Patent US 4,247,774

A dual-energy detector system for use in computer assisted tomography. This system produces two independent sets of information from one scan, namely, high-energy and low-energy data. The system employs two cooperating detectors. The first one responds primarily to low-energy photons, allowing most high-energy photons to pass through. The second detector lies behind the first and detects the remaining photons. Thus, two electrical signals are generated which contain information in two different energy ranges, which signals can be computer-processed. The attenuation coefficients at these two energies are sufficiently different so that differential diagnosis and chemical identification may be aided. The computer-processed signals may be employed to provide any of (a) beam-hardening correction, (b) chemical identification and composition of tissues, such as lesions, bone, etc., (c) localization of injected contrast material, or (d) attenuation coefficients for radiation therapy planning.