The pinhole gamma camera is the basis of the newly developed method of high-resolution pinhole single photon emission computed tomography (SPECT). In this paper, a pinhole gamma camera system was examined using the channel model of information theory. The model pinhole gamma camera was simplified from a noisy, lossy channel to a noiseless, lossless channel by assuming a plane source. An approximate formula of average mutual information for the pinhole gamma camera was then derived from the model. Imaging experiments validated the applicability of the analytic formula. The findings demonstrated that the pinhole gamma camera can be adequately described using the channel model of information theory, and that average mutual information can be considered a figure of merit for the optimizing design of the pinhole gamma camera. The pinhole gamma camera was the basis of the newly developed method of high-resolution pinhole single photon emission computed tomography (SPECT). In this paper, a pinhole gamma camera system was examined using the channel model of information theory. The model pinhole gamma camera was simplified from a noisy, lossy channel by assuming a plane source. An approximate formula of average mutual information for the pinhole gamma camera was then derived from the model. The experiments were performed on the analytic formula. The show demonstrated that the pinhole gamma camera can be adequately described described using the channel model of information theory, and that average mutual information can be considered a figure of merit for the optimizing design of the pinhole gamma camera.