Feasibility of In Vivo Imaging of Fibroblast Activation Protein in Human Arterial Walls

Increased expression of fibroblast activating protein (FAP) in fibrous caps may contribute to progression of atherosclerotic plaques. Methods: Forty-one patients who underwent gallium-68-conjugated quinoline-based FAP inhibitor (68Ga-FAPI-04) PET/CT for non-cardiovascular indications were retrospectively analyzed. Correlations were assessed between the uptake of 68Ga-FAPI-04 in large arterial walls (SUVmax and target-to-background ratio, TBR) and degree of calcification and cardiovascular risk factors. Results: Focal arterial uptake of 68Ga-FAPI-04 or calcification was detected in 1,177 arterial segments in all 41 patients. TBR was negatively correlated with the degree of calcification (HU) (r = -0.27, P < 0.01). Mean TBR in higher-risk patients was greater than lower-risk patients (2.2 ± 0.3 vs. 1.8 ± 0.3, P < 0.01). Immunohistochemical labeling of carotid plaques exhibited prominent FAP expression in a thin fibrous cap and moderate FAP expression in a thick cap. Conclusion:68Ga-FAPI-04 PET/CT might have potential for imaging fibroblastic activation in the arterial wall.