Abstract: Objective To explore the correlation of the position and height of the examination couch with the accuracy of image
registration in an exact effective field of vision (FOV) of single photon emission computed tomography/computed tomography
(SPECT/CT) and determine the optimal position of the examination couch for best image registration. Methods The tests were
performed on a SPECT/CT with 6 radioactive 153Gd sources in 3 groups (two in each group with energy peak of 40.9 Kev, 41.54
Kev, and 103.18 Kev) in an assorted standard pattern. Thirteen groups of slice data were obtained by changing the position and
height of the bed but keeping the tomograpy slice constant. The bias of the accuracy of image registration was acquired using
ALIGNMENT software and compared for different examination couch positions and heights. Results The position of the
examination couch at 0 cm in the Z axis and -4 cm in the Y axis showed the least error of image registration. Conclusion To
achieve optimal SPECT and CT image fusion, quality control must be implemented and calibration of image registration
accuracy should be done when necessary.