Correct diagnosis and definition of the functional and anatomic status of lesions in cancer patients are of clinical importance. The value of hybrid imaging using a gamma camera-based PET/CT and (18)F-FDG in determining the relationship between mass and cancer was assessed.
Methods: Hybrid imaging was performed using a device combining low-dose CT and gamma camera-based PET. Ninety-one patients with histologically proven malignancy and 190 suspected sites of disease were evaluated. Camera-based PET was performed after the injection of 296-370 MBq (18)F-FDG. The presence of organomegaly or an abnormal mass on CT and of abnormal uptake of (18)F-FDG was assessed for each suspected lesion. The presence of malignancy at each site was determined by biopsy, imaging follow-up, or clinical outcome.
Results: Five imaging patterns were found. Pattern 1 showed congruent abnormal (18)F-FDG uptake and a mass on CT in 110 of the lesions. One hundred two sites (93%) had active cancer. Pattern 2 showed a mass on CT, larger than the area of abnormal (18)F-FDG uptake, and was found in 5 lesions. Active malignancy was proven in 3 sites (60%). Pattern 3 showed an abnormal mass on CT with no (18)F-FDG uptake and was found in 52 lesions. Thirteen of these lesions (25%) had active tumor. Pattern 4 showing abnormal (18)F-FDG uptake with no mass on CT was found in 23 lesions. Sixteen of these sites (70%) were malignant. Pattern 5 showed normal CT findings and no abnormal (18)F-FDG uptake in 11 patients. Two of these patients (18%) had active disease. Hybrid imaging was of value in establishing the correct relationship between CT and (18)F-FDG findings in 98 of the 190 lesions (52%).
Conclusion: A range of patterns presenting with or without abnormal (18)F-FDG uptake on camera-based PET and a mass on CT may occur in suspected cancer sites. Both structural changes on CT and increased cell metabolism expressed by abnormal (18)F-FDG uptake should be considered in oncologic imaging. Hybrid imaging, a combined physiologic and anatomic modality, appears to provide new diagnostic opportunities in characterizing function and morphology in malignancies.