Naoki Ohno1, Tosiaki Miyati1, Marina Takatsuji2, Mitsuhito Mase3, Tomoshi Osawa3, and Yuta Shibamoto4
1Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan, 2Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Kanazawa, Japan, 3Department of Neurosurgery and Restorative Neuroscience, Graduate School of Medical Sciences, Nagoya City University, Nagoya, Japan, 4Department of Radiology, Nagoya City University, Nagoya, Japan
Synopsis
Apparent diffusion coefficient (ADC) of the brain significantly
changed during the cardiac cycle because of the water-molecule fluctuation.
Moreover, this information assists in the diagnosis of idiopathic normal
pressure hydrocephalus (iNPH). However, these changes (ΔADC) are affected by cerebral
blood flow. Therefore, we corrected the effect of blood flow by using the
diffusion data to evaluate hemodynamic-independent water fluctuation in iNPH. Corrected-ΔADC
was significantly higher in iNPH group compared with control and atrophic
ventricular dilatation groups. Hemodynamically independent analysis for water
fluctuation MRI makes it possible to obtain more detailed information on
biomechanical properties in iNPH.INTRODUCTION
We have
reported that the apparent diffusion coefficient (ADC) of the brain
significantly changed during the cardiac cycle because of the water-molecule
fluctuation, and this information assists in the diagnosis of idiopathic normal
pressure hydrocephalus (iNPH) [1]. However,
these changes are affected by cerebral blood flow as a driving force for
fluctuating water-molecules [2]. Therefore, we
corrected the effect of blood flow by using the diffusion data to evaluate
hemodynamic-independent water fluctuation in iNPH.
METHODS
On a 1.5 T MRI, ECG-triggered single-shot
diffusion echo-planar imaging was performed with the following parameters: repetition time, 2 R-R intervals; echo time, shortest; flip angle,
90°; section thickness, 4 mm; imaging matrix, 64×64 ; field of view, 256 mm;
number of signals averaged, 2; cardiac phases (different phases acquired by
varying the ECG trigger delay), 20; b-values, 0, 500, and 1000 s/mm
2;
separate measures in the X-, Y-, and Z-axis directions; parallel imaging
factor, 2; and half-scan factor, 0.6. Under these imaging conditions, the
duration of data-sampling window can be 8.5 ms. Next, we determined the peak ADC with b =
0-500 (ADC
peak: perfusion-related diffusion component) and maximum
change in ADC with b = 0-1000 (ΔADC: water fluctuation component) in the
cardiac cycle, and divided the ΔADC by the ADC
peak
(Corrected-ΔADC). We compared the
Corrected-ΔADC and ADC
peak
in the white matter among iNPH (n=17), atrophic ventricular dilatation
(atrophic VD group; n=9), and healthy volunteers (control group; n=8).
RESULTS AND DISCUSSION
Corrected-ΔADC was significantly higher in the iNPH
group compared with the control and atrophic VD groups as well as the non
Corrected-ΔADC (Figs. 1 and 2), whereas there was no significant
difference in ADC
peak among the groups (Fig. 3). These results indicate that hemodynamic-independent
water fluctuation, ie., biomechanical property of the brain between the cerebral blood flow
(input) and water fluctuation (output), is increased in iNPH because of low
compliance.
CONCLUSION
Corrected-ΔADC analysis, as a noninvasive
MRI method to assess the degree of fluctuation of the water molecules
hemodynamic-independently, makes it possible to obtain more detailed
information on biomechanical properties in iNPH.
Acknowledgements
No acknowledgement found.References
[1] Ohno N, Miyati T, Mase M, et al. Idiopathic normal-pressure
hydrocephalus: temporal changes in ADC during cardiac cycle. Radiology. 2011;261:560-565.
[2] Takatsuji M, Miyati T, Ohno N, et al. Self correction of blood
flow effect for brain-fluctuation MRI. Proc.
Intl. Soc. Mag. Reson. Med.
2014;22:4551.