### Abstract

In recent years, much effort has been made to increase our ability to infer nerve fiber direction through the use of diffusion MR. The present study examines the effect of the rotational angle (α), i.e. the angle between the diffusion sensitizing gradients and the main axis of the fibers in the nerves, on different NMR indices. The indices examined were the apparent diffusion coefficient (ADC), extracted from low b-values (b_{max} ≈ 1200 s/mm^{2}), and the root mean square (rms) displacement of the fast and the slow-diffusing components extracted from high b-value q-space diffusion MR data. In addition, the effect of both the diffusion time and myelination was evaluated. We found that the most sensitive index to the rotational angle is the rms displacement of the slow-diffusing component extracted from the high b-value q-space diffusion MR experiment. For this component the rms displacement was nearly constant for α values ranging from -10° to +80° (where α = 0° is the z direction), but it changed dramatically when diffusion was measured nearly perpendicular to the nerve fiber direction, i.e., for α = 90 ± 10°. The ADC and the rms displacement of the fast-diffusing component exhibited only gradual changes, with a maximal change at α = 45 ± 15°. The sensitivity of the rms displacement of the slow-diffusing component to the rotational angle was found to be higher at longer diffusion times and in mature fully myelinated nerves. The relevance of these observations for determining the fiber direction is briefly discussed.

Original language | English (US) |
---|---|

Pages (from-to) | 33-42 |

Number of pages | 10 |

Journal | Journal of Magnetic Resonance |

Volume | 190 |

Issue number | 1 |

DOIs | |

State | Published - Jan 2008 |

Externally published | Yes |

### Fingerprint

### Keywords

- Apparent diffusion coefficient (ADC)
- Diffusion MRS
- Fiber direction
- Nerves
- q-Space diffusion

### ASJC Scopus subject areas

- Molecular Biology
- Physical and Theoretical Chemistry
- Spectroscopy
- Radiology Nuclear Medicine and imaging
- Condensed Matter Physics

### Cite this

**The effect of the rotational angle on MR diffusion indices in nerves : Is the rms displacement of the slow-diffusing component a good measure of fiber orientation?** / Bar-Shir, Amnon; Cohen, Yoram.

Research output: Contribution to journal › Article

*Journal of Magnetic Resonance*, vol. 190, no. 1, pp. 33-42. https://doi.org/10.1016/j.jmr.2007.10.007

}

TY - JOUR

T1 - The effect of the rotational angle on MR diffusion indices in nerves

T2 - Is the rms displacement of the slow-diffusing component a good measure of fiber orientation?

AU - Bar-Shir, Amnon

AU - Cohen, Yoram

PY - 2008/1

Y1 - 2008/1

N2 - In recent years, much effort has been made to increase our ability to infer nerve fiber direction through the use of diffusion MR. The present study examines the effect of the rotational angle (α), i.e. the angle between the diffusion sensitizing gradients and the main axis of the fibers in the nerves, on different NMR indices. The indices examined were the apparent diffusion coefficient (ADC), extracted from low b-values (bmax ≈ 1200 s/mm2), and the root mean square (rms) displacement of the fast and the slow-diffusing components extracted from high b-value q-space diffusion MR data. In addition, the effect of both the diffusion time and myelination was evaluated. We found that the most sensitive index to the rotational angle is the rms displacement of the slow-diffusing component extracted from the high b-value q-space diffusion MR experiment. For this component the rms displacement was nearly constant for α values ranging from -10° to +80° (where α = 0° is the z direction), but it changed dramatically when diffusion was measured nearly perpendicular to the nerve fiber direction, i.e., for α = 90 ± 10°. The ADC and the rms displacement of the fast-diffusing component exhibited only gradual changes, with a maximal change at α = 45 ± 15°. The sensitivity of the rms displacement of the slow-diffusing component to the rotational angle was found to be higher at longer diffusion times and in mature fully myelinated nerves. The relevance of these observations for determining the fiber direction is briefly discussed.

AB - In recent years, much effort has been made to increase our ability to infer nerve fiber direction through the use of diffusion MR. The present study examines the effect of the rotational angle (α), i.e. the angle between the diffusion sensitizing gradients and the main axis of the fibers in the nerves, on different NMR indices. The indices examined were the apparent diffusion coefficient (ADC), extracted from low b-values (bmax ≈ 1200 s/mm2), and the root mean square (rms) displacement of the fast and the slow-diffusing components extracted from high b-value q-space diffusion MR data. In addition, the effect of both the diffusion time and myelination was evaluated. We found that the most sensitive index to the rotational angle is the rms displacement of the slow-diffusing component extracted from the high b-value q-space diffusion MR experiment. For this component the rms displacement was nearly constant for α values ranging from -10° to +80° (where α = 0° is the z direction), but it changed dramatically when diffusion was measured nearly perpendicular to the nerve fiber direction, i.e., for α = 90 ± 10°. The ADC and the rms displacement of the fast-diffusing component exhibited only gradual changes, with a maximal change at α = 45 ± 15°. The sensitivity of the rms displacement of the slow-diffusing component to the rotational angle was found to be higher at longer diffusion times and in mature fully myelinated nerves. The relevance of these observations for determining the fiber direction is briefly discussed.

KW - Apparent diffusion coefficient (ADC)

KW - Diffusion MRS

KW - Fiber direction

KW - Nerves

KW - q-Space diffusion

UR - http://www.scopus.com/inward/record.url?scp=36849039451&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=36849039451&partnerID=8YFLogxK

U2 - 10.1016/j.jmr.2007.10.007

DO - 10.1016/j.jmr.2007.10.007

M3 - Article

VL - 190

SP - 33

EP - 42

JO - Journal of Magnetic Resonance

JF - Journal of Magnetic Resonance

SN - 1090-7807

IS - 1

ER -