Can ct of chest with contrast rule out lung cancer?

Not completely: If there is a suspicious density in the lung , definitive way to rule out if it is due to malignancy , or to detect its nature of it , is by biopsy only .And tissue examination ( pathological examination ).

No: CT scans of the chest are used to find lung nodules or other chest pathology. Once a nodule is found, a workup is done to see if it is cancer. 95% of nodules found are benign.