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

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RESEARCH ARTICLE

Variable echo time imaging for detecting the short T2* components of the sciatic nerve: a validation study Paolo Florent Felisaz1,2 · Eugenio Belatti1 · Xeni Deligianni3,4   · Niels Bergsland5,6 · Francesco Santini3,4 · Matteo Paoletti1 · Francesca Solazzo1 · Giancarlo Germani1 · Andrea Cortese7,8 · Elisa Vegezzi7 · Oliver Bieri3,4 · Stefano Bastianello1,7 · Anna Pichiecchio1,7 Received: 30 April 2020 / Revised: 27 August 2020 / Accepted: 1 September 2020 © The Author(s) 2020

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: intrarater 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  Magnetic resonance imaging · Peripheral nerves · Fibrosis · Validation study

Introduction MR neurography has gained increasing interest for the study of nerves in different conditions and new biomarkers sensitive to pre-clinically evident nerve damage are emerging [1, 2]. Compared to muscles in which degenerative changes Paolo Florent Felisaz and Eugenio Belatti are equal first authors. * Xeni Deligianni [email protected] 1

are readily depicted as fat infiltration [3, 4], nerve degeneration is not commonly studied with MRI. The possibility to detect both early inflammation and chronic dystrophic changes could help to expand the role of MR neurography and its applicability to neuromuscular diseases in which the nerve is primarily concerned. MR neurography protocols typically comprise conventional sequences that can detect signal from the long T2 5



Department of Neurology, Buffalo Neuroimaging Analysis Center, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, State University of New York, Buffalo, NY, USA



Department of Neuroradiology, IRCCS Mondino Foundation, Pavia, Italy

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Department of Radiology, Desio Hospital, ASST Monza, Desio, Italy



IRCCS, Fondazione Don Carlo Gnocchi, Milan, Italy