| line focus principle | relationship between actual and effective focal spots |
| what is the actual focal spot | where electrons from tube current bombard the target, dependant of size of filament |
| effective focal spot size | focal spot size measured under the anode target |
| what is the difference between a large focal and a small | large can withstand heat, small has better image quality |
| typical anode target angle | 5-20 |
| what determines the size of effective focal spot | target angle |
| the relationship between target angle and effective focal spot is? | directly proportional |
| anode heel effect | x-ray beam has more x-rays on the cathode side because of target angle |
| spatial resolution determines | accuracy anatomic structural lines |
| spatial resolution refers to? | the smallest detectable object in an image |
| greater spatial resolution means | sharper image |
| first and second step for controlling voluntary patient movement | communication and reduced exposure time |
| patient movement while imaging does what? | decrease sharpness |
| diagnostic quality is achieved by? | maximizing spatial resolution and minimizing distortion |
| distortion is | misrepresentation of size or shape of anatomic structure |
| when an image is distorted, what happens to spatial resolution | it decreases |
| another name for size distortion | magnification |
| do parts closer or father way from the IR experience more size distortion | far away |
| name two types of shape distortion | elongation and foreshortening |
| what can cause shape distortion? | alignment of tube, body part or IR |
| what 2 factors determine amount of magnification | SID and OID |
| spatial frequency | unit of lines per mm |
| relationship between spatial resolution and spatial frequency | direct |
| what directly impacts a systems ability to demonstrate spatial frequency | pixel size |
| focal spot size on a standard unit | .5-1.2mm |
| small focal spot size range | .5-.6mm |
| large focal spot range | 1-1.2mm |
| focal spot size is determined by | filament size |
| when selecting the focal spot size what else are you selecting? | filament size |
| is high or low mA used for small focal spot | low |
| is high or low mA for a large focal spot | high |
| what can focal spot size effect? | spatial resolution |
| what is the relationship between focal spot size and spatial resolution? | inverse |
| what happens if you use the small focal spot for many images? | tube overheating and decrease tube lifetime |
| what is a benefit of a small focal spot? | increased spatial resolution |
| inverse square law | intensity of x-ray beam is inversely proportional to the square of the distance from the source |
| as SID increases what happens to the x-ray beam? | the intensity spreads over a larger area, decreasing IR exposure |
| relationship between SID and mAs? | inverse |
| when SID increases by 40cm what do you do to mAs? | double it |
| what is the relationship between sid and spatial resolution? | direct |
| what is the relationship between sid and size distortion? | inverse |
| what does an air gap do | reduces scatter |
| what does reducing scatter do? | increases radiographic contrast |
| relationship between oid and magnification | direct |
| relationship between oid and spatial resolution | inverse |
| how can size distortions from OID be reduced? | increasing SID |
| magnification factor | indicates how much distortion or magnification is in an image |
| what is the magnification formula? | MF=SID/SOD |
| what does SOD stand for? | source to object distance |
| formula for SOD? | SOD=SID-OID |
| what does am MF of 1 mean? | no magnification |
| size distortion can be increased by | decreasing SID or increasing OID |
| if magnification increases what happens to spatial resolution | decreases |
| when tube is angled the source to ir distance | increases |
| geometric properties look at? | shapness of the image |
| what increases when there is no patient movement? | spatial resolution |
| what is the relationship between filament size and size of the electron stream | direct |
| what way should x-ray beam be to decrease distortion? | perpendicular |
| what is the point of the line focus principle? | target angle so the actual focal spot stays large and the effective spot stays small |
| the accuracy of the anatomic structural lines displayed in a radiographic image is determined by? | spatial resulution |
| size distortion is known as? | magnification |
| the size of the area that is exposed to electrons from the tube current? | actual focal spot |
| increasing the focal spot size? | decreases the spatial resolution |
| spatial resolution is decreased by? | patient movement |
| as SID increases | beam intensity decreases |
| the air gap technique | improves radiographic contrast and decreases scatter photons reaching the IR |
| increasing pixel density means? | increases spatial resolution |
| the misrepresentation of an image is? | distortion |
| the smaller the anode target angle | the smaller the effective angle |
| standard formula for converting analog data into discreet digital units | nyquist frequency |
| if sod increases and sid decreases what happes? | increase magnification |
| what is the only geometric factor that increases image contrast? | air gap because scatter is decreased |
