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Clinical Investigations |
1 National Institutes of Health, Bethesda, Maryland
2 Hadassah University Hospital, Jerusalem, Israel
Standardized uptake value (SUV) is often used to quantify 18F-FDG tumor use. Although useful, SUV suffers from known quantitative inaccuracies. Simplified kinetic analysis (SKA) methods have been proposed to overcome the shortcomings of SUV. Most SKA methods rely on a single time point (SKA-S), not on tumor uptake rate. We describe a hybrid between Patlak analysis and existing SKA-S methods, using multiple time points (SKA-M) but reduced imaging time and without measurement of an input function. We compared SKA-M with a published SKA-S method and with Patlak analysis. Methods: Twenty-seven dynamic 18F-FDG scans were performed on 11 cancer patients. A population-based 18F-FDG input function was generated from an independent patient population. SKA-M was calculated using this population input function and either a short, late, dynamic acquisition over the tumor (starting 2535 min after injection and ending
55 min after injection) or dynamic imaging 10 or 25 min to
55 min after injection but using only every second or third time point, to permit a 2- or 3-field-of-view study. SKA-S was also calculated. Both SKA-M and SKA-S were compared with the gold standard, Patlak analysis. Results: Both SKA-M (1 field of view) and SKA-S correlated well with Patlak slope (r > 0.99, P < 0.001, and r = 0.96, P < 0.001, respectively), as did multilevel SKA-M (r > 0.99 and P < 0.001 for both). Mean values of SKA-M (25-min start time) and SKA-S were statistically different from Patlak analysis (P < 0.001 and P < 0.04, respectively). One-level SKA-M differed from the Patlak influx constant by only 1.0% ± 1.4%, whereas SKA-S differed by 15.1% ± 3.9%. With 1-level SKA-M, only 2 of 27 studies differed from Ki by more than 20%, whereas with SKA-S, 10 of 27 studies differed by more than 20% from Ki. Conclusion: Both SKA-M and SKA-S compared well with Patlak analysis. SKA-M (1 or multiple levels) had lower variability and bias than did SKA-S, compared with Patlak analysis. SKA-M may be preferred over SUV or SKA-S when a large unmetabolized 18F-FDG fraction is expected and 13 fields of view are sufficient.
Key Words: 18F-FDG Patlak standardized uptake value
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