The Radiographic Image
Course Number: 571
Image Resolution
Image resolution is the details that an image can contain. The details depend on the following factors:
Contrast Resolution
Contrast resolution refers to an imaging system’s ability to differentiate between multiple levels of density in a radiographic image. In digital imaging, contrast resolution is determined by bit-depth. An 8-bit system can display 256 shades of gray, whereas a 12-bit system presents 4096 shades. While an 8-bit system is considered high contrast due to its limited grayscale range, a 12-bit system—if capable of distinguishing subtle differences between nearby gray values—offers superior contrast resolution (Figure 6).1,3,6,7
Figure 6.
Comparison of 2 systems. In each rectangle, there is a square with a grey value close to the grey value of the rectangle. A has a low contrast resolution. B has a high contrast resolution.
Spatial Resolution
Spatial resolution in radiology defines an imaging system’s capability to distinguish between two closely positioned objects. In digital imaging, it is determined by pixel size—larger pixels reduce resolution and make it harder to separate adjacent structures. Spatial resolution is measured in line pairs per millimeter (Figure 7).1,4,7,9-11
Figure 7.
Comparison of 2 systems: A has a low spatial resolution, and B has a high spatial resolution.