3 Main Factors Affecting Recorded Detail kVp & mAsTechnique Selection (Time)MotionObject UnsharpnessFocal Spot SizeSID (Source to Image Distance)OID (Object to Image Distance)Material Unsharpness/ Film ScreenCombo
4 Factors that affect Recorded Detail Geometric unsharpnessOID SID SIZE SHAPEMotion unsharpness (blurring)Intensifying ScreensFilm Speed / CompositionFilm – Screen contactKvp & Mas (density / visibility)
19 Blurring of image due to patient movement during exposure.
20 Focal Spot Size Smaller x-ray beam width will produce a sharper image. Fine detail = small focal spot (i.e. small bones)General radiography uses large focal spotBeam from penlight size flashlight vs. flood light beam
25 Object UnsharpnessMain problem is trying to image a 3-D object on a 2-D film.Human body is not straight edges and sharp angles.We must compensate for object unsharpness with factors we can control: focal spot size, SID & OID
27 SID Source to Image Distance The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image sharpness.Standard distance = 40 in. most examsException = Chest radiography 72 in.
28 SIDShine a flashlight on a 3-D object, shadow borders will appear “fuzzy”On a radiograph it’s called ______________A true border – _____Farther the flashlight from object = sharper borders. Same with radiography.
29 OID Object to Image Distance The closer the object to the film, the sharper the detail.OID , penumbra , sharpness OID , penumbra , sharpness Structures located deep in the body, radiographer must know how to position to get the object closest to the film.
38 Distortion (x-ray beam not centered over object & film) Distortion (object & film not parallel)
39 Central Ray Radiation beam diverges from the tube in a pyramid shape. Photons in the center travel along a straight line – central rayPhotons along the beam’s periphery travel at an angleWhen central ray in angled, image shape is distorted.
40 Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.
41 Central Ray Angulation Body parts are not always 90 degrees from one anotherCentral ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts.Body part rotation or obliquing the body can also help visualize superimposed anatomy.NAME 3 EXAMPLES
42 MAGNIFICATION caused by: TUBE CLOSE TO THE PART (↓SID)PART FAR FROM THE CASSETTE(↑ OID)Compensate for MAG : ↑ OID by ↑ SID =“increase SID 7” for every 1” OID”
43 Size Distortion & SID Major influences: SID & OID As SID , magnification Standardized SID’s allow radiologist to assume certain amt. of magnification factors are presentMust note deviations from standard SID
62 Screen SpeedEfficiency of a screen in converting x-rays to light is Screen Speed.
63 Spectral Matching (F/S) What does it mean?Name the two types of screen phosphorsWhat light spectrum do they emit?
64 Spectral SensitivityFilm is designed to be sensitive to the color of light emitted by the intensifying screens.Blue LIGHT– Conventional Calcium Tungstate screenGreen, Yellow-Green LIGHT– Rare Earth screen
74 QUANTUM MOTTLE Film grain, or graininess, refers to the tiny black spots that make up the visible image, one grain from each silver halide crystal exposed MORE COMMON IN CR SYSTEMS NOW NOT ENOUGH PHOTONS TO CREATE IMAGE
79 a densitometer,measures film blackness.Film blackness is the relationship of the intensity of the light that hits the film from the view box (incident intensity) to the intensity of the light transmitted through the film (transmitted intensity).These measurements plotted on a graph produce a characteristic curve. The limitations of the human eye determine the useful density range in diagnostic radiography.The diagnostically useful range of densities is 0.25 to 2.5.The later module on exposure calculation considers this in more detail.
80 Film latitude ? What does it mean how does it plot on the curve?