Laser alignment system for helical pinhole SPECT

Pinhole single photon emission computed tomography (SPECT) is very sensitive to mechanical alignment because it is a magnifying geometry. Because of magnification, small mechanical shifts of the aperture result in a large change in the projection data. Helical orbits may be used for pinhole SPECT to improve the completeness of the projection data. This has been done by using a research scanner to provide rotation while a linear stage produces axial movement. The combined effect is a helical orbit. However, reconstruction quality may be limited by the alignment of the linear stage with the axis of rotation of the scanner. We have developed a laser system for aligning the linear stage. We present the system design and estimate the accuracy of its alignment. Experimental helical pinhole SPECT data are presented.