Introduction: Undergoing complex diagnostic investigation of positron emission tomography-computed tomography (PET-CT) scans is associated with high levels of distress, fear, and anxiety in oncological patients. This study evaluated the effects of a single 20-min session of an innovative mindfulness-based swinging technique (MBST) intervention on emotional distress in cancer patients scheduled for PET-CT scans. Material and Methods: Adult cancer patients undergoing PET-CT scans (n = 57) were assigned to the intervention group (n = 27) or the control group (n = 30). The emotion thermometer (ET) was used to measure distress, anxiety, depression, anger, and need for help at baseline and after the PET-CT scan. Participants in the intervention group received a 5-min psycho-education followed by listening to an audio recording of the MBST intervention just before their PET-CT scan. The session included mindfulness-based visualization, imaginary swinging activity, and synchronized breathing. The control group participants received brief 5-min counseling. Results: There was a statistically significant reduction in distress (p < 0.001), anxiety (p < 0.001), depression (p < 0.001), anger (p = 0.002), and need for help (p < 0.001) in the intervention group compared with the control group. Safety: None of the participants reported adverse events caused by the MBST intervention. The intervention was well accepted by the participants. However, n = 3 participants could not complete the intervention due to mind wandering, inability to focus, difficulty complying with the guided instructions, falling asleep, and physical discomfort unrelated to the intervention. Conclusion: The findings suggest the potential role of MBST intervention in mitigating emotional distress in patients undergoing complex diagnostic imaging procedures. Integrating this with conventional care in nuclear medicine settings can provide patient-centered care that addresses their unmet requirements. There is a need for further validation with a larger sample size. Clinical Trial Registration Number: CTRI/2023/04/051243 (Registered prospectively on 03/04/2023).