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A highly sensitive capacitive micromachined ultrasound transducer (CMUT) cell with an ultra-narrow gap was investigated. The electromechanical coupling coefficient (kT) as a figure of merit of sensitivity of ultrasound transducers was 0.67 in a 30-MHz CMUT cell with a 30-nm height vacuum gap and in 100-nm thick dielectric layers, and the coefficient was superior to that of piezoelectric transducers...
We have developed and here propose a novel capacitive micromachined ultrasound transducer (CMUT) cell structure that has a long breakdown lifetime against high DC bias voltage. The structure extends the distance between the top and bottom electrodes by means of an additional insulating layer inserted at the cavity edge. The structure's electric breakdown voltage was increased by 1.2 times so that...
Capacitive micromachined ultrasound transducers (CMUTs) have emerged as a candidate for ultrasound transducers to achieve high resolution imaging. To achieve high quality tissue harmonic imaging (THI) with a sufficient signal-to-noise ratio (SNR), we propose a novel harmonic signal extraction technique named amplitude modulated pulse inversion (AMPI) with low frequency (LF) component. The AMPI+LF...
Tissue harmonic imaging (THI) based on amplitude modulation by controlling the number of driving elements (AM-CNDE) with a prototype CMUT probe is demonstrated. AM-CNDE requires multiple transmission pulses and the amplitude of each pulse is controlled by changing the number of driving channels in a probe. The harmonic signals are extracted clearly even if the CMUTs have large nonlinearity. The beam...
Artery-wall motion due to the pulsation of the heart is often measured to evaluate mechanical properties of the arterial wall. Such motion is thought to occur only in the arterial radial direction because the main source of the motion is an increase of blood pressure. However, it has recently been reported that the artery also moves in the longitudinal direction. Therefore, a 2D motion estimator is...
Red blood cell (RBC) aggregation, which is one of the induces showing blood viscosity, plays an important role in blood rheology. RBC aggregation is formed by adhension of RBCs because electrostatic repulsion between RBCs weakens as protein and saturated fatty acid in blood increase. Excessive RBC aggregation promotes various circulatory diseases in the clinical situation. The purpose of this study...
Recently, cardiovascular disease has become the second most common cause of death in Japan following malignant neoplasm formation. Therefore, it is necessary to diagnose atherosclerosis during its early stages because atherosclerosis is one of the main causes of cardiovascular diseases. The carotid sinus is a site that is easily affected by atherosclerosis [C. K. Zarins et al.: Circ. Res. 53 (1983)...
Pathological changes in arterial walls significantly influence their mechanical properties. We have developed a correlation-based method, the phased tracking method, for measuring the regional elasticity of the arterial wall. Using this method, elasticity distributions of lipids, blood clots, fibrous tissue, and calcified tissue have already been measured in vitro. However, these elasticity distributions...
To provide useful information for diagnosis of atherosclerosis in addition to the imaging of morphology using the B-mode ultrasonography, we have developed a method in which an elasticity image is classified into tissue components using the reference data obtained by in vitro experiments. We have already measured the elasticity distributions for lipids, blood clots, fibrous tissue, and calcified tissue...
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