A new single acquisition, two-image difference method for determining MR image SNR

A new method for computing the signal-to-noise ratio (SNR) of magnetic resonance images is presented. The proposed method is a "difference of images" based technique where two images are produced from one acquisition in which the readout direction field of view (FOV) and matrix size are doubled compared to the phase encode direction. Two "normal" unaliased FOV images are produced by splitting (undersampling) the even versus odd data points in the read direction into two separate raw data sets. After image reconstruction, conventional difference of images SNR computations are applied. [Signal defined as mean within signal producing region of interest (ROI) in one image, noise defined as standard deviation of the difference between the two images using the same signal ROI position and size, divided by sqrt(2) to account for the subtraction process.] This method combines the desirable minimal acquisition time of a single image acquisition technique and the superior noise quantification characteristics of the difference of images methodology. The proposed method is more robust against system drift than existing SNR difference of images methods because the two images are effectively acquired nearly simultaneously in time. This method is compatible with phased array coils and is useful for parallel image reconstruction analysis because it is very stable. This method produces results that can be made equivalent to, and compared with, other existing SNR methods with simple known scale factors, assuming the image noise follows theoretical expectations.