Background and purpose: One of the main mechanism of chemotherapy is inducing tumor apoptosis. Molecular imaging can allow noninvasively and dynamically monitor tumor apoptosis in vivo

and help to drug screening and therapeutic evaluation. The purpose of this study was to evaluate the feasibility of 18F-SFB-Annexin B1 in detecting apoptosis at an early phase after chemotheraphy. Methods: Annexi

n B1 was labeled with 18F using SFB as a chelating agent. Tissue distribution of

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F-SFB-Annexin B1 was studied in healthy mice by the dissection method. W256 tumor-bearing rats were injected with

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F-SFB-Annexin B1 intravenously at 24 h after the treatment of cyclophosphamide (CTX 200 mg/kg) or saline. Then imaging was acquired at 1

2

3

and 4 h postinjection on a PET/CT

and the tumor-to-muscle ratio of SUV

max

(T/M) and the AI from TUNEL testing were compared. Results:

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F-SFBAnnexin B1 had a radiochemical pruity (RCP)95%. Biodistribution of this probe showed a predominant uptake in the kidney

then was liver

spleen

and myocardium

rapid clearance from blood and urinary was observed. The radios of T/M were 4.38±0.56

6.75±1.16

6.44±1.12

4.81±0.17

respectively at 1

2

3

4 h post injection of the chemotherapy group

much higher than that of the saline group (2.35±0.14

2.99±0.55

3.04±0.41

2.33±0.47

respectively). The differences between the two groups were significant (F=23.790

16.913

14.046

77.517

respectively

all P0.05). TUNEL staining revealed that chemotherapy treatment significantly increased the percentage of apoptosis cells with an AI of (21.00±0.04)% in the chemotherapy group

higher than that in the saline group (8.58±0.01)%

the difference was significant (F=21.539

P＜0.05). The radios of T/M were significantly correlated with the values of AI (r=0.91

P＜0.05). Conclusion:

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F-SFB-Annexin B1 can be used to apoptosis imaging and early therapeutic evaluation in vivo because it can reflect apoptosis at an early stage after chemotheraphy.