Extracting morphometric information from rat sciatic nerve using optical coherence tomography

Abstract

We apply three optical coherence tomography (OCT) image analysis techniques to extract morphometric information from OCT images obtained on peripheral nerves of rat. The accuracy of each technique is evaluated against histological measurements accurate to þ∕ − 1 μm. The three OCT techniques are: (1) average depth-resolved profile (ADRP), (2) autoregressive spectral estimation (AR-SE), and (3) correlation of the derivative spectral estimation (CoD-SE). We introduce a scanning window to the ADRP technique, which provides transverse resolution and improves epineurium thickness estimates-with the number of analyzed images showing agreement with histology increasing from 2∕10 to 5∕10 (Kruskal-Wallis test, α ¼ 0.05). A method of estimating epineurium thickness, using the AR-SE technique, showed agreement with histology in 6∕10 analyzed images (Kruskal-Wallis test, α ¼ 0.05). Using a tissue sample in which histology identified two fascicles with an estimated difference in mean fiber diameter of 4 μm, the AR-SE and CoD-SE techniques both correctly identified the fascicle with larger fiber diameter distribution but incorrectly estimated the magnitude of this difference as 0.5 μm. The ability of the OCT signal analysis techniques to extract accurate morphometric details from peripheral nerves is promising but restricted in depth by scattering in adipose and neural tissues.

Organotopic Organization of the Cervical Vagus Nerve

“…Techniques allowing imaging of the anatomy of peripheral nerve in vivo include photoacoustic tomography, magnetic resonance imaging (Rangavajla et al, 2014), optical coherence tomography (OCT) (Raphael et al, 2007; Hope et al, 2018; Carolus et al, 2019; Vasudevan et al, 2019) and ultrahigh-frequency and high-resolution ultrasound (Beekman and Visser, 2004; Cartwright et al, 2017; Settell et al, 2021). Unfortunately, none have sufficient tissue contrast, resolution, clarity and penetration depth to trace fascicles confidently along the entire length of the vagus nerve which is >60cm in large animals such as the pig or humans.…”

Analysis of low-scattering regions in optical coherence tomography: applications to neurography and lymphangiography

“…Fascicles are bound together by epineurium tissue tens of microns thick [29]. Nerve fibers themselves are positively contrasted in the OCT images but electrically insulating tissues around them are semi-transparent [30]. To date, reports of OCT nerve imaging outside of ophthalmology have been limited to visualization of large (∼1 mm in diameter) peripheral nerves in animal models following traumatic crush injury, suture ligation, and transection [31][32][33].…”

Infrared neurostimulation in ex-vivo rat sciatic nerve using 1470 nm wavelength

“…confinement region), we can predict the instantaneous temperature rise at the nerve surface (26.1 ± 5.6 • C). If the averaged thickness of the epineurium and perineurium combined (∼90 µm) is taken into account [85], the estimated temperature rise at the level of the first nerve fibres is 16…”