Article Figures & Data
Figures
- FIGURE 1.
Differences in tracer concentrations in vascular volume determined with compartment model and single-capillary microvascular model. (Left) Measured inlet time–activity curve after tracer bolus. During dynamic phase, ROI inlet concentration Ci(t) rises (A), reaches its maximum, and falls (B) toward steady state (C). (Right) Concentration profiles in capillary at times tA, tB, and tC, corresponding to situations A, B, and C, respectively. Arrows show direction of flow. Dotted lines show inlet concentrations used in compartment model. Dashed lines show spatially averaged concentrations used in microvascular models. Use of inlet concentrations overestimates amount of tracer present in organ in rising part of bolus (A) and underestimates it in falling part of bolus (B). Error is most significant in early dynamic phase with large gradients. Later, when steady state is approached (C), error becomes smaller.
- FIGURE 2.
Typical time–activity curves after 15O-CO inhalation (pig 4). (A) Black circles = HA blood time–activity curve; white circles = PV blood time–activity curve. (B) Black circles = liver tissue PET time–activity curve; white circles = dual-input blood time–activity curve.
- FIGURE 3.
Typical liver tissue PET time–activity curve after 15O-CO inhalation (pig 2), fitted with 2 models. Only initial 2.5 min are shown, when differences between models were most pronounced. Black circles = liver PET data; dashed line = compartment model with dual input; solid line = multiple-capillary microvascular model. Fit obtained with single-capillary microvascular model has time course very similar to that of fit obtained with multiple-capillary microvascular model.
- FIGURE 4.
Scaled sensitivity function Sp(t) obtained with data from pig 2. Scaled Sp(t) is calculated at each point, and lines are linear interpolations. All sensitivity functions are scaled to emphasize shapes. (A) Standard compartment model. Circles = V0. (B) Single-capillary microvascular model. Circles = Vb; squares = F. (C) Multicapillary microvascular model. Circles = Vb; squares = F; triangles = σ.
- FIGURE 5.
Regional blood flow estimated by single-capillary microvascular model plotted against normalized total flow measured by flow meters (n = 8). Triangles = flow estimated without synchronization; squares = flow estimated with synchronization; solid line = identity line. In all instances, synchronization brings data sets together and induces lower flow estimates in closer agreement to normalized organ blood flow.
- FIGURE 6.
Regional blood flow estimated by multiple-capillary microvascular model with synchronization plotted against normalized total flow measured by flow meters (n = 8). Solid line = linear regression through origin; dotted lines = 95% confidence intervals.
- FIGURE 7.
Fractional difference in AIC scores between compartment model and single-capillary microvascular model with synchronization as function of data acquisition time. Points represent mean fractional difference in AICs calculated as (AIC for the compartment model − AIC for the microvascular model)/AIC for the microvascular model (n = 8). Shorter data acquisition times were simulated by skipping late PET data. When all data up to 5 min were used, AICs were almost the same for 2 models, but as data acquisition time became shorter, the effect on AICs of using physiologically richer microvascular model became more apparent.
