In a real fluoroscopic system experimental evaluations of the DQE may pretty soon run into difficulties. Easy as it might be to satisfy the need for linearity by means of correction look-up tables, the evaluation of the NPS is more tricky, because of various time integration mechanisms. In order to deal with such effects in a quantitatively correct manner the concept of a spatial-temporal1 DQE has been suggested. We have performed computer-aided DQE-evaluations 2,4,5 on a surgical C-arm, using MTF and NPS. Furthermore, we have attempted to estimate the time behavior of the spatial-temporal system transfer function. Using X-ray pulses in the ms regime, we have generated nearly 'lag-free' flat-field images. Our experiments showed two interesting results. The comparison of flat-field images in the continuous 'Fluoro' mode and the 'lag-free' mode revealed the theoretically expected highly overestimated DQE in the first case. The corresponding scaling factor could be derived quantitatively from the motion experiments with an X-ray contrast pulse (Cu-rod). More worth while noticing is the fact that we observed structural anomalies in the two-dimensional NPS that could not compensated for by a simple scaling factor but vanished only in the 'lag-free' mode. This can be explained theoretically by taking into account a mixing behavior between the spatial and temporal NPS components, i.e. the failure of the spatial-temporal separability of the system transfer function.

Date Published: 3 May 2002
PDF: 12 pages
Proc. SPIE 4682, Medical Imaging 2002: Physics of Medical Imaging, (3 May 2002);

Published in SPIE Proceedings Vol. 4682:
Medical Imaging 2002: Physics of Medical Imaging
Larry E. Antonuk; Martin Joel Yaffe, Editor(s)