(CECT) Contrast agents are used during contrast enhanced computed (or computerized) tomography examinations to highlight specific tissues and parts of the body. Bones can be clearly seen on x-ray images, the visualization of some other organs and soft tissues is more difficult. Sufficient contrast is important in perceiving a difference in the density between areas of a CT image. The identification of a disease may be challenging due to very low contrast between pathological tissues (for example tumors, metastases and abscesses), normal organ structures and surrounding tissues.
Contrast agents are used in CT angiography (CTA) to delineate vessels, in multiphasic CT studies to provide dynamic information of blood supply (e.g., liver CT) and in CECT studies of various body parts to achieve opacification of tissue of interest (e.g., kidney CT) in relation to the background tissue. Contrast enhanced multi-detector row CT (MDCT) replaces several conventional diagnostic imaging methods such as intravenous urography, cholangiography, or catheter angiography, due to advanced CT studies with fast examination times, high contrast enhancement, perfusion measurement and multiplanar reformatting capabilities.
See also Contrast Media Injector, Single-Head CT Power Injector, Multi-Head Contrast Media Injector, Syringeless CT Power Injector, CT Power Injector.

A computed tomography (CT) of the abdomen images the region from the thoracic diaphragm to the pelvic groin. The computed tomography technique uses x-rays to differentiate tissues by their different radiation absorption rates.
Oral contrast material can be given to opacify the bowel before scanning. An i.v. injection of a contrast agent (x-ray dye) improves the visualization of organs like liver, spleen, pancreas and kidneys and provides additional information about the blood supply.
Spiral- or helical CT, including improvements in detector technology support faster image acquisition with higher quality. Advanced CT systems can usually obtain a CT scan of the whole abdomen during a single breath hold. This speed increases the detection of small lesions (caused by differences in breathing on consecutive scans) and is beneficial especially in pediatric, elderly or critically-ill patients.
Changes in patient weight require variations in x-ray tube potential to maintain constant detector energy fluence. An increased x-ray tube potential improves the contrast to noise resolution (CNR).

An abdominal CT is typically used to help diagnose the cause of abdominal pain and diseases such as:
Other indications for CT scanning of the abdomen/pelvis include planning radiation treatments, guide biopsies and other minimally invasive procedures. Advanced techniques include for example 3D CT angiography, multiphasic contrast-enhanced imaging, virtual cystoscopy, virtual colonoscopy, CT urography and CT densitometry.

See also Contrast Enhanced Computed Tomography.

(CT or CAT scan) Computed tomography is a diagnostic imaging technique, previously also known as computerized axial tomography (CAT), computer-assisted tomography (CAT), computerized tomographic imaging, and reconstructive tomography (RT).
A CT scan is based on the measurement of the amount of energy that a tissue absorbs as a beam of radiation passes through it from a source to a detector. As the patient table moves through the CT scanner, the CT tube rotates within the circular opening and the set of x-ray detectors rotate in synchrony. The narrow, fan-shaped x-ray beam has widths ranging from 1 to 20 mm. The large number of accurate measurements with precisely controlled geometry is transformed by mathematical procedures to image data. Corresponding to CT slices of a certain thickness, a series of two-dimensional cross-sectional images is created.
A CT is acquired in the axial plane, while coronal and sagittal images can be rendered by computer reconstruction. Although a conventional radiography provides higher resolution for bone x-rays, CT can generate much more detailed images of the soft tissues. Contrast agents are often used for enhanced delineation of anatomy and allow additional 3D reconstructions of arteries and veins.
CT scans use a relatively high amount of ionizing radiation compared to conventional x-ray imaging procedures. Due to widespread use of CT imaging in medicine, the exposure to radiation from CT scans is an important issue. To put this into perspective, the FDA considers the risk of absorbed x-rays from CT scans to be very small. Even so, the FDA recommends avoiding unnecessary exposure to radiation during diagnostic imaging procedures, especially for children.
CT is also used in other than medical fields, such as nondestructive testing of materials including rock, bone, ceramic, metal and soft tissue.

See also Contrast Enhanced Computed Tomography.

Contrast is the relative difference of intensities in two adjacent regions of an image. When referring to computed tomography (CT), contrast is defined as a difference in Hounsfield units between structures. The measurement of contrast resolution in CT imaging involves determining how easy it is to differentiate tissues whose CT density is similar to that of their surroundings. An image lacks contrast when there are no sharp differences between black and white. Brightness refers to the overall lightness or darkness of an image.
The contrast between air, soft tissue, and bones in x-ray and CT images is based on their different absorption of x-rays. Differences in tissue density, thickness and changes of the x-ray spectrum have consequences for image contrast, image noise as well as patient dose.
Optimized tube current, collimation, pitch and image reconstruction improves the contrast. Higher image contrast is produced by increased slice thickness, smaller matrix, and large field of view which results in large voxel size; high mAs to reduce noise; low pass filter.

See also Contrast Enhanced Computed Tomography.

(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.