Article Figures & Data
Figures
- Fig 1.
Definition of the regions of interest in the adult brain. 1 indicates corpus callosum; 2, white matter.
- Fig 2.
Eigenvalue space plots as defined by Bahn (33), plotted for anisotropy index FA. FA is high (bright) for both λ3/λ1 and λ2/λ1 close to zero, which corresponds to a cigar-shaped diffusion ellipse. But FA is still relatively large for λ2/λ1 close to 1, the pancake-shaped diffusion ellipse.
- 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).
- 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.
- 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.
- Fig 6.
Relative change in FA, RA, and Am as a function of a change in one of the eigenvalues λ1, λ2, and λ3. 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 λ1 > λ2 > λ3.
- Fig 7.
Average absolute values for the ADC (top image), the three eigenvalues λ1, λ2, and λ3 (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.
- 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).
Tables
- TABLE 1:
Equations for the anisotropy indexes evaluated in this study and the authors who introduced them
Index Introducing Authors (reference no.) Equation FA Basser and Pierpaoli (12) 
RA Basser and Pierpaoli (12) VR Le Bihan et al (14) Cl Peled et al (31) Cp Peled et al (31) Am Conturo et al (32) Note.—All indexes are scaled to make isotropic diffusion 0 and anisotropic diffusion 1. λ1 is the largest eigenvalue, λ3 the smallest.
Input Settings Eigenvalues SNR λ1 (10−9 m2/s) λ2 (10−9 m2/s) λ3 (10−9 m2/s) Corpus callosum Adult 1.6 0.7 0.35 64 Neonatal 2.0 1.2 0.65 35 White matter Adult 1.2 0.8 0.45 64 Neonatal 2.0 1.6 1.3 35 Isotropic ADC Adult 0.88 0.88 0.88 64 Neonatal 1.3 1.3 1.3 35
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