All 14 X-Cal phantoms (4 in batch 1 and 10 in batch 2) were scanned on a PET/CT scanner (General Electric Discovery STE, General Electric Healthcare, Waukesha, Wisconsin) at the University of Washington Medical Center. These initial characterization scans were performed on July 31, 2011, for batch 1 phantoms (age 37 days) and between April 1, 2013, and July 9, 2013, for batch 2 (age 12–111 days). The phantom assembly was centered in the field of view and its axis was aligned with the axis of the scanner. A CT scan of the phantom was performed before the PET acquisition. CT images were used for attenuation correction and to check for PET/CT alignment.
Data were acquired in 3D acquisition mode with a single-bed position and a duration of 5 minutes. Scanner corrections were calibrated for 68Ge/68Ga nuclides. Images were reconstructed by the ordered-subsets expectation maximization algorithm with 4 iterations and 28 subsets. Smoothing after imaging was done by convolution with a 3D Gaussian kernel having a width of 8 mm in the 2 transaxial dimensions and 4.6 mm in the axial dimension. Voxel size was 5.5 × 5.5 × 3.3 mm3 for all reconstructions in batch 1 and 2.7 × 2.7 × 3.3 mm3 for all reconstructions in batch 2.
Data were acquired in 3D acquisition mode with a single-bed position and a duration of 5 minutes. Scanner corrections were calibrated for 68Ge/68Ga nuclides. Images were reconstructed by the ordered-subsets expectation maximization algorithm with 4 iterations and 28 subsets. Smoothing after imaging was done by convolution with a 3D Gaussian kernel having a width of 8 mm in the 2 transaxial dimensions and 4.6 mm in the axial dimension. Voxel size was 5.5 × 5.5 × 3.3 mm3 for all reconstructions in batch 1 and 2.7 × 2.7 × 3.3 mm3 for all reconstructions in batch 2.