Analysis of Multiple B-Value Diffusion-Weighted Imaging in Pediatric Acute Encephalopathy

<div><p>Acute encephalopathy is a disease group more commonly seen in children. It is often severe and has neurological sequelae. Imaging is important for early diagnosis and prompt treatment to ameliorate an unfavorable outcome, but insufficient sensitivity/specificity is a problem. To overcome this, a new value (fraction of high b-pair (F_H)) that could be processed from clinically acceptable MR diffusion-weighted imaging (DWI) with three different b-values was designed on the basis of a two-compartment model of water diffusion signal attenuation. The purpose of this study is to compare F_H with the apparent diffusion coefficient (ADC) regarding the detectability of pediatric acute encephalopathy. We retrospectively compared the clinical DWI of 15 children (1–10 years old, mean 2.34, 8 boys, 7 girls) of acute encephalopathy with another 16 children (1–11 years old, mean 4.89, 9 boys, 7 girls) as control. A comparison was first made visually by mapping F_H on the brain images, and then a second comparison was made on the basis of 10 regions of interest (ROIs) set on cortical and subcortical areas of each child. F_H map visually revealed diffusely elevated F_H in cortical and subcortical areas of the patients with acute encephalopathy; the changes seemed more diffuse in F_H compared to DWI. The comparison based on ROI revealed elevated mean F_H in the cortical and subcortical areas of the acute encephalopathy patients compared to control with significant difference (P<0.05). Similar findings were observed even in regions where the findings of DWI were slight. The reduction of mean ADC was significant in regions with severe findings in DWI, but it was not constant in the areas with slighter DWI findings. The detectability of slight changes of cortical and subcortical lesions in acute encephalopathy may be superior in F_H compared to ADC.</p></div

Categorization of ROIs of each patient in encephalopathy group.

<p>ROIs: regions of interest, AESD: acute encephalopathy with biphasic seizures and late reduced diffusion, ANE: acute necrotizing encephalopathy, UC: uncategorizable.</p

Outline of 4bDWI sequence.

<p>4bDWI: Four b-value diffusion-weighted imaging sequence, TR: repetition time, TE: echo time, NEX: number of excitations, FOV: field of view.</p

Calculation of F_H.

<p>The graph illustrates typical in vivo signal attenuation of diffusion-weighted imaging (DWI). S₀ to S₂₅₀₀ are the signal intensities of the corresponding b-values. S_0high and S_0low are the theoretical S₀ values calculated from a different data pair (pair of S₅₀₀ and S₁₅₀₀, and pair of S₁₅₀₀ and S₂₅₀₀, respectively) using a monoexponential fitting (which becomes a straight line in this semi-logarithmic graph). Fraction of high b-pair (F_H) equals S_0high/S_0low.</p

Regions of interest (ROIs) for the ROI-based study.

<p>A, B: Images acquired from a 1-year-old boy of unspecific acute encephalopathy. The images show the two specific slice levels selected for evaluation: the slice at the level of cerebral hemisphere (A), and the slice at the level of cerebral basal ganglia (B). Ten regions of interests (ROIs) were set as schematically illustrated for further assessments. C, D: A sample of accurate ROI 1 (frontal lobe of left cerebral hemisphere) acquired from a 2-year-old boy with suspected labium dyskinesia but which regressed a while after the examination (control group). C: Diffusion-weighted image before setting ROIs. D: Brightened area indicates the selected ROI, from which the pixels of cerebrospinal fluid and deep white matter were excluded as much as possible.</p

Mean F_H and ADC calculated in the encephalopathy group for analysis.

<p>Mean fraction of high b-pair (F_H) and apparent diffusion coefficient (ADC) for statistics were calculated for each patient. For the patients in the encephalopathy group, mean F_H and ADCs were calculated for each category separately by averaging F_H and ADCs across the regions of interests (ROIs) corresponding to each category. In this case (same case as in Fig. 2), five ROIs (ROIs 1, 3, 4, 5, and 8) corresponded to the “Severe” category, so the mean F_H and ADC (only ADC calculated by b-value = 0 and 1500 (ADC_0–1500) is shown here as example) for the “Severe” category was the averaged F_H and ADC of the five ROIs. In this case, ROIs 7, 9, and 10 were categorized as “mild” and ROIs 2 and 6 as “indistinct”. Note: the schematic ROIs illustrated on the images seem to include deep white matter and cerebrospinal fluid, but the accurate ROIs for assessments did not include these areas (Fig. 2; D).</p