Densitometry


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Densitometry

 

a branch of photographic sensitometry devoted to measurements of the absorption and scattering of light by developed photographic layers.

The methods of densitometry make possible the quantitative evaluation of the final photographic effect based on the optical density of blackening in the photosensitive layer. There is a nearly linear relationship between the surface concentration of silver in the blackened area and the optical density; their ratio is called the photometric equivalent of blackening. The optical density increases with the degree of dispersion of the silver in the blackened area. Correspondingly, the extent of the optical usefulness of the silver in the blackened area increases with the disperseness of the silver halide in the original light-sensitive layer and with the relative magnitude of the exposure of this layer to light. Because of the nonhomogeneous nature of the blackened areas, the light absorption in these areas is accompanied by strong diffusion. Therefore, the magnitude of optical density depends on the geometric structure (aperture) of the light beams that are incident on the blackened area and are directed to a receiver after passing through the blackened area.

A distinction is made between regular density (D ║) and integral density (DE), which are measured upon illumination of the blackened area by a beam of parallel light rays and upon reception, in the first case, of only that part of the light beam that has not changed direction during passage through the blackened area and, in the second case, of the entire light beam. In addition, diffuse density (D#), which is measured using an ideally diffuse beam of light to illuminate the blackened area, and effective density (D ψ), which is measured under intermediate conditions encountered in practice, are also distinguished. The difference D ║ -DE is a measure of the light diffusion in blackened areas. The diffuse density is commonly used in sensitometry.

The optical density of blackening is measured using densitometers and microphotometers.

The measurement of color fields in developed materials for color photography constitutes a special branch of densitometry.

References in periodicals archive ?
The Medicare Bone Mass Measurement Coverage Standardization Act of 1998 widened the Medicare indications for bone densitometry so that more women can have the test every 2 years without having to pay for it.
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In this update of the 2003 and 1998 editions, a pioneer in the field of bone densitometry discusses the evolution, expanding applications, and pros and cons of available risk assessment tools, and provides more guidance in assessing fracture risk beyond dual- energy x-ray absorptiometry (DXA) measurements.
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Proposed changes include accepting a third pathway to sonography certification, dropping the recertification requirement for bone densitometry registration and modifying several continuing education requirements for renewal of registration.
The International Society for Clinical Densitometry (ISCD) website for updates and guidelines on densitometry at www.
Saint Clare's will utilize the space as a free-standing imaging center featuring the latest imaging technologies and equipment, including computed tomography (CT), ultrasound, diagnostic x--ray, mammography and bone densitometry.