Saul N Friedman BSc, Presenter: Nothing to Disclose

Ian A. Cunningham PhD, Abstract Co-Author: Nothing to Disclose

To provide a description of a spatio-temporal detective quantum efficiency (DQE) and its application in clinical fluoroscopic systems as a metric of system performance and “dose efficiency.”

We use a spatio-temporal DQE defined in terms of a spatio-temporal noise power spectrum (NPS) and a presampling spatio-temporal modulation transfer function (MTF), describing spatio-temporal noise and resolution respectively. The spatio-temporal NPS is measured from a sequence of fluoroscopic frames forming multiple 3D regions of interest and spatio-temporal detrending to produce zero-mean datasets. Measurement of the spatio-temporal MTF requires an assumption of separability between space and time, and the use of both stationary and moving slanted-edge methods. The resulting calculation produces a 3D DQE expressed as a function of two spatial and one temporal-frequency axes. The spatio-temporal DQE was evaluated for both a bench-top x-ray image intensifier and clinical flat-panel-based systems.

Spatio-temporal DQE values along the spatial axes showed the same decrease in values as the (conventional) DQE. Information along the temporal axis is provided to 15 Hz, corresponding to the temporal cut-off frequency. A decrease in DQE values is also noted along the temporal frequency axis starting at 5 Hz with a 30% decrease in value by 15 Hz, and is due to a combination of non-ideal temporal behavior and temporal noise aliasing. The spatio-temporal DQE differs from previous descriptions of fluoroscopic DQE as it does not assume ideal temporal response, and lag is therefore not assumed to be deterministic in nature.

Non-ideal system temporal response, as evident from decreasing DQE values along the temporal frequency axis, shows that a full 3D spatio-temporal approach to the DQE is required for the systems tested. The resulting understanding of system temporal response may enable improved design and performance of fluoroscopic systems.

The spatio-temporal DQE provides a measure of system performance and dose efficiency, important for fluoroscopic system design and quality assurance programs.

Friedman, S, Cunningham, I, The Spatio-Temporal Detective Quantum Efficiency: A Three-dimensional Approach to Fluoroscopic System Dose Efficiency.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8016214.html