Hello Noemie,
I hope the attached script will help. Please, note that the script will linearly change the threshold for Spot detection over time. Best would be to allocate the same value for the lowerBoundThreshold2 and upperBoundThreshold2 (lines 31 & 32) to keep it constant (using the attached script)--- you can load the script using the script editor plugin, navigate up to your folder of interest (containing your images for detection), and click on run. An .xls file will be created for each image or each stack; in page 2 of the .xls file, you will find the summary of your detection. In page 1, you will find a more exhaustive description of your detections.
Hope this will help -- otherwise, don't worry, there are a lot of talented people running this platform.
Julien