Fluoroscopy is used to study moving body structures in real time. A fluoroscope is used to produce a continuous (advanced fluoroscopy machines provide pulsed techniques to lower the amount of radiation) x-ray beam, passing through the body part being examined and transmitted to a monitor so that dynamic images of deep tissue structures can be visualized. Fluoroscopy is primarily used for gastrointestinal exams, genitourinary studies, cardiovascular imaging and for invasive procedures performed by interventional radiologists and angiographers under fluoroscopic guidance. Fluoroscopy can also produce a static record of an image formed on the output phosphor of an image intensifier. The image intensifier is an x-ray image receptor that increases the brightness of a fluoroscopic image by electronic amplification and image minification. Modern fluoroscopy systems combine less radiation with better image quality due to digital image processing and flat-panel technology.
Roentgen's discovery of x-rays related directly to fluoroscopy, because fluorescence on the material in the room draws his attention to the x-ray's properties. In 1896, Thomas A. Edison created the first fluoroscope, consisting of a zinc-cadmium sulfide screen that was placed above the patient's body in the x-ray beam and provides a faint fluorescent image. In first-generation units, the exam room required complete darkness. The users wear red goggles for up to 30 minutes prior to the examination, to adapt the eyes to darkness. After this, the radiologist stared directly at a yellow-green fluorescent image through a sheet of lead to prevent the x-ray beam from striking the eyes.

The half value layer (also half value thickness) is the amount of absorbing material, which is needed to reduce the x-ray intensity by one half.
The half value layer provides important information about the energy characteristics of the radiation. A low (or thin) half value layer for a given x-ray beam indicates that the x-ray beam contains more low energy and less penetrating radiation. An x-ray beam containing high energy or highly penetrating radiation has a high (or thick) half value thickness.

(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.

Fog in radiology refers to darkening of images by sources other than the radiation of the primary beam to which the film was exposed. This can be due to chemicals in the processing solutions, light, or non primary beam radiation.

The grid efficiency or grid selectivity describes the efficiency in % of the primary beam transmission / % of transmitted scatter. The absorption of the primary beam is around 20 - 40%.