The dose limit is the highest value of an applied or allowed radiation exposure. The radiation dose is limited in order to prevent the occurrence of radiation-induced deterministic effects or to limit the probability of radiation-related stochastic effects to an acceptable level.

See also Whole Body Counter, Thermoluminescent Dosimeter, Dosimetrist, Annual Limit On Intake, Committed Effective Dose Equivalent, Computed Tomography Dose Index, Directional Dose Equivalent, Doubling Dose.

Image quality is an important value of all radiographic imaging procedures. Accurate measures of both image quality and patient radiation risk are needed for effective optimization of diagnostic imaging. Images are acquired for specific purposes, and the result depends on how well this task is performed. The imaging performance is mainly influenced by the imaging procedure, examined object, contrast agents, imaging system, electronic data processing, display, maintenance and the operator. Spatial resolution (sharpness), contrast resolution and sensitivity, artifacts and noise are indicators of image quality.
A high image contrast provides the discrimination between tissues of different densities.
The image resolution states the distinct visibility of linear structures, masses and calcifications.
Noise and artifacts degrade the image quality. In computed tomography (CT), high spatial resolution improves the visibility of small details, but results in increased noise. Increased noise reduces the low contrast detectability. Noise can be reduced by the use of large voxels, increased radiation dose, or an additional smoothing filter, but this type of filter increases blurring.
An image acquisition technique taking these facts into account maximizes the received information content and minimizes the radiation risk or keeps it at a low level.

See also As Low As Reasonably Achievable.

A radiation meter is used to measure radioactivity.
Beta emitting isotopes, such as C-14, P-32, P-33, and S-35, are best detected with a Geiger-Mueller counter (GM).
Gamma emitting isotopes, such as I-125, I-123, I-131, and Tc-99m are easily detected with a gamma meter equipped with a sodium iodide (NaI) probe.
An isotope that cannot be detected with most survey meters, unless present in large activities, is tritium (H-3). Tritium emits beta particles with energies insufficient to enter the sensitive volume of most detectors.

Raw data are the values of all measured detector signals during a scan. After calibration for fluctuations in tube output and beam hardening, the attenuation properties of each x-ray signal are accounted and correlated with the ray position. From these data the CT images are reconstructed including the use of mathematical procedures like convolution filtering and back projection.
Raw data can also be used for later reconstruction of additional planes and images by using a different convolution filter, zoom reconstruction, or an alternative CT number scale.

See also Magnification, Archiving, Number of Measurements and Convolution.

(Sv) The sievert is the SI unit of a dose equivalent, which accounts for relative sensitivities of different tissues and organs exposed to radiation. The effective dose, usually measured in millisievert (mSv), attempts to reflect the biological effects of radiation. One sievert equals an ionizing x-ray or gamma radiation energy loss of 1 joule per kilogram of body tissue (1 gray). One sievert is equivalent to 100 rem.
It is named after Rolf Sievert, a Swedish medical physicist.