This study is an open-labeled phase II diagnostic clinical trial to explore the safety and clinical value of FBY in suspected adult brain tumor patients. The investigation regarding the clinical value of FBY includes 1) the metabolic characteristics of FBY in suspected malignant brain tumors; 2) role of FBY to differentiate tumor progression from pseudoprogression. A single dose of 0.10 mCi/kg FBY will be intravenously injected for PET examination. Quantitative features will be extracted to analysis the PET images. Cranial MRI (with contrast enhancement) will also performed as diagnostic comparison with FBY. For patient who took surgery after multiple examination, histopathology, molecular pathology and LAT-1 immunohistochemistry will also be obtained.

FBY is a new PET tracer derived from tyrosine, with the carboxyl group replaced by boron trifluoride, and is transferred across cell membrane through LAT-1. LAT-1 is a sodium independent amino acid transporter and is highly expressed in tumor cells. Considering the significant role in cancer development as well as in nutrient delivery, FBY could be a promising PET tracer to reflect altered metabolism in tumors.

This study aim to observe the safety of FBY, and investigate the diagnostic value of FBY in the patient with suspected brain tumors. Patients who meet the eligibility criteria are included in clinical trials after fully communicating the condition, explaining the benefits and risks of clinical trials, clarifying the patient's willingness to include the clinical trial, and signing informed consent. The cohort number, FBY administrative dose, imaging protocols are decided based on the investigators' preliminary data. The diagnosis and post-examination treatment are based on the recommended guideline, combined with the subject's own situation for standardized diagnosis and treatment.

Inclusion Criteria:

• 1. Have suspected diagnosis of brain tumors, based on clinical performance and MRI results.
• 2. Meet the indications for PET examination, show a clear indication and no contraindications;
• 3. Have a performance status of score ≥70 on KPS scale or score 0-1 points on ECOG scale, a relatively good general situation;
• 4 Does not appear agonal stage, deep coma, over grade 2 major organ dysfunction (heart, lung, liver, kidney and other major organ include), acute or life-threatening status of infection;
• 5. Be ≥ 18 years of age on day of signing informed consent.
• 6. Be willing and able to understand the research content and provide written informed consent/assent for the trial.

Exclusion Criteria:

• 1. Have a history of imaging agent allergies;
• 2. Does not meet the PET-CT scan sedation requirements, or there are contraindications for PET-CT examination;
• 3. Be pregnant or breastfeeding, or expecting to conceive or father children within the projected duration of the trial;
• 4. Unable to adhere strictly to protocol requirements.