54. Spatio-temporal generalisation of Model Observer for Low Contrast Detectability assessment of dynamic angiographic images: comparison with an innovative Statistical method and 2AFC experiments

Abstract

Purpose Evaluate the feasibility of different less time consuming approaches for protocol optimisation in interventional radiology. Methods A Allura FD20 (Philips, The Netherlands) has been employed in this study. Low Dose Fluoroscopy was selected due to its spatial resolution, characterised by a lower enhancement compared to other modalities. Simulated images have been obtained adding a blurred circular insert to a series of acquired homogeneous images. A total of 3 insert dimensions (1.25, 2, 3 mm of diameter), 25 contrast levels and 4 different visualised frame rate (5, 10, 15 and 30 fps) have been selected to characterise low contrast detectability. A series of 2AFC experiments have been performed by two observers. Two different Model Observers has been considered: Non-PreWhitening Eye filter (NPWE) with spatio-temporal contrast sensitivity function and Channelized Hotelling Observer (CHO) with spatio-temporal Gabor filters. Furthermore, Low Contrast Detectability has been evaluated with a statistical method using uniform images. This analysis has been performed on an averaging of frames depending from the visualised fps. In particular, the averaging process was performed on groups of frames that correspond to the noise integration time of human eye-brain system of 200 ms, e.g. 3 frames with 15 fps. Results Analysis with both Model Observers and 2AFC experiments suffered from the general low quality of the protocol considered (Fig. 1). Nevertheless, a good agreement ( Conclusions The agreement with human observer experiments underlines the feasibility of the proposed generalisations. Thus, they could be introduced for a deeper modalities characterisation, in terms of image quality, or for clinical protocol optimization involving cine images.