FDG PET/CT versus CT, MR imaging, and 67Ga scintigraphy in the posttherapy evaluation of malignant lymphoma.

Malignant lymphoma is the most common form of hematologic cancer, yet because of advanced methods of assessment, the traditional histology-based classification of lymphoma is insufficient for understanding lymphoma imaging. Still, radiologists should be familiar with the imaging findings in lymphoma. Integrated positron emission tomography (PET)-computed tomography (CT) allows improved diagnostic accuracy, and uptake of 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) can help predict response during treatment. The sensitivity and specificity of FDG PET are superior to those of gallium 67 scintigraphy in all but indolent lymphoma. Both magnetic resonance (MR) imaging and CT allow excellent assessment of bone texture, but FDG PET is superior in demonstrating bone marrow metabolic activity. Thus, FDG PET is important in both the primary diagnosis and the evaluation of therapy in lymphoma. It may be difficult to determine whether residual abnormalities seen after the completion of chemotherapy-radiation therapy represent residual tumor or fibrotic tissue, but PET/CT may allow more accurate diagnosis than MR imaging or CT, thereby helping identify patients who require more intensive treatment. Some diagnostic pitfalls are encountered at FDG PET. However, anatomic CT helps localize and define disease and avoid these potential pitfalls.