TABLE 1.

Biokinetic Fitting Functions Available in MIRDfit

Function	Description	Example use
$\text{[math]}$	Physical decay only	No biologic clearance
$\text{[math]}$	Monoexponential (biologic clearance with physical decay)	General use
$\text{[math]}$	Biexponential (first phase, biologic clearance with physical decay; second phase, physical decay only)	General use
$\text{[math]}$	Biexponential (first phase, rapid biologic clearance with physical decay; second phase, slow biologic clearance with physical decay)	General use
$\text{[math]}$	Biexponential (first phase, uptake with physical decay; second phase, biologic clearance with physical decay)	Regions with initial uptake period (function constrained though origin)
$\text{[math]}$	Biexponential (first phase, rapid biologic clearance with physical decay; second phase, slow biologic clearance with physical decay)	Whole body, whole blood (intravenous administration); stomach contents (oral administration)
$\text{[math]}$	Biexponential (first phase, rapid biologic clearance with physical decay; second phase, slow biologic clearance with physical decay)	Well-perfused organs (intravenous administration)

A₁, A₂ = exponential amplitude coefficients (%); λ₁, λ₂ = biologic clearance constants (h⁻¹); λ_phys = physical decay constant (h⁻¹); %_blood = percentage of total blood mass within source region (g/g × 100%).