The Usefulness of F-18-FDG PET and The Effect of Scan Protocol in Diagnosis of Intraocular Tumors / 대한핵의학회잡지

PURPOSE: It is important to differentiate malignant from benign lesions of intraocular masses in choosing therapeutic plan. Biopsy of intraocular tumor is not recommended due to the risk of visual damage. We evaluated the usefulness of F-18-FDG PET imaging in diagnosing intraocular neoplasms. MATERIALS AND METHODS: F-l8-FDG PET scan was performed in 13 patients (15 lesions) suspected to have malignant intraocular tumors. There were 3 benign lesions (retinal detachment, choroidal effusion and hemorrhage) and 10 patients with 12 malignant lesions (3 melanomas, 7 retinoblastomas and 2 metastatic cancers). Regional eye images (256*256 and 128*128 matrices) were obtained with or without attenuation correction. Whole body scan was also performed in eight patients (3 benign and 6 malignant lesions). RESULTS: All malignant lesions were visualized while all benign lesions were not visualized. The mean peak standardized uptake value (SUV) of malignant lesions was 2.64+/-0.57 g/ml. There was no correlations between peak SUV and tumor volume. Two large malignant lesions (>1000 mm3 ) showed hot uptake on whole body scan. But two medium-sized lesions (100-l000 mm3) looked faint and two small (<100 mm3) lesions were not visualized. The images reconstructed with 256*256 matrix showed lesions more clearly than those with 128X128 matrix. CONCLUSION: F-18-FDG PET scan is highly sensitivity in detecting malignant intraocular tumor. For the evaluation of small-sized intraocular lesions, whole body scan is not appropriate because of low sensitivity. A regional scan with sufficient acquisition time is recommended for that purpose. Image reconstruction in matrix size of 256*256 produced clearer images than the ones in 128X128, but it does not affect the diagnostic sensitivity.

The Differentiation of Benign from Malignant Soft Tissue Lesions using FDG-PET: Comparison between Semi-quantitative Indices / 대한핵의학회잡지

The purpose of this study is to evaluate the diagnostic accuracy of various quantitative indices for the differentiation of benign from malignant primary soft tissue tumors by FDG-PET. A series of 32 patients with a variety of histologically or clinically confirmed benign (20) or malignant (12) soft tissue lesions were evaluated with emission whole body (5min/bed position) PET after injection of [18F]FDG. Regional 20min transmission scan for the attenuation correction and calculation of SUV was performed in 16 patients (10 benign, 6malignant) followed by dynamic acquisition for 56min. Postinjection transmission scan for the attenuation correction and calculation of SUV was executed in the other 16 patients (10 benign, 6 malignant). The following indices were obtained : the peak and average SUV (pSUV, aSUV) of lesions, tumor-to-background ratio acquired at images of 51 min p.i. (TBR51), tumor-to-background ratio of areas under time-activity curves (TBRarea) and the ratio between the activities of tumor ROI at 51 min p.i. and at the time which background ROI reaches maximum activity on the time-activity curves (T51/Tmax). The pSUV, aSUV, TBR51, and TBRarea, in malignant lesions were significantly higher than those in benign lesions. We set the cut-off values of pSUV, aSUV, TBR51, TBRarea and T51/Tmax for the differentiation of benign and malignant lesions at 3.5, 2.8, 5.1, 4.3 and 1.55, respectively. The sensitivity, specificity and accuracy were 91.7%, 80.0%, 84.4% by pSUV and aSUV, 83.3%, 85.0%, 84.4% by TBR51, 83.3%, 100%, 93.8% by TBRarea and 66.7%, 70.0%, 68.8% by Tsl/Tmax. The time-activity curves did not give additional information compared to SUV or TBR. The one false negative was a case with low-grade fibrosarcoma and all four false positives were cases with inflammatory change on histology. The visual analysis of FDG-PET also detected the metastatic lesions in malignant cases with comparable accuracy. In conclusion, all pSUV, aSUV, TBR51, and TBRarea are useful metabolic semi-quantitative indices with good accuracy for the differentiation of benign from malignant soft-tissue lesions.