NCCT means a Non - Contrast CT Scan or a Plain CT PNS (Para-Nasal Sinuses). It is the gold standard investigation for diagnosing Sinus related problems.
Contrast injection is only used in special cases.
Newer CT Scan machines have a higher radiation exposure, but at the same time are able to give higher resolution scanning which is necessary to see the wafer thin bony partitions of the sinuses. They can also scan in multiple planes and are very quick, requiring just a couple of minutes for a scan.
The amount of X-ray radiation exposure can be reduced by reducing the resolution if such High Resolution (HRCT) if it is not required in your case.