High-Precision Digitization--DALSA Life Sciences

High-Precision Digitization

It takes high-precision digitization to preserve the dynamic range of a good sensor

What is involved in high-precision digitization?

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"High-precision digitization" usually means providing 12, 14, 16 or more bits of detail (e.g. 65536 gray levels). This level of detail is critical for x-ray imaging in order to capture subtle variations--you must be able to tell the difference between healthy tissue and lesion, for example, to be sure you've removed all of a tumor.

Anyone can digitize to 14 or 16 bits, but the important part is providing 14 or 16 bits of signal, and not 8 bits of signal with 6 bits of noise. Signal-to-noise ratio is key, and since medical applications would generally prefer to keep their x-ray dose as low as possible ("first, do no harm"), medical imagers need to deal with very low signal levels. That makes noise reduction paramount.

The output noise from a CCD camera (the signal output when the camera receives no incident energy such as light or x-rays) is ultimately limited by the noise generated by the CCD's on-chip output amplifier. The best noise performance is achieved when the operating level of the output amplifier is set to produce its lowest noise level and all other noise sources within the CCD are suppressed well below this level. Achieving this goal requires very careful adjustment of CCD operating voltages and clock levels and the elimination of a phenomena known as kTC noise. kTC noise is a function of temperature and some of the characteristics of the CCD design (such as the FET gate switch capacitance). Proper electronic design uses techniques such as cooling and correlated double sampling (CDS) to virtually eliminate kTC noise.

Because the output amplifier noise is the ultimate limit to CCD noise performance, the actual system noise achieved by the camera's CDS circuits is strongly related to the rate at which pixel data is processed. The rms output noise is proportional to the square root of the pixel processing rate (quadrupling the data rate doubles the rms noise). As a result, camera designs must trade off speed with noise performance.

Why does DALSA Life Sciences excel?

With years of experience and expertise, DALSA Life Sciences has honed its low-noise techniques. We use some of the best CCDs in the industry, carefully optimizing their voltages and clock levels to minimize noise. All DALSA Life Sciences cameras use CDS, and we use effective cooling, slow scan rates, and proprietary technology to ensure the images we capture have the lowest noise possible.

For more information, contact Sales.