It is often necessary to inspect a region inside a confined area. In medicine, an endoscope is used to look inside the body to examine organs. Endoscopes can examine gastro-intestinal, respiratory and urinary tracts as well as internal organs through a small incision. An endoscope captures images through its long tube, which can be rigid or flexible. Additional instruments for cutting, grasping and other functions are often attached to the endoscope to permit minimally invasive procedures that improve patient care and minimize recovery time. When used in a technical application to inspect confined spaces, it is often referred to as a borescope. Borescopes are used to inspect machinery interiors, building walls and to search for victims in collapsed buildings.
Endoscopes, or borescopes, have three basic requirements in common:
- A light source and tube are used to guide the light to the subject A light source to illuminate the subject
- A tube to guide the light to the subject
- A lens or fiber optic system to capture light reflected from the subject
- An image-capture system to capture, process and store or display the image
TI’s broad product portfolio supports the entire image chain: generating light, capturing an image, signal conditioning and image processing.
LED drivers supply a bright light source with excellent directionality and minimal waste heat. These drivers are versatile and permit selection of LEDs optimized for an application’s spectral requirements. The resolution of current steps impacts the precision of the illumination control; 14-bit LED controllers allow for precise control of illumination levels and illumination timing.
The image sensor detects the reflected light and converts the light to an analog electrical signal. Depending on the image sensor’s location, low-noise line drivers may be needed to transmit the signal over the light tube’s length. Critical considerations for line drivers are low power, noise immunity and data rate. LVDS technology provides up to 800Mbps with voltage swings of a few tenths of a volt and high rejection of common-mode noise.
Essential to the final image quality is the Analog Front-End, AFE. The AFE conditions the sensor’s analog electrical signal and converts image information to a digitized representation. Critical to AFE selection is the ability to condition the signal to correct sensor-induced distortions such as: dark current cancellation; reset level variations; defective pixel correction; and DC off-set variations. Depending on the signal level, the presence of Programmable Gain Amplifiers (PGAs), the linearity of the PGAs and the range of gains available may also be important. During digitization, the number of bits will determine the contrast of the image. Typically, one wants to digitize the initial data with two to four bits more precision than is desired in the final image. Thus, if 8-bits of final image data are required, then initially digitize to 10-bits to allow for rounding errors during image processing. Finally, when color reproduction is critical, then the Differential and Integral Non-Linearity (DNL, INL) should be minimized.
Endoscope: A lighted optical instrument used to get a deep look inside the body and examine organs such as the throat or esophagus. An endoscope can be rigid or flexible.
Specialized endoscopes are named depending where they are intended to look. Examples include: cystoscope (bladder), nephroscope (kidney), bronchoscope (bronchi), laryngoscope (larynx + the voice box), otoscope (ear), arthroscope (joint), laparoscope (abdomen), and gastrointestinal endoscopes.
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