A Weight Index for the Standardized Uptake Value in 2-Deoxy-2-[F-18]fluoro-d-glucose-Positron Emission Tomography

Known errors in the standardized uptake value (SUV) caused by variations in subject weights W encountered can be corrected by lean body mass or body surface area (bsa) algorithms replacing W in calculations. However this is infrequently done. The aims of the work here are: quantify sensitivity to W, encourage SUV correction with an approach minimally differing from tradition, and show what improvements in the SUV coefficient of variation (cv) for a population can be expected. Selected for analyses were 2-deoxy-2-[F-18]fluoro-d-glucose (FDG) SUV data from positron emission tomography (PET) and PET/computed tomography (CT) scans at the University of Tennessee as well as from the literature. A weight sensitivity index was defined as −n=slope of ln(SUV/W) vs. lnW. The portion of the SUV variability due to this trend is removed by using the defined $${\text{SUV}}_{n} = {Q \times W^{n} \times W_{{{\text{avg}}}} ^{{1 - n}} } \mathord{\left/ {\vphantom {{Q \times W^{n} \times W_{{{\text{avg}}}} ^{{1 - n}} } {{\text{ID}}}}} \right. \kern-\nulldelimiterspace} {{\text{ID}}}$$ , or a virtually equal SUV m using $$w = n:{\text{SUV}}_{m} = Q \times {{\left( {wW + {\left( {1 - w} \right)}W_{{{\text{avg}}}} } \right)}} \mathord{\left/ {\vphantom {{{\left( {wW + {\left( {1 - w} \right)}W_{{{\text{avg}}}} } \right)}} {{\text{ID}}}}} \right. \kern-\nulldelimiterspace} {{\text{ID}}}$$ , with Q and ID being tissue specific-activity and injected dose. $$F = {{\left( {{\text{cv}}\,{\text{of}}\,{\text{SUV}}_{n} \,or\,{\text{of}}\,{\text{SUV}}_{m} } \right)}} \mathord{\left/ {\vphantom {{{\left( {{\text{cv}}\,{\text{of}}\,{\text{SUV}}_{n} \,or\,{\text{of}}\,{\text{SUV}}_{m} } \right)}} {{\left( {{\text{cv}}\,{\text{of}}\,{\text{traditional}}\,{\text{SUV}}} \right)}}}} \right. \kern-\nulldelimiterspace} {{\left( {{\text{cv}}\,{\text{of}}\,{\text{traditional}}\,{\text{SUV}}} \right)}}$$ measures performance. Adapting to animal studies’ tradition, $${\% W_{m} ID} \mathord{\left/ {\vphantom {{\% W_{m} ID} {wt}}} \right. \kern-\nulldelimiterspace} {wt} = 100 \times {\text{SUV}}_{m}$$ is preferred over the conventional $${\% {\text{ID}}} \mathord{\left/ {\vphantom {{\% {\text{ID}}} {wt}}} \right. \kern-\nulldelimiterspace} {wt} = 100 \times Q \mathord{\left/ {\vphantom {Q {{\text{ID}}}}} \right. \kern-\nulldelimiterspace} {{\text{ID}}}$$ . For FDG in adults $$n = w = 0.44 \pm 0.03{\left( {{\text{s}}.{\text{e}}.} \right)}$$ from averaging over most tissues. In children, however, $$n = w = 0.67 \pm 0.05$$ . Tissues have the same index if their influx constants are independent of W. Suggested, therefore, is a very simplified $${\text{SUV}}_{m} = Q \times \frac{1}{2}{{\left( {W + W_{{{\text{avg}}}} } \right)}} \mathord{\left/ {\vphantom {{{\left( {W + W_{{{\text{avg}}}} } \right)}} {{\text{ID}}}}} \right. \kern-\nulldelimiterspace} {{\text{ID}}}$$ , which is dimensionless and keeps the same population averages as traditional SUVs. It achieves $$F = {\left( {{1 - 0.011} \mathord{\left/ {\vphantom {{1 - 0.011} {{\left( {{\text{cv}}\,{\text{of}}\,{\text{SUV}}} \right)}^{2} }}} \right. \kern-\nulldelimiterspace} {{\left( {{\text{cv}}\,{\text{of}}\,{\text{SUV}}} \right)}^{2} }} \right)}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}}$$ . Hence, for cv’s of SUVs below ∼1/3 improvements over tradition are possible, leading to F’s<0.95. Accounting additionally for height, as in SUVbsa, gives very little improvement over the simplified approach here and gives essentially the same F’s as SUV m . Introduced here is a weight index useful in reducing variability and further understanding the SUV. Addressing weight sensitivity is appropriate where the cv of the SUVs is below about 1/3. Proposed is the very simple approach of using an average of an adult patient’s weight and ∼70 kg for FDG SUV calculations. Unlike other approaches the dimensionless population average of SUV m s is unchanged from tradition.