Digital images can be manipulated for evaluation in various ways. Post-processing includes: Subtraction, addition, rotation, inversion, multiplanar reconstruction (MPR), maximum intensity projection (MIP), etc.
Subtraction is particularly useful in contrast enhanced examinations. The pre contrast images are subtracted from the images after an injection of contrast agents (sometimes also called dye) for better tumor detection. See also Contrast Enhanced Computed Tomography, Digital Subtraction Angiography and Active Zone.

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:

Syringeless CT power injectors (also called pressure injectors) have been developed as a solution to reduce contrast fluid waste. The Joint Commission does not allow the reuse of unused cans from disposable syringes, so the syringeless option allows facilities to use contrast media as efficiently as possible.
A syringeless CT (computed tomography) contrast media injector permits delivery to be made directly from standard contrast media bottles, featuring multi-dosing and programmable automatic saline flush. This higher loading capacity for contrast agent ( up to two contrast bottles or 1000 ml) and a bag of saline at initial setup, enables to perform multiple contrast enhanced CT scans without reloading contrast agent; resulting in increased efficiency and less waste.

See also Single-Head Contrast Media Injector, Dual-Head CT Power Injector, CT Power Injector, Multi-Head Contrast Media Injector.

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.