(ARS) The acute radiation syndrome is a form of radiation sickness. An acute radiation syndrome can be developed after the exposition to a high radiation dose received in a short period of time (e.g., x-rays or gamma rays). ARS subsyndromes include hematopoietic, cutaneous, gastrointestinal, and neurovascular diseases. The reaction will vary with dose and factors like age, medical co-morbitdity and immunosuppression.

Adverse reactions on contrast agents are rare, but like all other pharmaceuticals, contrast media are not completely without side effects.
Adverse effects to contrast media include allergic symptoms, anaphylactoid reactions, chemotoxic reactions, idiosyncratic reactions, contrast-induced nephropathy, iodide-induced hyperthyroidism and local tissue damage. An adverse reaction can be related to dose, the toxicity, and the physio-chemical properties of the contrast agent, for example osmolality, viscosity, and hydrophilicity.
Side effects such as a metallic taste in the mouth, generalized warmth or flushing, nausea and vomiting, increase with rapid flow and large volume of the injected agent. Although venous tolerance is usually good, there have been reports of sensation like burning, stinging or numbness and of venospasm.

Characterization of adverse reactions include:

(ALI) The annual limit on intake refers to the body intake of radionuclides by inhalation, ingestion or through the skin in one year, which would result in a committed dose equal to the relevant dose limit.

Dosage is an important factor in the use of ionization radiation as well as in application of contrast agents or radiopharmaceuticals and the dosage should be comply with the ALARA principle (As Low As Reasonably Achievable).
Ionizing radiation comes from natural and artificial sources. Radiation effects depend on the type of radiation, and various units are used for measurement of dosages including gray, sievert, radiation absorbed dose (RAD), roentgen equivalent in man (REM), and roentgen. The amount of radiopharmaceutical given to a patient is measured in becquerels (Bq).
The dosage of contrast media in radiographic or computer-tomographic procedures should be tailored according to the diagnostic indications, the iodine concentration, and the patient's body size and age.

See also Administrative Dose Guidelines.

Fractionation is the delivery of a given total radiation dose as several smaller doses, separated by intervals of time to minimize side effects.