Integrated 18F-FDG PET/MRI Versus PET/CT in Malignant Tumor Liver Metastasis, Lymphoma Hepatic Infiltration

A preliminary comparative study presented at the 2024 Society of Nuclear Medicine and Molecular Imaging Annual Meeting suggests that integrated positron emission tomography and magnetic resonance imaging (PET/MRI) is superior to positron emission tomography and computed tomography (CT) in diagnosing malignant tumor liver metastasis/lymphoma hepatic infiltration.

Dr. Jia Guo, of the Chengdu University DICOM Medical Imaging Diagnostic Center, and colleagues designed the study to compare and analyze the diagnostic value of integrated ¹⁸F-FDG PET/MRI versus PET/CT in the detection of malignant tumor liver metastasis/lymphoma infiltration. The goal was to provide an improved 1-step assessment method for hepatic lesions.

A total of 16 patients were included in the study with confirmed malignant tumors and suspected liver metastasis/lymphoma infiltration from January 2021 to January 2023. All patients underwent ¹⁸F-FDG PET/CT imaging followed by integrated PET/MRI imaging of the upper abdomen. Clinicians allowed for no more than 30 minutes between the examinations.

A nuclear medicine physician and a radiologist independently analyzed the imaging results, counting the metastatic/infiltrative lesions found by PET/CT and PET/MRI. They then compared these results with pathological results, clinical data, and a series of radiological data—including enhanced CT and MRI.

After a follow-up period of 6 to 12 months, all patients with malignant tumors had confirmed liver lesions, 15 of which were due to tumor metastasis and the remaining 1 due to indolent lymphoma. While PET/CT diagnosed 14 cases—missing 1 oligometastatic lesion and misdiagnosing 1 case of multiple indolent lymphoma infiltrations in the liver—PET/MRI diagnosed all 16 cases.

A total of 41 lesions from malignant tumor liver metastasis/lymphoma infiltration were found in the 16 patients. PET/CT diagnosed 33 lesions with a sensitivity of 80.5% and a miss rate of 19.5%; PET/MRI diagnosed all 41 lesions with a sensitivity of 100% and a miss rate of 0%.

Among the 33 lesions diagnosed by PET/CT, all had varying degrees of fluorodeoxyglucose (FDG) uptake. CT showed low or slightly low density, with diameters ranging from 0.5 cm to 8.7 cm. One very small metastatic lesion (0.3 cm in diameter) was missed, with no definite change in density on CT and no increased FDG uptake. One case of multiple indolent lymphoma infiltrations in the liver was misdiagnosed, with 7 lesions.

On PET/MRI images, liver metastases/lymphoma infiltrations appeared as single or multiple lesions within the liver, researchers noted. These lesions had varying degrees of FDG uptake, with the very small lesions not taking up FDG.

“Integrated PET/MRI is superior to PET/CT in the diagnostic performance for malignant tumor liver metastasis/lymphoma hepatic infiltration, especially for very small lesions, lesions with inactive glucose metabolism, and indolent lymphoma types, facilitating the localization, quantification, and characterization of lesions,” Dr. Guo and colleagues concluded.