This study is a single-center, open-label first-in-human clinical study. Patients with clinically suspected or confirmed malignant solid tumors will undergo [68Ga]Ga-FAP PET imaging or [177Lu]Lu-FAP SPECT imaging as well as [18F]FDG PET imaging to determine the presence or absence of lesions, and to assess lesion location, characteristics, and metastasis. Histopathological diagnosis or follow-up results will serve as the reference standard. The diagnostic efficacy of [68Ga]Ga-FAP PET imaging or [177Lu]Lu-FAP SPECT imaging for malignant tumors will be evaluated. Additionally, the study will analyze the biodistribution and dosimetry of [177Lu]Lu-FAP following a single administration, explore the correlation between tumor uptake values on imaging and immunohistochemical FAP expression levels, and evaluate the safety and tolerability of a single low-dose intravenous injection of [68Ga]Ga-FAP or [177Lu]Lu-FAP for diagnostic imaging.

Inclusion Criteria:

1. Voluntary participation and the patient or their legal representative is able to sign an informed consent form.
2. Adult patients (aged 18 or above), regardless of gender.
3. Patients with an ECOG performance status of 0 to 1 and able to tolerate PET and SPECT/CT examinations.
4. Patients with histopathologically or clinically confirmed malignant solid tumors who have measurable lesions according to RECIST 1.1 criteria.
5. Patients with expected survival>6 months.
6. Female patients of childbearing potential must have a negative pregnancy test, and all patients (including male patients) agree to use effective contraceptive measures during the study period and for at least three months after study drug administration.

Exclusion Criteria:

1. Patients who are pregnant or breastfeeding, or plan to become pregnant during the study period or within three months after study drug administration (excluding those who have been postmenopausal for at least one year, or those who are surgically sterilized, such as bilateral tubal ligation without recanalization, bilateral oophorectomy, or hysterectomy); or patients who plan to donate sperm or eggs during the study period or within three months after study drug administration.
2. Patients with known or suspected allergy to the investigational drug or any of its components, or patients with severe allergic constitution.
3. Patients who have undergone procedures within 6 months prior to study entry that, in the investigator's judgment, may affect drug absorption, distribution, metabolism, or excretion.
4. Patients with positive syphilis or HIV test results at screening.
5. Patients with abnormal liver or kidney function: serum total bilirubin (TBIL) > 31.5 umol/L; aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 120 U/L, or > 200 U/L if the elevation is considered to be related to liver metastases from solid tumors; serum creatinine (Scr) > 150 umol/L, or creatinine clearance < 60 mL/min (according to the Cockcroft-Gault formula).
6. Patients with abnormal bone marrow parameters: absolute neutrophil count < 1.5 x 10^9/L, hemoglobin < 10 g/dL, serum albumin < 2.8 g/dL (normal range 3.5-5.5 g/dL), platelets < 100 x 10^9/L (normal range 100-300 x 10^9/L), international normalized ratio (INR) > 1.5 (normal range 0.8-1.3) in patients not taking warfarin, or prothrombin time (PT) > 2 x ULN (normal range 11-15 seconds).
7. Patients with active infection (e.g., acute bacterial infection, tuberculosis, active hepatitis B/C, active syphilis, etc.). Active hepatitis B is defined as: positive HBsAg or HBcAb, or results outside the normal reference range, accompanied by hepatitis B virus DNA titer > 2500 copies/mL or > 500 IU/mL. Active hepatitis C is defined as: positive hepatitis C antibody, or results outside the normal reference range, and positive HCV-RNA.
8. Patients with dysuria or urinary incontinence due to any cause.
9. Patients with claustrophobia or other conditions that preclude cooperation with PET/MR and SPECT/CT examinations.
10. Patients with psychiatric disorders such as depressive symptoms, schizophrenia, delusions, hallucinations, or suicidal ideation.
11. Patients with severe cardiovascular disease, including but not limited to New York Heart Association (NYHA) class II to IV congestive heart failure, or left ventricular ejection fraction (LVEF) < 50% or below the lower limit of normal.
12. Patients with other conditions that, in the investigator's opinion, make the patient unsuitable for participation in this study.