1. A non-transitory computer readable medium having stored thereon a computer program comprising instructions, which, when executed by a computer, cause the computer to: access a set of image data acquired from a patient, the set of image data comprising spectral computed tomography (CT) data; identify a plurality of target regions of interest (TROIs) in the patient from the set of image data; identify a reference region of interest (RROI) in the patient from the set of image data; extract a plurality of target spectral Hounsfield unit (HU) curves from image data representing the plurality of TROIs; extract a reference spectral HU curve from image data representing the RROI; normalize the plurality of target spectral HU curves with respect to the reference spectral HU curve; and display the plurality of normalized target spectral HU curves.