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AJNR - American Journal of Neuroradiology

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Selecting the Best Index for Following the Temporal Evolution of Apparent Diffusion Coefficient and Diffusion Anisotropy After Hypoxic-Ischemic White Matter Injury in Neonates

Carola van Pul^a,d, Jan Buijs^b, Maurice J. A. Janssen^a,e, George F. Roos^c, Marinus T. Vlaardingerbroek^a and Pieter F. F. Wijn^a,d

^a Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands
^b the Department of Neonatology, Maxima Medical Center, Location Veldhoven, The Netherlands
^c Department of Radiology, Maxima Medical Center, Location Veldhoven, The Netherlands
^d Department of Clinical Physics, Maxima Medical Center, Location Veldhoven, The Netherlands
^e the Department of Biomedical Engineering ORL, University Hospital Maastricht, The Netherlands

View larger version (122K): [in a new window]   FIG 1. Definition of the regions of interest in the adult brain. 1 indicates corpus callosum; 2, white matter.

View larger version (59K): [in a new window]   FIG 2. Eigenvalue space plots as defined by Bahn (33), plotted for anisotropy index FA. FA is high (bright) for both 3/1 and 2/1 close to zero, which corresponds to a cigar-shaped diffusion ellipse. But FA is still relatively large for 2/1 close to 1, the pancake-shaped diffusion ellipse.

View larger version (23K): [in a new window]   FIG 3. A–D, Average ADC, eigenvalues, and anisotropy indexes in frontal white matter (WM) and in the corpus callosum (CC), measured in 16 adult volunteers (A and B) and in 10 full-term neonates with normal MR images (C and D).

View larger version (138K): [in a new window]   FIG 4. A–C, Eigenvalue space plots, as introduced by Bahn (33) (explained in Fig 2), for FA, RA, and Am. In the middle row, the corresponding anisotropy maps are shown for a neonate with lesions (arrow) in the frontal white matter and occipital white matter. Note the increased anisotropy corresponding to the low ADC area. In the bottom row, T2-weighted image, IR image, and ADC map in the same neonate are shown.

View larger version (25K): [in a new window]   FIG 5. A–D, Results of simulations of the effect of random noise on ADC and eigenvalues (A and C) and anisotropy (B and D) for the adult case (A and B) and neonate case (C and D). Open symbols indicate the input values (Table 2); filled symbols, the values after noise was added. The error bars show the standard deviation of the simulated results.

View larger version (66K): [in a new window]   FIG 6. Relative change in FA, RA, and Am as a function of a change in one of the eigenvalues 1, 2, and 3. The change is defined as a factor times the original value; the factor is displayed on the x-axis. The relative change is shown for three input settings, corresponding to adult white matter (top row), neonatal white matter (middle row), and a case close to isotropic (bottom row). The gray area is the area in which the function is valid, that is where 1 > 2 > 3.

View larger version (38K): [in a new window]   FIG 7. Average absolute values for the ADC (top image), the three eigenvalues 1, 2, and 3 (middle row), and the three anisotropy indexes FA, RA, and Am (bottom row) as a function of time after the onset of symptoms for neonates with a white matter lesion.

View larger version (29K): [in a new window]   FIG 8. A–C, Time evolution of the relative change (Change equation) in ADC values (A), the three eigenvalues (B), and the anisotropy indexes FA, RA, and Am (C) after hypoxic-ischemic brain injury in neonates. Trend lines are shown only if the trend was significant (P < .05).