PROPER DIFFUSION-WEIGHTED WINDOW LEVEL IN MR IMAGING IN ACUTE VIRAL ENCEPHALITIS AND HYPOXIC ISCHAEMIC ENCEPHALOPATHY
Introduction: Diffusion-weighted magnetic resonance (MR) imaging provides image contrast that is different from that provided by conventional MR techniques. Improper Paper Submission DateDiffusion weighted (DW) window level obscures the diffuse cortical abnormality on DW image, hence proper windowed Diffusion weighted images are must for evaluation of cortical & deep grey matter nuclei abnormality. The increased sensitivity of DWI sequences with regard to viral encephalitis/hypoxic ischaemic encephalopathy (HIE) has been shown in several studies This study was performed to evaluate the role of proper DWI window level (250/150) in the diagnosis of viral encephalitis & HIE vs improperly windowed (500-850/250-Paper Publication Date 400) DW images for evaluation of cortical & deep grey matter nuclei.
 Material and Methods: We performed conventional MRI including T1, T2-Weighted and DOI fluid attenuated inversion recovery (FLAIR) sequences and DWI in 16 patients with viral encephalitis & 02 patients of hypoxic ischaemic encephalopathy diagnosed on the basis of laboratory, clinical and radiologic findings. Gradient B value of diffusion was 0, 400 & 800. Properly windowed (250/150) DW image versus an improperly windowed (500-850/250-400) DW image were evaluated for evaluation of cortical & deep grey matter nuclei signal intensity.
 Results: Axial DW images were reviewed at a consistent window level of 250/150. DW image with proper window level of 250/150 shows that the cortical/ deep gray matter nuclei abnormality is more evident. Apparent diffusion coefficient (ADC) map further illustrates the cortical restricted diffusion. Although with improperly windowed DWI (500-850/250-400), there is accentuated grey–white matter differentiation, but improper window level obscures the diffuse cortical abnormality on DW image. With proper window level of DW images, diffusion restriction was picked up in all the 16 cases of acute viral encephalitis and 02 patients of HIE.
 Conclusion: Proper window level of DWI (250/150) is helpful in early diagnosis of acute viral encephalitis & hypoxic ischaemic encephalopathy.