This is a prospective, single-center, diagnostic study designed to compare the accuracy of \[68Ga\]Ga-CTR-FAPI PET/MRI and \[18\]F-FDG PET/MRI for the detection of lymph node metastasis in patients with initially untreated, resectable middle to high rectal cancer. The study aims to evaluate whether \[68Ga\]Ga-CTR-FAPI PET/MRI provides higher sensitivity and specificity than traditional 18F-FDG PET/MRI at both the patient level and the lymph node level.
Confirmed rectal adenocarcinoma by pathological biopsy.
Lower margin of the tumor is ≥ 5 cm and ≤15 cm from the anal verge.
Planned to undergo radical surgery.
ECOG performance status score ≤ 2.
History of pelvic radiotherapy or chemotherapy.
Concurrent with other malignant tumors or active infections.
Pregnant or unable to sign the informed consent form.
Claustrophobia or inability to tolerate MRI examinations due to other reasons.
Single group
PET/MRI with 18F-FDG and [68Ga]Ga-CTR-FAPI
Diagnostic testDiagnostic Test: 18F-FDG PET/MRI Description: Patients receive an intravenous injection of 18F-FDG (3.7-5.5 MBq/kg). Diagnostic Test: \[68Ga\]Ga-CTR-FAPI PET/MRI Description: Patients receive an intravenous injection of \[68Ga\]Ga-CTR-FAPI (1.8-3.7 MBq/kg).
Sensitivity and Specificity of Lymph Node Metastasis Detection
Comparison of the sensitivity and specificity of \[68Ga\]Ga-CTR-FAPI and 18F-FDG PET/MRI in determining lymph node metastasis at both the individual lymph node level and the patient level. Sensitivity is defined as the proportion of imaging-positive and pathology-positive nodes out of all pathology-positive nodes. Specificity is defined as the proportion of imaging-negative and pathology-negative nodes out of all pathology-negative nodes.
False Positive and False Negative Rates
Analysis of the false positive and false negative rates of FAPI and FDG imaging, exploring underlying pathological bases such as inflammation or micrometastasis.
Correlation Between Radiomics Features and Tumor Microenvironment
Extraction of lymph node radiomics features to evaluate their association with tumor microenvironmental markers, determined via automatic immunohistochemistry scoring.
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