1. A method of identifying material boundaries of a test object, the method which comprises: acquiring three-dimensional image data of the test object, wherein image values of the image data are obtained or have been obtained using invasive radiation; defining an evaluation line for evaluating the image data in relation to the test object, the evaluation line extending through a point on an expected boundary surface of a material of the test object and having a direction, at the point, perpendicular to the expected boundary surface, wherein the point and the expected boundary surface are identified from information regarding a desired condition of the test object; and evaluating the image values lying along the evaluation line to thereby determine a location of a material boundary in the test object, such that an amount of a first partial derivative of the image values in a direction of the evaluation line has a local maximum at the location of the material boundary.