title: Percutaneous single-fiber reflectance spectroscopy of canine intervertebral disc: is there a potential for in situ probing of mineral degeneration?
abstract: OBJECTIVE
  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. Currently, PLDA is performed on thoracolumbar discs with the same laser energy applied regardless of the differing extent of degeneration among mineralized discs. In a previous study performed on 15 normal and 6 degenerated intervertebral discs in chondrodystrophoid canine species, it was demonstrated that percutaneous single-fiber reflectance spectroscopy (SfRS) detected increased light scattering from mineralized intervertebral discs when comparing to normal discs. The objective of this study is to evaluate how SfRS evaluation of mineralized discs in situ fairs with X-ray radiography and computed tomography (CT) diagnoses and if SfRS sensing of the scattering changes correlates with the level of mineral degeneration in nucleus pulposus.
  
  
  METHODS
  Percutaneous SfRS was performed on a total of 28 intervertebral discs of three dogs post-mortem, through a 20 gauge spinal needle standard to PLDA. The raw SfRS measurement was normalized to extract a dimension-less spectral intensity profile, from which the average over 600-900 nm was used as the SfRS intensity index to compare among the measured discs. The discs were imaged prior to percutaneous SfRS by radiography and CT, and harvested after percutaneous SfRS for histopathologic examinations.
  
  
  RESULTS
  Five among 10 discs of dog #1, six among 9 discs of dog #2, and nine out of 9 discs of dog #3 were determined by histopathology to have central focal or multi-focal areas of mineralization occupying 5-75% of the examined area of nucleus pulposus. The overall numbers of discs with detectable and undetectable central mineralization were 20 and 8, respectively. CT resulted in one false positive (FP) and four false negative (FN) diagnoses for dog #1, three FP and zero FN diagnoses for dog #2, and zero FP and one FN diagnosis for dog #3. Of the total 28 discs the CT had an overall positive predictive value (PPV) of 78.8% and an overall negative predictive value (NPV) of 44.4%. X-ray radiography gave five FN diagnoses for dog #1, two FN diagnoses for dog #2, and eight FN diagnoses for dog #3. Of the total 28 discs the radiography had an overall PPV of 100% and an overall NPV of 30.4%. The receiver-operating-characteristic analysis of the SfRS measurement was performed on 24 discs that had a central mineralization not greater than 50%. An area-under-curve of 0.6758 infers that the SfRS intensity weakly indicates the level of mineralization.
  
  
  CONCLUSIONS
  Percutaneous SfRS may be useful as an in situ sensing tool for assessing the level of mineral degeneration in intervertebral discs for the prospect of disc-specific dosage adjustment in PLDA.
authors.affiliation: School of Electrical and Computer Engineering, Oklahoma State University, 202 Engineering South, Stillwater, Oklahoma, 74078.
authors.forename: Daqing
authors.initials: D
authors.lastname: Piao
authors.forename: Kelci L
authors.initials: KL
authors.lastname: McKeirnan
authors.forename: Nigar
authors.initials: N
authors.lastname: Sultana
authors.forename: Melanie A
authors.initials: MA
authors.lastname: Breshears
authors.forename: Anqi
authors.initials: A
authors.lastname: Zhang
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Bartels
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004285:Dogs; D005336:Fiber Optic Technology; D066298:In Vitro Techniques; D007405:Intervertebral Disc Displacement / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000378:metabolism; D008903:Minerals / Q000378:metabolism; D011237:Predictive Value of Tests; D013057:Spectrum Analysis / Q000379:methods*; D014057:Tomography, X-Ray Computed
chemical_list: D008903:Minerals
keywords: intervertebral disc degeneration; percutaneous laser disc ablation; scattering; single-fiber reflectance spectroscopy