Photoacoustics spectral analysis for in vivo detection of collagen contents in cancers

Noninvasive in vivo real-time measurements of the collagen contents offer valuable information for studying the state of cancers. In this study, the feasibility of semi-quantitatively detecting the collagen contents in cancers based on photoacoustics spectral analysis (PASA) was investigated. The parameter "area of power spectrum density (APSD)" was used to quantify the energy of photoacoustic (PA) signals produced by biomacro-molecules inside cancers. The relative collagen contents on the maximum cross-section of cancers were evaluated by the pathological staining and were regressed against the APSD spectra pre-processed by the Savitzky-Golay (S-G) 1st method utilizing the Partial least squares (PLS) algorithm. The correctness of the regression model was confirmed by calculating the loadings and the variable importance in projection (VIP) scores to determine the wavelengths at which APSD had a more significant influence on the regression. The results show that the PASA method achieves detecting the collagen contents in cancers at a tolerable accuracy (the Pearson correlation coefficients reached 0.66 for in vivo tests) and is valid (the APSD at collagen-dominated absorption wavelength had the greatest weight). The proposed method indicates that PASA for semi-quantifying collagen contents is promising for the clinical assessment of cancers.