A method of analysing breast tissue from an image of a breast comprising the steps of: providing an electronic image of tissue (100,400,450,600,800,1100); running an inner breast edge detection algorithm on the electronic image to detect the inner breast edge on the image; determining a reference spot(1070,1170,1270) based upon an analysis of either breast tissue internal to the inner breast edge or breast tissue between the inner breast edge and an outer breast edge; calculating h int and h fat values for pixel values P(x,y) measured at co-ordinates x,y in the image, wherein h int is thickness of interesting tissue comprising fibrous tissue, glandular tissue, water or cancerous tissue, and h fat is thickness of fat; establishing an h int representation (500,700) of the image; using the h int representation in analysis of the tissue; summing the h int and h fat values to quantify the breast tissue; adjusting a calibration error value until image data for the reference spot matches theoretical data for the reference spot; and checking if the calibration error value is acceptable; wherein the adjusting of the calibration error value comprises adjusting a value of κ, wherein κ is a linear confidence metric, in the following equation until the left hand side of the equation, representing the image data for the reference spot, and the right hand side of the equation, representing the theoretical data for the reference spot, match thereby to determine a value of the linear confidence metric for the reference spot E primary imparted x, y = κφ V t, x, y A p t s ∫ 0 E max N 0 rel V t, ε S ε G ε e − μ luc ε h plate e − hμ x, y, ε ε dε where φ is photon flux, V t is x-ray tube voltage, A p is the area of the pixel, t s is the time of exposure, N 0 rel is relative number of incident x-ray photons for the tube voltage V t at energy ε, S(ε) is detector absorption, G(ε) is grid transmission, e - μ luc ( ε) h plate is attenuation due to compression plate used for the measurement e - hμ ( x,y,ε) is attenuation due to the breast. providing an electronic image of tissue (100,400,450,600,800,1100); running an inner breast edge detection algorithm on the electronic image to detect the inner breast edge on the image; determining a reference spot(1070,1170,1270) based upon an analysis of either breast tissue internal to the inner breast edge or breast tissue between the inner breast edge and an outer breast edge; calculating h int and h fat values for pixel values P(x,y) measured at co-ordinates x,y in the image, wherein h int is thickness of interesting tissue comprising fibrous tissue, glandular tissue, water or cancerous tissue, and h fat is thickness of fat; establishing an h int representation (500,700) of the image; using the h int representation in analysis of the tissue; summing the h int and h fat values to quantify the breast tissue; adjusting a calibration error value until image data for the reference spot matches theoretical data for the reference spot; and checking if the calibration error value is acceptable; wherein the adjusting of the calibration error value comprises adjusting a value of κ, wherein κ is a linear confidence metric, in the following equation until the left hand side of the equation, representing the image data for the reference spot, and the right hand side of the equation, representing the theoretical data for the reference spot, match thereby to determine a value of the linear confidence metric for the reference spot E primary imparted x, y = κφ V t, x, y A p t s ∫ 0 E max N 0 rel V t, ε S ε G ε e − μ luc ε h plate e − hμ x, y, ε ε dε where φ is photon flux, V t is x-ray tube voltage, A p is the area of the pixel, t s is the time of exposure, N 0 rel is relative number of incident x-ray photons for the tube voltage V t at energy ε, S(ε) is detector absorption, G(ε) is grid transmission, e - μ luc ( ε) h plate is attenuation due to compression plate used for the measurement e - hμ ( x,y,ε) is attenuation due to the breast. V t is x-ray tube voltage, A p is the area of the pixel, t s is the time of exposure, N 0 rel is relative number of incident x-ray photons for the tube voltage V t at energy ε, S(ε) is detector absorption, G(ε) is grid transmission, e - μ luc ( ε) h plate is attenuation due to compression plate used for the measurement e - hμ ( x,y,ε) is attenuation due to the breast.