Neurofluid fluctuation analysis using dynamical network biomarker MRI in idiopathic normal pressure hydrocephalus.

PURPOSE: To apply dynamical network biomarker (DNB) theory to diffusion MRI and develop the diffusion MRI-derived DNB (dMRI-DNB) index for evaluating neurofluid fluctuation in idiopathic normal pressure hydrocephalus (iNPH).

METHODS

Seventeen patients with iNPH (12 men, 5 women; mean age, 76.6 ± 4.9 years) and ten controls (4 men, 6 women; mean age, 71.8 ± 6.8 years) underwent electrocardiogram-triggered single-shot diffusion echo-planar imaging with b-values of 0, 500, and 1000 s/mm2. We calculated the fast- and slow-diffusion coefficients (Df and Ds, respectively) for each cardiac phase. The dMRI-DNB index was defined as the product of the mean coefficient of variation of these two diffusion coefficients (CVmean) and their correlation coefficient (CC). These parameters in the bilateral frontal white matter were compared between groups.

RESULTS

The dMRI-DNB index was significantly higher in the iNPH group than in the control group (10.3 ± 3.1 vs. 6.5 ± 1.9). Both CVmean and CC were also significantly higher in the iNPH group (CVmean: 15.3% ± 3.8% vs. 11.1% ± 2.9%; CC: 0.661 ± 0.090 vs. 0.576 ± 0.055, respectively). There was no significant correlation between CVmean and CC in either group (iNPH: R = -0.115, P = 0.660; controls: R = 0.127, P = 0.726).

CONCLUSIONS

The dMRI-DNB index, an integrated metric reflecting both the amplitude (CVmean) and correlation (CC) of neurofluid fluctuation, was elevated in iNPH. This index may provide a novel approach for evaluating intracranial condition.