For general radiography, an MTF value of 1 is

• A. average
• B. suboptimum
• C. theoretically impossible
• D. a function of mAs

Answer: (C)

The main idea is that MTF shows how well an imaging system preserves image contrast at different levels of detail. An MTF of 1 would mean perfect transfer of contrast at that spatial frequency—no blur, no loss of sharpness. In practice, general radiography can’t achieve that because every real system has some unsharpness from multiple sources: the finite size of the focal spot causes geometric blur, the detector and phosphor layer introduce blur, patient motion can smear detail, and there’s always some sampling and noise. Because of these inevitable blur factors, the maximum MTF you can achieve for any meaningful, nonzero spatial frequency is always less than 1. So, an MTF value of 1 is a theoretical limit that isn’t attainable in real-world radiography. It’s not determined by exposure factors like mAs, and it isn’t simply an average or suboptimal level—it reflects the inherent limits of the imaging chain.