## 8 Conclusions  
In this paper, we briefly outlined a demand for three-dimensional visualization systems in diagnostic radiology and visualization methods that were proposed for the implementation. The lack of experimental evaluation for specific user performance constrains the further implementation of new visualization devices for professional purposes. We developed an experimental design for the assessment of radiologists' performance using a visual search experiment on a volumetric display. This work allowed us to describe how radiologists, residents, and students searched three-dimensional visual information presented on the display, depending on stimulus physical properties. Radiologists largely demonstrated the image manipulation strategy that allowed them to find visual information quickly by inspecting the entire three-dimensional image. Residents preferred inspecting images selectively by slices, however, they were not inferior in temporal aspects of performance when compared with radiologists. Generally, visual search accuracy varied depending on the physical properties of the demonstrated stimuli but appeared to be independent of the amount of radiologist's experience in the absence of medical semantic context in the images. We concluded that the experienced radiologists' search benefited from seeing the entire three-dimensional view of image, whereas residents and students were overwhelmed by the amount of presented information and largely focused on the selective inspection of image elements. These findings are expected to be useful in the development of new ergonomic three-dimensional visualization stations for professional purposes.  
In a future study, we plan to render a more complex visual environment, typical to medical images, and apply additional options for three-dimensional image manipulation to broaden understanding about the usability of novel three-dimensional visualization systems for medical image reading. In addition to the detailed assessment of user feedback and global performance, we also intend to gain insight into the search patterns and deployment of visual attention in the three-dimensional visual environment when medical professionals view real three-dimensional images by investigating their oculomotor behavior.  
Conceptualization, T.P., R.P., K.P. and G.K.; Formal analysis, M.D.-V.; Funding acquisition, G.K.; Investigation, T.P. and V.A.; Methodology, T.P.; Project administration, T.P. and G.K.; Resources, R.P. and V.A.; Supervision, G.K.; Validation, T.P. and G.K.; Visualization, M.D.-V.; Writing--original draft preparation, T.P.; Writing--review and editing, T.P., M.D.-V., R.P., K.P. and G.K.  
The work presented in this article is a part of the research project supported by the University of Latvia (No. AAP2015/B003; No. ZD2014/AZ77) and LightSpace Technologies (\"3D volumetric screen and the functionality of the visual system\", No. ZD2017/20467, \"Evaluation of volumetric display's 3D image effect on human visual system\", No. ZD2019/20807). This work has been also supported by the European Regional Development Fund, project No. 1.1.1.1/18/A/179 \"Development of a compact, high-brightness laser image projection system for application in volumetric 3D displays\".  
**Acknowledgments:** The authors are grateful to the radiologists, residents and students who volunteered their time, and the authorities of the following institutions: Children's Clinical University Hospital, Pauls Stradins Clinical University Hospital, Riga East Clinical University Hospital, University of Latvia, Riga Stradins University, Lithuanian University of Health Sciences and Vilnius University.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.