We demonstrate longitudinal simultaneous whole-cortex Ca2+ imaging and fMRI in mice expressing GCaMP in one of five different cell types (excitatory, inhibitory, two interneuron subtypes, and astrocytes). The high SNR of our dual-imaging approach is shown by the indistinguishable Ca2+ responses to hind-paw or visual stimulation measured inside and outside the scanner. We optimize a spatially variable, three-parameter gamma-variant to investigate the transfer function between the BOLD and Ca2+ signals throughout the cortex. This approach is applied in functionally and anatomically defined ROIs. Results show that 1/3rd of the variance in BOLD is accounted for from spontaneous excitatory Ca2+ activity.