Highlights
- Longitudinal whole-body 3D SPECT imaging from 2 to 120 h post injection
- Imaging following an administered activity of only 0.4 MBq
- 30-minute acquisitions across four longitudinal time points
- Interpretable whole-body imaging with activity during acquisition down to 0.11 MBq at 120 h
Introduction
Longitudinal SPECT imaging enables non-invasive assessment of radiopharmaceutical distribution across multiple time points, allowing changes in uptake and whole-body distribution to be followed over time.
In this study, ¹⁷⁷Lu-Trastuzumab was evaluated in a SKOV-3 xenograft model using longitudinal 3D SPECT under low-activity conditions. Imaging was performed from 2 to 120 h post injection, as the available activity progressively decreased throughout the study.
Study design
¹⁷⁷Lu-Trastuzumab was administered at an activity of 0.4 MBq in a SKOV-3 xenograft model.
Whole-body 3D SPECT acquisitions were performed at 2, 24, 48 and 120 h post injection, with a scan duration of 30 min at each time point.
Activity during imaging progressively decreased across the longitudinal series:
- 2 h: 0.27 MBq
- 24 h: 0.23 MBq
- 48 h: 0.2 MBq
- 120 h: 0.11 MBq
Results
Longitudinal imaging under low-activity conditions
Longitudinal 3D SPECT provided whole-body visualization of ¹⁷⁷Lu-Trastuzumab distribution across all four imaging time points, from 2 to 120 h post injection.
At the early 2 h time point, activity was predominantly distributed in the thoracic region. At subsequent time points, this background signal progressively cleared, while tumor-associated uptake became increasingly distinct and remained visible throughout the longitudinal series.
Despite the progressive decrease in available activity, interpretable 3D SPECT images were maintained throughout the complete longitudinal series. At the final 120 h time point, whole-body imaging remained informative with only 0.11 MBq of activity during acquisition.
The longitudinal sequence therefore captures both the evolving biodistribution of ¹⁷⁷Lu-Trastuzumab and persistent tumor-associated uptake over five days, while demonstrating imaging performance under progressively reduced count conditions.
Figure 1: Longitudinal 3D SPECT imaging of ¹⁷⁷Lu-Trastuzumab in a SKOV-3 xenograft model following 0.4 MBq administered activity. Imaging performed at 2, 24, 48 and 120 h post injection. Activity during imaging: 0.27, 0.23, 0.2 and 0.11 MBq, respectively. Scan duration: 30 min per time point.
Conclusion
Longitudinal 3D SPECT enabled whole-body assessment of ¹⁷⁷Lu-Trastuzumab distribution from 2 to 120 h post injection, capturing the transition from early thoracic distribution to increasingly distinct tumor-associated uptake at later time points.
Interpretable imaging was maintained throughout the longitudinal series as available activity progressively decreased, reaching 0.11 MBq at the final 120 h time point. This approach supports extended longitudinal evaluation of radiopharmaceutical distribution while reducing the activity required for repeated preclinical imaging.