An infrared scanning system was used along with inverse heat conduction methods in IR computerized axial tomography (IR CAT scan). The method consists of scanning the exposed surfaces of an object with an unknown inner boundary geometry and reconstructing section views of the object using the surface temperature data and the boundary condition prescribed along the inner boundary as input in an analysis. The mathematical theory and operational procedures of IR CAT scan are developed, and they are applied to the successful reconstruction of a section of a test model with a Dirichlet condition prescribed along the inner boundary. The sensitivity of the method to erroneous input temperature data is discussed. The mathematical theory of the IR CAT scan method developed in this paper is general and can be applied to other situations when Neumann or Robin conditions are prescribed along the inner boundary.