Researchers recommend routine use of contrast enhancement in PET/CT

The use of intravenous contrast material during a PET/CT exam does not significantly affect the interpretation of the PET component. Contrast-enhanced PET/CT can be used routinely for oncologic imaging, according to researchers from the University of Texas M.D. Anderson Cancer Center in Houston.

IV contrast is generally not used for attenuation correction in whole-body integrated PET/CT. Contrast media elevate the CT Hounsfield units, resulting in an overestimation of PET attenuation factors.

Previous studies looking at this problem have used phantoms or have compared contrast-enhanced CT attenuation-corrected PET images with non-corrected images. Researchers at M.D. Anderson directly compared PET images corrected for attenuation using contrast-enhanced and unenhanced CT images.

Dr. Osama Mawlawi and colleagues performed contrast-enhanced and noncontrast PET/CT exams in nine patients. They quantified the effect of contrast media on standardized uptake values (SUV) by drawing similar regions of interest for the subclavian vein, heart, liver, spleen, and site of malignancy on both CT and corresponding reconstructed PET images (AJR 2006;186:308-319).

Examination of the PET images by two physicians blinded to the CT attenuation correction maps used to reconstruct those images revealed no differences in the clinical interpretations of the PET scans of all nine patients. However, there were differences in reported maximum SUV of the malignancies on PET images reconstructed with contrast-enhanced CT scans compared with the same PET images reconstructed with unenhanced CT scans

The subclavian vein region on the ipsilateral side of contrast administration had the highest increase in CT Hounsfield units with a corresponding increase in SUV. The heart and the site of malignancy also showed an increase in the maximum attenuation value with a corresponding increase in SUV.

The increase in SUV, however, was clinically insignificant in oncologic staging and would not have been misinterpreted as sites of metastases.

"We recommend that a separate contrast-enhanced diagnostic CT not be performed and advocate that IV contrast media could be used routinely when integrated PET/CT is performed to evaluate oncologic patients," the researchers said.

The study will bolster the case for Society of Nuclear Medicine guidelines for PET/CT oncologic imaging to be published in its journal in May. The document lays out a minimum amount of training for nuclear medicine physicians to interpret the CT component of a PET/CT exam - whatever the protocol.

Those guidelines are at odds with requirements from the American College of Radiology, which maintains that the minimum training conditions allow nuclear physicians to interpret only a non-contrast-enhanced CT used for attenuation correction.

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