Fig. 1.

Endogenous tissue chromophores in photoacoustic imaging. (a) Optical absorption spectra of the main tissue chromophores, including DNA (data adapted from [20]), RNA (data adapted from [22]), oxyhaemoglobin, deoxyhaemoglobin (150 g L⁻¹), melanin (data from https://omlc.org/spectra/), water and lipid (data adapted from [18]). (b) Ultraviolet localised photoacoustic (PA) image of a fibroblast cell with lipids, protein and nucleic acids contents shown in pseudo-coloured blue, green and red, respectively. This image was adapted from Ref [21] with permission. (c) PA image of a melanoma mouse model in vivo. Melanoma (pseudo-coloured brown) visualised with 784 nm excitation was surrounded by microvasculature (pseudo-coloured red) visualised at 584 nm with six orders of vessel branching. M, Melanoma. This image was adapted from Ref. [15] with permission. (d) PA image of a human lymph node with lipid (grayscale) and haemoglobin (pseudo-coloured red) contrast with optical excitation at 1210 nm and 530 nm, respectively. This image was adapted from Ref. [26] with permission. (e) Multispectral PAI of a mouse tumour model. Oxyhaemoglobin and deoxyhaemoglobin distributions were pseudo-coloured in red and blue, respectively. White arrows indicated the region of a tumour core with a low level of blood oxygen concentration. Inset is a photograph of the corresponding cross-section of the imaged tumour region. This image was adapted from Ref. [6] with permission.