The terms MTF cutoff frequency, limiting resolution, and resolving power have all been used interchangeably to define the smallest target that can be resolved with an imaging system. Although the term 'limiting resolution' is often used to describe the smallest target length that can be imaged. It was shown above that the limiting resolution of a system is a complex concept. For example, high frequency targets can be reproduced from their low frequency fundamentals and phase errors can produce 'phantom' images that resemble high frequencies. Neglecting the problems associated with determining the limiting resolution, if one ideally defines limiting resolution of an imaging system as the smallest size target that does vanish into the noise threshold, the question arises as to what happens to the target image on the way down to the limiting threshold.

Clinical test have related a 3% MTF modulation as an accurate prediction of limiting resolution[x]. However, as was proven earlier, the low frequency components of target are the most useful in resolving bar targets. Use of the limiting MTF threshold is therefore quite limited in its utility, as it does not include the MTF at any other frequency.

The common tests for resolution are capable of reasonable high precision among observers but are not very accurate. It is for all practical purposes useless in its use for comparison between two different image systems.