Basic structure of an ultrasound diagnostic instrument

Ultrasound diagnostic instruments, as precise and expensive clinical diagnostic medical equipment, are now widely used in hospitals at all levels. Although there are many brands and model specifications, the working principle is basically the same: the instrument emits ultrasonic waves through the probe, and the ultrasonic waves produce reflections at the interface of various tissues in the human body. Due to the different reflected waves of various tissues, the probe receives reflected waves containing characteristic information of various tissues, and then transmits them back to the host for signal reconstruction and image processing, finally storing the image and displaying it on the monitor. According to the principle and daily maintenance, we can roughly divide the ultrasound diagnostic instrument into the following parts: probe, host, power supply, monitor, and peripherals.

The probe is one of the core components of the ultrasound diagnostic instrument, and it is expensive. Due to frequent use, it is the easiest part to be damaged. The probe is generally composed of a transducer, acoustic lens, housing and sheath, cable, and other accessories. In addition, 3D and 4D probes also have a drive motor. In general, it is possible to preliminarily judge whether there is a fault by interchanging the probe or placing the ear close to the probe to listen for the working sound of the probe.

The transducer is an important component of the probe, also known as a crystal or sound head, which is made of piezoelectric ceramics. Its task is to convert electrical signals into ultrasonic signals for transmission and to convert ultrasonic signals into electrical signals after reception. Long-term use of the transducer will cause natural aging, and incorrect use or external impacts such as dropping or bumping will also cause damage to the crystal, resulting in image reduction, shadows, black stripes, interference, missing parts, and blind areas. If there are obvious dark channels in the ultrasonic image, after ruling out faults in the cable and acoustic lens, it can generally be preliminarily judged as a crystal fault, and the fault is mostly caused by a short circuit in the chip. The short circuit of the chip can be judged by measuring the supply voltage of the chip. If the supply voltage of a certain chip or chip group is lower than that of others, it can be judged that there is a short circuit in the chip or chip group. Replacing the corresponding chip or chip group restores the probe to its previous characteristics, and the interference disappears.

3. Acoustic Lens

The acoustic lens is a gel-like special substance on the top of the probe that contacts the human body. Long-term use will cause natural wear, scratches, cracks, corrosion, degumming, and blistering, especially corrosion caused by the coupling agent entering the underlying layer, which will not only cause artifacts and blind areas, but more seriously, it will damage the probe crystal or cause leakage, endangering the patient's body. Therefore, if this situation occurs, timely repair and replacement should be carried out to ensure safety and avoid greater losses. The acoustic performance of the acoustic lens fault is manifested as local shadows in the ultrasonic image, but if appropriate force is applied to the shadow area, the shadow will disappear. This method can quickly distinguish whether it is a problem with the acoustic lens or the sound head.

The housing is the outer casing of the sound head, and damage is usually caused by accidents. After the sound head casing is broken, the coupling agent will penetrate into the probe, causing oxidation and corrosion of the sound head crystal. In addition, the 3D and 4D probe housings also contain the freezing oil of the cooling motor, and the breakage of the housing will cause liquid leakage. Therefore, the fault of the sound head housing also needs to be repaired as soon as possible. The sheath is a rubber sleeve that strengthens the connection between the probe and the cable. Its function is to prevent the cable from being bent at a right angle. If it is damaged, it will damage the quality of the shielding layer, causing image interference and unclear images. If the cable is broken, it will further affect the ultrasonic image, and in severe cases, it may even cause leakage.

The cable is composed of hundreds or even hundreds of multi-core, highly shielded cables with high quality requirements, generally including signal lines, ground lines, control lines, and power lines. The voltage of the ultrasonic transmitting and receiving signal lines during transmission is more than one hundred volts. Cable faults can lead to system crashes, black lines, interference, probe non-recognition, and ghosting. Cables, especially those near the sound head, are in a bent state for a long time, which can cause damage to the cable outer skin and even breakage, making them unusable. When the above faults occur, the faulty part of the cable generally needs to be cut and reconnected, and sometimes the entire cable needs to be replaced.

Now, the host of the ultrasound diagnostic instrument generally includes a front-end part and a computer control part. The front-end part generally consists of a transmitting pulse generation, control circuit, ultrasonic signal receiving and processing circuit, digital scanning conversion device, digital image processing circuit, and other modules. Damage to these modules can cause the probe to fail to work, no image in the sector, interference in the sector image, artifacts, and various other faults. It is generally possible to determine the fault range by exchanging or plugging and unplugging modules. The fault location can also be preliminarily judged through fault code prompts and circuit board indicator lights. The computer control part is generally composed of a high-configuration PC or industrial motherboard. The principle is the same as that of a general computer, and the faults are similar, such as hard disks, graphics cards, memory sticks, and system software, which are all parts prone to faults.。

The function of the power supply module is to convert AC power into various working voltages required by various parts of the machine; the power supply is also a part where faults frequently occur in ultrasound diagnostic instruments. Due to power grid fluctuations and high power consumption and temperature of the power supply part, the failure rate is very high. The manifestations of power supply failures are also diverse, often manifested as failures of the entire system or a certain part of the system. Interference introduced by the power supply part that prevents the instrument from working normally also belongs to this type of fault. When the fault range cannot be determined, the operation of the power supply part is generally checked first. In particular, rectifying bridges, voltage regulators, and field-effect transistors, which are high-power, high-current, and high-heat-generating components, are extremely prone to burnout and damage.

The monitor is similar in principle to an ordinary computer monitor, except that it has higher resolution. Faults often occur in the scanning part, with the highest failure rate in the line scanning part. Similar to the power supply part, the line scanning part works under high voltage and high current, consuming more than half of the monitor's power. During normal operation, there are a series of heat-generating components, such as the line output tube, line output transformer, and line correction coil. When the heat dissipation is poor, these components can be damaged due to overheating or the circuit board can be opened.

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