Noise is an undesirable background interference or disturbance that affects image quality. The image noise is commonly characterized by the standard deviation of CT numbers in the image of a uniform object (phantom - generally water) relative to the difference in CT numbers between water and air.
Noise is an important limiting factor of CT image quality and is characterized by a grainy appearance, sometimes described as a salt and pepper pattern. Noise as a result of low radiation dose requires a higher tube current (mA) in combination with narrow slices to maintain image noise at an acceptable level.

Patents can unintended respond with an idiosyncratic reaction to the application of contrast media. Idiosyncratic reactions to contrast agents start usually within 20 minutes after injection and occur more frequently in patients 20 to 40 years old.
Idiosyncratic reactions may or may not be dependent on the amount of dose injected, the speed of injection, the mode of injection and the radiographic procedure.


See also Adverse Reaction and Anaphylactoid Reaction.

The acute dose is the amount of energy accommodated in human tissue or in biological systems.

See also Acute Exposure, Acute Radiation Syndrome, Biodosimetry and Annual Limit On Intake.