Basic steps and methods of full digital B-ultrasound imaging (personal opinion arrangement)

Through a large number of literature studies, the basic steps of B-ultrasound imaging include:Beam formation, digital signal processing, and digital image processing.

Digital beam synthesis is the basis for digital signal processing and imaging in the later stage. It is also the first step in the long journey. Direct image imaging is the result of beam synthesis.

Digital beam synthesis usually requires basic processing technologies such as focusing technology, dynamic aperture, and amplitude-trace transformation. Before the beam is formed, the ultrasonic echo signal needs to be amplified and A/D converted. Early A/D conversion of the Ultrasonic Echo Signal is performed, this helps us to transplant digital signals to PCs for processing, reducing hardware costs and difficulty in development.

Digital beam synthesis technology is a hot research technology in digital B imaging systems over the years. It is also the most important technology in the digital technology of ultrasonic systems. This technology involves three steps: focusing on technology, amplitude variation technology, and dynamic aperture technology. Each step is very difficult to implement, in addition, the imaging modes corresponding to the structures of different ultrasound systems also have an impact, making it more difficult to reasonably match each link. If the digital beam synthesis technology can be well implemented in the ultrasonic imaging system, the resolution of the image can be significantly improved, the dynamic range can be increased, and the random noise can be reduced based on the existing hardware platform of the ultrasonic system, obtain better ultrasonic image quality.

In digital beam synthesisFocus on TechnologyThere are three kinds of focus Methods: Fixed-Point focus, dynamic focus, and segmented dynamic focus. They are respectively studied to compare their implementation process and the obtained ultrasonic image quality effects.

In the sound field formed by the transmission and receipt of ultrasonic signals, apart from the main lobe that determines the image resolution, the beam also has some side lobe. One of the reasons for the production of a pseudo image is that its size will affect the final image quality. The technical way to suppress the side lobe is to adopt the amplitude variation technology. ImplementationAmplitude VariationThe method is to apply the amplitude weighting to the transmitted (or received) element, which usually maximizes the emission strength of the central element and minimizes the emission strength of the edge element, the specific amplitude functions can be different.

The so-calledDynamic ApertureIn the receiving mode, only a few central elements are activated at the beginning to receive ultrasonic signals. Other elements are in the closed state. As the receiving depth increases, more and more receiving channels are enabled, and the receiving aperture increases gradually until the depth increases to the maximum, and all receiving elements are enabled.

After the beam synthesis, the ultrasonic echo signal has completed focusing, tracing, and variable aperture processing, forming an ideal beam distribution in the detection space, then we need to process such echo signals, including dynamic filtering, envelope detection, and log compression.

After the echo signal is synthesized by a digital beam, it entersDynamic FilteringIn this phase, dynamic filtering is proposed to solve the different attenuation of ultrasonic energy at different frequencies in human tissues. The Implementation of Dynamic Filtering is directly related to the imaging resolution of the digital B super imaging system. It is another key component of the imaging system.

After the echo signal is dynamically filtered, it is obtained that both the amplitude and the phase are modulated. To further obtain the echo amplitude information for imaging, this must be performed hereEnvelope Detection.

The ultrasonic signal after the envelope detection is a amplitude envelope line of the ultrasonic signal, and the value of the envelope line cannot be directly imaged. Because the value range of the normally obtained envelope line after normalization is between [0,255], while the imaging grade of the ultrasound imaging system is generally, the original value range of the envelope line needs to be mapped to the imaging interval of the ultrasound imaging system. Generally, ing is not performed in a linear manner, that is, 2 1u = 255 U, 1u is the original value of the envelope, and 2u is the value of the mapped imaging, this linear ing method is ineffective in ultrasound imaging of reflected echo signals in non-strongly focused areas. The commonly used ing method isLog Compression.

after digital signal processing, digital image processing technology must be used to process and optimize digital signals. This process needs to be applied to the digital scanning and transformation technology (coordinate transformation, linear interpolation) and frame-related technology. The Ultrasonic Echo Signal received by the convex array probe is a sector-shaped area ultrasonic scanning in the form of polar coordinates. If the signal is directly scanned and the image is displayed in Cartesian coordinates, the result will be incorrect, therefore, Coordinate Transformation is required. The coordinate point after coordinate transformation does not necessarily fall into the receiving scanning line of the convex array probe, nor is it necessarily in the depth corresponding to the echo data point. Therefore, we need to use linear interpolation to obtain the value of the Change Point. Generally, we use 4-point linear interpolation. When a relatively static human organ is scanned by ultrasound, the obtained B-ultrasound image is superimposed on multiple images for average processing, so that noise on the image is restrained, this is the idea of frame-related .