(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.

(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.

(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.

A biopsy is a procedure in which tissue samples are collected. This can be done with a needle, which is inserted into the abnormal area.
An example is the needle breast biopsy. Needle biopsies are usually guided by different imaging techniques like ultrasound, computed tomography, or magnetic resonance imaging. Stereotactic-assisted breast biopsies use computer maps to guide the needle. The location of the breast lump is provided from digital mammograms taken from two angles.
The cells can be removed and examined under a microscope to determine whether the abnormality is cancerous.

See also CT Guided Biopsy.

A myelography is a radiographic imaging procedure to visualize the spinal canal, the spinal cord, cerebrospinal fluid (CSF), intervertebral disks and nerve roots. A special contrast agent (dye) is injected through a needle into the subarachnoid space of the spinal canal. A myelogram provides a very detailed picture of the spinal cord and spinal column. A fluoroscopy displays the bones and the fluid-filled space of the spine also in motion. An additional computerized tomography (CT or CAT) scan helps to differentiate the spinal conditions better. The indications include disc herniation, spinal stenosis, tumor, and vertebral fracture.

See also Myeloscintigraphy, Fluoroscopic System, Hounsfield Unit, Bone Densitometry, Nonionic Contrast Agents.