A method of photoacoustic imaging (PAI) or ultrasound (US) imaging of biological tissue , in particular a body part, said method comprising: recording 2D-PAI and/or US images of said biological tissue , each 2D-PAI or US image being associated with a corresponding image plane , wherein said method further comprises providing, prior to recording said 2D-PAI or US images of said biological tissue , an optical pattern on or close to a surface of said biological tissue, said optical pattern comprising one or more optical dyes configured for absorbing light at a pattern-characteristic wavelength, and wherein said method comprises recording 2D-PAI images using pattern-imaging light pulses having a pattern-characteristic wavelength for which the absorption by said one or more dyes is sufficiently high such that said optical pattern is visibly represented in said 2D-PAI images , wherein said optical pattern is configured such that the location of the image plane with respect to the optical pattern can be determined at least approximately from said representation of the optical pattern in said 2D-PAI image and/or that the relative location of consecutively taken 2D-PAI images with respect to each other can be at least approximately determined, wherein said method further comprises determining one or both of - the location of the image plane of each given 2D-PAI or US image of said biological tissue with respect to the optical pattern , and - the relative location of consecutively taken 2D-PAI or US images from the representation of the optical pattern in said given 2D-PAI image(s) , or in one or more 2D-PAI images recorded while a PAI probe is in the same position or a position close to the position in which the given 2D-PAI or US image(s) of said biological tissue is recorded. recording 2D-PAI and/or US images of said biological tissue , each 2D-PAI or US image being associated with a corresponding image plane , wherein said method further comprises providing, prior to recording said 2D-PAI or US images of said biological tissue , an optical pattern on or close to a surface of said biological tissue, said optical pattern comprising one or more optical dyes configured for absorbing light at a pattern-characteristic wavelength, and wherein said method comprises recording 2D-PAI images using pattern-imaging light pulses having a pattern-characteristic wavelength for which the absorption by said one or more dyes is sufficiently high such that said optical pattern is visibly represented in said 2D-PAI images , wherein said optical pattern is configured such that the location of the image plane with respect to the optical pattern can be determined at least approximately from said representation of the optical pattern in said 2D-PAI image and/or that the relative location of consecutively taken 2D-PAI images with respect to each other can be at least approximately determined, wherein said method further comprises determining one or both of - the location of the image plane of each given 2D-PAI or US image of said biological tissue with respect to the optical pattern , and - the relative location of consecutively taken 2D-PAI or US images - the location of the image plane of each given 2D-PAI or US image of said biological tissue with respect to the optical pattern , and - the relative location of consecutively taken 2D-PAI or US images from the representation of the optical pattern in said given 2D-PAI image(s) , or in one or more 2D-PAI images recorded while a PAI probe is in the same position or a position close to the position in which the given 2D-PAI or US image(s) of said biological tissue is recorded. <EOS>