This coronal reformat of a CT of the chest shows the havoc that can be wrought by tube arcing. There is a band of markedly increased noise over approximately 1cm of craniocaudal distance on this CTPA study. Tube arcing occurs when there is a short-circuit within the tube, typically from cathode to tube envelope. This causes a momentary loss of xray output. New tubes are more prone to this problem due to residual gas within them.
Credit: Dr Laughlin Dawes