Nitish-DT-MREIT_Canine brain

Implementation of anisotropic conductivity in canine brain using a combination of DTI and MREIT

Nitish Katoch1, Bup Kyung Choi1, Woo Chul Jeong1, Saurav Z.K. Sajib1, Hyung Joong Kim1, Oh In Kwon1 and Eung Jee Woo1

1 Impedance Imaging Research Center, Kyung Hee University, Korea2 Department of Mathematics, Konkuk University, Korea

Introduction • Conductivity of the biological tissue can be described using cell-suspension model

where the tissues or cell are assumed to the submerged in the extracellular fluid contain-ing ions.

• The cell medium is separated by the thin membrane.

• For the uniform suspension of the sphere the observed conductivity depends on the ex-tracellular volume fraction (f) and the conductivity of the extracellular medium σe

,

• Tissue anisotropy arise due to the shape, orientation and density of the cell.

Anisotropic conductivity in canine brain using a combination of DTI and MREIT IBEC 2015

1.Roth, B. J., 2000, 2nd Edition. Ed. Joseph D. Bronzino, Boca Raton: CRC Press LLC.2.Cole K.S., Li C.L. and Bak A.F., 1967, Exp. Neurol. 24, 459-473.

MREIT data acquisition

MREIT pulse sequence diagram Calculation of magnetic flux density


1. Parck C. et al., 2007, Physiol. Meas., 28, 117-127.2. Minhas A. S. et al.,2011, MRM, 66, 957-965.

Requirement in MREITAnisotropic conductivity in canine brain using a combination of DTI and MREIT IBEC 2015

Seo J.K. and Woo E.J. , 2013, ch-9, Wiley Chicherter, UK.

Focused current density, JF

The relation between the measured Bz data and the current density J based on Ampere’s law :

Using the Biot-Savart law :

Focused current density, JF:

Bzd is Bz – Bz

0 , B0 represents the background magnetic flux density

u0 is the voltage potential

Current density imaging in MREIT

magnetic permeability of free space

Jx Jy Jz

Bx By Bz

Jx0 Jy

0 Jz0

Bx0 By

0 Bz0

is the magnetic flux density due to the current I along the external wires.

μ0=4𝜋×10−7


Jeong W.C. et al., IEEE Trans. Biomed. Eng., 2014.


Reconstruction algorithms in MREIT

1. Kwon et al., 2002, IEEE Trans. Biomed. Eng., 49(2),160-167.2. Khang et al., 2002, IEEE Trans. Biomed. Eng., 21 (6), 695-702.3. Seo et al., 2003, IEEE Trans. Biomed. Eng., 50 (9), 1121-1124.4. Oh et. al., 2003, Phys. Med. Biol., 48, 3101-3116.5. Park et al., 2004, IEEE Trans. Med. Imaging, 28 , 388-394.6. Nam et al., 2007, Phys. Med. Biol., 57, 6717-6730.7. Nam H S, Park C and Kwon O.I., 2008, Phys. Med. Biol., 53, 6947-6961.

Background• DT-MREIT technique is developed for the anisotropic conductivity

estimation.

• DTI is utilized to provide the directional information of the conduc-tivity tensor and its magnitude is estimated from measured MREIT magnetic flux density data.

Scale factor estimation using MREIT

Diffusion tensor Conductivity tensor


Kwon et. al., Phys. Med. Biol., 2014.


Here, are the intra and extracellular diffusion coefficient and is the extracellu-lar conductivity. The diffusivity and conductivity Eigen values are represented by, , respectively.

where scale factor, =

• With the assumption of small intracellular diffusivity, the Eigen-values of the effective conductivity and the diffusivity tensor () are proportional,

is the diffusion tensors is the conductivity tensors is the extracellular conductivity , di are the extracellular and intracellular diffusion coefficient

• Since the effective conductivity depends on the concentration and the effective mobility of ion therefore, it requires an experimental technique to measure the scale factor.

Relation between D and C

Tuch et al.

𝛁 lnη× (𝐃−1 𝐉 )=𝛁× (𝐃−1 𝐉 )

Phantom 𝐁𝐳 𝐜𝐅𝐀

Measured data set

Reconstructed scale factor

a.

σ 11 σ 22 σ 33

σ 12 σ 13 σ 23

σ 11 σ 22 σ 33

σ 12 σ 13 σ 23

[S/m]

0

2

0

2-0.15

0.15

-0.15

0.15

b.

c.

b). Reconstructed conductivity tensor using the pro-posed method. c. Reconstructed conductivity tensor without using current density information.


Combining DTI and MREIT

a). Method to reconstruct anisotropic conductivity tensor by incorporating the directional information from DT-MRI and the magnetic flux density from MREIT experiment.

Kwon et. al., Phys. Med. Biol., 2014.

Purpose

• To map the electrical conductivity distribution in an anisotropic as well as isotropic regions of brain tis-sues using DT-MREIT technique.


Experimental parameter and Sequence

Imaging parametersImaging pulse sequence diagramDTI MREIT


Experimental setup

• Imaging object: A postmortem canine.

• MRI scanner: 3 T Achieva TX (Philips, The Nether-

land)

• RF coil: 8-channel knee coil

• MREIT Constant current source

• Electrode

− Carbon-hydrogel electrode.

− Diameter: 30 mm

− Distance: 30 mm


Experimental setup for DT-MREIT imaging experiment.

Result: Measured imagesAnisotropic conductivity in canine brain using a combination of DTI and MREIT IBEC 2015

(a) MR magnitude image. (b, c) Bz,1 and Bz,2 images subject to the horizontal and ver-tical current injections. (d) Color-coded fractional anisotropy map from the diffusion tensor images.

Result: Reconstructed scale factor

Reconstructed scale factorProjected current density

Diffusion tensor



Anisotropic conductivity tensor map

(b) Recovered conductivity tensor (C = D) from the estimated scale factor and the DTI data.

Table. Reconstructed conductivity values with-in the chosen four ROIs.

(a) MR magnitude image during MREIT experiment. The circle shows the location of the ROI to measure the conductivity values in table. (b) Collected image induced due to 10 mA current injection. (c) Color-coded frac-tional anisotropy map from the diffusion tensor images.

Reconstructed scale factor

MR FAcc

Conclusion

• DT-MREIT method can quantitatively recovers the direction and magnitude of an aniso-tropic conductivity tensor as well as the isotropic conductivity value of brain tissues.

• There could be numerous potential applications for the brain and muscle including is-chemia, inflammation, bleeding and tumor.

• Future studies should include more rigorous validations of this method through in vivo an-imal experiments.


Thanks for your attention.!

Nitish KatochKyung Hee UniversityE mail: nitish@ khu.ac.kr

Prof. Eung Je Woo, Ph.D.E mail: ejwoo@ khu.ac.kr


Nitish-DT-MREIT_Canine brain

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