Principles, Structure, and Common Troubleshooting and Repair of Electronic Endoscopes

Electronic endoscopes place a miniature charge-coupled device (CCD) at the tip of the endoscope. The CCD converts dynamic optical images into electrical signals, which are then processed and stored by the image processing center. The images are then reproduced on a monitor and output by a printing device.

01

Main Characteristics of Image Sensors

(1) Spectral Characteristics:

CCD image sensors have a very wide photosensitive spectral range, usually extending to the infrared region. Using this characteristic, with auxiliary infrared light source illumination at night, the CCD can also produce clear images. N-P structure CCDs have high sensitivity, but these CCDs are prone to halos and trailing in strong light; N-P-N structure CCDs can effectively suppress halos and trailing caused by strong light irradiation, but this reduces sensitivity, and the spectral range is compressed to the visible light region [1].

(2) Resolution:

Generally represented by the device's modulation transfer function, this is one of the important parameters of a CCD image sensor.

(3) Dark Current:

Image sensors generate electron-hole pairs due to thermal excitation, resulting in the generation of electrical signals even in non-illuminated environments. Dark current limits the sensitivity and dynamic range of the device; its magnitude is related to the ambient temperature. As the temperature decreases, the dark current decreases.

(4) Sensitivity and Dynamic Range:

Sensitivity is generally expressed by the minimum illuminance. High sensitivity requires that a relatively clear image can be output even under very low illuminance; a wide dynamic range of the image sensor requires the ability to proportionally collect the signal charge generated by the minimum to maximum light amounts into the potential well. The dynamic range depends on the difference between the maximum charge amount that the potential well can collect and the minimum charge amount determined by noise.

(5) Pixels:

Refers to the maximum pixel value of the sensor. Some provide the number of pixels in the horizontal and vertical directions, such as 822H × 508V; others provide the product of the first two, such as 410,000 pixels. A larger value indicates a higher image resolution.

02

Basic Structure of Electronic Endoscopes

Electronic endoscope equipment includes the endoscope, image processing center, and cold light source. The endoscope is composed of seven parts, including the operating section.

(1) Operating Section:

Includes a biopsy valve, suction button, air/water injection buttons, angle adjustment button, and angle locking button. The operating section is connected to the image processing center via a remote control switch.

(2) Distal End:

Includes the CCD, forceps channel opening, air/water injection nozzles, and fiber optic terminal.

(3) Insertion Section:

Includes two bundles of light guide fibers, a CCD video signal cable, a water injection tube, an angle adjustment wire, and a biopsy channel. These tubes are wrapped in a metal mesh, with a polyester sheath over the metal mesh.

(4) Bending Section:

The angle adjustment knob controls the bending of the endoscope's bending section up, down, left, and right, with a maximum angle of 180°～210° up, 180° down, 160° left, and 160° right.

(5) Electronic Processing Section:

Includes the light guide fiber bundles and video signal cable. The video signal cable is connected to the CCD at the distal end of the electronic endoscope and, along with the light guide fiber bundles, passes through the insertion section and operating section to couple with the electronic endoscope light source and image processing center. In addition, air/water injection tubes are also included.

(6) Connecting Section:

In addition to the light source head, air injection connector, suction tube connector, and water bottle interface, the electronic endoscope connecting section also has a video cable connector.

(7) Air/Water Injection and Suction/Biopsy System:

The design of the air/water injection and suction/biopsy channels in the electronic endoscope is the same as that of a fiber endoscope. An electromagnetic air pump is also installed inside the electronic endoscope light source and is connected to the air/water injection pipes. A suction nozzle is connected to the negative pressure suction end at the connection between the endoscope and the light source.

(8) Image Processing Center:

The image processing center, also known as the electronic endoscope host, processes the photoelectric signals transmitted by the endoscope and reproduces them on the monitor screen. The processing center has an average light/peak switching function, ensuring that the brightness of any part of the image is optimal; in addition, it also has an automatic white balance function to ensure that the image colors are not distorted. The electronic endoscope has image freeze and dynamic/static switching functions. After the main image is frozen, a secondary image is displayed in the lower corner, facilitating comparative observation of local lesions. The recording system records the endoscope images to the hard disk and can be output via a printer. Monitors used to display all information currently include cathode ray tubes (CRT), liquid crystal displays (LCD), and plasma displays (PDP) [2].

(9) Cold Light Source:

The cold light source provides high-brightness illumination for the image sensor, generally using a high-pressure xenon lamp. An electromagnetic air pump is also installed inside the light source.

03

Common Malfunctions and Repairs

3.1 Malfunction 1

Malfunction: No image.

Cause: Broken cable inside the bending section.

Solution: Replace the internal cable.

3.2 Malfunction 2

Malfunction: Intermittent image.

Cause: Short circuit inside the cable.

Solution: Carefully check for the short circuit point, cut it, reinstall it, and adjust the cable direction.

3.3 Malfunction 3

Malfunction: Image color distortion.

Cause: Leakage from forceps channel, water/air tube, or bent rubber; poor sealing of objective lens and prism.

Solution: Immediately heat and dry the leaking area for more than 48 hours; replace the faulty part and reseal.

3.4 Malfunction Four

Malfunction: Foggy image in the center.

Cause: Aging of the CCD sealant at the tip.

Solution: Remove the sealant, fold the bent rubber, dry for more than 48 hours, and reseal.

3.5 Malfunction Five

Malfunction: Image becomes blurry after use for some time.

Cause: Slight seepage at the tip of the forceps channel tube.

Solution: Remove the original sealant and tip cap; seal with mixed adhesive at the forceps channel fixed tube.

3.6 Malfunction Six

Malfunction: Irregular lines in the image.

Cause: Scratched CCD objective lens glass.

Solution: Replace the objective lens glass.

3.7 Malfunction Seven

Malfunction: Blurry image.

Cause: Contaminated CCD cover glass.

Solution: Clean the cover glass.

3.8 Malfunction Eight

Malfunction: Normal brightness in close-up images, dark brightness in distant images.

Cause: Xenon lamp light decay exceeds the threshold, resulting in decreased brightness.

Solution: Replace with a new xenon lamp [3].

04 

Summary

Electronic endoscopes are now widely used in clinical practice. Mastering the principles, structure, and common troubleshooting of electronic endoscopes is particularly important for personnel in the medical engineering profession.

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