Naoki Ohno1, Tosiaki Miyati1, Shinnosuke Hiratsuka2, Shota Ishida3, Noam Alperin4, Satoshi Kobayashi1, and Toshifumi Gabata5
1Faculty of Health Sciences, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University, Kanazawa, Japan, 2Department of Radiology, Shiga University of Medical Science Hospital, Otsu, Japan, 3Division of Health Sciences, Graduate School of Medical Science, Kanazawa University, Kanazawa, Japan, 4Department of Radiology, University of Miami, Miami, FL, United States, 5Department of Radiology, Kanazawa University, Kanazawa, Japan
Synopsis
To quantify the effect of posture on intracranial condition, we assessed
intracranial volume change (ΔICVC),
pressure gradient (ΔPG), intracranial
compliance index (ICCI), and apparent
diffusion coefficient (ADC) change of the brain during the cardiac cycle (ΔADC) in head-down tilt (HDT) and
horizontal supine positions. ΔPG was significantly increased on HDT compared with that in the horizontal
supine position because of the intracranial pressure compensatory mechanism.
However, there were no significant differences in other parameters between
postures. ΔPG analysis in the HDT and horizontal supine
positions makes it possible to evaluate intracranial conditions concerning the
intracranial pressure compensatory faculty.Introduction
Assessment
of intracranial condition using magnetic resonance imaging (MRI) is usually
performed in the horizontal supine position. However, intracranial
hydrodynamics and cerebral hemodynamics are strongly affected by body posture
because of gravity-related hydrostatic pressure change [1].
In particular, the head-down tilt (HDT) position which simulates the
microgravity environment has been widely used to evaluate the change of
intracranial physiology in space [2]. The
changes in intracranial physiology depending on body posture could provide more
detailed information on intracranial conditions (eg., homeostasis,
biomechanical properties). Therefore, to quantify the effect of posture on
intracranial condition, we assessed the intracranial physiology-related
parameters in the HDT and horizontal supine positions.
Methods
On a 3.0-T MRI, we set a transverse slice at the C2
level, and a retrospective ECG-synchronized phase-contrast cine-MRI was used to
obtain transcranial blood flow, CSF flow, and spinal cord displacement. Next,
we calculated intracranial volume change (
ΔICVC),
pressure gradient (
ΔPG), and
intracranial compliance index (
ICCI).
Moreover, ECG-triggered single-shot diffusion EPI was performed with
sensitivity encoding and half-scan techniques to minimize the bulk motion.
Next, apparent diffusion coefficient (ADC) images of about 30 phases in the
cardiac cycle were calculated. Then, we determined the ADC change of the brain
during the cardiac cycle (
ΔADC). The
above-mentioned parameters were evaluated and compared in healthy volunteers
(n=10) both in the HDT (ranged from -6 to -8 degrees) and horizontal supine
positions (Fig. 1).
Results and Discussion
ΔPG was significantly increased on HDT (
P < 0.05) compared with that in the
horizontal supine position because of the intracranial pressure compensatory
mechanism (Fig. 2). However, there were no significant differences in
ΔICVC,
ICCI, and
ΔADC between
postures (Figs. 3-5).
Conclusion
ΔPG analysis in the HDT and horizontal supine
positions makes it possible to evaluate intracranial conditions concerning the
intracranial pressure compensatory faculty.
Acknowledgements
No acknowledgement found.References
[1] Alperin N, Lee SH, Sivaramakrishnan A, et al. Quantifying the
effect of posture on intracranial physiology in humans by MRI flow studies. J Magn Reson Imaging. 2005;22;591-596.
[2] Rao LL, Zhou Y, Liang ZY, et al. Decreasing ventromedial
prefrontal cortex deactivation in risky decision making after simulated
microgravity: effects of -6° head-down tilt bed rest. Front Behav Neurosci. 2014;8:187.