Longitudinal Cell Tracking and Simultaneous Monitoring of Tissue Regeneration after Cell Treatment of Natural Tendon Disease by Low-Field Magnetic Resonance Imaging
Exemplary transverse -weighted gradient echo images of a horse with severe tendinopathy (upper row, A–E) and a horse with moderate tendinopathy (lower row, F–J) that were both treated with labelled cells, and boxplots displaying the signal intensities of regions of interest measured for cell tracking and the areas covered by hypointense artefact in T1-weighted gradient echo (T1w) and -weighted gradient echo () images. All separate examinations before injection (A + F, pre) and directly (B + G, post) as well as 2 (C + H, 2 w), 4 (D + I, 4 w), and 8 (E + F, 8 w) weeks after injection are displayed. Before injection, no hypointense areas were visible within the lesion except for 1 case. Directly after injection, hypointense artefacts were located within the lesion and surrounding tissue (arrows). At week 2, week 4, and week 8, the hypointense areas were decreasing gradually but still visible. Furthermore, in the case displayed in the lower row, the artefacts appeared to be located more within the tendon lesion at week 8 compared to week 2 or week 4. Lateral is displayed on the left. The upper boxplot illustrates that signal intensities within hypointense areas relatable to labelled cells (MSC) were low in all cases and mostly within the same range as signal intensity of the corresponding healthy deep digital flexor tendon (DT). The plot also displays the one case in which a false-positive judgement had been made (F-P), showing that this case could be discriminated by the higher signal intensity within the area that had been mistaken for being induced by labelled cells. The lower boxplot shows the decreasing trend in the area covered by hypointense artefacts.