Peak/Band Detection and Deconvolution Previous Top Next

Peak Detection
Once the raw data has been processed the peaks (bands in gel images) need to be identified.

Peaks are detected as local maxima. A correct peak detection is tricky because the peaks within a sample can overlap. The trace curve is the sum of all peak signals. Small peaks can even hide in more prominent peaks (see the examples below).

Correction
The peak detection algorithm should extract the original peaks from the trace signal. The problem is complicated by overlapping peaks. There are several possibilities how to carry out the peak detection and correction:
·     Curve fitting and calculation of residuals
·     Wavelets
·     Fourier Transformation

The following table illustrates how two overlapping peaks and their heights influence the final appearance of the trace curve. The stronger peak is shown in green and the weaker one in blue. The trace signal is the sum of the peak areas, i.e. the upper red line in the graphs.

Table 1. These images show how the appearance of the final trace data is influenced by the heights and the overlapping areas of two peaks. If the peak bases have an overlap (examples 2. to 4) the trace signal is the sum of individual peak signals.
 Comments The images in this column were generated using peaks with height of 1000 and 100. For all images in this column the peaks exhibit heights of 1000 or 800, respectively. 1. Two non-overlapping peaks Here both peaks are clearly separated. The peaks can be easily detected by searching for local maxima. 2. Two slightly overlapping peaks Both peaks have a slight overlap. The midpoint of the smaller peak is located near the base point of the larger peak. A double peak will be visible in the trace data. 3. Flank overlap The smaller peak has its mid point in the middle of the flanking region of the higher peak. If the smaller peak is much more weaker than the higher one, a shoulder is visible (left image). The right image shows a shoulder on the left side of the stronger peak. Please note: The location of the weaker peak is exactly the same as in the left image. 4. Near center overlap If the peak maxima are close together shoulders are hardly visible. However, this also depends on the height-to-width-ratio of the individual peaks.

See