for each denoised peak-energy image I ˚pEq, which is obtained by reshaping the vector X ˚pE, :q, and the corresponding ROI image I ROI pEq. Here, x‚, ‚y denotes the inner product of two matrices and } ‚ } 2 F denotes the squared Frobenius norm of a matrix. Note that Equation 14 is normalized with respect to the ROI images and implies a better denoising performance for a higher coefficient.