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. 2021 Jun;34(3):411-419.
doi: 10.1007/s10334-020-00886-w. Epub 2020 Sep 22.

Variable echo time imaging for detecting the short T2* components of the sciatic nerve: a validation study

Paolo Florent Felisaz #  1   2 , Eugenio Belatti #  1 , Xeni Deligianni  3   4 , Niels Bergsland  5   6 , Francesco Santini  7   8 , Matteo Paoletti  1 , Francesca Solazzo  1 , Giancarlo Germani  1 , Andrea Cortese  9   10 , Elisa Vegezzi  9 , Oliver Bieri  7   8 , Stefano Bastianello  1   9 , Anna Pichiecchio  1   9
Affiliations

Variable echo time imaging for detecting the short T2* components of the sciatic nerve: a validation study

Paolo Florent Felisaz et al. MAGMA. 2021 Jun.

Abstract

Objective: The aim of this study was to develop and validate an MRI protocol based on a variable echo time (vTE) sensitive to the short T2* components of the sciatic nerve.

Materials and methods: 15 healthy subjects (M/F: 9/6; age: 21-62) were scanned at 3T targeting the sciatic nerve at the thigh bilaterally, using a dual echo variable echo time (vTE) sequence (based on a spoiled gradient echo acquisition) with echo times of 0.98/5.37 ms. Apparent T2* (aT2*) values of the sciatic nerves were calculated with a mono-exponential fit and used for data comparison.

Results: There were no significant differences in aT2* related to side, sex, age, and BMI, even though small differences for side were reported. Good-to-excellent repeatability and reproducibility were found for geometry of ROIs (Dice indices: intra-rater 0.68-0.7; inter-rater 0.70-0.72) and the related aT2* measures (intra-inter reader ICC 0.95-0.97; 0.66-0.85) from two different operators. Side-related signal-to-noise-ratio non-significant differences were reported, while contrast-to-noise-ratio measures were excellent both for side and echo.

Discussion: Our study introduces a novel MR sequence sensitive to the short T2* components of the sciatic nerve and may be used for the study of peripheral nerve disorders.

Keywords: Fibrosis; Magnetic resonance imaging; Peripheral nerves; Validation study.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
From left to right three axial sections of the right thigh, obtained with the vTE sequence. a Echo 1 with TE1 = 10.9 ms. b Echo 2 with TE2 = 5.37 ms. c Subtraction image. At the bottom, a zoom on the neurovascular fasciculus (white rectangle) visualizes the sciatic nerve. Image (a, b) has quite similar appearance; in a, short T2* components are present but masked by the longer T2* components; in b, short T2* components are completely decayed and only long T2* components are highlighted (both images are fat suppressed). In the subtraction image (c), the longer T2* components are suppressed and tissues made of short T2* components are highlighted. The nerve visualization (red arrow) changes in the Subtraction image (c): some of the fascicles disappear, others are encompassed in brighter areas. In muscles, tendons and fascial structures (yellow arrows) appear dark in figures (a, b), while in the subtraction image, they appear distinctly bright
Fig. 2
Fig. 2
Graph representing the side differences obtained with the Wilcoxon test within the male group (nine subjects) and the female group (six subjects). The Wilcoxon test revealed no significant differences in side for aT2* (females p = 1.000; males p  = 0.300)
Fig. 3
Fig. 3
Graph representing the side differences obtained with the Wilcoxon test within the "young" group (ten subjects) and the "senior" group (five subjects). The Wilcoxon test revealed no significant differences in side for aT2 * (young p = 1.000; senior p = 3.125)
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