The charge-coupled device (CCD) was developed originally for a different reason. It originally replaced the television camera in the fluoroscopic chain.
The part that is sensitive in the CCD is a layer of crystalline silicon. When the silicon illuminates, an electrical charge is generated, which is then bundled into a sampling pixel by pixel, and than manipulated, to produce a digital image.
The CCD is mounted on the output phosphor of the image-intensifier tube and is coupled together by fiber optics or a lens system.
The main advantage of a CCD system is their small size and durability.
The spatial resolution of a CCD is determined by its physical size and pixel count.
Systems with a 1024 matrix (as mentioned in Digital Fluoroscopy Part I) can produce images with 10 lp/mm (line pairs/millimeter).
Television cameras show spatial distortion what is sometimes known as to “pin cushioning” or “barrel artifacts”.
There is no such distortion of these types with a CCD units.
The CCD has a higher sensitivity to light which is known as detective quantum efficiency (DQE) and has a lower level of electronic noise than you find on a television camera.
The sensitivity, or quantum efficiency, is simply the fraction of incident photons detected on the chip.
There is on average an 80% efficiency.
Because of this, there is higher signal-to-noise ratio (SNR) and better contrast resolution.
This results in lower patient exposure dose and the CCD response to light is consistent.
The CCD does not need to be warmed up and the image does not demonstrate a delay or lag in being seen.
The CCD unit itself has little or no maintenance.
The main feature of a CCD is it's response. In general, it has what is known as a linear response, which means as the exposure increases the response increases and as the exposure decreases the response decreases in a linear fashion.
Other image receptors have a sigmoid-shaped (S-shaped) response, which makes it difficult to image either very dim or very bright objects.
Information found on the graph in the high and low regions on a sigmoid shaped of response are lost.
The key point is with the linear response it makes it very useful for subtraction imaging (taking out only the important information from the image).
The result is improved dynamic range (images in motion) and better contrast resolution (shades of gray and blacks and whites are seen better).
END- Digital Fluoroscopy-Part II
Disclainer: "Capital Medical Equipment, Inc. and Sharon Moore will not be held liable for written materials within this blog or any future blogs. This blog was created as an educational tool and for no other purpose. It will be prohibitted by law to copy, reprint or publish this material without written permission of the author or Capital Medical Equipment, Inc."
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