Diagnostic ultrasound is an ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons and many internal organs to capture their size, structure and any pathological lesions using real-time tomographic images.
Ultrasound has been used by radiologists and sonographers to image the human body for many years and has become one of the most widely used diagnostic tools in modern medicine. The technology is relatively inexpensive and portable, especially when compared with other techniques, such as digital radiography magnetic resonance imaging and computed tomography.
Diagnostic ultrasound is a noninvasive medical test that helps physicians diagnose and treat medical conditions. Ultrasound images of the musculoskeletal system provide pictures of muscles, tendons, ligaments, joints and soft tissue throughout the body.
Diagnostic ultrasound is also used to visualize fetuses during routine and emergency prenatal care. Such diagnostic applications used during pregnancy are referred to as obstetric sonography.
The diagnostic ultrasound involves exposing a targeted part of the body to high-frequency sound waves to produce pictures of the inside of the body. Ultrasound exams do not use ionizing radiation. Nonetheless, care should be taken to use low power settings and avoid pulsed wave scanning of the fetal brain, unless specifically indicated in high-risk pregnancies.
Because ultrasound images are captured in real-time, they can show the structure and movement of the body’s internal organs, as well as blood flowing through blood vessels.
Diagnostic ultrasound scanners have different Doppler-techniques to visualize arteries and veins. The most common is color Doppler or power Doppler, but also other techniques are used to show blood flow in an organ. By using pulsed wave Doppler or continuous wave Doppler blood flow, velocities can be calculated.
Diagnostic ultrasound has the advantage of not needing direct contact with the inner limbs of the body. Consequently, the transducer diagnostic ultrasound part can be moved and angulated for the best possible scan view. Typical diagnostic ultrasound parts consist of front-end, beam former, back-end and application blocks.
The front-end block diagnostic ultrasound part contains the transducer, the transducer elements switching system, the transmitter power amplifier, the low noise input amplifier and the analog to digital converter. The beam forming is achieved by a factory programmed integrated circuit diagnostic ultrasound part.
The back-end diagnostic ultrasound part includes various imaging reconstruction and enhancement algorithms. Color Doppler, harmonic, deconvolution, non-linear processing, frequency, special compound, and scan conversion with interpolation are the most commonly used technologies.
The applications become more and more important in the current trend of ultrasound imaging systems. PC-based applications are adopted in current commercial systems. They provide friendly user interface, easy-access database, remote diagnostic, and data-storage for later analysis. Phased array is widely used in the transducers of diagnostic ultrasound systems.
The beam-former diagnostic ultrasound part of the transmitter determines the delay pattern and pulse train that set the desired transmit focal point. The outputs of the beam-former are then amplified by high-voltage transmit amplifiers that drive the transducers. These amplifiers may be controlled digitally to shape the transmit pulses for better energy delivery to the transducer diagnostic ultrasound part elements. Typically, multiple transmit focal regions are used.
The field to be imaged is divided up, by focusing the transmitted energy at progressively deeper points in the body. The main reason for doing this is to increase the transmitted energy to points that are deeper in the body, because the signal becomes thinner and weaker as it travels into the body.
In diagnostic ultrasound systems, the echo signal sampling is the start of the back-end process. The acquired signals can be combined to extract the useful part of the signal. Next, a user-controlled amplifier sets the information signals amplitude, in order to achieve the best image.
The application block of the diagnostic ultrasound is designed to process the basic information in various ways. It can, for example, generate 2D, 3D and 4D images, harmonic imaging (the second harmonic image has greater clarity, contrast and detailing than the fundamental frequency range) and color Doppler. It can also improve the image quality by filtering out noise and artifacts.
Last, but not least, the scan conversion takes the filtered data of the diagnostic ultrasound and puts it into a presentable form for display. It converts the polar coordinates to rectangular pixel positions. Normally this interpolation is done at the same time during conversion.