  Ghost imaging is a method to nonlocally image an object by transmitting pairs
of entangled photons through the object and a reference optical system
respectively. We present a theoretical analysis of the quantum noise in this
imaging technique. The dependence of the noise on the properties of the
apertures in the imaging system are discussed and demonstrated with a numerical
example. For a given source, the resolution and the signal-to-noise ratio
cannot be improved at the same time .
