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Purpose To measure regional changes in hyperpolarized 129 Xe MRI signal and apparent transverse relaxation ( ) because of instillation of SPION‐labeled alveolar‐like macrophages (ALMs) in the lungs of rats and compare to histology. Methods MRI was performed in 6 healthy mechanically ventilated rats before instillation, as well as 5 min and 1 h after instillation of 4 million SPION‐labeled ALMs into either the left or right lung. maps were calculated from 2D multi‐echo data at each time point and changes in were measured and compared to control rats receiving 4 million unlabeled ALMs. Histology of the ex vivo lungs was used to compare the regional MRI findings with the locations of the SPION‐labeled ALMs. Results Regions of signal loss were observed immediately after instillation of unlabeled and SPION‐labeled ALMs and persisted at least 1 h in the case of the SPION‐labeled ALMs. This was reflected in the measurements of . One hour after the instillation of SPION‐labeled ALMs, the decreased to 54.0 ± 7.0% of the baseline, compared to a full recovery to baseline after the instillation of unlabeled ALMs. Histology confirmed the co‐localization of SPION‐labeled ALMs with regions of signal loss and decreases for each rat. Conclusion Hyperpolarized 129 Xe MRI can detect the presence of SPION‐labeled ALMs in the airways 1 h after instillation. This approach is promising for targeting and tracking of stem cells for the treatment of lung disease.
Riberdy et al. (2019) studied this question.