Coil :

Single or multiple loops of wire (or other electrical conductor such as tubing) designed to either produce a magnetic field from current flowing through the wire or receive an induced voltage in the loop arising from a changing magnetic held.

   Collimation :

The use of lead shutters to control the effective thickness of the X-ray beam and thus the slice thickness. Pre-patient collimation is next to the X-ray tube. Positioning of the shutters requires high precision and accuracy as the beam will diverge, thus the shutter collimation has to less than the nominal slice thickness. Pre-patient collimation markedly affects patient radiation dose. Post-patient collimation is next to the detectors. This will reduce scatter and also controls the nominal slice thickness. Thin-section CT can be more easily acquired with post-patient collimation, but accurate alignment between pre- and post-patient collimation is required to optimize radiation dose.

   Cone beam :

Descriptive term for the shape of the “swept volume” passed through by the CT beam for a detector row away from the centre of the fan-beam on multislice CT. Because this beam is not perpendicular to the detectors, it generates image artefacts. Corrections for the “cone beam geometry” of the data acquisition from multislice scanners are under development to enable wider banks of detectors to further increase the volume scanned per rotation.

   Contrast resolution :

Ability to resolve structures according to density difference. Influenced on CT by the noise in the image, improved by higher mAs (radiation dose).

   Convolution :

Computer manipulation of raw data to generate an image (usually by back projection).

   CT Artefact :

A fault in the image not representing an object in the scanned volume. Artefacts may be generated by the imaging equipment or by patient motion during scanning, or by many other confounding factors.

   CT fluoroscopy :

Rapid serial display of images from a single-slice location to provide an image updated between one and several times a second, used to guide interventional procedures by CT. Fast image reconstruction algorithms, often without the usual correction steps and utilizing some of the already back-projected data from the previous image, can result in a moving image in” near real-time”, less than 250ms later.

   Maximum intensity projection :

Computed image derived from a stack of CT images which displays the stack from any direction, with the image density related to the peak pixel value seen from that direction throughout the stack volume. This technique is used to demonstrate vascular enhancement in an “angiogram-like” way.

   CT Window :

The window width is the range of CT numbers that will occupy the entire grayscale of the display monitor; the window level is the CT number at the midpoint of that range. Altering the width and level therefore alters contrast and brightness of the image, allowing the entire image density range to be interrogated on the monitor.

   CTDI :

CT dose index. Used to make comparisons of dose between scanners as simple mAs exposure levels do not give comparable doses between different scanners.

   Curie (Ci) :

The curie is a unit used to measure a radioactivity. One curie is that quantity of a radioactive material that will have 37,000,000,000 transformations in one second. Often radioactivity is expressed in smaller units like: thousandths (mCi), one millionths (uCi) or even billionths (nCi) of a curie. The relationship between becquerels and curies is: 3.7 x 1010 Bq in one curie.

   Diamagnetic substance :

A substance that will slightly reduce the strength of a magnetic field in which it is placed. The polarity of the magnetization induced in a diamagnetic substance (most organic material) is opposite to that of the surrounding magnetic fields, and has negative susceptibility. These substances have no unpaired orbital electrons.