RenoSim

RenoSim is a Renography Simulation program.
It simulates the time/activity curves obtained in the kidneys and the plasma after an i.v. inj. of a radioactive tracer which is extracted in the kidneys.
The simulation is based upon a pre-renal 2-compartment model representing the intra- and extravasculer distribution volumens.
To account for the bolus a central volume of distribution is defined.
The renal uptake system is defined by the Renal Plasma Flow (RPF) and the Extraction Ratio (E) of the tracer. The uptake is assumed to follow a simple first order differential equation:

dQ(t)/dt = E*RPF*Cp(t)

where Q(t) is the amount of tracer taken up by the kidney at time t, and Cp(t) is the plasma concentration of the tracer at time t. E and RPF is assumed to be constant in the observation period.
The fluid transport through the nefron system, collecting ducts, calysis and renal pelvis is modeled as a collection of parallel tubes with different length, distributed equaly between a minimum length and a maximum length. The transittime through these tubes consist of an urine flow independent part and a part which is inverse proportional to the urine flow. These tubes drains into a compartment (or 2 parallel compartments if a hydronephrosis is present) to simulate the renal pelvis. The mean transittime through this compartment is given by:

MTT = Vpelvis/UF

where Vpelvis is the volume of the renal pelvis and UF is the urine flow through that kidney.
In case a hydronephrosis is present a second compartment in parallel with the normal pelvis compartment is introduced. This compartment accounts for the long transittimes due to the large pelvisvolumen. For simplicity it is assumed that the urine flow is distributed equaly between the two compartments.

For further information contact Michael Lehd Møller at: michael@gamma-soft.dk