PURPOSE: The presence of contrast materials on computed tomography (CT) images can cause problems in the attenuation correction of positron emission tomography (PET) images. These are because of errors converting the CT attenuation of contrast to 511-keV attenuation and by the change in tissue enhancement over the duration of the PET emission scan. Newer CT-based attenuation correction (CTAC) algorithms have been developed to reduce these errors. METHODS: To evaluate the effectiveness of the modified CTAC technique, we performed a retrospective analysis on 20 patients, comparing PET images using unenhanced and contrast-enhanced CT scans for attenuation correction. A phantom study was performed to simulate the effects of contrast on radiotracer concentration measurements. RESULTS: There was a maximum difference in calculated radiotracer concentrations of 5.9% within the retrospective data and 7% within the phantom data. CONCLUSION: Using a CTAC algorithm that de-emphasizes high-density areas, contrast-enhanced CT can be used for attenuation mapping without significant errors in quantitation.