A familiar example of waves are sound wave in air that are used as a medium for communication without being aware of their presence. At the same time, sound waves, particularly ultrasound are positively utilized as a collection tool of information in non-destructive testing and acoustical imaging. Generally, waves exhibit phenomena like diffraction, reflection, and interference. Radiation pressure is also one of the phenomena that waves have in common with each other. Acoustic radiation pressure is exerted on an interface that separates two acoustically different fluids and is provided by the difference of the acoustic energy densities in both fluids. Hence, it is regarded as a non-zero net pressure of the second order of smallness. Practically, acoustic radiation force is of importance in applications where evaluation is performed by integrating the radiation pressure over an obstacle surface. Although the radiation force is small as well, it can be utilized for non-contact levitation and manipulation of small obstacles by focusing ultrasound waves on them. This report overviews second-order classical phenomena caused by acoustic energy; specifically, the phenomena of waveform distortion, radiation pressure, and acoustic streaming.

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Evaluation of tissue viscoelastic properties is a promising method in ultrasonic wave medical diagnosis, because shear wave propagation characteristics, such as shear wave velocity, shear wave absorption, and dispersion characteristics are closely related to tissue mechanical properties. Several imaging methods based on shear wave propagation have been proposed, and many studies have been done using these imaging systems. However, the estimated shear velocity often does not match with the tissue stiffness identified by hand, and the variation in the measured value is sometimes larger than expected. In this review, characteristics of shear waves are summarized and important points are discussed regarding use of shear waves for tissue characterization. In addition, a shear wave wavefront reconstruction method developed in our laboratory is presented, as well as some phantom and in vivo experimental results.

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The findings of stress echocardiography provide detailed diagnostic information in each cardiac disease. In ischemic heart disease, evaluation of left ventricular (LV) segmental wall motion at rest and with exercise determines the presence of ischemia. In dilated cardiomyopathy, systolic reserve, dyssynchrony, and functional mitral regurgitation (MR) are assessed. A poor prognosis has been reported in functional MR due to exercise-induced worsening. In hypertrophic cardiomyopathy, the LV outflow tract should be assessed because exercise often triggers LV outflow tract obstruction. In organic MR, exercise-induced pulmonary hypertension (PH) is assessed because many patients with exercise-induced PH reveal cardiac events and reduced exercise tolerance. The pressure gradient between the left atrium and ventricle is also evaluated in mitral stenosis; a high pressure gradient requires percutaneous transluminal mitral commissurotomy and/or surgical intervention even in mild mitral stenosis. The pressure gradient between the left ventricle and aorta during exercise and exercise-induced PH stratify risks for aortic stenosis. Stress echocardiography with dobutamine is useful in patients with reduced LV ejection fraction and those with paradoxical low-flow, low-gradient aortic stenosis. In aortic regurgitation, assessment of systolic reserve is recommended even in patients without LV dilatation because it predicts reduced cardiac function after aortic valve replacement. Exercise-induced PH is regarded as useful in the early diagnosis of pulmonary arterial hypertension due to a reduction of the pulmonary vascular bed at an early stage.

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Abdominal ultrasonography is widely applied in cancer screening and/or health checkups, but the quality of screening ultrasonography has not always been well controlled. Recently, three medical societies—the Japan Society of Ultrasonics in Medicine, the Japanese Society of Gastrointestinal Cancer Screening, and the Japan Society of Ningen Dock—jointly published the Manual for Abdominal Ultrasound in Cancer Screening and Health Checkups. This manual is composed of two parts. The first part is Standard Procedure for Abdominal Ultrasound Cancer Screening, and the second is Categorized Criteria for Abdominal Ultrasound Cancer Screening. We expect the manner of screening ultrasonography to be standardized, and its quality well controlled at a high level, based on the propagation of this manual. Also, we hope the efficacy of abdominal ultrasound cancer screening for decreasing cancer mortality will be confirmed in the near future.

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Transperineal ultrasonography (TPUS) is a versatile diagnostic tool in urogynecological outpatient practices. It provides rich information that helps us understand the structural and functional integrity of the pelvic floor and the lower urinary tract. TPUS is subdivided into two classes: translabial ultrasonography (TLUS) and introital ultrasonography (IUS). TLUS is used to detect sites of mechanical failure within the pelvic floor. This procedure is usually performed in the context of dynamic ultrasonography, by normal convex probe adequately covered, with squeezing, coughing, and straining efforts that the subject addresses to the pelvic floor. The subject is normally placed in the gynecologic position during this procedure, but an examination in a semi-crouching position may reveal another pelvic floor weakness that has been masked while the subject was placed horizontally. IUS is an emerging method of examination to detect acoustic alterations in the pelvic floor, by breaking down three-dimensional high-resolution ultrasonographic data. Many of the obstetric injuries in the perineum, in the anus, and in the pelvic diaphragm are visualized by this technique. TPUS helps screen the cases that may benefit from surgical treatment. If this procedure is put in practical use widely by gynecological and urological outpatient clinics, it will enable them to determine which cases should be referred to which advanced medical facilities. TPUS may assume a substantial role in reassigning the tasks in the field of urogynecology, forging a new relationship between clinics and hospitals.

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A 74-year-old male with a chronic kidney disorder was admitted to our hospital because of general malaise and dyspnea during hemodialysis. On his initial visit, he was hypoxic. A chest X-ray showed bilateral congestion shadow and dilatation of heart shadow. He had a diagnosis of acute heart failure. Transthoracic echocardiography (TTE) revealed reduced cardiac ejection fraction and an intramyocardial dissecting hematoma (IDH) at the apical lesion. Based on coronary angiography and myocardial scintigraphy, the hematoma was assumed to have been induced by pre-existing asymptomatic myocardial infarction. This was not a case of acute myocardial infarction, and repeated TTE did not show enlargement of the hematoma or increase in pericardial effusion. Therefore, we treated him conservatively. The fluid volume was controlled with hemodialysis and his symptom improved. He was discharged within about one month. After discharge, the hematoma was invariant for 12 months on TTE, and the patient made steady progress. Although IDH is a potentially lethal disease, we concluded that surgery was not always essential for all patients with IDH based on frequent observations.

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A 40-year-old woman presenting with erythema was admitted to dermatology, where a mass 30 mm in diameter was detected on abdominal computed tomography (CT) at segment 4/8 of the liver. Abdominal ultrasonography (US) showed a hyperechoic mass with cystic change. Contrast-enhanced US revealed homogeneous hyperenhancement in the arterial phase, but consisting of a non-enhanced area with a cystic lesion, and hypoechoic in the post-vascular phase around normal liver parenchyma, with a defect was seen in the Kupffer phase. These findings were not specific for any tumor, so we performed a percutaneous tumor biopsy, and diagnosed primary hepatic neuroendocrine tumor (PHNET). We performed percutaneous transportal embolization before hepatectomy (right trisectionectomy and caudate lobectomy). Immunohistochemically, the tumor cells were positive for the neuroendocrine markers (chromogranin A, synaptophysin) and the Ki-67 index was 1.4%. No primary lesion was found, leading to a classification of primary hepatic neuroendocrine tumor (PHNET) grade 1 and over. PHNET is rare and has a poor prognosis. We report a case of PHNET with a review of the literature.

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