Counting and determining size and shape of nanoparticles

[monaco]

Hello all,

I am starting to use ImageJ for the purpose of nanoparticle characterization of TEM images. I currently use the PSA macro (http://code.google.com/p/psa-macro/) to analyze TEM images but encounter a few problems. If the background is somewhat different from image to image, it is difficult to set the same threshold for all pictures, so size of the particles might be therefore different from image to image which is severe in those dimensions. Another problem is the crossover particle-background which is sometimes blurry and therefor hard to find the exact end of the particle. My question is now is there any macro available which makes evaluation easier or lets say more similar for each image, so that evaluation is the same with the same threshold for every image.
Moreover is there any possibility to determine or evaluate ellipses? Some of the particles seem to have an elliptic shape and I do not want to miss them because of lack in circularity. Ideal would be a macro which also counts the ellipses and determines area (A=pi*ab) and converts this area to a particle with a spherical shape and calculate the radius of this spherical shape.
Wow so many questions. I appreciate any help and look forward to you answers and hints!
Thank you so much.

Regards,
monaco