To make it possible to share a normal database in single photon emission computed tomography (SPECT) studies, we developed a new method for converting a SPECT image in one physical condition to that in another condition for data acquisition and reconstruction. A Hoffman 3-dimensional brain phantom experiment was conducted to determine systematic differences between collimators and reconstruction processes. SPECT images for the brain phantom were obtained using fan-beam collimators with scatter and attenuation corrections and using parallel-hole collimators without any correction. Dividing these two phantom images after anatomical standardization by Statistical Parametric Mapping 99 (SPM99) created a 3-dimensional conversion map. This conversion map was applied to convert an anatomically standardized SPECT image using parallel-hole collimators without any correction to that using fan-beam collimators with scatter and attenuation corrections in eleven subjects who underwent sequential SPECT measurements using different collimators after injection of 99mTc ethyl cysteinate dimer. The SPM99 demonstrated adequate validity of this conversion in comparative analyses of these sequential SPECT images with different collimators. This may be a promising approach for further sharing of a normal database in SPECT imaging between different cameras.