Role of optical spectroscopy using endogenous contrasts in clinical cancer diagnosis

Table 1 Primary absorbers and scatterers present in tissues

Light-tissue interaction	Source
Absorption	Hemoglobin, β-carotene, water, lipid
(Raleigh) scattering	Nuclei, mitochondria, collagen fibers
Raman scattering	Cell cytoplasm, cell nucleus, fat, collagen, cholesterol-like lipid deposits and water

Table 2 Primary endogenous fluorophores, their peak excitation-emission wavelength pairs and location in human epithelial tissues[13]

Category of fluorophores	Endogenous fluorophores	Peak excitation-emission wavelength pair (nm)	Primary tissue location
Structural protein	Collagen	325-400	Stroma
Electron carrier	FAD	450-535	Cells
	NADH	351-460	Cells
Amino acid	Tryptophan	280-350	Proteins

FAD: Flavin adenine dinucleotide; NADH: Reduced nicotinamide adenine dinucleotide.

Table 3 Summary of techniques, patient population and accuracy in previous optical spectroscopy studies for intraoperative breast margin assessment

Author	Techniques	Patient population	Accuracy
Bigio et al[41]	Elastic-scattering spectroscopy (a special diffuse reflectance spectroscopy)	31 women, a total of 72 histology sites in breast tissue	Sensitivities of 69% and specificities of 85% for breast tissue
Haka et al[42]	Raman spectroscopy	9 patients undergoing partial mastectomy procedures	Accuracy of 100% for carcinoma; accuracy of 93.3% for distinguishing cancerous from normal and benign tissues
Ramanujam et al[43]	Diffuse reflectance spectroscopy in spectral imaging	55 margins in 48 patients.	Sensitivity of 79% and specificity of 67% for detection of residual tumor, with an 89% sensitivity for ductal carcinoma in situ alone
Keller et al[44]	Autofluorescence and diffuse reflectance spectroscopy and spectral imaging	145 normal spectra were obtained from 28 patients, and 34 tumor spectra were obtained from 12 patients	Differentiate normal tissue or tumor with 85% sensitivity and 96% specificity