A technique was developed to non-destructively measure the three-dimensional soot deposition thickness profiles in diesel engine exhaust components using a digital neutron imaging technique. In this technique, the test component positioned on a rotating platform is exposed to a thermal neutron beam from a nuclear reactor and the flux transmitted through the test object is measured using a digital neutron imaging system. The thickness of the diesel soot is then determined by analyzing the attenuation of this neutron flux. The technique was applied here to an aluminum pipe that was fouled for approximately 12 h by diesel exhaust from a diesel generator. The analysis of the neutron images indicated that the average soot thickness in the fouled pipe decreased nonlinearly along the pipe. It was also found that the measurements using this technique were within 16% of the direct destructive measurements of the thickness determined after sectioning the pipe. (C) 2004 Elsevier Ltd. All rights reserved.