High spike in pi/po scan

I burned on some -/+dvdr media from different companies and I have all the time high spikes in PI/PO graphs , here is an example of it : http://club.cdfreaks.com/attachment.php?attachmentid=21999&stc=1
1.what can cause it?
2.if I have high po like in the image can it make the dvd media to be unreadable in the future?
thanks:)

I just put an attached file of the scan


Did you perform the test with the burner or another drive?

It was scanned by pioneer 108

I see similar spikes when using my Pioneer 108 to read many different discs, disregard these single spikes, as artefacts only.