Studying the relative impact of ghosting and noise on the perceived quality of MR images

Abstract

In current magnetic resonance (MR) imaging systems, design choices are confronted with a trade-off between structured (i.e. artifacts) and unstructured noise. The impact of both types of noise on perceived image quality, however, is so far unknown, while this knowledge would be highly beneficial for further improvement of MR imaging systems. In this paper, we investigate how ghosting artifacts (i.e. structured noise) and random noise, applied at the same energy level in the distortion, affect the perceived quality of MR images. To this end, a perception experiment is conducted with human observers rating the quality of a set of images, distorted with various levels of ghosting and noise. To also understand the influence of professional expertise on the image quality assessment task, two groups of observers with different levels of medical imaging experience participated in the experiment: one group contained fifteen clinical scientists or application specialists, and the other group contained eighteen naïve observers. Experimental results indicate that experts and naïve observers differently assess the quality of MR images degraded with ghosting/noise. Naïve observers consistently rate images degraded with ghosting higher than images degraded with noise, independent of the energy level of the distortion, and of the image content. For experts, the relative impact of ghosting and noise on perceived quality tends to depend on the energy level of the distortion and on the image content, but overall the energy of the distortion is a promising metric to predict perceived image quality.Keywords: MRI, perceived image quality, ghosting, noise, human visual system PURPOSEIn current magnetic resonance (MR) imaging systems, a variety of artifacts and noise, affecting the perceived quality of MR images is generated. Ghosting, which is a cross-talk type of artifact that generates a lower-intensity double image, spatially shifted with respect to the original content, is just one example of such an artifact. In an MR imaging system, there are situations where structured noise (e.g. ghosting) on one hand can be traded off with unstructured noise on the other hand. For example, one of the processing steps to avoid ghosting in the system is to redistribute its energy so that it appears as random noise spread over the entire image. Whether this way of processing changes the perceived quality of MR images, and if so, to what extent is so far unknown. Therefore, it is of fundamental importance to understand the relative impact of structured versus unstructured noise on the perceived quality of MR images, in order to improve MR imaging systems. In addition, it is worthwhile to investigate the influence of professional expertise on image quality perception. The impact of professionalism on diagnostic quality, of course, is known to be huge ([1]-[3]), but in case the impact of professionalism on perceived image quality is limited, larger-size studies could be undertaken without being too much of a burden for the limited number o...

The Relative Impact of Ghosting and Noise on the Perceived Quality of MR Images

“…Since the impact of professionalism on the perceived quality of MR images was proved significant [32], the perception experiments were conducted with clinical application specialists. All participants were recruited from clinical scientists or application specialists at Philips Healthcare, Best, The Netherlands.…”