(FDA) An agency of the US federal government established by Congress in 1912 and presently part of the US Department of Health and Human Services. The FDA gives classifications of medical devices according to potential risks and controls the safety of marketed drugs.
For more details please visit the FDA's 'Our Mission and Mandate'.

See also Class I II III Devices and Phase 1 2 3 4 Drug Trials.

The gantry tilt is the angle between the vertical plane, and the plane containing the x-ray beam and the detector array. The gantry angulation allows aligning the selected anatomic region with the scanning plane.
A CT gantry can typically be angled up to 30° forward or backward. However, the gantry angulation is determined by the manufacturer and varies among CT systems. In a series of CT scans made with a tilted gantry the anatomy shifts in location from scan to scan.

In nuclear medicine a hot spot describes a strong activity enrichment in one or more ranges of the organ or body part which is examined.
A pinhole collimator may be used if images of a hot spot and the surrounding with very high resolution are necessary. Zoom magnification or a converging collimator also may be used to improve resolution and assign the hot spot.

Patents can unintended respond with an idiosyncratic reaction to the application of contrast media. Idiosyncratic reactions to contrast agents start usually within 20 minutes after injection and occur more frequently in patients 20 to 40 years old.
Idiosyncratic reactions may or may not be dependent on the amount of dose injected, the speed of injection, the mode of injection and the radiographic procedure.


See also Adverse Reaction and Anaphylactoid Reaction.

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.