A low-cost needle-based single-fiber reflectance spectroscopy method to probe scattering changes associated with mineralization in intervertebral discs in chondrodystrophoid canine species – A pilot study

Abstract

Background and objectives:Intervertebral disc herniation is a common disease in chondrodystrophic dogs, and a similar neurologic condition also occurs in humans. Percutaneous laser disc ablation (PLDA) is a minimally invasive procedure used increasingly for prevention of disc herniation. PLDA is performed on thoracolumbar discs to which the same laser energy is applied regardless of their mineral content. Knowledge of individual disc mineral composition would allow laser energy dosage adjustments and more accurate treatment of degenerative discs. Usually, PLDA is guided by radiography/fl uoroscopy, which has a limited sensitivity of approximately 60 % for identifi cation of mineralized discs. An imaging or sensing technology that provides a more accurate pre-operative in-situ assessment of the disc mineralization, and potentially rapid post-operative feedback, could optimize the outcome of the PLDA procedure. A sensing technology of needle-probing single-fi ber refl ectance (SFR) spectroscopy is therefore proposed that is considered to be compatible with PLDA work fl ow. The objective of this study was to demon strate the feasibility of this technology in assessing the increased light scattering associated with mineralization in intervertebral discs in chondrodystrophoid canine species. Materials and methods: A pilot study was performed on a total of 21 intervertebral discs from two cadaveric dogs ( " Dog A " and " Dog B " ). The discs were imaged by computed tomography (CT), radiography, and SFR spectroscopy, before histopathologic examination. SFR spectroscopy in the visible/near-infrared band was performed on the nucleus pulposus of the intervertebral disc through a 20-gauge spinal needle placed percutaneously for PLDA. A normalization method was applied to the raw remission spectra to extract a dimension-less and wavelength-dependent intensity profi le in the 500 -950 nm spectral range. Results: In total, six discs were determined to be degenerative on histopathology, fi ve discs of " Dog A " and one disc of " Dog B " . CT diagnosed all six degenerated discs, whereas radiography missed two of the fi ve degenerated discs of " Dog A " . The wavelength-dependent mean scattering intensity profi les of the six degenerated discs were noticeably higher than the mean scattering intensity profi les of the 15 " normal " or insignifi cantly mineralized discs over the entire spectral range. The mean scattering intensities, averaged over each of the entire profi les, were 2.79 ± 0.58 (mean ± SD) for the six degenerated discs and 1.48 ± 0.37 for the 15 " normal " or insignifi cantly mineralized discs. A two-sample t -test showed p < 0.001 for the difference of the averaged scattering intensity between these both groups of discs. Conclusions: SFR spectroscopy measurements indicate that the increase of light scattering intensity across the entire 500 -950 nm spectral range is associated with the mineralization in canine intervertebral discs. However, the scattering characteristics of the nucleus pulposus measured in this stu...

Percutaneous single‐fiber reflectance spectroscopy of canine intervertebral disc: Is there a potential for in situ probing of mineral degeneration?

“…As intervertebral disc is nearly avascular , SfRS of intervertebral disc is expected to be nearly devoid of spectral modulation by hemoglobin and thereby responds to the changes in scattering properties of the nucleus pulposus. In our previous study performed on 15 normal and 6 degenerated intervertebral discs of two dogs of chondrodystrophoid species, it was demonstrated that the light scattering as measured by interstitial or percutaneous SfRS from the 6 mineralized discs was generally stronger than that from the 15 normal discs, though notable intra‐subject and inter‐subject variations existed. That pilot study also performed CT and radiography, and CT diagnosed all six degenerated discs whereas radiography missed two degenerated discs.…”

“…The reflectance spectrum R tissue ( λ ) of SfRS when the fiber is placed interstitially in a scattering medium or tissue comprises of light scattered from the tissue, light reflected at the fiber/medium interface, and light reflected internally within the fiber paths. By normalizing R tissue ( λ ) according to the following equation where R water (λ) and R air (λ) are the reflectance spectra measured from fiber placed in water and fiber placed in air, respectively, we have …”

“…The normalized SfRS measurement R norm ( λ ) as shown in Equation is free of the effect of source spectral variation. In a tissue medium whose absorption is very small, like the avascular nucleus pulposus of interveterbral disc, the exponential term in Equation is nearly one for a sub‐millimeter path‐length in tissue as a result of SfRS measurement by a 320 µm fiber . The normalized spectral profile R norm ( λ ) should then demonstrate a characteristic of being dependent mainly on .…”

“…It should be noted that, as the SfRS system used by this study is different from the one used in Ref. , the SfRS measurements from these two studies are different in the intensity scale and the spectral range even after applying similar normalization procedure. As a result a qualitative comparison of the SfRS features between these two studies may be meaningful but a direct quantitative integration of the SfRS results from the two studies is not rendered.…”

“…The sample size of this current study is still quite small, but 20 mineralized discs from three dogs permits a better informed comparison of the diagnostic yield of SfRS with respect to that of CT and radiography than in Ref. , and the opportunity to examine correlative features between SfRS outcome and the histopathological determination of the extent of mineral degeneration.…”