Ultrasound irradiation of tissue and cells is effective in enhancing drug targeting, lowering systemic drug toxicity, and improving drug absorption rates. Ultrasound catheters to enhance the effects of thrombolytic agents have proven beneficial in treating patients with acute stroke, deep vein thrombosis, and pulmonary embolism in ongoing clinical trials. The revival of ultrasound for use in therapy after decades of dormancy has brought attention to usage in various fields such as thrombolysis, vascular therapy, cancer therapy, regenerative medicine, and gene therapy. Efficient delivery of a drug into target cells or tissues for therapeutic purposes has always been a big challenge requiring multidisciplinary efforts by experts in different scientific fields. Recent studies have shown that combining microbubbles and ultrasound energy could be applied to targeting or controlling drug release. In this paper, several therapeutic systems are cited as well as the mechanisms of ultrasound-mediated drug delivery. Current advances in molecular imaging and therapy will also be discussed.

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Management of patients with aortic stenosis (AS) relies on accurate assessment of symptoms, AS severity, and left ventricular ejection fraction (LVEF). AS severity is best described by the measurements of maximum velocity, mean gradient, and valve area. In clinical practice, some patients have an apparent discrepancy in stenosis severity between those defined above. The continuous wave beam parallel to the stenotic jet should be taken using the best of multiple windows to avoid measurement error. Loading conditions influence velocity and pressure gradients; therefore, these parameters vary depending on cardiac output. Hence, no single calculated number should be relied on for final judgment. Evaluation of AS based on data obtained from echocardiography will play a more and more important role in the grading of AS.

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Although palpation, joint range of motion, and measurement by hardness meter are used to represent muscle hardness, all of them have some weak points. Palpation is easy and cost-effective, but it is a subjective method. Joint range of motion may represent muscle hardness indirectly, but it is influenced by bony abnormalities, tight capsule, shortening of the ligament, and adhesion of the joint. Hardness meter is an objective method, but it measures the total hardness under skin tissue. US elastography produces a two-dimensional hardness map, so we can measure the hardness of each muscle. Compartment syndrome is characterized by severe pain and extremely hard muscles caused by high intra-muscular pressure. Delayed diagnosis and treatment are known causes of severe physical impediment. US elastography made it possible to visualize the affected muscles, allowing us to perform selected fasciotomy with small skin incision and intra-operative monitoring under US elastography. As muscle hardness changes with the status of activities of daily living and sports, knowing muscle hardness may be useful for improving performance and avoiding injuries associated with daily and sports activities.

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Purpose: Development of a technique to confirm the focus position in advance is desired for safe and reliable treatment with high-intensity focused ultrasound (HIFU). The purpose of this study is to induce displacement by means of acoustic radiation force generated by a low-energy HIFU pulse to make displacement images using ultrasound, and visualize the focal spot. Subjects and Methods: The optimal interval between the end of exposure and observation of displacement may differ in the case of sensitivity and accuracy. Hence, we set the time interval between the end of exposure and imaging of the focal spot to 0.3 ms, 0.8 ms, and 1.3 ms to compare the predicted focal spot with the actual thermocoagulation spot by HIFU. The experiment sample was porcine liver. Results and Discussion: The sensitivity was sufficient at every time interval. On the other hand, accuracy decreased as the time interval increased. A thermocoagulation spot with a size of 1.1 mm×3.6 mm was predicted with accuracy of 0.8 mm at 0.3 ms, but due to a change in displacement distribution, the accuracy and precision decreased at 0.8 ms and 1.3 ms. This result was explained with shear wave propagation. It became clear that it was necessary to consider the speed of shear waves in order to visualize the focal spot correctly when configuring the conditions for making displacement images. Conclusion: Using focal spot imaging, the operator can predict the thermocoagulation spot in advance. This technique overcomes the issue of targeting the focal spot during HIFU exposure, and since it is a compact system using an ultrasonic device, use of HIFU treatment may become more widespread at medical institutions for a wider range of diseases.

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