Can chest ct with contrast rule out trachea cancer?

Depends on size: Tracheal cancer on chest ct can look like a nodular growth arising from the tracheal wall or irregular wall thickening; this may be a tough finding to detect but likely to be visible in most cases. However, the cancer could be very subtle or not noticeable at all if small; ct would not be able to detect it in those cases.

Possibly: The cancer would have to be a certain size to be visible. So if it were large enough to be seen, then the diagnosis could be made. Not visible may mean it is too small to be seen with ct.