Over the past decades, ultrasound imaging technology has made tremendous progress in obtaining important diagnostic information from patients in a rapid, noninvasive manner. Although the technology has benefited from sophisticated signal processing technology and imaging system integration, much of this progress has been derived from the development of ultrasonic transducers that are in direct contact with patients. An overview of medical ultrasonic imaging transducers is presented in this review that describes their structure, types, and application fields. The structural components of a typical transducer are presented in detail including an active layer, acoustic matching layers, a backing block, an acoustic lens, and kerfs. The types of transducers are classified according to the dimensions of ultrasound images: one-dimensional array, mechanical wobbling, and two-dimensional array transducers. Advantages of each transducer over the other and the technical issues for further performance enhancement are described. Application of the transducers to various clinical imaging fields is also reviewed.
Acoustics ; Diagnostic Imaging* ; Humans ; Transducers* ; Ultrasonics* ; Ultrasonography

No abstract available.
Ultrasonography*

Conventional biomedical imaging modalities in wide clinical use, such as ultrasound imaging, X-ray computed tomography, magnetic resonance imaging, and positron emission tomography, can provide morphological, anatomical, and functional information about biological tissues. However, single mode imaging in conventional medicine provides only limited information for definitive diagnoses. Thus, combinational diagnosis using multiple imaging modalities has become increasingly important. Recently, photoacoustic imaging (PAI) has gained significant attention, and several PAI prototypes have been used in clinical trials. At the same time, PAI has been tested in combination with conventional imaging modalities. For all these imaging modalities, various contrast-enhancing agents have been developed for various purposes. In this review article, we will focus on recent progress in developing dual mode contrast agents for PAI in combination with other conventional imaging modalities.
Contrast Media ; Diagnosis ; Magnetic Resonance Imaging ; Positron-Emission Tomography ; Tomography, X-Ray Computed ; Ultrasonography

With focused ultrasound (FUS) and microbubbles, BBB can be transiently disrupted with a localized and non-invasive approach. BBB disruption induced by FUS has made progressions to move forward on delivery of therapeutic agents into a brain in a specific area of brain for better treatment of neurological diseases. In addition to be used as an improvement of drug delivery, BBB disruption has been found to induce biological effects such as a clearance of protein aggregation which cause Alzheimer's disease, regulation of proteins which facilitate drug uptake, and modulation of neuronal function and neurogenesis. In this review, we discuss overview about the principles of BBB opening with FUS and milestones in these biological effects of FUS-induced BBB disruption.
Alzheimer Disease ; Brain ; Microbubbles ; Neurogenesis ; Neurons ; Ultrasonography*

The concept of focused ultrasound (FUS) and its application in the field of medicine have been suggested since the mid-20th century. However, the clinical applications of this technique in central nervous system (CNS) diseases have been extremely limited because the skull inhibits efficient energy transmission. Therefore, early application of FUS treatment was only performed in patients who had already undergone invasive procedures including craniectomy and burr hole trephination. In the 1990s, the phased array technique was developed and this enabled the focus of ultrasonic energy through the skull, and in conjunction with another technique, magnetic resonance thermal monitoring, the possibility of applying FUS in the CNS was further strengthened. The first clinical trial using FUS treatment for CNS diseases was performed in the early 21(st) century in patients with glioblastoma, which consists of highly malignant primary brain tumors. However, this trial resulted in a failure to make lesions in the tumors. Various causes were suggested for this outcome including different acoustic impedances across heterogeneous intracranial tissue (not only brain tissue, but also fibrous or tumor tissue). To avoid the influence of this factor, the targets for FUS treatment were shifted to functional diseases such as essential tremor, Parkinson's disease, and psychiatric disease, which usually occur in normal brain structures. The first trial for functional diseases was started in 2010, and the results were successful as accurate lesions were made in the target area. Nowadays, the indication of FUS treatment for functional CNS diseases is gradually widening, and many trials using the FUS technique are reporting good results. In addition to the lesioning technique using high intensity FUS treatment, the possibility of clinical application of low intensity FUS to CNS disease treatment has been investigated at a preclinical level, and it is expected that FUS treatment will become one of the most important novel techniques for the treatment of CNS diseases in the near future.
Acoustics ; Brain ; Brain Neoplasms ; Central Nervous System Diseases ; Central Nervous System* ; Essential Tremor ; Glioblastoma ; Humans ; Parkinson Disease ; Skull ; Trephining ; Ultrasonics ; Ultrasonography*

HIFU (high-intensity focused ultrasound) ablation is an emerging therapeutic modality that induces thermal coagulative necrosis of biological tissues by focusing high-energy ultrasound waves onto one small spot. This technique is at various stages of clinical applications in several organs. However, it has increasingly been used in the treatment of symptomatic uterine fibroids, a common condition affecting women. Since its first clinical use for symptomatic uterine fibroids, this technique has been recognized for safety, satisfactory therapeutic efficacy in symptom control, uterus-preserving ability, radiation-free nature, and because of the fact that it does not require hospitalization. Owing to its numerous benefits, HIFU ablation is currently one of the major therapeutic options for symptomatic uterine fibroids. In this review, several aspects ranging from the physical principle of HIFU to the long-term outcomes are summarized from the perspective of the clinical application for uterine fibroids.
Female ; High-Intensity Focused Ultrasound Ablation* ; Hospitalization ; Humans ; Leiomyoma* ; Necrosis ; Ultrasonic Waves

Recent studies have shown that real-time, two-dimensional shear-wave elastography (2D-SWE) can monitor liver fibrosis by measuring tissue elasticity (i.e., elastic modulus). Two clinical studies of 2D-SWE in the liver have shown that there are several practical issues that can compromise quantitation of liver tissue elasticity. Both general ultrasound (US) limitations and limitations in the 2D-SWE method itself resulted in significant variability in estimated liver elasticity. The most common US limitations were: poor acoustic window, limited penetration, and rib/lung shadows. The most common 2D-SWE limitations were: reverberations under the liver capsule, respiratory/cardiac motion, and vessel pulsation/loss of SWE signal. Based on these studies, scan protocols have been optimized to minimize the influence of these limitations on liver elasticity quantification. These refined protocols should move non-invasive SWE closer to becoming the preferred tool to diagnose and manage many chronic diseases of the liver.
Acoustics ; Artifacts* ; Chronic Disease ; Elasticity ; Elasticity Imaging Techniques* ; Fibrosis ; Liver Cirrhosis ; Liver* ; Methods ; Ultrasonography

Ultrasound was developed several decades ago as a useful imaging modality, and it became the second most popular diagnostic tool due to its non-invasiveness, real-time capabilities, and safety. Additionally, ultrasound has been used as a therapeutic tool with several therapeutic agents and in nanomedicine. Ultrasound imaging is often used to diagnose many types of cancers, including breast, stomach, and thyroid cancers. In addition, ultrasound-mediated therapy is used in cases of joint inflammation, rheumatoid arthritis, and osteoarthritis. Microbubbles, when used as ultrasound contrast agents, can act as echo-enhancers and therapeutic agents, and they can play an essential role in ultrasound imaging and ultrasound-mediated therapy. Recently, various types of ultrasound contrast agents made of lipid, polymer, and protein shells have been used. Air, nitrogen, and perfluorocarbon are usually included in the core of the microbubbles to enhance ultrasound imaging, and therapeutic drugs are conjugated and loaded onto the surface or into the core of the microbubbles, depending on the purpose and properties of the substance. Many research groups have utilized ultrasound contrast agents to enhance the imaging signal in blood vessels or tissues and to overcome the blood–brain barrier or blood-retina barrier. These agents are also used to help treat diseases in various regions or systems of the body, such as the cardiovascular system, or as a cancer treatment. In addition, with the introduction of targeted moiety and multiple functional groups, ultrasound contrast agents are expected to have a potential future in ultrasound imaging and therapy. In this paper, we briefly review the principles of ultrasound and introduce the underlying theory, applications, limitations, and future perspectives of ultrasound contrast agents.
Arthritis, Rheumatoid ; Blood Vessels ; Breast ; Cardiovascular System ; Contrast Media ; Inflammation ; Joints ; Microbubbles* ; Nanomedicine ; Nitrogen ; Osteoarthritis ; Polymers ; Stomach ; Thyroid Neoplasms ; Ultrasonography*

The most troublesome of ultrasonic B-mode imaging is the difficulty of accurately diagnosing cancers, benign tumors, and cysts because they appear similar to each other in B-mode images. The human soft tissue has different physical characteristics of ultrasound depending on whether it is normal or not. In particular, cancers in soft tissue tend to be harder than the surrounding tissue. Thus, ultrasound elasticity imaging can be advantageously used to detect cancers. To measure elasticity, a mechanical force is applied to a region of interest, and the degree of deformation measured is rendered as an image. Depending on the method of applying stress and measuring strain, different elasticity imaging modalities have been reported, including strain imaging, sonoelastography, vibro-acoustography, transient elastography, acoustic radiation force impulse imaging, supersonic imaging, and strain-rate imaging. In this paper, we introduce various elasticity imaging methods and explore their technical principles and characteristics.
Elasticity Imaging Techniques ; Elasticity* ; Humans ; Methods ; Ultrasonics ; Ultrasonography*

In this paper, we extend our previous work on deformable image registration to inhomogenous tissues. Inhomogenous tissues include the tissues with embedded tumors, which is common in clinical applications. It is a very challenging task since the registration method that works for homogenous tissues may not work well with inhomogenous tissues. The maximum error normally occurs in the regions with tumors and often exceeds the acceptable error threshold. In this paper, we propose a new error correction method with adaptive weighting to reduce the maximum registration error. Our previous fast deformable registration method is used in the inner loop. We have also proposed a new evaluation metric average error of deformation field (AEDF) to evaluate the registration accuracy in regions between vessels and bifurcation points. We have validated the proposed method using liver MR images from human subjects. AEDF results show that the proposed method can greatly reduce the maximum registration errors when compared with the previous method with no adaptive weighting. The proposed method has the potential to be used in clinical applications to reduce registration errors in regions with tumors.
Humans ; Liver ; Methods