Image Resolution

Image resolution is the details that an image can contain. The details depend on the following factors:

Contrast Resolution

It is the ability of an imaging system to distinguish between multiple densities in the radiographic image. In the case of digital imaging, it depends on the bit-depth of the system. As noted earlier, an 8-bit system can show only 256 gray values as opposed to a 12-bit system, which shows 4096 gray values. The 8-bit system shows less gray values and is a high contrast system than the 12-bit system that shows more gray values and is a low contrast system. However, if the 12-bit-system can clearly show two near-by gray value intensities, the system will have a high contrast resolution (Figure 6).1,3,6,7

Figure 6.
Comparison of 2 systems
Comparison of 2 systems. In each rectangle, there is a square that has 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 refers to the ability of an imaging system to differentiate between two near-by objects. In digital imaging, it depends on the size of the pixel used. A large pixel size will be unable to resolve two near-by structures as compared to a small pixel size. Spatial resolution is measured in line-pairs per millimeters (Figure 7).1,4,7,9-11

Figure 7.
Comparison of 2 systems
Comparison of 2 systems: A has a low spatial resolution and B has a high spatial resolution.