SNRMapCalc[data1,noisemap] calcualtes the signal to noise ratio of the data using MN[data]/(1/sqrt[pi/2] sigma), where sigma is the local mean of the noise map assuming it is a rician distribution. SNRMapCalc[{data1,data2}] calcualtes the signal to noise ratio from two identical images using MN[data1,data2] / (.5 SQRT[2] STDV[data2-data1]). SNRMapCalc[{data1, .. dataN}] calcualtes the signal to noise ratio of the data using MN/sigma where the mean signal MN is the average voxel value over all dynamics N and the sigma is the standard deviation over all dynamics N.