From: Benjamin Lemasson Parametric response mapping as a new MRI approach for the characterization of posttraumatic cerebral edema

Purpose: Cerebral edema is usually assessed with mean ADC value obtained with MRI. We aimed to use parametric response mapping (PRM), a voxel-based analysis, in a rat model of traumatic brain injury (TBI) to characterize the cerebral edema and to compare findings to those obtained with the classical global mean ADC analysis. Ultimately we wished to test whether early PRM analysis could identify the vasogenic or cellular edematous pattern two hours after trauma. Materials and Methods Experiments were conducted in a rat model of TBI in accordance with French Government guidelines. Eighteen traumatic brain-injured rats (TBI group) were compared to 7 sham-operated rats (Sham group). Diffusion-weighted images were acquired before and immediately (H0), 60min (H1) and 120min (H2) after the trauma. Two regions of interest (ROI) including cortex (cortical-ROI) and the whole brain (brainROI) were manually delineated. Results Averaged ADC value in cortical-ROI was significantly reduced at H2 in the TBI group versus Sham group (715±24 vs 781±16 µm²/sec; p=0.04), not in brain-ROI (748±27 vs 801±18 µm²/sec; p=0.32). By contrast, PRM values were significantly changed in these two ROIs at as soon as H1 in the TBI group (27.5±4% of the voxels beyond the PRM threshold in TBI group vs 5.1±1% in sham group; p<0.01). PRM was able to identify the nature of post traumatic cerebral edema: vasogenic, cellular or mixed pattern. ADC data obtained immediately after TBI and analyzed using PRM correlated with ADC data obtained at H2. Conclusion The PRM approach is more sensitive than averaged ADC at detecting and identifying post-traumatic brain edema. It is able to PRM might be a promising tool to individualize the management of patients with posttraumatic brain edema.