Delay maps negative

[acalvet-idi]

Hey!
I'm using quantiphyse DSC to analyse stroke perfusion images. One of the most important maps to extract in this matter is the T max (time-to-maximum). I supposed that in your quantiphyse corresponds to the delay as it's descibed as time to peak of the deconvolved signal cure (in seconds). However, the maps obtained contain negative values which I don't understant as we are talking about seconds. Can you tell me why please?

Thank you!