Pinhole SPECT

High resolution SPECT systems can be produced using pinhole collimators, which are primarily used in small animal imaging. The high resolution results in the low sensitivity of the system. In order to compensate this, more pinhole (multipinhole) apertures are produced, which increase the sensitivity at the expense of the size of the field of view. Pinhole systems differ from the parallel hole collimator systems in that the head has to be moved along a helical trajectory instead of along a circular one. Tuy’s condition states that an object can only be reconstructed if an arbitrary slice intersecting the object has at least one intersection point with the trajectory.

In pinhole SPECTs precise geometric calibration has to be taken care of, since the position of the apertures, the movement and the inclination of the camera head are not known sufficiently accurately. That is why taking SPECT images of more point sources followed by performing a nonlinear multidimensional regression is necessary for calibration.

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