Multimodal in vivo imaging of rabbit DVT-induced inflammation

Aim

Deep vein thrombosis (DVT) induces a marked inflammatory response that contributes to vein wall fibrosis and results in post-thrombotic syndrome (PTS). Imaging of DVT-associated inflammation during catheter-directed thrombectomy could help stratify the risk of PTS and guide adjunctive inflammation-targeted therapies. Here, we developed and evaluated a novel intravascular molecular-structural near-infrared fluorescence-optical coherence tomography (NIRF-OCT) imaging approach to visualize inflammation in vivo in an experimental DVT model.

Methods

Jugular vein DVT was induced in New Zealand white rabbits (n=10) by venous clamping and intrapouch thrombin instillation. On day 6, the NIRF cathepsin-activatable imaging agent or saline was injected (ProSense VM110, n=8; saline, n=2). On day 7, external ultrasound assessed thrombi, then rabbits underwent surgical removal of venous clamps, followed by angiography, intravascular ultrasound (IVUS) and NIRF-OCT. After thrombus resection, ex vivo fluorescence imaging and histopathology were performed. The left non-thrombosed jugular vein served as a sham surgical control.

Results

DVT formed in all rabbits. Multimodal IVUS and NIRF-OCT demonstrated residual thrombus adherent to the vein wall. NIRF signal analyses revealed significantly increased inflammatory cathepsin activity in thrombosed veins with a 2.13[1.65-2.51] (p=0.031)-fold NIRF signal increase versus non-thrombosed segments (p=0.031). Ex vivo imaging corroborated these findings, showing marked elevation of the NIRF signal compared with the kidney (10.2-fold, p=0.016) and the contralateral jugular vein (17.1-fold, p=0.008). Compared to the sham control vein, histology of the DVT vein wall showed increased RAM11⁺ macrophages (p=0.002) and elevated collagen deposition by picrosirius red staining (p<0.0001), indicating enhanced inflammatory fibrosis.

Conclusion

Intravascular NIRF imaging enables real-time detection and quantification of DVT-associated inflammation, augmenting standalone IVUS and OCT imaging. These results provide a clinically translatable platform to assess post-thrombectomy DVT residual inflammation at the point of care and could motivate and guide adjunctive anti-inflammatory strategies to mitigate PTS.

Figure caption: Imaging jugular vein thrombosis in the rabbit: Before sacrifice, in vivo imaging was performed using external ultrasound (B-mode ultrasound before clamps were removed) (A). Intravascular imaging after clamps’ removal was then performed by angiography (B), intravascular ultrasound (C), and endovascular near-infrared fluorescence (D). After sacrifice, fluorescence reflectance imaging at 730 nm of the extracted vein is presented (E).Figure