What formula is used to calculate spatial frequency from pixel size in CR imaging?

What formula is used to calculate spatial frequency from pixel size in CR imaging?

• A. 1/(pixel size)
• B. 1/(2 x pixel size)
• C. 2 x pixel size
• D. 1/(4 x pixel size)

Answer: (B)

Spatial frequency is the number of repetition cycles per millimeter, and in digital radiography the pixel size (pitch) sets how finely you sample the image. To avoid aliasing you need at least two samples per cycle, which is the essence of the Nyquist limit. That means the highest spatial frequency you can accurately represent is half the sampling rate. The sampling rate is 1 divided by the pixel size, so the maximum resolvable spatial frequency becomes 1 divided by (2 × pixel size). Hence the correct formula is spatial frequency = 1/(2 × pixel size). The other options don’t reflect this Nyquist bound or misstate the relationship between pixel size and frequency.

Spatial frequency is the number of repetition cycles per millimeter, and in digital radiography the pixel size (pitch) sets how finely you sample the image. To avoid aliasing you need at least two samples per cycle, which is the essence of the Nyquist limit. That means the highest spatial frequency you can accurately represent is half the sampling rate. The sampling rate is 1 divided by the pixel size, so the maximum resolvable spatial frequency becomes 1 divided by (2 × pixel size). Hence the correct formula is spatial frequency = 1/(2 × pixel size). The other options don’t reflect this Nyquist bound or misstate the relationship between pixel size and frequency.