Medical Ultrasound Imaging
Saturday, 27 April 2024
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The definition of imaging is the visual representation of an object. Medical imaging is a broad term that encompasses various imaging modalities and techniques used in the field of medicine to visualize and study the body's anatomy and physiology. It includes both diagnostic and non-diagnostic imaging procedures, where diagnostic imaging specifically refers to the subset of medical imaging techniques that are primarily focused on diagnosing diseases or conditions. Medical imaging techniques are employed to obtain images or visual representations of the internal organs, tissues, and structures, aiding in the diagnosis, treatment, and monitoring of medical conditions.
The field of medical imaging has significantly evolved since the discovery of X-rays by Konrad Roentgen in 1896. Initially, radiological imaging involved focusing X-rays on the body and capturing the images on a single piece of film within a specialized cassette. Subsequent advancements introduced the use of fluorescent screens and special glasses for real-time visualization of X-ray images. A significant breakthrough came with the application of contrast agents, enhancing image contrast and improving organ visualization. In the 1950s, nuclear medicine studies utilizing gamma cameras demonstrated the uptake of low-level radioactive chemicals in organs, enabling the observation of biological processes in vivo. Currently, positron emission tomography (PET) and single photon emission computed tomography (SPECT) technologies play pivotal roles in clinical research and the diagnosis of biochemical and physiological processes. Additionally, the advent of the x-ray image intensifier in 1955 facilitated the capture and display of x-ray movies. In the 1960s, diagnostic imaging incorporated the principles of sonar, using ultrasonic waves generated by a quartz crystal. These waves, reflecting at the interfaces between different tissues, were received by ultrasound machines and translated into images through computer algorithms and reconstruction software. Ultrasound (ultrasonography) has become an indispensable diagnostic tool across various medical specialties, with immense potential for further advancements such as targeted contrast imaging, real-time 3D or 4D ultrasound, and molecular imaging. The first use of ultrasound contrast agents (USCA) dates back to 1968. Digital imaging techniques were introduced in the 1970s, revolutionizing conventional fluoroscopic image intensifiers. Godfrey Hounsfield's pioneering work led to the development of the first computed tomography (CT) scanner. Digital images are now electronic snapshots represented as grids of dots or pixels. X-ray CT brought about a breakthrough in medical imaging by providing cross-sectional images of the human body with high contrast between different types of soft tissue. These advancements were made possible by analog-to-digital converters and computers. The introduction of multislice spiral CT technology dramatically expanded the clinical applications of CT scans. The first magnetic resonance imaging (MRI) devices were tested on clinical patients in 1980. With technological improvements, such as higher field strength, more open MRI magnets, faster gradient systems, and novel data-acquisition techniques, MRI has emerged as a real-time interactive imaging modality capable of providing detailed structural and functional information of the body. Today, imaging in medicine offers a wide range of modalities, including:
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X-ray projection imaging;
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Fluoroscopy;
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Computed tomography (CT / CAT);
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Ultrasound imaging (US)
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Magnetic resonance imaging (MRI), Magnetic source imaging (MSI);
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Single photon emission computed tomography (SPECT);
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Positron emission tomography (PET);
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Mammography.
These imaging modalities have become integral components of modern healthcare. With the rapid advancement of digital imaging, efficient management has become important, leading to the expansion of radiology information systems (RIS) and the adoption of Picture Archiving and Communication Systems (PACS) for digital image archiving. In telemedicine, real-time transmission of all medical image modalities from MRI to X-ray, CT and ultrasound has become the standard. The field of medical imaging continues to evolve, promising further innovations and advancements in the future, ultimately contributing to improved patient care and diagnostics. See also History of Ultrasound Contrast Agents, and History of Ultrasound.  Further Reading: News & More:
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The traveling ultrasonic wave causes a low-level ultrasound radiation force when this energy is absorbed in tissues (absorbed dose). This force produces a pressure in the direction of the beam and away from the transducer. It should not be confused with the oscillatory pressure of the ultrasound wave itself. The pressure that results and the pressure gradient across the beam are very low, even for intensities at the higher end of the range of diagnostic ultrasound. Mechanical effects like radiation forces lead to stress at tissue interfaces. The effect of the force is manifest in volumes of fluid where streaming can occur with motion within the fluid. The fluid velocities which result are low and are unlikely to cause damage. The effects of ultrasound radiation force (also called Bjerknes Forces) were first reported in 1906 by C. A. and V. F. K. Bjerknes, when they observed the attraction and repulsion of air bubbles in a sound field. While incompressible objects do experience radiation forces, compressible objects driven at their resonant frequency experience far larger forces and can be observably displaced by low-amplitude ultrasound waves. A microbubble driven near its resonance frequency experiences a large net radiation force in the direction of ultrasound wave propagation. Ultrasound pulses of many cycles can deflect resonant microbubbles over distances on the order of millimeters. In addition to primary radiation force, which acts in the direction of acoustic wave propagation, a secondary radiation force for which each individual bubble is a source and receptor causes the microspheres to attract or repel each other. The result of this secondary force is that a much larger concentration of microbubbles collects along a vessel wall than might otherwise occur. See also Acoustically Active Lipospheres. Further Reading: News & More:
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