Purpose

The role of fibroblast activation protein (FAP)-targeted imaging in systemic vasculitis is currently unclear. We aimed to evaluate the clinical value of fluorine-18-labeled FAP inhibitor 42 ([¹⁸F]FAPI-42) in patients with systemic vasculitis and to compare with [¹⁸F]fluorodeoxyglucose (FDG) imaging.

Methods

Patients with systemic vasculitis who underwent dual-tracer PET/CT([¹⁸F]FDG and [¹⁸F]FAPI) imaging from September 2020 to March 2022 were retrospectively analyzed. Positive lesions are defined as vascular/extravascular lesions with increased tracer uptake above surrounding background, which cannot be attributed to the physiologic biodistribution of the radiotracer. The vascular/extravascular lesion detection rate and semiquantitative values (SUVmax, TBR_blood and TBR_liver) of [¹⁸F]FAPI and [¹⁸F]FDG were compared, and the correlation between the extent and range of tracer uptake and levels of inflammatory markers was investigated.

Results

Thirty patients (13 males and 17 females; mean age, 52.5 ± 17.2 years) with systemic vasculitis were included (17 large vessel vasculitis, 10 anti-neutrophil cytoplasmic antibody-associated vasculitis, 2 Behcet’s disease and 1 polyarteritis nodosa). [¹⁸F]FDG PET/CT had positive findings in 93.3% (28/30) of patients, while [¹⁸F]FAPI PET/CT had positive findings in all patients (100%, P = 0.500). Compared with [¹⁸F]FDG PET/CT, [¹⁸F]FAPI PET/CT detected more lesions (161/168 vs. 145/168, P = 0.005), and more extensive vascular involvement in 60% (18/30) of patients. Although SUVmax did not differ significantly between [¹⁸F]FAPI and [¹⁸F]FDG (median, 5.94 vs. 5.46, P = 0.517), [¹⁸F]FAPI had higher TBR_liver (median, 9.59 vs. 3.15, P < 0.001) and TBR_blood (median, 5.45 vs. 4.20, P = 0.006). The total number of positive lesions in FAPI PET/CT show a moderate correlation with erythrocyte sedimentation rate (r_s =0.478, P = 0.008) and C-reactive protein (r_s =0.486, P = 0.006). After treatment, follow-up FAPI PET/CT of 6 patients showed decreased SUVmax, TBR and number of detected lesions, paralleling the clinical remission.

Conclusion

[¹⁸F]FAPI PET/CT imaging is a promising imaging modality for the diagnosis and therapeutic monitoring of systemic vasculitis.

中文翻译：

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[18F]FAPI-42 和 [18F]FDG PET/CT 在系统性血管炎评估中的比较

 目的

成纤维细胞活化蛋白 （FAP） 靶向成像在系统性血管炎中的作用目前尚不清楚。我们旨在评估氟 18 标记的 FAP 抑制剂 42 （[¹⁸F]FAPI-42） 在系统性血管炎患者中的临床价值，并与 [¹⁸F] 氟脱氧葡萄糖 （FDG） 成像进行比较。

 方法

回顾性分析 2020 年 9 月至 2022 年 3 月接受双示踪剂 PET/CT （[¹⁸F]FDG 和 [¹⁸F]FAPI） 成像的系统性血管炎患者。阳性病变定义为血管/血管外病变，示踪剂摄取增加高于周围背景，这不能归因于放射性示踪剂的生理生物分布。比较 [¹⁸F]FAPI 和 [¹⁸F]FDG 的血管/血管外病变检出率和半定量值 （SUVmax、TBR_血液和 TBR_肝脏），并研究示踪剂摄取的程度和范围与炎症标志物水平之间的相关性。

 结果

纳入 30 例系统性血管炎患者 （13 例男性和 17 例女性;平均年龄 52.5 ± 17.2 岁） （17 例大血管炎、10 例抗中性粒细胞胞质抗体相关血管炎、2 例白塞病和 1 例结节性多动脉炎）。[¹⁸个地址]FDG PET/CT 在 93.3% （28/30） 的患者中有阳性结果，而 [¹⁸F]FAPI PET/CT 在所有患者中都有阳性结果 （100%，P = 0.500）。与 [¹⁸F]FDG PET/CT 相比，[¹⁸F]FAPI PET/CT 检测到更多的病灶 （161/168 vs. 145/168，P = 0.005），并且在 60% （18/30） 的患者中检测到更广泛的血管受累。 尽管 [¹⁸F]FAPI 和 [¹⁸F]FDG 之间的 SUVmax 没有显著差异（中位数，5.94 vs. 5.46，P = 0.517），但 [¹⁸F]FAPI 具有更高的 TBR_肝脏（中位数，9.59 vs. 3.15，P < 0.001）和 TBR_血液（中位数，5.45 vs. 4.20，P = 0.006）。 FAPI PET/CT 阳性病灶总数与红细胞沉降率 （r_s =0.478，P = 0.008） 和 C 反应蛋白 （r_s =0.486，P = 0.006） 呈中度相关性。 治疗后，6 例患者的随访 FAPI PET/CT 显示 SUVmax 、 TBR 和检测到的病灶数量降低，与临床缓解平行。

 结论

[¹⁸个地址]FAPI PET/CT 成像是一种很有前途的影像学检查方式，可用于诊断和治疗监测系统性血管炎。