Purpose: to assess if apparent diffusion coefficient (ADC) and magnetization transfer ratio (MTR) are more sensitive than T2W MRI in children with neurofibromatosis I (NF), leukodystrophy, hypoxic/ischemic encephalopathy (HIE), post-infectious encephalopathy (PIE), or chemotherapy-induced leukoencephalopathy (CIL)
Methods and Materials: Diffusion and magnetization transfer (MT) imaging was performed on 29 children (16 boys, 13 girls, age range: newborn to 18 yrs, average 7.08 yrs) with NF (6), leukodystrophy (7), HIE (4), PIE (7), and CIL (5) using a 1.5T magnet. The normal control group consisted of 85 boys and 48 girls (newborn to 18 yrs) with brain tumors who underwent MRI before treatment. These children were separated into groups according to gender and age. Axial TSE T2W images (4070/110/900/2 NEX/19 slices, 4 min, 211x512 matrix, 20cm FOV, 5mm thick, 1mm gap) and axial fat-saturated single-shot SE-EPI diffusion-weighted images (220/139/900/4/19, 50s, 128x128, EPI factor 128, b=0, 900 in 3 directions) were obtained. Axial 2D FLASH images were acquired (160/14/150/1/14, 1 min 26 s, 177x256) with and without MT pulse (1.5 kHz frequency offset, 8000). Regions of interest (ROI) were drawn on the cortical gray matter, frontal and parietal deep white matter, caudate nucleus, putamen, globus pallidus, thalamus, substantia nigra, tectum, middle cerebellar peduncle, and CSF on diffusion trace images, ADC map and FLASH images using T1W and T2W images as guide. MTR was calculated by (SI0-SIm )/SI0 x100 where SI0 and SIm were signal intensities of ROI on the FLASH images without and with MT pulse respectively. The ADCs and MTR were compared to the age- and sex-matched normal control using paired sample t-test. Significance was defined as p<0.05.
Results: T2-hyperintense gliosis of NF had significantly lower (p=0.036) MTR (38.39±8.99) in the globus pallidus and lower (p=0.022) ADC (1.12 x10-3±0.71 x10-8) in the tectum than normal control (42.73±1.75, 1.25 x10-3±1.22 x10-8). ADCs of T2-hyperintense parietal white matter of leukodystrophy (1.33 x10-3±3.22 x10-8) and frontal white matter of HIE (2.04 x10-3±1.89 x10-8) were higher (p=0.026, 0.021) than normal (1.19 x10-3±3.70 x10-8, 1.47x10-3±0.08x10-8). ADCs of cortical gray matter of PIE (1.23 x10-3±7.09 x10-8) were higher (p=0.039) than normal (1.06 x10-3±1.28 x10-8). MTRs and ADCs of other structures with normal T2 SI were not significantly different from normal controls.
Conclusion: ADC and MTR are not more sensitive than T2W imaging in assessing children with encephalopathy.