3D PRINTED MODEL FOR SIMULATION OF CEREBROSPINAL FLUID MOTION IN THE CERVICAL SPINAL SUBARACHNOID SPACE Suraj Thyagaraj1, 2, Soroush H Pahlavian1, 2, Morteza Vatani1, Jae-Won Choi1, Mark Goodin3, Alexander Bunck4, Theresia Yiallourou5, Francis Loth1, 2, Bryn A Martin1, 2 1
Department of Mechanical Engineering, The University of Akron, Akron, OH, USA, 2Conquer Chiari Research Center, The University of Akron, Akron, OH, USA, 3Simutech Group, Hudson, OH, USA, 4Department of Radiology, University of Münster, Münster, Germany, 5Laboratory of Hemodynamics and Cardiovascular Technology, Swiss Federal Institute of Technology Email:
[email protected], Web: http://uakron.chiari-research.org/
INTRODUCTION Detection of cerebrospinal fluid (CSF) motion by 4D phase-contrast MRI (4D PCMRI) has been used to provide quantitative flow-based parameters to assess cranio-spinal disorders such as type I Chiari malformation. However, studies have shown that 4D PCMRI measurements of CSF motion have large degree of noise and vary widely between MRI scanners [1]. The aim of this study was to construct and characterize an in vitro model of the upper cervical spine that will be used to test and optimize the 4D PCMRI scan [2]. METHODS High-resolution T2-weighted MRI images were acquired over the upper cervical spinal subarachnoid space (SSS) for a healthy male subject (age 22) with an isotropic spatial resolution of 0.8 mm. Phase-contrast MRI was obtained at C2 level to define the CSF flow waveform. Images were manually segmented to define the SSS in terms of the spinal cord and dura from ~2 cm cranial to the foramen magnum to ~5 cm caudal to C7. Idealized dorsal and ventral spinal cord nerve roots were added to the model based on measurements in the literature. Flow inlet and outlet extensions were added and an STL was created for the overall model and 3D printed with ~75 µm resolution (Figure 1). A pulsatile computer-controlled pump was constructed to input the subject-specific CSF flow waveform and DAQ system utilized to record unsteady pressure within the SSS at 2 cm intervals along the model. A rigid wall computational fluid dynamics (CFD) simulation was conducted for the model geometry with the same flow waveform boundary condition and results were compared in terms of differential pressure waveform along the model, DP(t), and longitudinal impedance (LI, ratio of the FFT of DP(t) to the FFT of Q(t) [3, 4]).
Figure 2: Comparison of CFD (red) and bench-top (blue) DP(t) waveforms (y-axis left) and phase relation with input mass flow rate (y-axis right). RESULTS AND DISCUSSION Comparison of CFD and bench-top DP(t) waveforms (Figure 2) showed similar trends with an RMS error equal to 11.8% of the mean amplitude of the two waveforms. CFD results revealed a complex CSF flow field due to the presence of nerve roots. LI based on CFD and bench-top results was 2840 and 2531 dyne/cm5, respectively. CONCLUSIONS An MRI compatible fluidic model of the cervical SSS was successfully constructed and characterized by CFD and preliminary bench-top testing. REFERENCES [1] Bunck, A. C., Kroeger, J. R., Juettner, A., Brentrup, A., Fiedler, B., Crelier, G. R., Martin, B. A., Heindel, W., Maintz, D., Schwindt, W., and Niederstadt, T., 2012, "MRI 4D flow analysis of CSF dynamics in Chiari I malformation," European radiology, 22(9), pp. 1860-1870. [2] Yiallourou, T. I., Kröger, J. R., Stergiopulos, N., Maintz, D., Martin, B. A., and Bunck, A. C., 2012, "Comparison of 4D Phase-Contrast MRI Flow Measurements to Computational …," PLoS ONE, 7(12), p. e52284. [3] Martin, B. A., Kalata, W., Shaffer, N., Fischer, P., Luciano, M., and Loth, F., 2013, "Hydrodynamic and longitudinal impedance analysis of cerebrospinal fluid dynamics," PLoS One, In Press. [4] Shaffer, N., Martin, B. A., Roque, B., Madura, C., Wieben, O., Iskandar, B., Luciano, M., Oshinski, J. N., and Loth, F., 2013, "CSF Flow Impedance is Elevated in Type I Chiari Malformation," J Biomech Eng-T Asme, In Press.
Figure 1: 3D printed model of the upper cervical spine with dorsal and ventral spinal cord nerve roots and flow extension inlet and outlets (cranial = left, caudal = right, anterior = bottom, posterior = top).
This work is supported by the American Syringomyelia and Chiari Alliance Project.
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