There are several approaches to retrieve good images. Thirst question is what do you really need/expect? You won't get any SUV from PET/CT until you made your own calibrations and very time consuming scans. To get nice images we use 25-30 min per bed position (about 18 cm with Philips Gemini TF and Time of Flight) for patients. I know that Philips was working on a calibration factor so that you can easily choose Y-90 like F-18 or Ga-68 in the acquisition protocol. I'm not sure if they succeeded or if such a calibration factor is available from GE. Maybe you've to contact GE Service. SPECT/CT is well described in several papers. One method is to use medium energy collimators and a wide energy window (20-30%) @75 keV to use Bremsstrahlung for imaging. This works fine for our Siemens Symbia T6 with 60 Frames over 360 degree with 15s per frame, continuous acquisition mode and auto contour. Reconstruction is 3DOSEM 8 iterations and 8 subsets and no filtering. It is necessary to perform scatter and attenuation correction. Maybe you have to set the energy to 75 keV for scatter and attenuation correction as well in your recon protocoll. I want to make clear that this is for routine use in patients, not for quantifying activity concentrations. There you may have to add more frames and more time per frame and play a little with reconstruction parameters. Hope this helps.  

Th following reference may be of help:

Br J Radiol 2012 Jul; 85(105): 1018-1019 and especially table 1:

Yttrium-90 (90Y) imaging protocol using first generation positron emission tomography (PET)/CTPET/CT scannerGeneral technique

Siemens Biograph LSO, Erlangen, GermanyImaging performed 6 h post-90Y injection; patient positioned supine with arms elevated; PET acquired in one bed position centred over the liver for 40 min

PET gantry information

Detector material: lutetium oxyorthosilicate; crystal dimension 6.45×6.45×25 mm; crystals per detector block 64; 144 detector blocks; 4 photomultiplier tubes per block; detector ring diameter 824 mm; 384 detectors per ring; 24 detector rings; total 9216 detectors

PET reconstruction parameters

PET matrix 128×128×47; attenuation weighted ordered subsets expectation maximisation iterative reconstruction; two iterations and eight subsets

CT parameters

Single-slice CT; 120 kVp; 90 mAs; field of view 50 cm; slice interval 3 mm

Any competent clinical physicist for nuclear medicine can derive modifications to suit your PET/CT.

Actually obtaining SUV values require a lengthy calibration, that same physicist should know about. It takes considerable effort.

Last congress of the EANM in Gothenburg [oktober 2014] there were some posters from groups that did it and even went further to true dosimetry.

It is likely that you can find some material on line about these projects.

I hope this helps you find your way.

 Thanks Dr Uwe and Dr Judocus for the helpful information. I may try to use the above suggestions. 

Thanks Dr Hofman.

Regarding Y90 PET acquisitions, a recent multi-institution phantom study, known as the QUEST study, found that the optimum reconstruction parameters for quantitative imaging using a GE Discovery ST was 3D OSEM with all pass filter: e.g. 2i 24 s. Image capture was for 2 bed positions, each of 20 minutes. A manuscript on this phantom study has been submitted for publication. This manuscript will have far more details, including expected recovery rates, error rates and coupled with the impact of time on the readings. The lead author of the paper is Dr Kathy Willowson, so keep an eye out for her manuscript in the coming weeks / months (fingers crossed!)! Good luck with the acquisitions!