Voormolen, M.M.

Comparison of fundamental, second harmonic, and superharmonic imaging: A simulation study (Article)

2011-11-01T00:00:00Z

In medical ultrasound, fundamental imaging (FI) uses the reflected echoes from the same spectral band as that of the emitted pulse. The transmission frequency determines the trade-off between penetration depth and spatial resolution. Tissue harmonic imaging (THI) employs the second harmonic of the emitted frequency band to construct images. Recently, superharmonic imaging (SHI) has been introduced, which uses the third to the fifth (super) harmonics. The harmonic level is determined by two competing phenomena: nonlinear propagation and frequency dependent attenuation. Thus, the transmission frequency yielding the optimal trade-off between the spatial resolution and the penetration depth differs for THI and SHI. This paper quantitatively compares the concepts of fundamental, second harmonic, and superharmonic echocardiography at their optimal transmission frequencies. Forward propagation is modeled using a 3D-KZK implementation and the iterative nonlinear contrast source (INCS) method. Backpropagation is assumed to be linear. Results show that the fundamental lateral beamwidth is the narrowest at focus, while the superharmonic one is narrower outside the focus. The lateral superharmonic roll-off exceeds the fundamental and second harmonic roll-off. Also, the axial resolution of SHI exceeds that of FI and THI. The far-field pulse-echo superharmonic pressure is lower than that of the fundamental and second harmonic. SHI appears suited for echocardiography and is expected to improve its image quality at the cost of a slight reduction in depth-of-field.

Contrast-enhanced three-dimensional dobutamine stress echocardiography: Between Scylla and Charybdis? (Article)

2008-11-01T00:00:00Z

Aims: Real-time three-dimensional echocardiography (RT3DE) allows quick volumetric scanning of the left ventricle (LV). We evaluated the diagnostic accuracy of contrast-enhanced stress RT3DE for the detection of coronary artery disease (CAD) in comparison with coronary arteriography as the reference technique. Methods and results: Forty-five consecutive patients (age 59 ± 10, 31 males) referred for coronary angiography were examined by contrast-enhanced RT3DE. Wall motion analysis was performed off-line by dedicated software. New or worsening wall motion abnormalities were detected in 17 of 28 patients with significant CAD (sensitivity 61%), and in two of 17 patients without significant CAD (specificity 88%). The sensitivity for detection of single-vessel CAD was 8/15 patients (53%), for two-vessel CAD 4/6 (67%), and for three-vessel CAD 5/7 (71%). In 35 patients, comparison with conventional RT3DE was available. The image quality index at rest improved from 2.5 ± 1.2 to 3.2 ± 1.0 (P < 0.001) with contrast and at peak stress from 2.3 ± 1.2 to 3.1 ± 1.0 (P < 0.001). Interobserver agreement on the diagnosis of myocardial ischaemia improved from 26 of 35 studies (74%, κ = 0.44) with conventional stress RT3DE to 30 of 35 studies (86%, κ = 0.69) with contrast-enhanced stress RT3DE. Sensitivity increased from 50 to 55% and specificity from 69 to 85% with contrast-enhanced stress RT3DE in this subset of patients. Conclusion: Despite some important practical and theoretical benefits, contrast-enhanced stress RT3DE currently has only moderate diagnostic sensitivity due to several technical limitations as temporal and spatial resolution.

Time Continuous Detection of the Left Ventricular Long Axis and the Mitral Valve Plane in 3-D Echocardiography (Article)

2008-02-01T00:00:00Z

Automated segmentation approaches for the left ventricle (LV) in 3-D echocardiography (3DE) often rely on manual initialization. So far, little effort has been put into automating the initialization procedure to get to a fully automatic segmentation approach. We propose a fully automatic method for the detection of the LV long axis (LAX) and the mitral valve plane (MVP) over the full cardiac cycle, for the initialization of segmentation algorithms in 3DE. Our method exploits the cyclic motion of the LV and therefore detects salient structures in a time-continuous way. Probabilities to candidate LV center points are assigned through a Hough transform for circles. The LV LAX is detected by combining dynamic programming detections on these probabilities in 3-D and 2D + time to obtain a time continuous solution. Subsequently, the mitral valve plane is detected in a projection of the data on a plane through the previously detected LAX. The method easily adjusts to different acquisition routines and combines robustness with good accuracy and low computational costs. Automatic detection was evaluated using patient data acquired with the fast rotating ultrasound (FRU) transducer (n = 11 patients) and with the Philips Sonos 7500 ultrasound system (Philips Medical Systems, Andover, MA, USA), with the X4 matrix transducer (n = 14 patients). For the FRU-transducer data, the LAX was estimated with a distance error of 2.85 ± 1.70 mm (mean ± SD) and an angle of 5.25 ± 3.17 degrees; the mitral valve plane was estimated with a distance of -1.54 ± 4.31 mm. For the matrix data, these distances were 1.96 ± 1.30 mm with an angle error of 5.95 ± 2.11 and -1.66 ± 5.27 mm for the mitral valve plane. These results confirm that the method is very suitable for automatic detection of the LV LAX and MVP. It provides a basis for further automatic exploration of the LV and could therefore serve as a replacement of manual initialization of 3-D segmentation approaches. (E-mail: marijn.vanstralen@erasmusmc.nl).

Aspects of left ventricular volume comparison between 3D echocardiography and MRI (Article)

2007-12-01T00:00:00Z

3D Harmonic Echocardiography: (Doctoral Thesis)

2007-10-17T00:00:00Z

Three dimensional (3D) echocardiography has recently developed from an experimental technique in the â€™90 towards an imaging modality for the daily clinical practice. This dissertation describes the considerations, implementation, validation and clinical application of a unique concept for harmonic 3D echocardiography. Part I firstly illustrates the advantages of harmonic imaging with a new transducer design tool, allowing the simulation of steered nonlinear acoustic beams. Then this dissertation introduces the fast rotating ultrasound (FRU-) transducer, which serves as a cost effective alternative for full- volume echocardiography with optimal harmonic capabilities. Measurement of the left ventricular (LV) volume has major diagnostic and prognostic importance. In the part II this basic application of the FRU-transducer is explored. Both a commercially available and self-developed quantification application are evaluated for LV volume measurement. Both quant! ification applications use advanced semi-automatic detection algorithms for endocardial border delineation. In addition, the efficiency of LV volume quantification is optimized by determining the minimal number of long-axis images required for accurate LV volume measurement. More advanced applications are investigated in part III. First, 3D echocardiography during hemodialysis is compared with two dimensional echocardiography. The study gives a good example of the flexible application of 3D echocardiography. Subsequently, the advantages of 3D contrast harmonic imaging are explored. Whether 3D echocardiography can assist in the implantation of resynchronization devices is investigated next. The feasibility of regional wall motion analysis for this purpose concludes part III.

Three-dimensional echocardiographic analysis of left ventricular function during hemodialysis (Article)

2007-10-01T00:00:00Z

Background: The effects of hemodialysis (HD) on left ventricular (LV) function have been studied by various echocardiographic techniques (M-mode, 2D echocardiography). These studies are hampered by a low accuracy of measurements because of geometric assumptions regarding LV shape. Three-dimensional echocardiography (3DE) overcomes this limitation. Methods: We tested the feasibility of 3DE assessment of LV function during HD. Conventional biplane Simpson rule (BSR) and single plane area length method (SPM) for LV function analysis were used as a reference. Results: 12 HD patients were studied and in 10 (83%) a total of 80 3D datasets were acquired. In 3 patients, one dataset (4%) was of insufficient quality and excluded from analysis. Correlation between SPM, BSR and 3DE for calculation of end-diastolic (EDV, r = 0.89 and r = 0.92, respectively), end-systolic volume (ESV, r = 0.92 and r = 0.93, respectively) and for ejection fraction (EF, r = 0.90 and r = 0.88, respectively) was moderate. Limits-of-agreement results for EDV and ESV were poor with confidence intervals larger than 30 ml. Both 2DE methods underestimated end-diastolic and end-systolic volume, while overestimating ejection fraction. Conclusion: 3DE is feasible for image acquisition during HD, which opens the possibility for accurate and reproducible measurement of LV function during HD. This may improve the assessment of the acute effect of HD on LV performance, and guide therapeutic strategies aimed at preventing intradialytic hypotension. Copyright

Efficient Quantification of the Left Ventricular Volume Using 3-Dimensional Echocardiography: The Minimal Number of Equiangular Long-axis Images for Accurate Quantification of the Left Ventricular Volume (Article)

2007-04-01T00:00:00Z

For quantification of the left ventricular volume from 3-dimensional echocardiograms a number of cross-sectional images are used. The goal of this study was to determine the minimum number of long-axis images necessary for accurate quantification of the left ventricular volume. A strong correlation was observed between volumes obtained from magnetic resonance imaging and 3-dimensional echocardiography using 16 equiangular images (r = 0.99; y = 0.95x + 3.3 mL; standard error of the estimate = 7.0 mL; N = 30). Comparison of these results with random subsets showed a significant difference for volumes obtained with 4 and 2 equiangular images (P < .005). However, when the subsets were selected to target the eccentric region of the endocardial border this was only the case for subsets of two images (P < .001). This study demonstrates that accurate left ventricular volume quantification can be performed with as little as 8 equiangular long-axis images. By selecting the correctly oriented image set, this number can even be brought down to 4, which will further reduce the analysis time.

Microbubble spectroscopy of ultrasound contrast agents (Article)

2007-01-22T00:00:00Z

A new optical characterization of the behavior of single ultrasound contrast bubbles is presented. The method consists of insonifying individual bubbles several times successively sweeping the applied frequency, and to record movies of the bubble response up to 25 million frames/s with an ultrahigh speed camera operated in a segmented mode. The method, termed microbubble spectroscopy, enables to reconstruct a resonance curve in a single run. The data is analyzed through a linearized model for coated bubbles. The results confirm the significant influence of the shell on the bubble dynamics: shell elasticity increases the resonance frequency by about 50%, and shell viscosity is responsible for about 70% of the total damping. The obtained value for shell elasticity is in quantative agreement with previously reported values. The shell viscosity increases significantly with the radius, revealing a new nonlinear behavior of the phospholipid coating.

Three-Dimensional Echocardiographic Analysis of Left Ventricular Function during Hemodialysis (Article)

2007-01-01T00:00:00Z

Assessment of left ventricular function by three-dimensional echocardiography. (Article)

2003-01-01T00:00:00Z

Accurate determination of LV volume, ejection fraction and segmental wall motion abnormalities is important for clinical decision-making and follow-up assessment. Currently, echocardiography is the most common used method to obtain this information. Three-dimensional echocardiography has shown to be an accurate and reproducible method for LV quantitation, mainly by avoiding the use of geometric assumptions. In this review, we describe various methods to acquire a 3D-dataset for LV volume and wall motion analysis, including their advantages and limitations. We provide an overview of studies comparing LV volume and function measurement by various gated and real-time methods of acquisition compared to magnetic resonance imaging. New technical improvements, such as automated endocardial border detection and contrast enhancement, will make accurate on-line assessment with little operator interaction possible in the near future.

Dynamic three-dimensional echocardiography combined with semi-automated border detection offers advantages for assessment of resynchronization therapy. (Article)

2003-01-01T00:00:00Z

Simultaneous electrical stimulation of both ventricles in patients with interventricular conduction disturbance and advanced heart failure improves hemodynamics and results in increased exercise tolerance, quality of life. We have developed a novel technique for the assessment and optimization of resynchronization therapy. Our approach is based on transthoracic dynamic three-dimensional (3D) echocardiography and allows determination of the most delayed contraction site of the left ventricle (LV) together with global LV function data. Our initial results suggest that fast reconstruction of the LV is feasible for the selection of the optimal pacing site and allows identifying LV segments with dyssynchrony.