Ex vivo imaging is beneficial for studying rodent brain microstructure in healthy and pathological tissue at high resolution. There are challenges however associated with changes in tissue properties resulting from fixation. We present a tissue preparation protocol optimised for diffusion MRI in the rat brain by varying fixative concentration, gadolinium concentration and rehydration time. By altering T1 and T2 relaxivity, we show how these factors can be combined to maximise SNR efficiency. Improving SNR efficiency in ex vivo diffusion MRI will allow higher spatial and angular resolution for studying tissue microstructure in the rodent brain.