Table 1.
Model results
| Experiment | Arterial Galactose, mmol l blood−1 |
Results from Nonlinear Regression 4k Model (90 min, using cdual) |
Results from Linear Regression 3k Model (40 min)
|
VmaxGal, μmol·min−1·l−1 | |||||
|---|---|---|---|---|---|---|---|---|---|
| K21(=Q), ml·min−1·ml−1 | k12, min−1 | k32, min−1 | k23, min−1 | KdualFDGal, ml·min−1·l−1 | KarterialFDGal, ml·min−1·l−1 | Emet | |||
| 1 | <0.01 | 0.965 | 0.376 (1.8) | 0.482 (2.5) | 0.021 (1.8) | 411.0 (2.4) | 403.5 (3.1) | 0.43 | n.d. |
| 2 | <0.01 | 1.054 | 0.277 (1.8) | 0.371 (2.7) | 0.020 (2.3) | 455.2 (2.6) | 431.5 (2.6) | 0.43 | n.d. |
| 3 | <0.01 | 0.787 | 0.349 (3.8) | 0.398 (6.2) | 0.013 (14.2) | 331.8 (1.4) | 293.3 (1.0) | 0.42 | n.d. |
| 4 | <0.01 | 1.076 | 1.215 (4.1) | 1.491 (4.6) | 0.018 (2.2) | 481.2 (2.1) | 441.4 (2.1) | 0.45 | n.d. |
| 5 | 0.49 | 0.499 | 0.401 (0.02) | 0.065 (0.03) | 0.000 (6.4) | 73.2 (0.2) | 70.0 (0.2) | 0.15 | n.d. |
| 6 | 0.62 | 0.594 | 0.987 (2.0) | 0.129 (4.2) | 0.004 (18.8) | 56.5 (0.4) | 55.9 (0.5) | 0.10 | n.d. |
| 7 | 3.06 | 0.853 | 1.011 (1.3) | 0.026 (9.7) | 0.004 (64.9) | 19.5 (0.9) | 18.7 (1.0) | 0.02 | 412 |
| 8 | 3.88 | 1.091 | 1.389 (1.2) | 0.030 (8.0) | 0.004 (51.4) | 21.8 (2.7) | 22.8 (2.5) | 0.02 | 584 |
| 9 | 6.60 | 0.853 | 1.251 (1.3) | 0.027 (10.5) | 0.007 (37.8) | 15.4 (2.3) | 16.6 (3.9) | 0.02 | 702 |
| 10 | 6.65 | 0.750 | 0.919 (0.3) | 0.018 (1.1) | 0.000 (76.5) | 15.2 (1.1) | 15.6 (5.4) | 0.02 | 701 |
Optimized values from kinetic fittings are given as estimates and standard errors of the estimates (percent). Standard errors or the estimates are based on the covariance matrix. The lower detection limit for arterial galactose is 0.01 ml/l blood. K21, k12, k32, and k23 are model parameters; K21 was set equal to the perfusion, Q, in each experiment (ml blood·min−1·ml tissue−1). KdualFDGal and KdualFDGal, net metabolic clearance of 2-[18F]-fluoro-2-deoxygalactose with dual tracer or single arterial input, respectively. The net metabolic extraction fraction during quasi-steady-state metabolism, Emet, was calculated as KdualFDGal/Q (Eq. 4). The maximal hepatic removal rate of galactose, VmaxGal, was calculated from Eq. 8a, which is only applicable in cases with near-saturation kinetics, viz. experiments 7–10. In these cases the kinetics approximated saturation with 94–97%. n.d., Not determined.