Soliter pulmoner nodüllerin benign malign ayrımında F18 FDG PET ile erken geç görüntülemenin rolü
Özet
A solitary pulmonary nodule is a round or oval opacity smaller than 3-4 cm in diameter that is completely surrounded by pulmonary parancyhma and is not associated with lymphadenopathy, atelectasis or pneumonia. Many malignant and benign processes occur in solitary pulmonary nodules? etiology and only 20-25% of them are symptomatic. F18-FDG PET has reached widespread application in the assessment of pulmonary nodules. 40-50% of these clinically detected nodules are malign lesions where as 50-60% are benign. When a nodule is detected by radiograms malignity must be excluded. F18-FDG PET is mostly used for excluding malignancy but false positive and false negative results must be considered in the diagnosis. Therefore, the usefulness of dual time PET imaging after F18 injection to distinguish benign processes from malignant lesions is reported in some studies.This recent study compares the diagnostic accuracy of standard F18-FDG PET scaning with those of dual time point PET scaning.MATERIAL- METHOD: 20 patients (16 men, 4 women, mean age 62±8.3 (52-80)) with 20 known or suspected malignant pulmonary nodules underwent PET of the thorax at 2 time points : scan 1 at 65.7(40-80)min and scan 2 at 137(90-168)min after the intravenous injection of 340-495 MBq (9,17-13.4 mCi) F-18 FDG. Regions of interest were overlaid onto each fully corrected image in the areas of the radiographically known lung densities. The standardized uptake values(SUV) were calculated for both time points.RESULTS: 20 lesions were evaluated in this 20 patients. 16/20 (80%) of this lesions were malignant where as 4/20 (20%) were negative for malignancy according to the histopathologic examination. The SUVmax values in malignity positive group were more than accepted threshold value(>2.5). The mean SUVmax value for whole body images (SUVmax 1) was calculated 10.82±4.38 and 14.46±6.14 for delayed static images (SUVmax 2).Additionally, SUVmax 1 was calculated 5.3±4.34 and SUVmax 2 was 8.05±7.48 in malignity negative group. The percentage between SUVmax 1 and SUVmax 2 values increased %36±0.225 for malignant lesions and %44.75±25.47 for non-malignant lesions.For standard whole body PET scanning with a threshold SUV of 2.5, the sensitivity was 100% and spesifity was 50%. For static delayed images sensitivity and spesifity was %100 and 25% respectively.The sensitivity was calculated 87.5% when the difference between SUVmax 1 and SUVmax 2 was more than 10%.CONCLUSION: The lesions with increased FDG uptake are mostly malignant but false positive results must be considered. In these cases, delayed images can be useful to differentiate malign lesions from benign ones. On the other hand, dual time imaging is not always necessary and it is more helpful to distinguish the lesions with mild FDG uptake. Thus, this method may be suggested only in selected patients.