A major challenge of low-k1 microlithography that has to be addressed by any photomask defect detection strategy is the complex relation between the signal of the defect in the detector and its impact, in terms of printing errors, on the processed wafer. This non-trivial relation is immanent to the large MEEF values characterizing lithography at sub-wavelength features. One common method to work around this problem is to use aerial imaging optics which emulates the stepper exposure process. Currently available aerial inspection and review tools based on the well established fact that CD variation in the aerial image closely represents the CD variation on the wafer. Published literature explains why a defect's printing effect can be captured, with high correlation, by aerial imaging optics. Here we describe a novel connection between a defect's detection signal and the printed CD variation on an adjacent pattern. This connection can be exploited by aerial imaging mask inspection systems to ensure that their detection thresholds are set to detect CD variation of a given threshold. We show that under aerial imaging conditions, the defect signal and CD variation are linearly related, regardless of defect's attributes, provided that the defect resides close to a pattern's transition edge, or is surrounded by a dense pattern. We present experimental results, demonstrating this linear scaling between the defect signal and CD variation, and show practical application results of aerial imaging mask inspection, with implications to production mask fab.