Ultrasound medical imaging equipment has experienced more than half a century of development, especially since the 1990s, with the rapid development of medical, mechanical materials, computer, and electronic engineering technologies, the performance of ultrasound diagnostic instruments has been continuously improved, functions have been continuously improved, and Applications have been continuously expanded. Now, no hospital can be separated from ultrasound imaging diagnostic technology. Ultrasound imaging diagnosis has the characteristics of high spatial resolution, high soft tissue contrast, real-time fast imaging, simple operation method, no contraindications, no damage, repeatable, portable, and economical. Together with CT, MRI, and isotope imaging, it constitutes the four indispensable imaging diagnostic technologies in clinical medicine.
I. Overview of the Application of Ultrasound Imaging Diagnostic Technology in Medicine
The application of ultrasound imaging diagnostic technology in medicine began in the mid-20th century. Initially, it only used A-type ultrasound instruments to detect the thickness of isolated organs and explore some clinical disease diagnoses; then, M-type ultrasound instruments were used to detect the hearts of normal people and patients with rheumatic heart disease; until the early 1970s, B-type ultrasound imaging technology, which can display changes in the morphology and structure of organs and lesions, was applied clinically, opening a new page for two-dimensional cross-sectional ultrasound imaging examination technology. In the mid-1980s, color Doppler ultrasound diagnostic instruments came into being. Because it can display both the morphological structure and hemodynamic changes of organs and lesions, it has further advanced the level of ultrasound imaging diagnostic technology. Until the 1990s, the widespread application of computer digital technology and the successful research of medical ultrasound three-dimensional imaging technology have brought ultrasound imaging diagnostic technology into a higher level and a new development stage. In other words, from the end of the last century to the beginning of this century, the development of ultrasound imaging diagnostic technology has been amazing, and it has made many significant technological breakthroughs. Throughout the development process of ultrasound imaging diagnostic technology, it is a process from "point" (A-type ultrasound) → "line" (M-type ultrasound) → "surface" (two-dimensional ultrasound) → "body" (three-dimensional ultrasound); it is a process from one-dimensional array to two-dimensional array to three-dimensional array; it is a process from static imaging to real-time dynamic imaging; it is a process from single-parameter diagnostic technology to multi-parameter diagnostic technology; it is also a process from anatomical structure morphology imaging to anatomical structure function imaging, metabolic imaging, enzyme and receptor and gene expression imaging fusion molecular imaging process.
II. Application of Digital Technology in Ultrasound Imaging Diagnostic Equipment
The digitalization of ultrasound diagnostic instruments, from the digital scan converter to today's fully digital ultrasound emission, reception, and imaging process, digital technology has been widely adopted by high-performance ultrasound imaging diagnostic equipment, such as new probe encoding emission and reception technology, digital acoustic beam technology, digital delay technology, dynamic aberration technology, dynamic electronic focusing, dynamic aperture technology, etc. The development and application of digital technology have also promoted and driven the high performance, intelligence, and miniaturization of ultrasound imaging diagnostic equipment. High-performance ultrasound imaging diagnostic devices can not only meet the various needs of clinical disease diagnosis, but also conduct in-depth research on relevant basic theories and clinical medicine, thereby further promoting the development of ultrasound imaging diagnostic technology from pure morphology to morphology, physiology, function, and molecular imaging. Intelligence can realize one-button operation, such as one-button multi-function, which can adjust TGC, receiving gain, dynamic range, and speed scale, Doppler baseline and many other parameters, thus avoiding complex and cumbersome adjustment operations during the examination. The miniaturization of ultrasound instruments under the premise of ensuring the required functions, its device structure is simple, such as the size of a laptop computer, whether it is bedside examination or outpatient or emergency rescue examination, it can better reflect the important clinical status and value of ultrasound imaging diagnostic technology, and at the same time, it also broadens the clinical application range of ultrasound diagnostic technology. In addition, with the rise of the information superhighway and the widespread application of communication and network technologies, ultrasound imaging diagnostic equipment of different manufacturers and different models currently have DICOM3.0 standard interfaces. In the DICOM3.0 standard, it not only covers the data dictionary, information interaction, network communication, media storage and file format, display printing, and management directly related to medical imaging, but also has a trend of gradually covering the capacity and data information exchange in the entire medical environment. In other words, ultrasound imaging diagnostic equipment or ultrasound imaging workstations can be integrated into the hospital image management and communication system (PACS), and even into the entire hospital information system.
III. Development of Ultrasound Imaging Diagnostic Instrument Probe Technology
The probe, also known as the transducer, is one of the most important components of an ultrasound imaging diagnostic instrument. Its main function is to emit ultrasound into the human body and then receive the ultrasound echo signals from the human body. High-performance and high-quality probes are not only a prerequisite for obtaining high-quality images, but also a technical guarantee for various new ultrasound imaging methods. The structure of the probe generally consists of three parts: the main body, the shell, and the wire. Among them, the piezoelectric material (chip) is the core of the main body. From single-chip, multi-chip to tens, hundreds, or even thousands of chips, and the number of probe array elements composed of several chips in parallel is constantly expanding. At present, the main development trends of probes are new materials, new processes, multi-array (high-density), high-frequency, wide-band, and special-purpose. New materials: mainly include composite materials and organic film materials; new processes: that is, piezoelectric ceramics and polymers are combined according to a certain connection method, a certain volume ratio, and a certain spatial geometric distribution, which has the advantages of high sensitivity, low impedance (favorable for matching with human tissues), and lower mechanical quality factor (favorable for bandwidth widening); high density: 1D (256 elements), 1.5D (8 × 128 elements), 2D (60 × 60 elements); high frequency: 3MHz - 7MHz frequency probes are used to diagnose abdominal and heart diseases, 10MHz-15MHz frequency probes are used to examine superficial organs, 20MHz-40MHz frequency probes are used for ultrasound imaging of eyes and skin, and 100MHz-200MHz frequency probes are mainly used for ultrasound microscopes; wide band: wide band refers to the upper and lower limits of the transducer's operating frequency, which can achieve emission and reception of ultrasound echo signals of different frequencies from high to low from shallow to deep during examination with one probe, and is also an important guarantee for realizing frequency domain composite imaging, harmonic imaging, and other nonlinear imaging new technologies; special-purpose: that is, the probe is made into a special shape, such as special-purpose intracavitary probes used for examinations of the esophagus, rectum, vagina, urethra, bladder, abdominal cavity, and blood vessels.
IV. Development of Several New Imaging Technologies in Ultrasound Imaging Diagnosis
1. Ultrasound three-dimensional imaging technology
Three-dimensional ultrasound imaging technology is a major breakthrough in the field of ultrasound diagnostic technology and an emerging new technology in clinical ultrasound. It can obtain image information in three-dimensional space, thus compensating for the shortcomings of two-dimensional planar imaging technology. According to the imaging principle, three-dimensional imaging technology can be divided into static three-dimensional imaging for observing non-moving organs and dynamic three-dimensional imaging and real-time three-dimensional imaging for observing the morphology and activity of the heart. Static three-dimensional imaging uses a two-dimensional probe for rotational scanning or fan-shaped scanning to acquire several sectional images within a certain period of time, which are then fed into a computer for image reconstruction to display a three-dimensional stereoscopic image of the organ. The reconstructed image is clear, with clear boundaries, strong surface contour and depth stereoscopic sense, and the morphology of the organ and lesion is characteristic. It is mainly used for organs with liquid presence or those surrounded by liquid, such as liver and kidney cysts and abscesses, biliary calculi and polyps, hydronephrosis and tumors; three-dimensional image reconstruction of the pancreas and duodenum can observe the three-dimensional anatomical structure of the pancreatic head and surrounding tissues, which is helpful for the diagnosis of pancreatic head and common bile duct lesions; three-dimensional vascular reconstruction can realize a tree-like image of blood vessels without substantial tissue reflection, which is helpful to understand the course, branching condition, malformation, and thrombosis of blood vessels in organs; it also has distinct characteristics for sand-like structural lesions such as ulcers, fetal facial deformities, and umbilical cord around the neck. In addition, three-dimensional ultrasound imaging can provide doctors with the spatial position and three-dimensional morphology of tumor lesions in the body, thus providing more accurate positioning information for ultrasound-guided interventional therapy, which helps to improve and further enhance the clinical treatment effect.
With the development of high-speed scanning and sampling technology, by adding the time parameter of electrocardiogram synchronization technology on the basis of static three-dimensional imaging, dynamic three-dimensional imaging (also known as four-dimensional parameter) with quasi real-time display can be realized; if speed information is added, real-time three-dimensional imaging (also known as five-dimensional parameter) can be realized. Dynamic three-dimensional imaging can display the origin, location, direction, and anterior-posterior and left-right relationships of large blood vessels, observe whether there are defects and judge the location, morphology, and size of defects, providing diagnosis and differential diagnosis for complex and difficult congenital heart diseases; it can accurately display the three-dimensional morphology of the heart, more precisely determine the cardiac function, observe the location, range, and degree of segmental wall motion disorders, providing diagnostic and therapeutic basis for coronary heart disease; it can display the overall structure of the valve orifice, which is of great significance for the diagnosis of valve stenosis and insufficiency, especially mitral valve leaflet rupture and prolapse, tendinous cord rupture and other valvular diseases; it can also display the three-dimensional dynamic image of intracardiac blood flow, which is of great significance for observing blood flow direction, reflux, and shunt. In short, dynamic three-dimensional imaging technology observes the three-dimensional morphology, spatial relationship, activity, and blood flow dynamics of various structures of the heart from different angles, thus greatly improving the accuracy of clinical diagnosis.
2. Panoramic Ultrasound Imaging Technology
Panoramic ultrasound imaging technology, also known as ultra-wide-field imaging, expanded field of view imaging, or panoramic ultrasound imaging technology, obtains a series of two-dimensional sectional images through probe movement and uses computer reconstruction methods to stitch these two-dimensional images into a continuous ultra-wide-field sectional image. The main characteristics of panoramic ultrasound imaging technology are that it can provide better structural hierarchy and spatial relationship, clearly display the location, size, range, internal echo, and adjacent areas of lesions, accurately measure the size and volume of large lesions or tumors, and better display and extend the pipeline structure. The main disadvantage is that it is susceptible to interference from the movement of tissues or organs, resulting in blurred images. Panoramic ultrasound imaging technology has been widely used in the diagnosis of diseases of the chest and abdomen, obstetrics and gynecology, breast, thyroid, testis and other small organs, as well as muscles, blood vessels and peripheral nerves in limbs and trunk. A panoramic ultrasound image can completely display the entire breast, and the obtained image morphology is the same as the natural morphology of the breast, with clear breast anatomical layers, clear lesion characteristics, obvious contrast in imaging of different tissue structures, and clear display of the relationship between breast augmentation surgery filling materials and pectoralis major muscle and mammary gland. A panoramic ultrasound image can also obtain the entire fetal image that cannot be obtained by conventional two-dimensional ultrasound, including the complete structure including the placenta. It is of great value for the judgment of multiple pregnancies, fetal position, assessment of amniotic fluid volume and distribution, placental localization, measurement and grading. In particular, for the limbs and trunk soft tissues, high-frequency linear array probes are used for large-area rapid tomographic scanning to obtain a panoramic tomographic anatomical image from the skin, subcutaneous tissue, muscle, tendon, blood vessel, peripheral nerve trunk, and periosteum, and the characteristics of each layer structure are clear at a glance. Panoramic ultrasound imaging technology has great development potential and good application prospects. Combining it with conventional real-time grayscale and color Doppler ultrasound will make modern ultrasound diagnostic technology more perfect, and it also lays the foundation for the research and application of ultrasound CT.
3. Molecular Imaging Technology
Molecular imaging is an imaging method that uses modern imaging technology, based on molecular biology, to study and observe the occurrence, development, pathophysiological changes, and metabolic functional changes of diseases at the molecular level, that is, to determine and describe in vivo biological processes at the cellular and molecular levels. This professional term first appeared in the late 1990s and was officially proposed and applied by the National Cancer Institute of the United States in 1998. Unlike traditional imaging methods, molecular imaging reveals the cellular and molecular abnormalities that cause human diseases, rather than the final anatomical and tissue structural abnormalities caused by changes in cells or molecules. Clinically, because many diseases have obvious changes in their function or cell molecules before pathological changes occur in the organs and tissues, therefore, through cell molecular imaging technology, not only can diseases be detected and determined earlier, but also the therapeutic effect of diseases can be directly evaluated at the cellular and molecular levels, thus establishing a new scientific understanding of the occurrence, development, and healing process of diseases. In molecular imaging, ultrasound uses targeted microbubble contrast agents such as monoclonal antibodies and peptide molecules for targeted diagnosis of cardiovascular diseases and tumors, treatment of thrombi and atherosclerotic plaques, and delivery of drugs and genes. Microbubbles and acoustically active substances can be used as targeted contrast agents for ultrasound imaging, carrying targeting ligands that can bind to living cells for molecular imaging and therapy. Targeted micro/nanobubbles have opened a new frontier in molecular imaging. Molecular imaging is the result of the combination of multiple disciplines such as molecular biology, biochemistry, nanotechnology, genetic engineering technology, data processing, and image processing, and is also a revolutionary development and the inevitable trend of future development of modern medical imaging technology.
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