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.

Hypaque Sodium is a high-osmolar, water-soluble contrast agent. In pure form, it contains 59.87 percent organically bound iodine.
The dosage of contrast media is depended on the type of radiological procedure and should be tailored individually according to age, body size, and indication for examination.

Omnipaque (iohexol) is a nonionic, low-osmolar contrast agent and is also available for oral use, offering gastrointestinal (GI) visualization with minimal side effects. Omnipaque has a neutral taste that even kids will drink.
Orally administered iohexol is poorly absorbed from the normal gastrointestinal tract. Omnipaque is well tolerated and absorbed if leakage into the peritoneal cavity occurs.
The recommended dosage of undiluted Omnipaque (at a concentration of for example 350 mg/mL) for computed tomography of the abdomen in adults is 500 mL to 1000 mL, diluted to concentrations of 6 mg/mL to 9 mg/mL. The oral dose should be administered about 20 to 40 minutes prior to the CT scan.

Prepcat (brand name Lafayette) is a barium sulfate suspension for computed tomography examinations of the gastrointestinal (GI) tract. The dosage and application depend on the specific procedure.
UPPER G.I. OPACIFICATION: The patient should drink 300 mL of ready-to-use Prepcat approximately 2 hours before the CT scan and an additional 300 mL approximately 15 minutes prior to examination.
If rapid upper gastrointestinal tract transit is desired, administer the product chilled.
TOTAL BOWEL OPACIFICATION: The patient should drink 300 mL the night preceding the examination, 300 mL two hours prior to the examination and 300 mL approximately 15 minutes prior to examination.

Baro-Cat® is a barium sulfate suspension for use as an aid for computed tomography of the gastrointestinal tract. The contrast medium contains additional pineapple-banana flavor suspending agents, simethicone, potassium sorbate, citric acid, sorbitol, artificial sweetener and water.
Individual technique will determine the suspension quantity and specific procedure used. For computed tomography of the upper gastrointestinal tract should the patient drink 300 mL Baro-Cat® approximately 2 hours before and an additional 300 mL approximately 15 minutes prior to the CT scan. For total bowel opacification the patient should drink additional 300 mL the night before the examination. If rapid transit is desired, administer the suspension chilled. Rectally administered the contrast agent should be at room temperature to body temperature.