Signal, Noise, and Contrast

T he accuracy or interpretation of MR images can be affected significantly by the presence of noise in the measurements. If the signal is in the noise level, it becomes impossible to differentiate the object itself from the noise; therefore, design and implementation of an imaging experiment requires a thorough understanding of signal and noise in MR. Since the signal has already been discussed at some length in Chapter B2, the noise behavior in MR (both in k-space and image domain) and its dependence on imaging parameters are the major focus of UNIT B6.1. Voxel signal, the noise distribution in the raw data, real and imaginary images, and magnitude, as well as phase images are discussed.