Principles, Structure, and Troubleshooting of Ultrasound Diagnostic Systems

 The  B-ultrasound diagnostic system is a product of the combination of acoustic, electronic, computer, and medical biological sciences. Ultrasound diagnosis plays a very important role in modern medicine. Ultrasound diagnosis is a non-invasive, non-radiation imaging diagnostic method. B-ultrasound imaging, radioisotopes, X-CT, and magnetic resonance imaging together constitute the four major imaging technologies of modern medicine. Doppler ultrasound systems are indispensable tools for the diagnosis of heart disease and cardiovascular diseases. Our hospital has introduced B-ultrasound equipment since 1978 and has purchased and used B-ultrasound diagnostic instruments of various models from many manufacturers.  
        B-ultrasound is a commonly used device in hospitals, with high frequency of use and many malfunctions. Due to its complex machine system structure and various models, especially since some devices do not have repair manuals, it has brought great difficulties to the maintenance work. However, although the instrument models vary and manufacturers are different, the basic working principles of the B-ultrasound system are the same. The structure is also similar. Therefore, it is possible to quickly and accurately find the fault point and repair the machine in the shortest possible time by familiarizing oneself with the basic principles of the B-ultrasound diagnostic system, using the information provided by the machine's self-test system as a clue, and analyzing the structure and function of the instrument in detail.   

   1. Principles and Instrument Structure of B-ultrasound Diagnostic System The B-ultrasound diagnostic system is divided into several parts according to its structure: mainly the probe, transmitting and receiving circuits, analog signal processing circuits, keyboard control circuits, digital scan converters, image display circuits, and power supply circuits.

Probes can be divided into linear array scanning probes and phased array scanning (sector scan) probes according to their scanning methods. The basic principle of linear array scanning is that several transducers are arranged in a linear array to form a linear array transducer. An electronic switch is used to control the transducers to work in turn, sequentially exciting from one side of the probe to the other side, generating the transmission and reception of a synthesized beam. The basic principle of phased array scanning is that different excitations are given to each element of the linear array, and the excitation pulses applied to each element have an equivalent time difference, so that the direction of the synthesized beam has a phase difference with the normal direction of the element array plane. By uniformly changing the time difference, the phase difference also changes uniformly. Through time control, the phased array scanning of the ultrasonic beam is realized, that is, sector scanning. The B-ultrasound diagnostic instrument uses luminance modulation to display the reflected echoes of all interfaces in the depth direction. By using a fast scanning method in the horizontal direction, the ultrasonic echoes are transmitted and received sequentially, and a two-dimensional ultrasonic tomographic image in the vertical plane, that is, a linear scan tomographic image, can be obtained. If the angle of the ultrasonic beam is changed to perform fast scanning, a two-dimensional ultrasonic tomographic image in the vertical fan-shaped surface, that is, a sector scan tomographic image, is obtained. The transmitting circuit provides excitation voltage to the probe, and realizes the scanning and focusing of the ultrasonic system beam through the control and excitation delay of different arrangements and combinations of the transducers. The receiving circuit performs phase shift synthesis of the ultrasonic echo signal. The analog signal processing circuit includes a preamplifier, TGC circuit, dynamic filter circuit, logarithmic amplifier circuit, etc. The ultrasonic echo signals obtained by the image detection circuit and Doppler detection circuit are further processed by the scan converter. The essence of the digital scan converter is a digital image processing system with an image memory. Its main function is to realize the digitization of ultrasonic signals, and then process them, and finally realize TV display on the monitor. The image processing circuit includes gray-scale processing, histogram processing, data interpolation processing, etc. The main purpose is to improve the image quality.   

2. Troubleshooting and Repair Methods for B-ultrasound Diagnostic Systems

First, before carrying out specific repair work, as a professional engineering and technical personnel engaged in B-ultrasound repair, one should first be familiar with the working principle and specific circuit structure of this type of machine. This will help to understand the various phenomena manifested by the fault from the essence of the fault and improve the repair quality.

Second, before carrying out specific repairs, one should also first be familiar with the main functions of the instrument and various functional operations related to repair. In this way, from the various functions and the interrelationship between various functional operations, it is helpful to compress the fault range, find the fault location of the instrument, and shorten the repair time.   
       
Third, before repair, carefully observe and investigate various phenomena before and after the fault occurs, especially to understand the occurrence process and background of the fault in detail from the operator. B-ultrasound is a large and expensive instrument, and repair work is a complex project. Without a full understanding of the fault situation and accurate judgment of the nature of the fault, do not rashly repair.   
       
Fourth, the power supply part is one of the parts where faults frequently occur in the B-ultrasound diagnostic system. Because the power supply part consumes large power and has high temperature, the failure rate is also high. The manifestations of power supply failures are also diverse, often manifested as failures of the entire system or a part of the system. Faults caused by interference introduced by the power supply part that prevent the instrument from working normally also belong to this category. In most cases, the normal operation of the power supply part should be checked first.   
       
Fifth, the peripheral part of the B-ultrasound diagnostic system is also a part where faults often occur, but the peripheral part is relatively intuitive, the structure is not complex, and each part is relatively independent, so the fault diagnosis and location are relatively easy. For example, monitors, trackballs, printers, etc., I have learned in the repair center that the elimination of such faults is relatively simple.   
       
Sixth, for the remaining components of the ultrasound diagnostic system, such as various system circuit boards, due to the high degree of circuit integration and mostly special-purpose devices, usually only board-level maintenance can be achieved. In the process of fault finding and diagnosis, the circuit principle should be followed, combined with the description of the fault background and phenomena by the instrument operator, the fault codes displayed by the instrument, one's own understanding and investigation of the instrument fault phenomena, and other aspects for comprehensive judgment to determine the fault location. If there are B-ultrasound machines with the same or similar models, the same circuit boards can be found and swapped to find the fault.  

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