The study was a parallel-group randomized controlled trial. It was conducted in Wuhan, China, from March 2020 to September 2020. Participants were randomized into two groups in a 1:1 ratio: (1) a 3D holographic intervention group or (2) a 2D CT control group.

We randomly selected radiologists, surgeons, and medical students from our institution and asked them to participate in this study. The radiologists, surgeons, and medical students were eligible to participate in this trial if they had not previously seen 3D holograms of lungs affected by COVID-19. The study involved 60 participants, including 20 radiologists, 20 surgeons, and 20 medical students. Each of the three groups was randomly divided into two groups: (1) the 2D CT group and (2) the 3D holographic group (Figure S1 in Multimedia Appendix 1). Exclusion criteria were as follows: surgeons and medical students trained in COVID-19 lung CT imaging, and participants that had previously seen 3D holograms of COVID-19 lungs.

For this study, 3D reconstructions of patients’ lungs were made using data from CT scans using a StarCloud workstation (a 3D reconstruction software from Visual3D). Polygon mesh files were exported from the StarCloud workstation. These were uploaded into the StarCloud Mixed Reality system (Visual3D). After uploading the data, 3D holographic images were automatically converted as a case-specific computer graphic for mixed reality, referred to as a hologram. The data pertaining to the hologram can be downloaded onto a Microsoft HoloLens (Microsoft Corp).

The two groups completed the same task, which involved identifying lesion areas in the lungs of 6 cases of COVID-19 using a 2D CT or 3D hologram of the lungs. The 6 cases of COVID-19 used for the study involved moderate to severe COVID-19 (Table S1 in Multimedia Appendix 1).

An independent radiology professor rated the participants' performance (out of 100). All participants in the two groups completed a Likert scale questionnaire regarding the educational utility and efficiency of 3D holograms. The National Aeronautics and Space Administration Task Load Index (NASA-TLX) was completed by all participants. The NASA-TLX is a multidimensional rating procedure that provides an overall workload score between 0 and 100 based on a weighted average of ratings on 6 subscales [9]: (1) mental demands (“How mentally demanding was the task?”), (2) physical demands (“How physically demanding was the task?”), (3) temporal demands (“How hurried or rushed was the pace of the task?”), (4) own performance (“How successful were you in performing the task?”), (5) effort (“How hard did you have to work to achieve your level of performance?”), and (6) frustration (“How insecure, discouraged, irritated, stressed, and annoyed were you?”). The ethics committee of Wuhan Union Hospital, Tongji Medical College, Huazhong University of Science and Technology approved this study, and all participants provided signed informed consent.

Statistical analyses were performed using SPSS (version 19; IBM Corp). Continuous variables were expressed as means and standard deviations. Results of the NASA-TLX questionnaires were summarized in terms of means and standard deviations. Data were processed using analysis of variance to determine possible relationships between individual characteristics and workload.

Participant baseline characteristics are described in Table 1. The study involved 60 participants, including 20 radiologists, 20 surgeons, and 20 medical students. Each of the three groups was randomly divided into two groups: (1) the 2D CT group (n=30; mean age 29 years [range 19-38 years]; males=20) and (2) the 3D holographic group (n=30; mean age 30 years [range 20-38 years]; males=20; Figure S1 in Multimedia Appendix 1).

Clear 3D visual holographic renderings were obtained for the lungs of patients with COVID-19 (Figure 1). In the 3D holographic (mixed reality) group, the task scores for all participants (mean 91.98, SD 2.45), radiologists (mean 93.60, SD 2.25), surgeons (mean 91.50, SD 2.31), and medical students (mean 91.25, SD 2.18) were significantly higher than that of the conventional (2D) group (all participants: mean 74.09, SD 7.59; radiologists: mean 82.63, SD 2.28; surgeons: mean 74.55, SD 2.52; medical students: mean 65.10, SD 65.10; P<.001). With the help of 3D holograms, surgeons and medical students achieved the same scores as radiologists and made obvious progress in identifying pulmonary lesions caused by COVID-19 (Figure 2, Table 2). The Likert scale questionnaire revealed that the 3D hologram group had superior results compared to the 2D CT group (teaching: 2D CT group median score 2, IQR 1-2 versus 3D group median 5, IQR 5-5; P<.001; understanding and communicating: 2D CT group median score 1, IQR 1-1 versus 3D group median 5, IQR 5-5; P<.001; increasing interest: 2D CT group median score 2, IQR 2-2 versus 3D group median 5, IQR 5-5; P<.001; lowering the learning curve: 2D CT group median score 2, IQR 1-2 versus 3D group median 4, IQR 4-5; P<.001; spatial awareness: 2D CT group median score 2, IQR 1-2 versus 3D group median 5, IQR 5-5; P<.001; learning: 2D CT group median score 3, IQR 2-3 versus 3D group median 5, IQR 5-5; P<.001; Figure 3, Table 2).

The 3D hologram group scored significantly lower than the 2D CT group on the “mental,” “temporal,” “performance,” and “frustration” subscales of the NASA-TLX. Compared with the traditional 2D group, the 3D hologram group reported higher physical demands. The main reason is that participants need to wear a mixed reality headset, but the weight of the mixed reality glasses was acceptable (Figure 4, Table 2).