Diffusion-Weighted Imaging of Edema following Traumatic Brain Injury in Rats: Effects of Secondary Hypoxia

Abstract

Hypoxia and edema are frequent and serious complications of traumatic brain injury (TBI). Therefore, we examined the effects of hypoxia on edema formation after moderate lateral fluid percussion (LFP) injury using NMR diffusion-weighted imaging (DWI). Adult Sprague-Dawley rats were separated into four groups: sham uninjured (S), hypoxia alone (H), trauma alone (T), and trauma and hypoxia (TH). Animals in Groups T and TH received LFP brain injury, with Groups H and TH undergoing 30 min of moderately severe hypoxia (FiO2 = 0.11) immediately after surgery or TBI (respectively). DWIs were obtained at 2, 4, and 24 h and at 1 week post injury, and apparent diffusion coefficient (ADC) maps were constructed. Animals in Groups T and TH showed an early decrease (p < 0.001) in ADC values in the cortex ipsilateral to TBI 4 hr post injury, followed by elevated ADCs 1 week later (p < 0.05). No significant differences in ADC values were seen between T and TH groups in the ipsilateral cortex. In contrast, the ipsilateral hippocampus for Group TH showed only increasing ADC values. This hyperintensity in the ADC map began at 2 h after TBI, was significant by 24 h (p < 0.05), and reached a maximum at 1 week. This hyperintensity was not observed in Group T. Histopathology seen in TBI animals corresponded well with the pathology observed with MRI. Midline shifts reflecting edema were only observed in TBI animals with little difference between normoxic (T) and hypoxic animals (TH). In sum, this study demonstrates that the development and extent of brain edema following TBI can be examined in vivo in rats using DWI technology. TBI resulted in an early decrease in ADC values indicating cytotoxic edema in the cortex that was followed at 1 week by an increase in the ADC that was associated with decreased tissue cellularity. Histopathology corresponded well to the regions of brain injury and edema visualized by T2 and DWI procedures. Overall, the addition of hypoxia to brain injury resulted in a small increase in the magnitude of edema in hippocampus and cortex over that seen with trauma alone.

Diffusion Tensor Imaging Reliably Detects Experimental Traumatic Axonal Injury and Indicates Approximate Time of Injury

“…At early stages, DWI is more sensitive than T2, but at subacute stages, T2 becomes more sensitive than DWI as the diffusion-weighted images undergo pseudonormalization (Schlaug et al, 1997;Copen et al, 2001;Schaefer et al, 2005). Similar changes in DWI signal characteristics over time after TBI have been observed in rats (Alsop et al, 1996;Albensi et al, 2000;Van Putten et al, 2005), pigs (Duhaime et al, 2003), and humans (Pasco et al, 2006). However, these studies did not use DTI and did not focus on white matter injury.…”

“…These studies were performed at only a single time point, 24 h after injury. It is unknown whether there are changes in the sensitivity of DTI over time, because only very limited clinical studies (Arfanakis et al, 2002;Naganawa et al, 2004;Voss et al, 2006) and none of the previous experimental animal studies (Hanstock et al, 1994;Kochanek et al, 1995;Alsop et al, 1996;Assaf et al, 1997;Albensi et al, 2000;Duhaime et al, 2003;Van Putten et al, 2005), to our knowledge, have performed DTI at multiple time points. For optimal clinical utility, a method should be robust across a variety of time points, given that it is rarely possible to scan patients at a fixed time point after injury.…”

Blockage of the Upregulation of Voltage-Gated Sodium Channel Nav1.3 Improves Outcomes after Experimental Traumatic Brain Injury

“…23 MRI scans were analysed with National Institutes of Health ImageJ 1.43 (National Institutes of Health, Bethesda, MD), and the degree of midline shift were measured directly by constructing a straight line from the midpoint of the longitudinal cerebral fissure to the middle of the mammillary body. The length from the lateral surface of the cortex to the midline was measured and a left-to-right ratio was calculated (Fig.…”

Prediction of neurological recovery in spontaneous spinal epidural hematoma using apparent diffusion coefficient values

“…This was followed by an increase in ADC values corresponding to demyelination and decreased tissue cellularity in the long term. 10,11 Spinal cord DWI A DWI of the spinal cord is technically demanding because of the small volume of the spinal cord. Physiological motion, including cerebrospinal fluid flow and cardiac and respiratory motion, also influenced the quality of images.…”