Comet Labs WN591 Manual de usuario descargar pdf (Pagina 5)

Help! There is a comet in my computer! 2

An annoying problem with computers is that, unless they crash, they will always give you

a result. The above story is true, but it is not about the comet assay. Nevertheless, it is

about measurement of the amount of DNA in nuclei on a microscope slide (to determine

genome size in different organisms). I have to admit here that I have never prepared one

single microscope slide for the comet assay. But I recently tried to find out how the comet

assay works and I talked to researchers and students from several comet labs. While I got

excellent explanations about DNA damage and variations in the procedure for preparation

of the slides, the image analysis part of the experiment was more obscure. In most cases,

the researchers bought the software and hardware, and then started to click. They had no

time to study image analysis. Still, it is not really sensible to treat the only part of the

experiment in which parameters are measured as a tightly closed “black box”.

Here are some arguments from the comet world. A colleague called me on the phone one

day saying that she noticed abnormal values for the comet parameters in recent

experiments. None of the researchers that spent days and months with the comet machine

knew what went wrong. I only saw this machine once for an hour or so. Nevertheless, I

was able to diagnose the problem and also propose the solution after only a few minutes of

phone conversation. How did I do it? Well, I previously borrowed the software user

manual, and because I know the principles of image analysis, I also understood how the

black box works.

On another occasion, I had the idea to write a macro program for the comet assay. So I

borrowed a CD with comet images from another colleague, who was then a comet

beginner using another comet software package than the one mentioned above. When I

viewed the images on my computer, I realised that there was something wrong with image

contrast. In addition, quite a few spots on the image were overexposed, which means

completely white. With such images, you do measure something with your computer, but

your results are either imprecise or wrong. Optimising the settings of the camera solved the

problem.

Now let us open the “black box”.

Although I tried to do my best, some statements in the following chapters may be incorrect. Please send your

corrections and other comments to barbara.vi[email protected].

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Comet Labs WN591 Manual de usuario Pagina 5