Neurological diseases are currently one of the main causes of disability and mortality worldwide. Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the two most common brain disorders with no cure. Neuroimaging based methods, such as magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging, have been used to diagnose AD and PD. However, PET requires a cyclotron onsite for generally short-lived isotopes. In addition, PET and MRI are more expensive and less accessible. SPECT not only costs less than PET and MRI, but also has longer half-life isotopes available. The aim of this study is to evaluate a high sensitivity multi-pinhole brain SPECT system. The proposed system sensitivity was evaluated using Geant4 Application for Tomographic Emission. We first determined the design parameters by maximizing the sensitivity for a target resolution of 12 mm and field of view of 200 mm. The preliminary simulation results showed that a system sensitivity of 0.204% was achieved, which is very high compared to existing clinical brain SPECT systems. The improved sensitivity of the device can be traded for better spatial resolution, reduced injection dose or shortened acquisition time.