Needle-based refractive index measurement using low-coherence interferometry

Abstract

We present a novel needle-based device for the measurement of refractive index and scattering using low-coherence interferometry. Coupled to the sample arm of an optical coherence tomography system, the device detects the scattering response of, and optical path length through, a sample residing in a fixed-width channel. We report use of the device to make near-infrared measurements of tissues and materials with known optical properties. The device could be used to exploit the refractive index variations of tissue for medical and biological diagnostics accessible by needle insertion.

Detecting precancerous lesions in the hamster cheek pouch using spectroscopic white-light optical coherence tomography to assess nuclear morphology via spectral oscillations

“…An average refractive index for the tissue of n = 1.38 was used to convert depth scan distances to optical path lengths. 15,16 Variation of the refractive index within the tissue is a potential limitation of the current method and is discussed further in the following.…”

Optical Coherence Tomography in a Needle Format

“…Alternatively, the relative displacement of scatterers in consecutive A-scans can be analyzed in order to determine the mechanical properties of soft tissue that lies ahead of the needle [58]. Processing of single A-scans acquired with point-sensing needles has been used to obtain localized tissue parameters such as the refractive index [59,60] or attenuation coefficient [4]. An exhaustive discussion of the technology and applications of point-sensing needles lies outside the scope of this section, and we will, therefore, focus our attention on imaging needles.…”

Staying coherent after kent: From optical communications to biomedical optics

“…This technique produced an average refractive index measured over the two peaks which could be used to readily scan a sample or make a point measurement [89]. We also implemented a version of this measurement in a needle format to access solid tissues [90]. The needle version came about because Adam Zysk, then a PhD student in Stephen Boppart's lab at the University of Illinois at Urbana Champaign, was working on refractive index tomography and noticed our work.…”