Synthetic white balancing for intra-operative hyperspectral imaging

Anisha Bahl*, Conor Horgan, Mirek Janatka, Oscar MacCormac, Philip Noonan, Yijing Xie, Jianrong Qiu, Nicola Cavalcanti, Philipp Furnstahl, Michael Ebner, Mads Bergholt, Jonathan Shapey, Tom Vercauteren

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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Abstract

Purpose
Hyperspectral imaging shows promise for surgical applications to non-invasively provide spatially-resolved, spectral information. For calibration purposes, a white reference image of a highly-reflective Lambertian surface should be obtained under the same imaging conditions. Standard white references are not sterilizable, and so are unsuitable for surgical environments. We demonstrate the necessity for in situ white references and address this by proposing a novel, sterile, synthetic reference construction algorithm.
Approach
The use of references obtained at different distances and lighting conditions to the subject were examined. Spectra and color reconstructions were compared with standard measurements qualitatively and quantitatively, using ΔE and normalised RMSE respectively. The algorithm forms a composite image from a video of a standard sterile ruler, whose imperfect reflectivity is compensated for. The reference is modelled as the product of independent spatial and spectral components, and a scalar factor accounting for gain, exposure, and light intensity. Evaluation of synthetic references against ideal but non-sterile references is performed using the same metrics alongside pixel-by-pixel errors. Finally, intraoperative integration is assessed though cadaveric experiments.
Results
Improper white balancing leads to increases in all quantitative and qualitative errors. Synthetic references achieve median pixel-by-pixel errors lower than 6.5% and produce similar reconstructions and errors to an ideal reference. The algorithm integrated well into surgical workflow, achieving median pixel-by-pixel errors of 4.77%, while maintaining good spectral and color reconstruction.
Conclusions
We demonstrate the importance of in situ white referencing and present a novel synthetic referencing algorithm. This algorithm is suitable for surgery whilst maintaining the quality of classical data reconstruction.
Original languageEnglish
JournalJournal of Medical Imaging
Publication statusAccepted/In press - 5 Jul 2023

Keywords

  • hyperspectral imaging
  • Multispectral imaging
  • intraoperative imaging
  • White balancing
  • Illuminant correction
  • Vignetting correction

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