Abstract
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Objectives Respiratory motion degrades FDG PET of the lower chest and liver as the blur introduced by breathing motion increases the apparent size of the moving tumor lesions and decreases their apparent uptake, likely reducing the sensitivity of PET in small-lesion detection. The purpose of this study is to assess the role of delayed and respiratory gated PET imaging acquisition on quantitative evaluation of lung and liver lesions.
Methods A retrospective analysis of 47 patients presenting with indeterminate lesions in the lower lungs or liver. A total of 64 lesions were evaluated (40 pulmonary and 24 hepatic). After initial non-gated whole body (WB) PET/CT (uptake time: 62.5 +/- 13.8 min), Respiratory gating (uptake time: 143.1 +/- 36.9 min) was performed with 15 min list mode, 1 field of view containing the lesion(s) in question. Ungated delayed images were obtained by summing all list mode data without considering the respiratory triggers. SUVmax adjusted for lean body mass (SUL) was measured in the initial whole body scan, delayed ungated, and individual gated bins for each lesion. Z-position of SULmax for each lesion in the five respiratory-gated bins was determined. Mean SUL of the non-pathological liver parenchyma was also recorded for each patient.
Results % increase (delayed - WB): 34.0 +/- 29.6. % increase (highest gated bin - delayed): 17.2 +/- 18.6. % increase (highest gated bin - WB): 55.6 +/- 38.6. % change in mean liver SUL: -6.3 +/- 7.8. Maximum lesion displacement: 6.2 +/- 5.0 mm.
Conclusions Delayed gated allows for a more accurate definition of the lesion’s volume and improves the quantitation of specific activity of the tracer in cancer lesions. This is very important in initial staging and in therapy followup when true metabolic activity in tumor lesions needs to be compared to adequately assess the efficacy of the treatment