Showing papers by "Johan M. Thijssen published in 2006"

P2D-3 Objective Performance Testing and Quality Assurance of Medical Ultrasound Equipment

Abstract: The goal of this study was to develop a test protocol that contains the minimum set of performance measurements for predicting the clinical performance of ultrasound equipment and that is based on objective assessments by computerized image analysis. The post-processing look-up-table (LUT) is measured and linearized. The elevational focus (slice thickness) of the transducer is estimated and the in plane transmit focus is positioned at the same depth. The developed tests are: echo level dynamic range (dB), contrast resolution (i.e., "gamma" of display, #gray levels/dB) and -sensitivity, overall system sensitivity, lateral sensitivity profile, dead zone, spatial resolution, and geometric conformity of display. The concept of a computational observer is used to define the lesion signal-to-noise ratio, SNRL (or Mahalanobis distance), as a measure for contrast sensitivity. The whole performance measurement protocol has been implemented in software. Reports are generated that contain all the information about the measurements and results, such as graphs, images and numbers. The software package may be viewed and a run-time version downloaded at the website: http://www.qa4us.eu

New reference values for echocardiographic dimensions of healthy Dutch children

Abstract: Aim: To renew the echocardiographic reference values of heart dimensions in healthy children.

2H-1 In Vivo 3D Cardiac and Skeletal Muscle Strain Estimation

Abstract: In this study, BiPlane imaging was adapted for measuring strain in actively deforming tissue in three orthogonal directions. BiPlane imaging assures a sufficient frame rate (75-120 Hz) for accurate strain estimation. A coarse-to-fine iterative 2D strain algorithm using spatial correction and local stretching was implemented. Considering the huge amount of generated data, a fast interpolation scheme was implemented for measuring sub-sample and sub-line displacements. Assuming a 2D parabolic shape of the cross-correlation function, a straightforward and direct calculation of the displacements is possible. The strain estimation method was validated by means of a simulation study and phantom experiments. Rf-data were acquired with a 3D X4 matrix array transducer (Philips Sonos 7500) in BiPlane mode. In vivo verification in human skeletal muscle was performed. Furthermore, cardiac strain imaging was conducted using cardiac BiPlane data of dogs. In a pilot animal study, beagles with an induced valvular aortic stenosis were monitored. The Field II simulation was used for determining the accuracy and detectibility of the algorithm and revealed excellent correlation between applied and measured axial strain (SNR = 43 dB) for a window of 0.60 mm. Obviously, a lower SNR was found in lateral and elevational direction. The in vivo verification experiment in the skeletal muscles revealed similar cumulative axial strain curves (up to 8%) in both the azimuth and elevational direction. The shape of the strain curve matched perfectly with the curve of the measured force. The lateral strain values parallel to the direction of the muscle fibers matched the axial strain curves, whereas the shape of the lateral strain in the perpendicular plane differed due to anisotropy. Finally, strain images of the beagles were calculated. The beagle with the most excessive pressure gradient revealed a decrease of the radial strain. Furthermore, an elongated plateau in the radial strain indicated hypertrophy. In conclusion, 3D cardiac and strain estimation is feasible using a real-time 3D scanner. Additional validation studies of full 3D imaging modes are required to fully validate the technique

Improvement of heart function after balloon dilation of congenital valvar aortic stenosis: A pilot study with ultrasound tissue Doppler and strain rate imaging

Abstract: The aim was to investigate the effects of balloon dilation of congenital valvar aortic (Ao) stenosis on heart function with conventional and with new echocardiographic techniques. Nine patients, preballoon and 1 to 4 d postballoon dilation of Ao-valve, were included in the study. Assessment of heart function was made by using conventional echo/Doppler, tissue Doppler imaging (TDI) and strain rate imaging (SRI). Mean (and standard deviation) of posttreatment drop of aortic valve pressure gradient was 34.1 (sd 14.0) mmHg, p < 0.01. Conventional echo/Doppler end-diastolic left ventricular posterior wall (LVPW) thickness and interventricular septum (IVS) thickness did not change significantly. Mean change of LV fractional shortening (FS) was -5.2 (sd 3.2)%, p < 0.01. The observed changes of FS did not significantly correlate to the magnitude of pressure gradient changes. Changes of TDI and SRI parameters indicated that an increase in absolute value is observed in most cases, but correlation to pressure gradient change remains poor, with a few exceptions, both in LV free wall (LVFW) and IVS. Data from IVS are more consistent than of LVFW. It is concluded that the global functional parameter FS assessed by conventional echo/Doppler has diagnostic value for the assessment of (improved) heart function already shortly after intervention, when compared with the pretreatment value. Local parameters from the new echographic techniques show less significant short-term effects attributable to the intervention. Improvement of the precision of SRI measurements is needed. A larger study is indicated to fully investigate the expected potentials of TDI and SRI for the assessment of local improvement of heart function early after intervention, as well as for revealing eventual late effects on these functional parameters.

Three-dimensional segmentation of the heart muscle using image statistics

Abstract: Segmentation of the heart muscle in 3D echocardiographic images provides a tool for visualization of cardiac anatomy and assessment of heart function, and serves as an important pre-processing step for cardiac strain imaging. By incorporating spatial and temporal information of 3D ultrasound image sequences (4D), a fully automated method using image statistics was developed to perform 3D segmentation of the heart muscle. 3D rf-data were acquired with a Philips SONOS 7500 live 3D ultrasound system, and an X4 matrix array transducer (2-4 MHz). Left ventricular images of five healthy children were taken in transthoracial short/long axis view. As a first step, image statistics of blood and heart muscle were investigated. Next, based on these statistics, an adaptive mean squares filter was selected and applied to the images. Window size was related to speckle size (5x2 speckles). The degree of adaptive filtering was automatically steered by the local homogeneity of tissue. As a result, discrimination of heart muscle and blood was optimized, while sharpness of edges was preserved. After this pre-processing stage, homomorphic filtering and automatic thresholding were performed to obtain the inner borders of the heart muscle. Finally, a deformable contour algorithm was used to yield a closed contour of the left ventricular cavity in each elevational plane. Each contour was optimized using contours of the surrounding planes (spatial and temporal) as limiting condition to ensure spatial and temporal continuity. Better segmentation of the ventricle was obtained using 4D information than using information of each plane separately.

P3A-5 3D Segmentation of the Heart Muscle in Real-Time 3D Echocardiographic Sequences Using Image Statistics

Abstract: A fully automated segmentation of the endocardial surface was developed by integrating spatio-temporal information of 3D 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

Three dimensional segmentation of the heart muscle in real-time 3D echocardiographic sequences using image statistics

Abstract: A fully automated segmentation of the endocardial surface was developed by integrating spatio-temporal information of 3D ultrasound image sequences. 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. 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 continuity.

Acoustic properties of healthy and reconstructed cleft lip

Abstract: The feasibility of echographic imaging of the tissues in healthy lip and in reconstructed cleft lip and estimating the dimensions and the normalized echo level of these tissues is investigated. Echographic images of the upper lip were made with commercial medical ultrasound equipment, using a linear array transducer (7-11 MHz bandwidth) and a non-contact gel coupling. Tissue dimensions were measured by means of software calipers. Echo levels were calibrated and corrected for beam characteristics, gel path and tissue attenuation by using a tissue-mimicking phantom. At central position of philtrum, mean thickness (and standard deviation) of lip loose connective tissue layer, orbicularis oris muscle and dense connective layer was 4.0 (sd 0.1) mm, 2.3 (sd 0.7) mm, 2.2 (sd 0.7) mm, respectively, in healthy lip at rest. Mean (sd) echo level of muscle and dense connective tissue layer with respect to echo level of lip loose connective tissue layer was in relaxed condition: - 19.3 (sd 0.6) dB and - 10.7 (sd 4.0) dB, respectively. Echo level of loose connective tissue layer was +25.6 (sd 4.2) dB relative to phantom echo level obtained in the focus of the transducer. Color mode echo images were calculated, after adaptive filtering of the images, which show the tissues in separate colors and highlight the details of healthy lip and reconstructed cleft lip. Quantitative assessment of thickness and echo level of various lip tissues is feasible after proper calibration of the echographic equipment. Diagnostic potentials of the developed quantitative echographic techniques for non-invasive evaluation of the outcome of cleft lip reconstruction are promising.