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 68Ga-conjugated quinoline-based FAP inhibitor (68Ga-FAPI-04) PET/CT for noncardiovascular 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 (Hounsfield units) (r = -0.27, P < 0.01). Mean TBR in higher-risk patients was greater than in 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.