Routine conventional x-rays and ultrasound have been used for the diagnosis of sinus infections for years. However they have recognized limitations. The ethmoid sinuses, which are most commonly involved in sinusitis, are not adequately seen on conventional x-rays. X-rays often falsely diagnose maxillary sinus disease. Ultrasound techniques are also not particularly helpful. They can only evaluate the maxillary sinuses. While ultrasound is more sensitive than plain x-rays for imaging the maxillary sinuses, the findings are less specific and less reliable. PET (positron emission tomography) scans are currently being developed for sinus imaging. They are not routinely available and are investigational aids in the diagnosis and treatment of sinus cavity cancers.