 QC testing of screen speed should occur on acceptance and then yearly.  Evaluate first whether similar cassettes marked with the same relative speed are the same using the following procedure

 Make an exposure of a step-wedge or homogenous phantom onto an image receptor so that the center of the image has an optical density of about 1.5  Expose each image receptor to the same technical factors.  Process, and take optical density readings of the same center area in each. If all have the same relative speed, the optical density should not vary by more than

 During manufacturing processes, inconsistencies may occur in which the phosphor layer is applied more thickly at one portion of the screen than at another.  Sometimes during cleaning excessive rubbing may remove more of the phosphor layer.  Screen uniformity testing should be performed on acceptance and then yearly.

 Make an exposure of a step-wedge or homogenous phantom onto an image receptor so that the center of the image has an optical density of about 1.5  Process and take optical density readings in the center and in each of the four quadrants of the image. It should not be more than  Any film/screen image receptors that exceed this limit should be removed from service.

 The film and intensifying screen should match each other because the film are sensitive to a specific color.  A blue-violet emitting screen phosphor should be used with a monochromatic films.  A green-emitting screen phosphor should use with an orthochromatic film.

 Is a type of black-and-white photographic film that is sensitive to all wavelengths of visible light.  A panchromatic film therefore produces a realistic image of a scene. Almost all modern photographic film is panchromatic,

 Orthochromatic photography refers to a photographic emulsion that is sensitive to only blue and green light, and thus can be processed with a red safelight.  It is used on all radiographic films.

 Intensifying screens should be able to demonstrate clear images of patient anatomy so that the proper diagnosis can be obtained.  The ability of an imaging system to accurately display images.  There are two types of resolution  Contrast resolution  Spatial resolution

 Is the ability of an imaging system to distinguish structures with similar x-ray transmission as separate entities (in short separate shades of grays)  It is affected by the sensitivity of the image receptor speed and the amount of radiographic mottle (noise).  If the radiographic mottle is increased, contrast resolution is decreased.

 Is that the faster the screen speed screens, the lower the mAs values are used, which in turns increases the quantum mottle and lowers the contrast resolution.

 Is the ability of an imaging system to create separate images of closely spaced objects.  In other words, do the two object appear sharp and clear, or do they blur together?  This is determined by the amount of light diffusion that occurs between the screen and film.

 It is affected by:  Screen thickness  Phosphor crystal size  Film/screen contact.  The most common method of measuring spatial resolution is the spatial frequency.  The unit of spatial frequency is the line pairs per millimeter (lp/mm).

 a line pair is a space and line each being 0.1mm wide.  The greater the line pairs per millimeter value the smaller the object that can be imaged and the better the spatial resolution.  The human eye can read up to 5lp/mm, but most screen system cannot provide this level of spatial resolution.

 Point spread function (PSF)  Line spread function (LSF)  Edge spread function (ESF)  Modulation transfer function (MTF)

 Is a graph that is obtained with a pinhole camera and a microdensitometer.  The pinhole camera creates a black dot in the center of a film and microdensitometer is used to take readings.  The values are plotted on a graph versus the distance from the center of the point.  The narrower the peak on the graph, the better spatial resolution and image quality.

 Is a graph that is more accurate and easier to obtain than the PSF graph.  It requires an aperture with a slit that is 10um wide instead of the pinhole camera.  The density readings are taken of the centerline and plotted.

 It requires a sheet of lead to be placed on a cassette and exposed.  Density readings are taken at the border between the black and white areas and plotted on a graph.

 Is a numeric value that is used to measure the spatial resolution and is obtained from the LSF graph with a mathematical process known as fourier transformation.

 Intensifying screens must be free of dirt, stains and defects to properly function.  A regular schedule at least every 6 months of screen cleaning with an antistatic solution should be a standard department policy.  A UV light may be used to examine the surface of the screen if there are any stains.

film/screen contact test

 Frequency of test  Yearly  As necessary  Equipment required  Cassette to be tested  Test tools: ▪ Box of paper clips or sheet of perforated zinc or fine wire mesh, large enough to cover a 35 x 43cm (14 x 17” film), with a square hole, about 10cm from one edge, approximately 2 to 2cm square)

 Load the cassette to be tested and place it face up on the tabletop  Cover the whole of the cassette with the test tool (if cassette distribute evenly).  Set a FFD (SID) of 150cm[60”] ( the longer FFD (SID) reduces geometric unsharpness)  Collimate to cover whole of cassette  Make exposure using a 50kVp and 6mAs  Process film

 If a densitometer is available measure the image.  Inspect the image, looking for areas that look blurred.  A noticeable area of unsharpness could be caused by:  Damaged cassette  Screen packing, deterioration  An air pocket  When using a close mesh wire test the poor film/screen contact areas may also have a higher density.