[18F]FDG PET/CT for the assessment of the volume of the spleen.

BACKGROUND: The aim of this study was to report on the feasibility and accuracy of spleen volume determination on FDG PET/CT imaging using region growing and the CT part of the PET/CT examination as anatomical landmark (PET-CT based spleen volume method PBM) and volume summation of axial CT sections of the spleen as gold standard (true spleen volume (TSV). We also aimed to compare results obtained to the estimative methods (ESV).

METHODS: Thirty-nine FDG PET/CT images taken from 32 patients (15 women, age range: 16-83 years) suffering from lymphoma, covering a wide range of spleen volumes based on visual CT assessment, in whom CT as well as FDG PET images revealed no focal spleen abnormalities were included for analysis. ESV1, ESV2 and PBM were determined on all examinations and compared to TSV.

RESULTS: ESV1 volumes were significantly larger (median 668 cm3 [range: 121-4303 cm3] [P=0.0001]) and ESV2 volumes significantly smaller (median 424 cm3 [range: 84-2679 cm3] [P=0.0001]) when compared to TSV volumes (median 582 cm3 [range: 105-4847 cm3] which was not so for PBS volumes (median 540cm3 [range: 120-4560 cm3]). Time needed for TSV assessment (median: 17 min. [range: 6-65 min.]) was related to spleen volume (r=0.691 [P=0.0001]). The mean and standard deviation of the percentage spread (ESV1, ESV2, PBM-TSV/100%) around the mean (ESV1, ESV2, PBM+TSV/2) were respectively 18%±15.6% (ESV1 vs. TSV), -25%±15.6% (ESV2 vs. TSV) and -2.8%±12.3% (PBM vs. TSV). Mean SUVmax of the spleen was 4.8 SUV (SD: 2.6 SUV), mean percentage cut-off for region growing was 7.3% (sd: 5.8%). Spleen volumes defined by PBM correlated with their corresponding SUVmax value (r=0.469 [P=0.03]). Time needed for PBM measurements was between 2-3 min in all patients.

CONCLUSION: Spleen volumes may be rapidly and accurately derived from the FDG PET part of the PET/CT examination through region growing and by using the CT part of the PET/CT examination as anatomical landmark for contour delineation. As opposed to ESV1 and ESV2, the PBM method does not suffer from a systematic bias and shows a smaller variation against the mean percentage difference. Combining functional and morphological data for spleen volume assessment is time-saving.