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.

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.

(CTA) A computed tomographic angiography or computerized tomography angiogram is a diagnostic imaging test that combines conventional CT technique with that of traditional angiography to create images of the blood vessels in the body - from brain vessels to arteries of the lungs, kidneys, arms and legs.
High resolution CT scans with thin slices and intravenous injection of iodinated contrast material provide detailed images of vascular anatomy and the adjacent bony structures. CTA requires rapid scanning as the imaging data are typically acquired during the first pass of a bolus of contrast medium. The selection of acquisition timing is important to optimize the contrast enhancement, which is dependent on contrast injection methods, imaging techniques and patient variations in weight, age and health. CT angiography is less invasive compared to conventional angiography and the data can be rendered in three dimensions.

CTA techniques are commonly used to:
See also Cardiovascular Imaging, Magnetic Resonance Angiography MRA, Coronary Angiogram, Computed Tomography Dose Index and Computed or Computerized Axial Tomography.

Cheetah® 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 200-300 mL Cheetah® approximately 30-45 minutes before and an additional 200-300 mL approximately 5-10 minutes prior to the CT scan.
For total bowel opacification an additional 250-450 mL dose of Cheetah® may be given the evening before the examination. Approximately 1-2 hours before the examination should the patient drink 250-450 mL and 5-10 minutes before the CT scan another 250-450 mL. If rapid transit is desired, the suspension can be administered chilled. Rectally use of the contrast agent should be at room temperature to body temperature.

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.