Image-Derived Input Function for Assessment of ¹⁸F-FDG Uptake by the Inflamed Lung

Delineation (white outlines) of blood-pool ROIs in descending aorta (AO) and in RH cavities (RHC) and LH cavities (LHC) on representative image slice: regional activity after intravenous single-bolus injection of ¹³N-nitrogen dissolved in saline (A) and ¹⁸F-FDG activity, on identical scale, shortly after tracer injection and at end of imaging (B and C, respectively). The 3 ROIs are shown together only for illustration purposes.

Evaluation of model fit and effect of ROI volume on estimated parameter SC: representative model fit according to Equation 2 for dynamic PET data measured in blood-pool ROI over LH cavities (A), average SC obtained for blood-pool ROIs of varying size, illustrating how algorithm adjusts SC to different conditions (B); normalized SC/(1 − RC), illustrating differences in ¹⁸F-FDG uptake rates (C). Error bars are ±1 × SE. ROIs with lowest volume were used for analyses.

Convergence of iterative algorithm (Fig. 1) for model parameters RC and SC. Plot was generated for blood-pool ROIs in LH. Error bars are ±1 × SE.

mse between model-adjusted input function and manually sampled input function as function of time point of first calibration measurement, t₁. Plot shows results for blood-pool ROIs in RH and LH cavities (RHC and LHC, respectively) and descending aorta (AO). Values are out of scale for t₁ = 0.25 min, t₁ = 0.75 min, and t₁ > 25 min (not shown).

Comparison of activity in manual blood samples of pulmonary artery plasma, raw PET signal from blood-pool ROI in LH cavities, and model-adjusted input function: example of calibration measurements at t₁ = 4.5 min and t₂ = 50 min (A); example of longer tracer injection time (90 s instead of 1 min) and shorter initial PET frames (15 s instead of 30 s), with t₁ = 15 min and t₂ = 50 min (B). Discontinuity during peak was due to delay between end of tracer injection and flush of saline used to remove remaining tracer from infusion system.