Imaging 2 M1L3

• what factors determine a good image: contrast, brightness and image detail
• controlling influencing factor for brightness is mAs
• contrast resolution in DR and CR is affected by the amount of scatter reaches the IR (proper collimation and use of grids). Also influences by the dynamic range of system
• Dynamic range: allows for many shades of grey to be displayed. Is related to wide exposure latitude and produces proper gray scales at high and low exposure values
• CR and DR has less spatial resolution then film, but has better contrast resolution due to dynamic range
• CR and DR images produced at high exposures have low quantum noise but an increase in dose. Quality assurance for patient dose should be in place to prevent chronic overexposure. Dose Creep - always keep patient dose ALARA
• things that will affect spatial resolution: focal spot size (smaller = more resolution), SID (more= increase resolution), OID (more = decreases resolution), motion and IR size (CR) and FOV size (DR)
• in DR, the term Spatial Frequency may be used instead of Spatial Resolution
• The term Spatial Frequency is used to describe the number of details that can be seen in a set distance. Pixel size and the distance between pixels determine how much detail can be resolved.
• spatial frequency is measured in lp/mm. Two pixels need to make a line pair
• As spatial frequency increases, so does ability to image sharp detail
• Spatial frequency (resolution) for CR is determined by: phosphor thickness ( thin layer = increase resolution) and IR (smaller IR = improved spatial resolution
• spatial frequency (resolution) for DR is determined by: pixel size and distance between pixels. And whether its direct or indirect system