Dear Lucy, dear David,
There's a so-called AAL-VOI version of the AAL atlas included in the commercial PMOD software, see http://doc.pmod.com/pneuro/6750.htm#o6751 , and this atlas has indeed some labels for the pons. I don't think it's available anywhere else, but I might be wrong.
It might be possible to derive a (preliminary) version of the probabilistic brainstem atlas and/or some of the labels as displayed in Iglesias et al. (2015, https://dx.doi.org/10.1016/j.neuroimage.2015.02.065 ). You would have to ensure that the labels agree well with the MNI space of your PET template.
Finally, based on http://adni.loni.usc.edu/methods/pet-analysis/ there seem to be some PET ROIs including the pons that were generated for the ADNI Study, possibly they are available somewhere.
Hope this helps a little
Helmut
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