Figure 8

Loss of information by prolonging the infusion duration. (A) Simulated IFs, bolus 10 s (dark line) and infusions 300 (dotted line) and 900 s (grey line). (B) Zoom into TAC generated with a typical set of rate constants K ₁ 0.328 mL/min/cm³ _, k ₂ 0.550 min⁻¹, k ₃ 0.079 min⁻¹, k ₄ 0 (dark line). An additional TAC was generated by increasing K ₁ by 10% (1.1 × K ₁). At the same time, k ₂ was also increased to match the original TAC as close as possible. The respective factor for k ₂ was 1.11 (1.11 × k ₂). TACs with either increased K ₁ or k ₂ are shown in addition. The newly generated TAC with 1.1 × K ₁ and 1.11 × k ₂ deviates from the original TAC around the infusion stop, i.e., around the peak of the IF. This difference is indispensable to distinguish between the effects of K ₁ and k ₂ on the TAC and thus for kinetic modeling. (C) TACs generated with the same rate constants as in (B) for the 300-s infusion and (D) for the 900-s infusion. The difference between the two TACs (indicated by an arrow in C) reduces as infusion duration increases, explaining the improper fit parameters with the simulated 900-s infusion protocol at longer sampling intervals. Note that (B) to (D) zoom into the TAC region of interest and the activity scale, therefore starts at 600 Bq/cm³.