University of Twente Student Theses


Improving signal-to-noise ratio in fluorescence detection for medical purposes

Binsbergen, Sven van and Frentrop, Raimond (2012) Improving signal-to-noise ratio in fluorescence detection for medical purposes.

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Abstract:The main task for this bachelor assignment was to identify the noise of the camera and see if this noise could be reduced to better detect fluorescent dyes used in research on labelling cancer tumors. Labelling tumors with a fluorescent dye enables surgeons to better identify tumors, resulting in a higher percentage of tumor clusters being removed in surgery. Because of the Flat Field Correction of the PixeLINK PL-B761 camera, there was a neglectable amount of dark current noise and flat field noise. The presence of any hot pixels depends on the exposure time. For short exposure times the images taken show that the hot pixels still have low values, much lower than the signal. This means that for short exposure times the noise mainly depends on the random noise (read/quantization noise and shot noise). Thus the exposure time should be chosen as short as possible, but high enough to get a detectable amount of signal. A short exposure time is in this case also advantageous because of the possible application of this technique in living tissue: the human body always moves, caused by all kinds of oscillations from for example the heart, muscles and deliberate movement. To get a sharp image the exposure time should be short. It was also proven that averaging a number of consecutive frames can significantly improve the image quality, by reducing noise and thus increasing the signal-to-noise ratio. Edges of dye-labelled tissue become clearer in this way. For the chosen camera the noise for exposure times smaller than 50 ms does not differ much and is all well below the quantization level (1 level is 64 counts, the average noise is 36 counts). Considering this, modulation of the signal to subtract noise does not improve the image quality by much. Averaging a lot of images still shows a pattern in the read noisewhich can be subtracted by using a noise mask, but for single frames this subtraction more often adds noise to the image instead of removing it. The fluorescent dyes used to label cancer cells can be detected at a short exposure time of 6 ms, even for very low concentrations (3.8 µg/L). The concentration of dye present in mouse tumors was estimated to be 155 µg/L, meaning that small amounts or thin slices of cancer cells will still be detectable by the camera. Colormapping the resulting image greatly improves the usability.
Item Type:Essay (Bachelor)
Faculty:TNW: Science and Technology
Subject:33 physics
Programme:Applied Physics BSc (56962)
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