Challenges and Limitations of Narrow-Band Optical Imaging for Intra-Operative Parathyroid Identification

Abstract

Background: Surgical resection of the parathyroid glands can be challenging due to poor visual contrast between the parathyroid and surrounding tissues. We hypothesized that narrow-band imaging (NBI) could enhance subtle differences in the colors of these tissues for improved visual contrast during parathyroid surgery. Methods: The diffuse optical reflectances of parathyroid, fat, muscle, and thyroid tissue were measured in vivo as a function of wavelength during six surgical procedures, using a fiber-optic probe and spectrophotometer. Analysis of these data led to three candidate NBI wavelength bands which exhibited the largest differences in reflectance between parathyroid and other tissue types. Color filters at these wavelength bands were attached to the surgeon’s loupes for qualitative visual assessment, and also to a digital camera for quantitative assessment of tissue contrast in seven additional surgeries. Results: Spectroscopic measurements showed that diffuse optical reflectance at green (515 - 565 nm), yellow (570 - 613 nm), and red (604 - 644 nm) wavelengths showed the greatest difference in intensity (appearing brighter or darker) between parathyroid and surrounding tissues. However, visual and digital NBI of the parathyroid using these wavebands generated measured intensities which were not significantly improved as compared to white light, providing only minimal contrast enhancement for the surgeon. Conclusions: Narrow-band color filters can be added to conventional loupes to selectively view the surgical field with light at specific wavelengths. When the parathyroid is viewed with filters chosen to maximize visual contrast between tissue types, there appears to be little benefit in contrast enhancement between tissues due to diminished overall brightness. J Curr Surg. 2016;6(1):14-20 doi: http://dx.doi.org/10.14740/jcs295w