[A high temporal resolution dynamic T₂*W imaging study based on step oxygen stimulation of rat kidneys]

To monitor the changes in oxygenation levels of rat kidneys under step oxygen stimulation by high temporal resolution dynamic T₂* weighted planar echo imaging (T₂*W-EPI).

Step oxygen stimulation was applied to SD rats (n=10) in the sequence of 2 min of hyperoxia (100% O₂) -10 min of hypoxia (10% O₂) -10 min of hyperoxia (100% O₂). Dynamic MRI data of the kidneys of multi-echo gradient echo (mGRE) sequence and gradient echo-planar imaging (EPI) sequence were continuously acquired on a 9.4T small animal magnetic resonance scanner. The time resolution of the two sequences were 9 s and 1 s, respectively. A second-order step response model was established for the dynamic time series curves of different regions of interest (ROIs) in rat kidneys, and the parameters of the step response model were obtained, including time delay ∆t, natural frequency ωn, damping constant D and oscillation period T. The performance of two MRI imaging methods with different temporal resolution in response to the step oxygen stimulation in the kidneys was compared.

Compared with the control experiment results of mGRE, the dynamic T₂*W-EPI technology proposed in this study increased the temporal resolution of monitoring renal step oxygen stimulation by 8 folds and improved the goodness of fit of the step response model. The model showed a shorter time delay ∆t (shortened by 29.4%, 42.6%, 56.4%, and 47.4%, respectively, in the CO, OSOM, ISOM and IM), a larger natural frequency ωn (increased by 21.1%, 28.6%, 52.2%, and 61.9%, respectively), and oscillation of each ROI (damping constant D<1) under the step oxygen stimulation.

In a step oxygen stimulation model of rat kidneys, the high temporal resolution dynamic T₂*W-EPI technique proposed in this study is capable of real-time monitoring of the changes in renal oxygenation levels for detection of abnormal renal conditions.