The spatial resolution of a radiographic system is measured in units of

• A. Line-pairs per millimeter (lp/mm)
• B. Milligray (mGy)
• C. Milligray-centimeter^2 (mGy/cm^2)
• D. Bit depth

Answer: (A)

Spatial resolution describes how finely a radiographic system can separate small details. It is quantified by line-pairs per millimeter, because one line pair includes a line and a space; counting how many such pairs fit in one millimeter measures how well adjacent structures can be distinguished. A higher lp/mm means sharper, more detailed images. The other quantities relate to dose or grayscale information rather than spatial detail: milligray measures patient exposure, milligray-centimeter squared is dose-area product, and bit depth refers to gray-level contrast, not how finely space is resolved. So line-pairs per millimeter is the correct measure of spatial resolution.