Accidental coincidence rate and scatter coincidence rate of 3-dimensional (3D) acquisition of positron emission tomograph (PET) are higher than 2-dimensional (2D) acquisition and count loss becomes higher because slice shield collimator is not used in 3D acquisition. If one could decrease the gamma ray from outside of the axial field of view (FOV), it may be possible to improve image quality of 3D acquisition. Thus, using a Shimadzu SET-2300W (Headtome V) PET camera, we developed and tested a front shield for brain study to shut off gamma ray from the outside of the axial FOV. Using the front shield, gamma ray from outside of the FOV and the accidental coincidence rate could be decreased. The count loss in high count rate was also decreased. With these effect, the image quality of the clinical studies in 3D acquisition could be increased.