Quantification of brain mu-opioid receptors with [11C]carfentanil: reference-tissue methods.

[(11)C]Carfentanil (CFN) is a mu-opioid agonist used for in vivo positron emission tomography (PET) studies of mu-opioid receptors. Previously, a tissue-ratio method was validated for the quantification of CFN binding. However, since that initial validation, several other blood independent (reference-tissue) methods have become available. To evaluate these methods, CFN PET studies with arterial blood sampling were acquired in six healthy male control subjects. Specific binding estimates obtained from reference-tissue methods were compared to those obtained with a more rigorous blood input modeling technique. It was determined that both a graphical method, and a simplified reference tissue model, were more accurate than the tissue-ratio method for quantification of CFN binding.