In this paper an existing ridge detector based on the Hessian tensor and a new one based on the structure tensor are evaluated for use in portal/simulator imaging. Tensor smoothing is introduced as a scaling parameter. By changing this scale, (as opposed to the image scale) the detectors can be tuned to suppress spurious ridges without moving them. Desirable ridge detector properties for portal/simulator imaging are described and the ridge definitions are tested accordingly. Experiments show our new ridge detector to outperform the existing one in simulator/portal image matching.