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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

An imaging system can distinguish between multiple densities in the radiographic image. In the case of digital imaging, it depends on the bit-depth of the system. An 8-bit system can show only 256 gray values instead of a 12-bit system, which shows 4096 gray values. The 8-bit system shows fewer gray values and is a high contrast system than the 12-bit system, which shows more gray values and is a low contrast system. However, if the 12-bit-system can clearly show two nearby gray value intensities, the system will have a high contrast resolution (Figure 6).1,3,6,7

Comparison of 2 systems

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 refers to the ability of an imaging system to differentiate between two nearby objects. In digital imaging, it depends on the size of the pixel used. A large pixel size will be unable to resolve two nearby structures compared to small pixel size. The measuring unit of spatial resolution is in line pairs per millimeter (Figure 7).1,4,7,9-11

Comparison of 2 systems

Figure 7.

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