Purpose Advances in photon‐counting detectors have enabled quantitative material decomposition using multi‐energy or spectral computed tomography ( CT ). Supervised methods for material decomposition utilize an estimated attenuation for each material of interest at each photon energy level, which must be calibrated based upon calculated or measured values for known compositions. Measurements using a calibration phantom can advantageously account for system‐specific noise, but the effect of calibration methods on t…