Raster-step size

The raster step size can be set to any desired value, but in the case of these experiments the step size was set to 120 xm, the same size of the laser spot size, to avoid over-sampling and to allow for repeated analysis of the same tissue section (6). 

D/A converters to generate raster. scan voltages. An important point to be noted is that D/A converters have finite step sizes. A typical D/A converter has a full range of 10 V, with 12-bit accuracy. Each step is 20 V/4096=4.88 mV. By using it directly to drive the x, y piezo with a typical piezo constant of 60 A/V, each step is about 0.3 A. If amplification is installed, the step size becomes larger. 

Typically, the tissue is rastered at step sizes equal to the laser spot size, but step sizes smaller than the laser spot size (oversampling) or even larger than the laser spot... 

Set the step size of the laser rastering, which determines the pixel number of the MALDI image. Typically, a step size of 60 (xm is used for brain tissue within the size range of 15-30 mm ( ggNote 10). 

Raster scans over single living cells were carried out with a computer-controlled x,y-stage in 2 pm steps at a laser spot size of 4xl0 cm. All experiments on the cell culture were carried out at 830 nm excitation. 

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