Dynamic changes in apparent diffusion coefficient of white matter and ventricular system during cardiac cycle in idiopathic normal pressure hydrocephalus

The purpose of our study was to compare temporal changes in the apparent diffusion coefficient （ADC） of the brain parenchyma and ventricular system independent of water restriction over the cardiac cycle among 14 patients with idiopathic normal‐pressure hydrocephalus （iNPH）, 9 patients with atrophic ventricular dilation （VD）, and 8 healthy control subjects. On a 1.5‐T magnetic resonance imaging system, electrocardiogram‐triggered single‐shot diffusion echo planar imaging was performed with sensitivity encoding and half‐scan techniques to minimize the bulk motion. Then, an ADC image of each cardiac phase was calculated. The normalized‐ΔADC image was calculated by using the following equation from all cardiac‐phase ADC images （20 phases） :Normalized‐ΔADC＝（ADCmax－ADCmin）/ADCmin, where ADCmax and ADCmin represent the maximum and minimum ADC during the cardiac cycle, respectively. We assessed the mean normalized‐ΔADC, maximum change in ADC（ΔADC）, and mean ADC of the cardiac phases at which the ADC change was stable （ADCstable） in the frontal white matter and the three ventricular regions. No significant differences were observed in the normalized‐ΔADCs of healthy subjects among the brain regions, whereas significant differences were observed in ΔADC and ADCstable between the frontal white matter and each ventricular region. The mean normalized‐ΔADCs of the third ventricle and frontal white matter were significantly higher in the iNPH group than in the control and atrophic VD groups. Normalized‐ΔADC analysis in the frontal white matter and third ventricle may provide more detailed information on intracranial conditions in iNPH, which may be useful for determining a diagnosis.