## 2 Materials and Methods
### Quantitative Study: Study Design and Participants  
In this study, a mixed-method intervention design incorporating both qualitative and quantitative components was employed. Initially, a non-randomized intervention using various teaching methodologies was executed, adopting a quantitative approach within a concurrent integrated design framework. The study's second phase introduced a qualitative method to delve into significant insights from the observed phenomena. Qualitative data collection occurred after the VR interventions, aiming to uncover underlying mechanisms that might explain the quantitative findings. This included exploring participants' experiences, effort, motivation, satisfaction, and adherence. An assessment of radiological technology students preparing \({}^{99\text{m}}\)Tc-MDP radiopharmaceuticals was carried out. The importance of selecting participants without previous experience was highlighted by [PERSON] and [PERSON], studying retrieval practice highlighted in the study subject to measure the true impact of retrieval practice [15]. Additionally, [PERSON] and [PERSON] emphasized the importance of accurately assessing prior knowledge to measure the effectiveness of new educational interventions [16]. This study sample size was based on research by [PERSON]'s research, \"Determining Sample Size\" [17], and consists of 29 second-year and 31 third-year radiological technology students (\(n=60\)). Both cohort groups were selected as having no previous experience of radiopharmaceutical preparation. The student selection criteria are detailed in the Supplementary Materials (Quantitative Study: Study Design and Participants section), the sample was selected using purposive sampling, which involves choosing individuals who meet specific criteria relevant to the research and who represent the studied population. One cohort (\(n=30\)) with no experience preparing radiopharmaceuticals viewed video tutorials preparing \({}^{99\text{m}}\)Tc-MDP radiopharmaceuticals and the quality control procedure (the control group). The second cohort (\(n=30\)) with no experience preparing radiopharmaceuticals viewed an immersive digital twin virtual reality simulation preparing \({}^{99\text{m}}\)Tc-MDP radiopharmaceuticals and the quality control procedure (the VR group). Both groups completed a questionnaire before and after viewing the video tutorial and the immersive digital twin virtual reality simulation. Both groups then completed a written test after viewing the video tutorial and completing the VR training. Furthermore, 1 month after the test, both groups completed the same test. Then, after 3 months, both cohort groups repeated the same test to re-evaluate the knowledge retention of both learning modules. The first cohort viewed a video tutorial preparing \({}^{99\text{m}}\)Tc-MDP radiopharmaceutical on a computer, and the same tutorial was considered by the second cohort using an immersive digital twin virtual reality simulation (Figure 1). Using photogrammetry [18], numerous photographs of the radiopharmaceutical hot lab and \({}^{99\text{m}}\)Tc-MDP preparation and quality control were superimposed to form a 3D virtual reality model. Photogrammetry is the generation of a digital replica, sometimes called a \"digital twin,\" of a tangible entity or physical environment using authentic photographic imagery [19]. Therefore, it pertains to reconstructing forms and estimating the spatial location and measurements of objects represented in photographic photographs. In this instance, we utilized an Insta360 X3 Action Camera (Arashi Vision Inc., Irvine, CA, USA) and then edited the filming on a Dell Optiplex 7010 SFF Plus i7-13700/16 GB/512 GB PCIe NVMe/Intel UHD Graphics 770/Windows 11 Pro (Dell Inc., Round Rock, TX, USA), with Adobe Premiere Pro 23.4 (Adobe Inc., San Jose, CA, USA). On completion, the photogrammetric 3D model was then viewed using an Oculus Quest 2 All-In-One VR Headset (128 GB) (Reality Labs, Menlo Park, CA, USA).