Role of IV iodinated contrast material in ¹⁸F-FDG PET/CT of liver metastases

OBJECTIVE. The purpose of our study was to investigate the role of IV iodinated contrast material in the evaluation of hepatic metastases at ¹⁸F-FDG PET/CT. MATERIALS AND METHODS. We retrospectively identified 39 patients (25 men and 14 women) with suspected isolated hepatic metastases from colorectal cancer who underwent FDG PET/CT. The CT protocol included acquisition of unenhanced and multiphase contrast-enhanced CT images through the liver. At two separate sittings, four readers (two radiologists and two nuclear medicine physicians) noted and characterized all hepatic lesions in consensus, first based on PET and unenhanced CT images and later based on PET and contrast-enhanced CT images. The nature of detected lesions was established by histopathologic or clinicoradiologic correlation. RESULTS. A total of 178 hepatic lesions were identified, consisting of 137 metastases and 41 benign lesions. Using lesion-based analyses with Obuchowski's method for paired observations, 172 of 178 lesions (97%) were detected at PET/contrast-enhanced CT compared with only 135 of 178 (76%) at PET/unenhanced CT (p = 0.0004). Specifically, 114 of 137 (83%) hepatic metastases were detected on PET/contrast-enhanced CT compared with 92 of 137 (67%) on PET/unenhanced CT (p = 0.012). One hundred thirty-one of 178 lesions (73%) were accurately characterized at PET/contrast-enhanced CT compared with 101 of 178 (57%) at PET/unenhanced CT (p = 0.004). CONCLUSION. IV iodinated contrast material administration improves the detection of hepatic metastases and the characterization of focal hepatic lesions at PET/CT.