Robert Klaua

IN VIVO TIME HARMONIC ELASTOGRAPHY OF THE HUMAN HEART

Time harmonic elastography is introduced as a modality for assessing myocardial elasticity changes during the cardiac cycle. It is based on external stimulation and real-time analysis of 30-Hz harmonic shear waves in axial direction of a parasternal line of sight through the lateral heart wall. In 20 healthy volunteers, the externally induced waves showed smaller amplitudes during systole (76.0 ± 30.8 μm) and higher amplitudes during diastole (126.7 ± 52.1 μm). This periodic wave amplitude alteration preceded ventricular contraction and dilation by about 100 ms. The amplitude ratio of 1.75 ± 0.49 indicates a relative change in myocardial shear elasticity on the order of 14 ± 11. These results well agree with observations made by cardiac magnetic resonance elastography for a similar displacement component and region of the heart. The proposed method provides reproducible elastodynamic information on the heart in real-time and may help in diagnosing myocardial relaxation abnormalities in the future.

Isovolumetric Elasticity Alteration in the Human Heart Detected by In Vivo Time-Harmonic Elastography

Time harmonic elastography (THE) has recently been introduced for measurement of the periodic alteration in myocardial shear modulus based on externally induced low-frequency acoustic vibrations produced by a loudspeaker. In this study, we propose further developments of cardiac THE toward a clinical modality including integration of the vibration source into the patient bed and automated parameter extraction from harmonic shear wave amplitudes, wall motion profiles and synchronized electrocardiographic records. This method has enabled us to evaluate the delay between wall motion and wave amplitude alteration for the measurement of isovolumetric times of elasticity alteration during contraction (τ(C)) and relaxation (τ(R)) in a group of 32 healthy volunteers. On average, the wave amplitudes changed between systole and diastole by a factor of 1.7 ± 0.3, with a τ(C) of 137 ± 61 ms and a τ(R) of 68 ± 73 ms, which agrees with results obtained with the more time-consuming and expensive cardiac magnetic resonance elastography. Furthermore, because of the high sampling rate, elasto-morphometric parameters such as transition times and the area of wave amplitude-cardiac motion cycles can be processed in an automated way for the future clinical detection of myocardial relaxation abnormalities.

P2L-4 Ultrasonic Detection and Quantitative Analysis of Microscopic Bubbles and Particles in Solution: Enhanced by Attenuation Compensation

In many technical and medical applications microscopic bubbles and particles play an important role. For a non-invasive and quantitative estimation of the particle characteristics acoustic properties along the path of sound propagation are of major concern. When applying clamp-on probes that can be used with a variety of tubes the compensation of the acoustic attenuation is crucial for reliable parameter estimation. In addition, the acoustic properties of the tube material vary as a function of environmental conditions. An ultrasonic probe that enabled an automated and real-time compensation for attenuation properties was under investigation. The set up employs ultrasound in pulsed wave Doppler mode to provide a higher sensitivity for moving objects. Experiments on different tubes (wall-thickness and material) were performed. Glass beads with Gaussian distributed diameters between 300 mum and 400 mum were used as bubble-phantoms. The means and standard deviations of the particle sizes were estimated from the compensated and uncompensated signals. Size estimates were in the range between 100 and 700 mum with a standard deviation of up to 100% when using uncompensated signals. Standard deviations of the estimates applying the compensation algorithm were 50% with mean values of approximately 380 mum. The described method for attenuation compensation was implemented in the bubble counter system BCC200 (GAMPT mbH, Zappendorf, Germany). It enables a precise monitoring of the occurrence of microscopic bubbles and solid particles for the application in open heart surgery and will increase the patient safety. With its performance the BCC200 can also be employed for the development of arterial filters and oxygenators in biomedical applications and for quality control in industrial applications