Hemodynamically self-corrected ΔADC analysis in idiopathic normal pressure hydrocephalus

Abstract

Objective: To clarify the cause of higher water fluctuation of the brain in idiopathic normal pressure hydrocephalus (iNPH), we assessed change in hemodynamic-independent apparent diffusion coefficient during the cardiac cycle (ΔADC) in iNPH.

Methods: Electrocardiographically synchronized single-shot diffusion echo-planer imaging (b = 0, 500, and 1000 s/mm²) was performed in healthy volunteers, atrophic ventricular dilation group, and iNPH group, respectively. The ΔADC (b = 0 and 1000 s/mm²) and maximum ADC (b = 0 and 500 s/mm²) in the cardiac cycles were measured at the frontal white matter in the brain. Then, self-corrected ΔADC was obtained from the ΔADC divided by the maximum ADC (ADC_peak: perfusion-related diffusion) to correct the blood flow effect.

Results: The ΔADC after correction was significantly higher in the iNPH group than in the other two groups. However, there was no significant difference in ADC_peak values among the groups.

Conclusion: Self-corrected ΔADC in iNPH increased because of changes in the biomechanical properties of the brain. Self-corrected ΔADC analysis makes it possible to obtain information on hemodynamically independent water fluctuation as well as perfusion in iNPH.

Advances in knowledge: Analysis self-corrected ΔADC provides simultaneously information on biomechanical properties, perfusion, and water fluctuation in iNPH.

Figure 1.

(a) Regions of interest (ROI) in the frontal white matter on apparent diffusion coefficient (ADC) maps, and (b) ΔADC and ADC_peak obtained from the ADC curve in the cardiac cycle.

Figure 2.

(a) Self-corrected ΔADC values for the control, asymptomatic ventricular dilation or brain atrophy (atrophic VD), and iNPH groups. Representative images of self-corrected ΔADC maps for the (b) control, (c) atrophic VD, and (d) iNPH groups. ΔADC, maximum change in apparent diffusion coefficient during the cardiac cycle; AU, arbitrary units; iNPH, idiopathic normal pressure hydrocephalus; NS, not significant.

Figure 3.

Non-corrected (ΔADC) values for the control, asymptomatic ventricular dilation or brain atrophy (atrophic VD), and iNPH groups. Representative images of non-corrected ΔADC maps for the (b) control, (c) atrophic VD, and (d) iNPH groups. ΔADC, maximum change in apparent diffusion coefficient during the cardiac cycle; iNPH, idiopathic normal pressure hydrocephalus; NS, not significant.

Figure 4.

ADC_{500 peak} values for the control, asymptomatic ventricular dilation or brain atrophy (atrophic VD), and iNPH groups. ADC_{500 peak}, peak apparent diffusion coefficient in the cardiac cycle using b-values of 0 and 500 s/mm²; iNPH, idiopathic normal pressure hydrocephalus; NS, not significant.

Figure 5.

Overview of the self-corrected ΔADC analysis. ΔADC (output), which reflects degree of water fluctuation in brain tissue is caused by cerebral blood flow (perfusion-related diffusion, i.e. peak ADC in the cardiac cycle with low b-value; input) as the driving force. Self-corrected ΔADC, which corresponds to the biomechanical properties, such as intracranial compliance, is calculated from ΔADC normalized by perfusion-related diffusion. ΔADC, maximum change in apparent diffusion coefficient during the cardiac cycle; iNPH, idiopathic normal pressure hydrocephalus; *, Results of this study.