title: Diffuse Reflectance Spectroscopy for Surface Measurement of Liver Pathology.
abstract: BACKGROUND
  Liver parenchymal injuries such as steatosis, steatohepatitis, fibrosis, and sinusoidal obstruction syndrome can lead to increased morbidity and liver failure after liver resection. Diffuse reflectance spectroscopy (DRS) is an optical measuring method that is fast, convenient, and established. DRS has previously been used on the liver with an invasive technique consisting of a needle that is inserted into the parenchyma. We developed a DRS system with a hand-held probe that is applied to the liver surface. In this study, we investigated the impact of the liver capsule on DRS measurements and whether liver surface measurements are representative of the whole liver. We also wanted to confirm that we could discriminate between tumor and liver parenchyma by DRS.
  
  
  METHODS
  The instrumentation setup consisted of a light source, a fiber-optic contact probe, and two spectrometers connected to a computer. Patients scheduled for liver resection due to hepatic malignancy were included, and DRS measurements were performed on the excised liver part with and without the liver capsule and alongside a newly cut surface. To estimate the scattering parameters and tissue chromophore volume fractions, including blood, bile, and fat, the measured diffuse reflectance spectra were applied to an analytical model.
  
  
  RESULTS
  In total, 960 DRS spectra from the excised liver tissue of 18 patients were analyzed. All factors analyzed regarding tumor versus liver tissue were significantly different. When measuring through the capsule, the blood volume fraction was found to be 8.4 ± 3.5%, the lipid volume fraction was 9.9 ± 4.7%, and the bile volume fraction was 8.2 ± 4.6%. No differences could be found between surface measurements and cross-sectional measurements. In measurements with/without the liver capsule, the differences in volume fraction were 1.63% (0.75-2.77), -0.54% (-2.97 to 0.32), and -0.15% (-1.06 to 1.24) for blood, lipid, and bile, respectively.
  
  
  CONCLUSIONS
  This study shows that it is possible to manage DRS measurements through the liver capsule and that surface DRS measurements are representative of the whole liver. The results are consistent with data published earlier on the combination of liver chromophores. The results encourage us to proceed with in vivo measurements for further quantification of the liver's composition and assessment of parenchymal damage such as steatosis and fibrosis grade.
authors.affiliation: Department of Clinical Sciences Lund, Surgery, Skåne University Hospital, Lund University, Lund, Sweden.
authors.forename: Jan H
authors.initials: JH
authors.lastname: Nilsson
authors.forename: Nina
authors.initials: N
authors.lastname: Reistad
authors.forename: Hannes
authors.initials: H
authors.lastname: Brange
authors.forename: Carl-Fredrik
authors.initials: CF
authors.lastname: Öberg
authors.forename: Christian
authors.initials: C
authors.lastname: Sturesson
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008099:Liver / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D061848:Optical Imaging / Q000379:methods*; D013057:Spectrum Analysis / Q000379:methods