An ultrasonic method to measure coagulation time for prothrombin time (PT) is discussed. This method is based on the measurement of ultrasonic scattering from spherical glass particles of 200-microns diameter kept in motion, inside of a holder containing 0.1 ml of plasma, by ultrasonic energy. The incident wave (2.7 MHz) not only keeps the particle in motion but also is the source for the scattered waves. A receiving transducer captures part of the scattered wave and generates at its electrical output a signal containing amplitude and phase fluctuations. The motion of the particles are strongly influenced by the rheological changes during the process of coagulation. When the clot is formed, the amplitude of the motion of these particles is significantly reduced and so the fluctuations on the received signal stop. The time from the start of the coagulation process until the end of the fluctuations at the received signal is the coagulation time. Experimental results demonstrate that the ultrasonic method has precision and accuracy compatible to those provided by the manual tilt-tube method when PT is measured with normal and abnormal samples of human plasma.

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Diffraction correction functions are assessed using a tissue equivalent calibrated phantom and compared to the theoretical model of Chen et al.

Ultrasonic attenuation coefficient, wave propagation speed and integrated backscatter coefficient (IBC) of human coronary arteries were measured in vitro over the -6 dB frequency bandwidth (36 to 67 MHz) of a focused ultrasound transducer (50 MHz, focal distance 5.7 mm, f/number 1.7). Corrections were made for diffraction effects. Normal and diseased coronary artery sub-samples (N = 38) were obtained from 10 individuals at autopsy. The measured mean ± SD of the wave speed (average over the entire vessel wall thickness) was 1581.04 ± 53.88 m/s. At 50 MHz, the average attenuation coefficient was 4.99 ± 1.33 dB/mm with a frequency dependence term of 1.55 ± 0.18 determined over the 36-to 67-MHz frequency range. The IBC values were: 17.42 ± 13.02 (sr.m) -1 for thickened intima, 11.35 ± 6.54 (sr.m) -1 for fibrotic intima, 39.93 ± 50.95 (sr.m) -1 for plaque, 4.26 ± 2.34 (sr.m) -1 for foam cells, 5.12 ± 5.85 (sr.m) -1 for media and 21.26 ± 31.77 (sr.m) -1 for adventitia layers. The IBC results indicate the possibility for ultrasound characterization of human coronary artery wall tissue layer, including the situations of diseased arteries with the presence of thickened intima, fibrotic intima and plaque. The mean IBC normalized with respect to the mean IBC of the media layer seems promising for use as a parameter to differentiate a plaque or a thickened intima from a fibrotic intima.

In order to characterize ultrasonic (US) transducers, several aspects may be studied, such as the shape of the beam in space, the US intensity along the central axis and the US intensity parallel to the face of the transducer. With focused beams, a focal region is usually defined. The need for a unique point in space to represent the focus may arise in theoretical models (for example, in geometrical acoustics).In this paper we present a least mean square method to estimate the focal position of US beams in two dimensions (2D) and some simulated and experimental results.