Acceptable gamma camera nonlinearities for SPECT imaging: myocardial, bones, and hot lesions

Gamma camera spatial nonlinearity can lead to serious artifacts in SPECT imaging. Most camera systems offer real time linearity correction. Recently, there is increased interest in the design of gamma cameras that can be used in both SPECT and coincidence modes. Such designs may rely on thicker scintillation crystals to increase coincidence sensitivity together with unconventional optical finishes to maintain SPECT resolution. These factors bear on camera spatial linearity. The question of acceptable gamma camera nonlinearity is addressed by simulating the spatial distortion field for the Siemens E.CAM^TM camera (59-PMT´s). The distortion field is modeled as a sinusoidal field of x- and y- displacements with respect to the PMT lattice. The calculated distortion field is imposed on either real or simulated SPECT projections. After reconstruction distorted versus undistorted image comparisons are made using human observers and numerical difference measures. The authors´ results indicate that gamma camera nonlinearities less than mm are generally acceptable; and distortions greater than 3 mm are generally unacceptable