Spatial resolution refers to the ability of an imaging modality to differentiate two adjacent structures as being distinct from one another. Other related terms include definition or visibility of detail.
Spatial resolution is expressed in line pairs per mm (lp mm).
The absence of spatial resolution in an image may be referred to as blur.
When optimized, screen film systems have excellent spatial resolution, whereas electronic detectors are limited by pixel size. Patient movement during image capture will also reduce the spatial resolution.
Human eyes have the capability of differentiating a spatial resolution of 5 line pairs per mm at a viewing distance of 25 cm 3.
Limiting resolutions of various modalities
film-screen mammography: 10 to 15 line pairs per mm 3
film-screen radiography: 8 to 12 line pairs per mm 1
digital mammography: 5 to 10 line pairs per mm 3
digital radiography: 3.5 to 5.5 line pairs per mm 1,3
digital subtraction angiography: 2 line pairs per mm 3
CT: 1.0-1.6 line pairs per mm 1
fluoroscopy: 1.0 to 1.5 line pairs per mm 3
MRI: 1 to 2 mm 4 (0.25 to 0.5 line pairs per mm)
gamma camera: 5 to 7 mm 1 (0.07 to 0.10 line pairs per mm)
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