I have been working on an exemple of segmentation, for this exemple a threshold must be provided :: isolatedConnected->SetLower( lowerThreshold )
So can any one give me an idea how can I specify this threshold for my image
and thank you in advance .

Thresholds are always content-specific. Take a look a the image in a viewer (e.g. Slicer), examine the intensities of the organs of interest, and that will give you an idea of what values you should supply as thresholds.