Observer-Usable Information as a Task-specific Image Quality Metric

Objective, task-based measures of image quality (IQ) have been widely advocated for assessing and optimizing medical imaging technologies. Besides signal detection theory-based measures, information-theoretic quantities have been proposed to quantify task-based IQ. For example, task-specific information (TSI), defined as the mutual information between an image and a task variable, represents an optimal measure of how informative an image is for performing a specified task. However, like the ideal observer from signal detection theory, TSI does not quantify the amount of task-relevant information in an image that can be exploited by a sub-ideal observer. A recently proposed relaxation of TSI, termed predictive V-information (V-info), removes this limitation and can quantify the utility of an image with consideration of a specified family of sub-ideal observers. In this study, for the first time, we introduce and investigate V-info as an objective, task-specific IQ metric. To corroborate its usefulness, a stylized magnetic resonance image restoration problem is considered in which V-info is employed to quantify signal detection or discrimination performance. The presented results show that V-info correlates with area under the receiver operating characteristic (ROC) curve for binary tasks, while being readily applicable to multi-class (>2) tasks where ROC analysis is challenging. Notably, V-info exhibits greater sensitivity in scenarios where conventional metrics saturate. These findings demonstrate that V-info represents a new objective IQ measure that can complement conventional signal detection theory-based ones.