as well as for the effects of the beam formation and attenuation of liver tissue on the echo level vs. depth. The residual attenuation coefficient (dB/cm) in fatty liver vs. normal liver was estimated and compensated for. Finally, echo level was estimated relative to the phantom used for calibration, and echo texture was characterized by the mean axial and lateral speckle size within the regions of interest. In the no fat/low fat group (n = 5) skin plus fat layer attenuation was 3.4 dB/cm. A correlation of skin layer thickness vs. fat score of r = 0:48 was found. The mean transcutaneous liver tissue echo level correlated well with fat score: r = 0:80. A residual liver attenuation coefficient of 0.76 dB/cm and 1.19 dB/cm was found in medium and high fat liver, respectively. In transcutaneous images, correlation of residual attenuation coefficient with fat score was r = 0:69. Axial and lateral speckle sizes were on the order of 0.2 and 1.0 cm, respectively, and no correlation was found with liver fat content. Results for transcutaneous and intraoperative images were similar. The authors conclude that this pilot study shows the feasibility Manuscript

International Symposium on Signals, Circuits and Systems, 2005. ISSCS 2005., 2005

This paper presents a fully automated method for endocardial and epicardial contour estimation fr... more This paper presents a fully automated method for endocardial and epicardial contour estimation from sequences of echocardiographic images using a short axis view of the left ventricle. The segmentation is performed by maximum likelihood estimation, separating the Rayleigh modes that model the regions of interest (inside endocardium, between endocardium and epicardium, or outside epicardium). The presented method leads to a

European journal of echocardiography : the journal of the Working Group on Echocardiography of the European Society of Cardiology, 2006

To renew the echocardiographic reference values of heart dimensions in healthy children. Group 1 ... more To renew the echocardiographic reference values of heart dimensions in healthy children. 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...

Ultrasound in medicine & biology, 1994

The image quality of two ultrasonic imaging techniques was studied: conventional echography and t... more The image quality of two ultrasonic imaging techniques was studied: conventional echography and the recently introduced elastography. The image quality was assessed by estimating the detectability of disc-shaped lesions of various sizes and contrast levels. The study was designed to verify the hypothesis that elastograms could show lesions at a higher subjective and objective level of detectability than echograms of the same object contrast. This hypothesis was adopted because homogeneous elastograms can present a higher point signal-to-noise ratio than uniform echograms. Both elastograms and echograms were generated by two-dimensional (2D) simulations. The subjective assessment was performed by psychophysical experiments using the staircase up-down method. The threshold contrast of detection for both modalities was determined at different diameters of the disc-shaped lesion. These values were used to construct the contrast-detail curves for both techniques. For identical object con...