Temporal constraints in renal perfusion imaging with a 2-compartment model

Objective: To assess the required temporal resolution and total acquisition time for renal perfusion and filtration measurements with a 2-compartment model. Material and Methods: Saturation-recovery TurboFLASH perfusion measurements of 15 healthy volunteers were acquired at 1.5 T, with a temporal resolution of I second during the first pass and a total acquisition time of 270 seconds. The time courses were then regridded and truncated to yield new data sets with temporal resolutions from I to 30 seconds in 1-second increments and with total acquisition times from 30 to 270 seconds in 5-second increments, respectively. Each new dataset was postprocessed by fitting the time courses to a 2-compartment model producing measures of perfusion and filtration: plasma volume (PV). plasma flow (PF), tubular volume (TV), and tubular flow (TF). The effect of reducing the temporal resolution or the total acquisition time was investigated by comparing the model parameters with those obtained at full temporal resolution and acquisition time and quantified by defining a discretization error (DE) and a truncation error (TE), respectively. For each parameter, the required temporal resolution and total acquisition times were defined by demanding a DE and TE of less than 10%. Results: It can be concluded from the analysis of the DE and TE that the acquisition of the parameters PF and TF requires a temporal resolution of at least 4 and 5 seconds, respectively. For the other 2 parameters, a temporal resolution of at least 9 seconds is sufficient. The required total acquisition times for PF and PV were 35 and 85 seconds, whereas for the parameters TF and TV, 230 and 255 seconds, respectively, are required. Conclusion: Renal perfusion measurements should be acquired with a temporal resolution of at least 4 seconds. To evaluate the renal excretory function adequately, the total acquisition time should be at least 255 seconds.