The Experimental Study Of Diffusion Tensor Imaing In Acute Diffuse Axonal Injury

ObjectiveTo explore the diagnostic value of DTI in acute DAI, cat models of acute DAI were made to analyze their changes in acute stage by MRI and DTI and compare with histopathological changes.MethodsTwenty-two cats were involved in the study. 10 cats undertook the scan of routine MRI and DTI, 6 cats were observated under HE and silver staining light microscope, and another 6 cats under transmission electron microscope. A rotating device was designed and made, which could move the cat head through 900 instantly. The rotating time was approximately 17.2±3.5ms and the angular acceleration was (6.43±0.15)×105rad·s-2. Routine MRI with T1-weighted imaging and T2-weighted imaging and DTI scan were performed before traumatic event and at the time points of 3h,24h,48h,72h just after traumatic event. The images of DWI,ADC,FA were generated automatically by computer after the data of DTI sent to Leonardo workstation of SIEMENS, the values of ADC and FA were measured within ROI. The results of routine MRI and DTI were studied comparing with the changes of histopathology found in cat models.ResultsTen cats undertook 60 MRI scans. 3 cats with SAH,3 cats with SDH/EDH,2 cats with PH,2 cats with contusion,2 cats with IVH were found by rountine MRI scan, but no direct visible changes were detected. The changes of ADC values in the 10 cats revealed the existences of cytotoxic brain edema and vasogenic brain edema. The decrease in ADC values was observed in 7 cats and reached the minimum at 24h-point; The increase in ADC values was observed in 3 cats and reached the maximum at 6h-point, this transient increase was followed by a continuing decrease in ADC value that began 24h post-injury; The gradual decrease in FA value happened at 3h-point, and reached the minimum value at 72h-point. Vasogenic brain edema,cytotoxic brain edema,axon swelling,axon disintegration,retraction ball and neuronal changes were found by histopathological observation.ConclusionsThe cat DAI model could be made by the injury device with the rotating accleration of (6.43±0.15)×10⁵ rad·s^-2. Cytotoxic brain edema and vasogenic brain edema were the two major types of brain edema after DAI in acute stage,and the former was the major type. The technique of DTI could be used as one method to study DAI without impairment in vivo. The ADC and FA values, two important parameters of DTI, could sensitively reveal the changes of brain edema and axonal structure. This experimental study showed that DTI was superior to the routine MRI in DAI diagnosis,it could reveal the abnormal changes of axon after injury which T1WI and T2WI could not found. It could be used to observe the pathological changes of DAI dynamically, evaluate the degree,pathological and the prognosis of DAI.