¹⁸F-FBPA and ¹⁸F-FAMT dynamic PET profile: evaluation of usefulness in differentiating malignant tumors from inflammatory lesions.

Objectives We evaluated the dynamic profile of 3-[¹⁸F]fluoro-α-methyl-L-tyrosine (FAMT) and 4-borono-2-[¹⁸F]fluoro-L-phenylalanine (FBPA) by small animal PET, estimating the usefulness in differentiating malignant tumors from inflammatory lesions.

Methods Rats were prepared as xenograft model of C6 glioma 14 days after the implantation (n=10) and subcutaneous inflammation model induced by turpentine oil 4 days after the injection (n=13). Dynamic PET scans were performed up to 70 min just after injection of FAMT or FBPA (n=6). The time activity curves (TACs) and SUVmax on static PET images at 60 min post injection were compared between the tumors and inflammatory lesions.

Results TAC of FAMT showed a rapid increase and continuous wash-out pattern in the tumors (peak SUV = 4.3±0.6), while low uptake and slow wash-out pattern in the inflammatory lesions (peak SUV = 0.77±0.14). Compared to FAMT, TAC of FBPA showed a slower uptake pattern in the tumors (peak SUV = 3.2±0.2) and higher uptake pattern in the inflammatory lesions (peak SUV = 1.4±0.2). In the static images at 60 min post injection, SUVmax of FAMT and FBPA were 1.33±0.29 / 3.23±0.40 in the tumors and 1.06±0.19 / 1.85±0.22 in the inflammatory lesions, respectively. The tumors showed significantly higher uptake than inflammatory lesions both in FAMT and FBPA (p=0.046 and p<0.01). The uptake of FAMT was significantly lower than that of FBPA in the inflammatory lesions (p<0.01), suggesting the tumor specificity of FAMT.

Conclusions This study demonstrated the feasibility of FAMT in differentiating malignant tumors from inflammatory lesion. FAMT showed significantly lower uptake in the inflammatory lesion compared to FBPA. However, optimal timing for the static image needs to be discussed due to the fast clearance of FAMT from the tumor.