Image size influences visual search and perception of hemorrhages when reading cranial CT: an eye tracking study

Objectives: To explore reader gaze, performance and preference during interpretation of cranial computed tomography (cCT) in stack mode at two different sizes. Background: Digital display of medical images allows for the manipulation of many imaging factors, like image size, by the radiologists, yet it is often not known what display parameters better suit human perception. Materials and Methods: Twenty-one radiologists provided informed consent to be eye tracked while reading 20 cCT cases. Half of these cases were presented at a size of 14x14 cm (512x512 pixels), half at 28x28 cm (1024x1024 pixels). Visual search, performance and preference for the two image sizes were assessed. Results: When reading small images significantly fewer, but longer fixations were observed, and these covered significantly more slices. Time to first fixation of True Positive findings was faster in small images, but dwell time on true findings was longer. Readers made more False Positive decisions in small images, but no overall difference in either JAFROC or reading time was found. Conclusions: Overall performance is not affected by image size. However, small stack mode cCT images may better support the use of motion perception and acquiring an overview, whereas large stack mode cCT images seem better suited for detailed analyses. Application: Subjective and eye tracking data suggest that image size influences how images are searched and that different search strategies might be beneficial under different circumstances.