Showing papers by "Johan M. Thijssen published in 2008"

Computer-aided B-mode ultrasound diagnosis of hepatic steatosis: a feasibility study

Abstract: 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 B- mode 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 of calibrated, computer-aided ultrasound for noninvasively diagnosing, possibly even screening, steatosis of the liver.

Modeling Envelope Statistics of Blood and Myocardium for Segmentation of Echocardiographic Images

Abstract: The objective of this study was to investigate the use of speckle statistics as a preprocessing step for segmentation of the myocardium in echocardiographic images. Three-dimensional (3D) and biplane image sequences of the left ventricle of two healthy children and one dog (beagle) were acquired. Pixel-based speckle statistics of manually segmented blood and myocardial regions were investigated by fitting various probability density functions (pdf). The statistics of heart muscle and blood could both be optimally modeled by a K-pdf or Gamma-pdf (Kolmogorov-Smirnov goodness-of-fit test). Scale and shape parameters of both distributions could differentiate between blood and myocardium. Local estimation of these parameters was used to obtain parametric images, where window size was related to speckle size (5 x 2 speckles). Moment-based and maximum-likelihood estimators were used. Scale parameters were still able to differentiate blood from myocardium; however, smoothing of edges of anatomical structures occurred. Estimation of the shape parameter required a larger window size, leading to unacceptable blurring. Using these parameters as an input for segmentation resulted in unreliable segmentation. Adaptive mean squares filtering was then introduced using the moment-based scale parameter (sigma(2)/mu) of the Gamma-pdf to automatically steer the two-dimensional (2D) local filtering process. This method adequately preserved sharpness of the edges. In conclusion, a trade-off between preservation of sharpness of edges and goodness-of-fit when estimating local shape and scale parameters is evident for parametric images. For this reason, adaptive filtering outperforms parametric imaging for the segmentation of echocardiographic images.

A modified algorithm for continuous wave near infrared spectroscopy applied to in-vivo animal experiments and on human skin

Abstract: Continuous wave Near Infrared Spectroscopy is a well known non invasive technique for measuring changes in tissue oxygenation. Absorption changes (DO2Hb and DHHb) are calculated from the light attenuations using the modified Lambert Beer equation. Generally, the concentration changes are calculated relative to the concentration at a starting point in time (delta time method). It is also possible, under certain assumptions, to calculate the concentrations by subtracting the equations at different wavelengths (delta wavelength method). We derived a new algorithm and will show the possibilities and limitations. In the delta wavelength method, the assumption is that the oxygen independent attenuation term will be eliminated from the formula even if its value changes in time, we verified the results with the classical delta time method using extinction coefficients from different literature sources for the wavelengths 767nm, 850nm and 905nm. The different methods of calculating concentration changes were applied to the data collected from animal experiments. The animals (lambs) were in a stable normoxic condition; stepwise they were made hypoxic and thereafter they returned to normoxic condition. The two algorithms were also applied for measuring two dimensional blood oxygen saturation changes in human skin tissue. The different oxygen saturation levels were induced by alterations in the respiration and by temporary arm clamping. The new delta wavelength method yielded in a steady state measurement the same changes in oxy and deoxy hemoglobin as the classical delta time method. The advantage of the new method is the independence of eventual variation of the oxygen independent attenuations in time.

BiPlane cardiac strain imaging: A study on valvular aortic stenosis

Abstract: In this study, the first preliminary results are reported of a beagle study on valvular aortic stenosis using BiPlane strain imaging A previously reported strain method was applied to BiPlane RF-data of the heart of four beagles A window-level tracking algorithm was devised, using a neighbour-based regularization force and a weighting factor that is highly depended on the cross-correlation values The tracking method was tested on a thick wall tube phantom that was heavily translated in axial and lateral direction, while the intraluminar pressure was varied Four healthy beagles underwent surgery at the age of six weeks One cusp of the aortic valve was fixated to the arterial wall Raw (RF) ultrasound data of the beagles' heart were acquired monthly with a Philips SONOS 7500 live 3D ultrasound system, equipped with an X4 matrix array transducer and an RF-interface BiPlane data were acquired using ECG-triggering at a frame rate of 100 Hz for at least one complete heart cycle Histological analysis of the heart muscle was performed after termination ROIs in the lateral wall in both the short and long axis view were manually segmented and subsequently tracked Displacements and strains were calculated and the ROIs were tracked using the proposed method In the phantom, each pixel within the ROI was tracked separately The local strains were reconstructed correctly after tracking, despite large translations and deformations In the animals, the strain curves were consistent with strain imaging results obtained in other animal and human studies Furthermore, the strain curves showed less drift and higher peak strain values after tracking Histological findings confirmed a successful creation of a valvular aortic stenosis and revealed a positive relation between severity of valvular aorta stenosis and the total amount of collagen The corresponding mean maximum radial indicated a negative relation between pressure and strain

Non-invasive staging of hepatic steatosis using computer-aided ultrasound diagnosis

Abstract: In this study, a computer-aided ultrasound (CAUS) diagnostic method for the detection and staging of hepatic steatosis (non-alcoholic fatty liver disease, NAFLD) is investigated using a bovine model (n=151). In humans as well as in cows, hepatic steatosis increases the risk of co morbidity. Assessment of liver fat content is mostly done by taking liver biopsies. The authors' goal was to estimate the liver fat content by using echographic parameters, i.e., non-invasively. Since skin and subcutaneous fat layer influence the characteristics of echographic B-mode liver-images, both transcutaneous and intraoperative images were acquired to study this effect. During image acquisition a fixed preset of the ultrasound equipment controls was used. One liver biopsy was taken from each animal to stage the NAFLD. Apart from the fat percentage, the triglyceride (TG) level was biochemically assessed and used in this study. The software package CAUS was developed to perform objective and unambiguous analysis on echographic B-mode images. Prior to image analysis, certain preprocessing steps were performed in order to achieve the relative echo strength in decibel (dB), rather than image gray level, as a quantitative parameter. Furthermore, corrections were made for ultrasound propagation through skin/fat layer and through an average ldquohealthy liverrdquo (automatic gain control, AGC). After these corrections, the estimated echographic parameters were correlated to the TG level by uni- and multivariate linear regression analysis. The regression formula was then used to predict the TG level in each animal. A retrospective classification was performed and ROC curves were obtained. High correlations with the liver TG score were found for several echographic and image parameters. ROC curve analysis show promising results for sensitivity (0.93), specificity (0.86) and area under the curve (0.93) in distinguishing fatty livers from healthy livers. This study showed the feasibility of computer-aided ultrasound for non-invasively diagnosing, or even screening, of liver steatosis.

Ultrasound strain imaging: From nano-scale motion detection to macro-scale functional imaging

Abstract: 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 recently applied this technique on hearts and skeletal muscles. Cardiac data was acquired in dogs with a valvar aorta stenosis. Muscle data was acquired from the orbicular oral muscle in the upper lip. For accurate assessment of deformation, the displacement of tissue can be determined at nanometer scale. Raw ultrasound data, containing the amplitude as well as the phase information is required for this analysis. A 2D coarse-to-fine strain estimation strategy is proposed to calculate the minute differential displacements in tissue, while the tissue itself is moving on a macro scale. The technique was validated using phantom experiments. These experiments demonstrated that accurate strain images can be determined using the proposed technique. Cardiac evaluation in dogs showed that the strain can be determined in three dimensions. The strain curves over the cardiac cycle are in correspondence with the severity of the stenosis of the aortic valve. In patients with a reconstructed cleft lip, the orbicular oral muscle in the reconstructed region showed decreased strain values. In normal individuals, similar strain values were found for all regions of the muscle. Ultrasound strain imaging is a promising technique enabling the addition of functional information to the geometrical information that is already provided by the conventional ultrasound imaging technique.

Cardiac output estimation in non-standard 3D echocardiographic images

Abstract: The aim of this study was to validate cardiac output (CO) values obtained by fully automated segmentation of the left ventricle (LV) against CO measured from the volume flow in the pulmonary artery. Segmentation of the LV in 3D echographic images may substantially support clinical diagnosis of (congenital) heart disease. Assumptions about shape and appearance of the heart are often incorporated in the segmentation method. This is advantageous when analyzing echographic images of normal heart geometries in standardized (apical) views. In abnormal heart geometries, for example in children with congenital malformations, this a priori knowledge about the shape and anatomy of the LV will result in erroneous segmentation results. Therefore, we developed an automated segmentation method without using a priori knowledge. Echocardiographic image sequences of five piglets were obtained in radiofrequency (rf) format. Cardiac blood flow was measured simultaneously in the pulmonary artery by an ultrasound flow probe. Three-dimensional adaptive filtering was performed on the demodulated rf-data to optimize the distinction between blood and myocardium. A 3D gradient-based deformable simplex mesh was then used to segment the endocardial surface. The method can be applied to non-standard heart geometries without having to impose shape constraints. Assuming the CO measurements from the flow probe as a gold standard, excellent correlation (r = 0.99) was observed with the CO estimates obtained from segmentation.