SU-E-I-104: Detector Lag Testing for Digital Radiography

Signal lag is an inherent property of the digital detectors used for radiography. The extent and impact of signal lag can vary. In this exhibit we aim to:'¢ provide context for detector lag testing as a matter of acceptance testing for detectors used in digital radiography (DR)'¢ provide example lag data from various DR systems. Lag measurement and analysis techniques have been published but without the expected results that are useful for benchmarking.'¢bring greater awareness and understanding to the impact of detector lag for the performance of digital detectors and the appearance of image ghosting in clinical images.

A standardized method was used for the quantification of lag similar to that described in the IPEM report 32 part vii [1]. Six different vended detector options were measured and compared.

Lag images were visually compared and lag measurement values were normalized using the measured signal transfer properties of each system. The results are shown as normalized with exposure. The results show a wide variety of lag responses, even for the same physical detector hardware but different vendor implementations.

The ultimate test for detector lag performance is whether residual 'ghost' images appear in clinical images. Some vendor systems are more prone to the appearance of lag than others. We attempt to quantify system properties at acceptance testing that can enable discriminationbetween systems which have poor or superior lag properties. A suggested easurement analysis technique which normalizes data to be linear with exposure does not appear to adequately assess the likelihood for the clinical appearance of lag. [1] Mackenzie A et al. Measurement of the Performance Characteristics of Diagnostic X-Ray Systems: Digital Imaging Systems. Institute of Physics in Medicine 2009 (IPEM Report 32, part vii). 2010.