(CA) Contrast agents are used to change the imaging characteristics, resulting in additional information about anatomy, morphology or physiology of the human body. Radiocontrast agents (also called photon-based imaging agents) are used to improve the visibility of internal body structures in x-ray and CT procedures. Contrast agents are also used to increase the contrast between different tissues in MRI (magnetic resonance imaging) and ultrasound imaging. The ideal imaging agent provides enhanced contrast with little biological interaction.
First investigations with radiopaque materials are done shortly after the discovery of x-rays. These positive contrast agents attenuate x-rays more than body soft tissues due to their high atomic weight. Iodine and barium have been identified as suitable materials with high radiodensity and are used until today in x-ray and CT contrast agents. Iodine-based contrast agents are water-soluble and the solutions are used nearly anywhere in the body. Iodinated contrast materials are most administered intravenous, but can also be introduced intraarterial, intrathecal, oral, rectal, intravesical, or installed in body cavities. Barium sulfate is only used for opacification of the gastrointestinal tract. Negative contrast agents attenuate x-rays less than body soft tissues, for example gas.

Iodinated contrast media are differentiated in;

Intravascular iodinated contrast agents are required for a large number of x-ray and CT studies to enhance vessels and organs dependent on the blood supply. Injectable contrast agents are diluted in the bloodstream and rapidly distributed throughout the extracellular fluid. The main route of excretion is through the kidneys, related to the poor binding of the agent to serum albumin. The liver (gall bladder) and small intestine provide alternate routes of elimination particularly in patients with severe renal impairment. The use of special biliary contrast agents is suitable for gallbladder CT and cholecystograms because they are concentrated by the liver to be detectable in the hepatic bile.
The introduction of fast multi-detector row CT technology, has led to the development of optimized contrast injection techniques. The amount of contrast enhancement depends on the contrast agent characteristics, such as iodine concentration, osmolality, viscosity, and the injection protocol, such as iodine flux and iodine dose. Adverse reactions are rare and have decreased with the introduction of nonionic contrast agents.
See also Contrast Enhanced Computed Tomography, Abdomen CT, Contrast Media Injector, Single-Head CT Power Injector, Multi-Head Contrast Media Injector, Syringeless CT Power Injector, CT Power Injector.

(FNH) The focal nodular hyperplasia is a hypervascular, benign focal liver lesion. Various liver imaging techniques are common to differentiate FNH from a malign lesion, such as contrast enhanced ultrasound, MRI or a CT multi phase study.

Iodinated contrast media contain small amounts of free iodide. Too much free iodide in the blood may cause hyperthyroidism in patients at risk, but contrast medium induced thyrotoxicosis is rare. The free iodide may also interfere with nuclear medicine diagnostic tests and treatment. However, iodinated contrast agents do not affect thyroid function tests (e.g., T3, T4, TSH) in patients with a normal thyroid.
Guidelines were prepared by the 'Contrast Media Safety Committee of the European Society of Urogenital Radiology' and discussed on the Tenth European Symposium on Urogenital Radiology in September 2003.
Tests of thyroid function before the injection of contrast agents may only be indicated in areas with dietary iodine deficiency. Patients with Graves' disease, multinodular goiter with thyroid autonomy, especially elderly and patients who lives in areas of iodine deficiency are at risk to develop thyrotoxicosis after IV contrast medium and should be monitored by endocrinologists after contrast enhanced CT exams. Prophylaxis may offer some protection in selected high-risk individuals but is not generally recommended.
The free iodide of iodinated contrast agents interferes with thyroidal iodide uptake and impedes diagnostic thyroid scintigraphy and radio-iodine treatment of thyroid malignancies for 2 months after administration.

A venography (also called phlebography) is the imaging of veins. To perform a venography, a contrast agent is injected into a vein during a fluoroscopy, to show the details of venous structure and abnormalities as for example blood clots and occlusions. The examination of the veins is called venogram.
Other methods include contrast enhanced MR venography and venous ultrasound techniques.

See also Angiogram, CT Angiography, Digital Subtraction Angiography and Computed Tomography.

Contrast media injectors are part of the medical equipment used to deliver fluids in examinations such as CT, MRI, fluoroscopy and angiography. Many of these diagnostic imaging procedures include the administration of intravenous contrast agents to enhance the blood and perfusion in tissues.

Mainly there are two types of injector technology:
See also Single-Head Contrast Media Injector, Dual-Head CT Power Injector, Syringeless CT Power Injector.

The use of x-ray contrast agents in computed tomography (CT) began with a hand injection by the radiologist in the scan room. During its history, CT scanners have made great improvements in speed and image quality. Actual CT systems with multiple detectors allow scan times of a few seconds per body region. Some CT protocols require multiphase scans, where a body region is imaged with a single bolus of contrast in different blood flow phases. Automatic power (pressure) contrast media injectors are required to provide precise control of flow rate, volume and timing of injection. The use of a saline bolus following contrast administration reduces the volume of contrast required.

Most relevant topics for the use of a power injector in medical imaging procedures such as contrast enhanced computed tomography (CECT):
Must have basic injector control options:
Examples of other injector control options: