The behavior of a piezoelectric transducer with a very high electromechanical coupling coefficient close to 1 was analyzed in three steps: intuitive modeling, analytic solution using a 1D model, and numerical simulation using a finite element code. The results were then compared with those from a conventional transducer using PZT, which confirmed that a high coupling coefficient should be utilized to enlarge the bandwidth of the transducer rather than only to increase the sensitivity. The intuitive modeling showed that a piezoelectric transducer with shunt electrodes behaved in a softer manner than with open electrodes. This is equivalent to the fact that the frequency minimizing the electrical impedance of the transducer (resonant frequency) is reduced from the frequency maximizing the electrical impedance (anti-resonant frequency) by the piezoelectricity, and explains why the very high coupling coefficient close to 1 can lead to the wide bandwidth of the transducer.

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Simulation of sound wave propagation is widely used thanks to advances in the computing environment and the spread of simple simulation algorithms such as the finite difference-time domain (FDTD) method. In this paper, the theoretical basis for the analysis of sound wave propagation is described, after which discretization using the FDTD method and the boundary conditions are described. The compact explicit-FDTD (CE-FDTD) method, which is a highly accurate version of the FDTD method, is also described. For application of simulation of sound wave propagation to auralization, sound field rendering, which is a technique for 3-D auralization on the basis of computerized 3-D numerical models, is also described.

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Ultrasonic diagnostic equipment is widely used in the medical field today. In particular, it is an established and indispensable diagnostic technology in obstetrics and gynecology. Recently, however, as high-frequency and high-intensity ultrasound is being increasingly used to expand diagnostic target regions and improve the diagnostic performance, it is necessary to validate the safety of ultrasonic diagnostic equipment. The effects of ultrasound radiation on the human body, including thermal effects, which generate heat, and non-thermal effects, which are mechanical oscillations, need to be investigated. Thermal effects occur as the ultrasound propagating in the body is attenuated and the energy is converted to heat. It is important to understand thermal effects when investigating the safety of ultrasonic diagnostic equipment. To predict thermal effects, it is critical to analyze the sound wave propagation inside the living body, obtain the calorific value of the ultrasound intensity, and analyze the heat conduction inside the living body. In this study, we used numerical simulations to analyze sound wave propagation and heat conduction for focused ultrasound irradiation. We also conducted an analysis of sound wave propagation and heat conduction in the presence of a thick blood vessel in the region of interest inside the living body and studied the effect of blood flow on heat diffusion.

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Ultrasonic B-mode images are affected by changes in scatterer distribution in tissue. It is hard to estimate the relationship between the ultrasonic image and the tissue structure quantitatively because we cannot observe the continuous stages of diseased tissue clinically, particularly the beginning stage. In this review, a simulation method of scattering echo that takes into account tissue acoustic structure is presented. The modeling method of scatterer distribution for normal and diffuse diseased livers can determine the expansion of nodules and fibers. Using B-mode images obtained from these scatterer distributions, we can analyze the relationship between the changes in the form of biological tissue and changes in the B-mode images during progressive liver cirrhosis.

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Purpose: Spatial resolution is one of the important factors that determines ultrasound image quality. In the present study, methods using the phase variance of ultrasonic echoes received by individual transducer elements have been examined for improvement of spatial resolution. Method: An imaging method, i.e., phase coherence imaging, which uses the phase coherence factor (PCF) obtained from the phase variance of received ultrasonic echoes, was recently proposed. Spatial resolution is improved by weighting ultrasonic RF signals obtained by delay-and-sum (DAS) beam forming using PCF. In the present study, alternative PCFs, i.e., exponential PCF, harmonic PCF, and Gaussian PCF, have been proposed and examined for further improvement of spatial resolution. Result: Spatial resolutions realized by the proposed PCFs were evaluated by an experiment using a phantom. The full widths at half maxima of the lateral profiles of an echo from a string phantom were 2.61 mm (DAS only), 1.46 mm (conventional PCF), and 0.48-0.62 mm (proposed PCFs). Conclusion: The PCFs newly proposed in the present study showed better spatial resolutions than the conventional PCF. The proposed PCFs also realized better visualization of echoes from a diffuse scattering medium than the conventional PCF.

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We report a case of idiopathic left atrial appendage (LAA) ostial stenosis found incidentally by transesophageal echocardiography (TEE) prior to radiofrequency catheter ablation for atrial fibrillation. A 65-year-old male had a history of paroxysmal atrial fibrillation (PAF), which had been treated for two years. He was referred to our department for the treatment of drug-refractory atrial fibrillation. TEE performed to search for an atrial thrombus showed a narrowed LAA orifice with a diameter of 3 mm. Color Doppler showed a turbulent flow across the LAA orifice. The peak velocity of the LAA orifice determined by continuous wave Doppler evaluation was 1.2 m/sec. Mild spontaneous echo contrast was observed in the left atrium, but no thrombus was found in the LAA and left atrium. After admission, pulmonary vein isolation with radiofrequency catheter ablation was performed. He had no relapse of atrial fibrillation after ablation therapy. With the exception of incomplete surgical ligation of the LAA, idiopathic LAA ostial stenosis is a rare entity. The etiology and clinical implications of this entity remain unclear. Further investigation will be required to confirm the clinical consequences of LAA ostial stenosis.

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The case involved a 63-year-old female who had complained of a hard reddish lump in the right breast. Although the lump initially appeared to be a phyllodes tumor, histopathology after initial surgery indicated mastopathy as a likely diagnosis. Two years later, regrowth of the lump at the same location prompted revaluation. Ultrasound scan (US) revealed the following features: a) an irregular low-signal lesion with a diameter of 5 cm in the right A region extending toward the hypertrophic epidermis, b) marked increase in blood flow on power Doppler, c) increased thickness between the skin and underlying pectoralis major, and d) irregular and unclear margin of low-echoic lesion. Based on those findings along with clinical symptoms, advanced stage of inflammatory breast cancer was suspected, and a second surgery was performed. Histopathology revealed infiltration of atypical spindle cells around normal mammary ducts, but it did not show the architecture of a phyllodes tumor. The atypical spindle cells were positive for vimentin and CD34 and negative for hormone receptors according to immunohistochemistry. These were consistent with the characteristics of periductal stromal sarcoma. The section diagnosed as mastopathy 2 years previously was re-evaluated by pathologists, and components of stromal sarcoma were found in the section. Stromal sarcoma is rare for the breast region and usually lacks specific features, which may make the precise diagnosis quite difficult. In our case, the following factors contributed to the misleading diagnosis: invasive growth without forming a firm mass, less prominent nuclear pleomorphism and low proliferation index, and inconsistent US features compared to the previous report, etc. The generally poor prognosis of this tumor should demand long-term observation even though no recurrence has been found after the second surgery.

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A 66-year-old female developed chronic thyroiditis with positive conversion of anti-thyroglobulin antibody 17 years after remission of Graves’ disease. She had been euthyroid and did not need hormonal replacement. At a follow-up visit, diffuse goiter and a broad low echoic region were incidentally identified on ultrasonography, and painless thyroiditis (PT) was suspected. She remained hypothyroid for 6 months, and levothyroxine administration was started. Contrary to the general course of PT, her anti-TSH receptor antibody (TRAb) level was exceptionally high. Thyroid-stimulating antibody (TSAb) level decreased during a follow-up period of 14 months (3,930%→127%), and TSH-stimulation blocking antibody (TSBAb) was extremely high (102.7%) at the last examination. Echography showed atypical findings of thyroid blood flow. In PT, the blood flow is generally decelerated during the acute phase and accelerated during the recovery phase, due to the action of thyrotropin. This case presented the opposite pattern; acceleration in the acute phase and deceleration in the recovery phase, probably caused by the change in TSAb and TSBAb levels. There have been some reports in which thyroid autoantibodies changed over time, complicating the disease state. However, there have been no reports of sonographic changes in blood flow. This case demonstrates the importance of echography in conjunction with serologic markers in proper assessment of autoimmune thyroid disease.

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