Analysis of patient bed positioning in SPECT-CT imaging for dedicated mammotomography
Patient positioning on a bed is an integral part of accurate imaging for dedicated 3D breast imaging. For both dedicated breast SPECT (single photon emission computed tomography) and breast CT (computed tomography or computed mammotomography, CmT) which are under development in our lab, maximum access to the breast in the imaging system's field of view is required to obtain the largest imaged breast volume. Accurate bed positioning will be necessary as it may be integrated with a guided biopsy apparatus. Thus, a patient bed with flexible 3D positioning capability is being integrated into the various independent and hybrid 3D imaging systems. The customized bed has both manual and computer controlled positioning capability, and the accuracy and reproducibility of the system are being characterized. Computer controlled positioning and feedback provide seemingly reproducible results. However, gross movements may vary in their accuracy to the given input position. While linear with slopes near 1.0 and intercepts near 0.0cm, lateral (Y) movement translates less than the input amount, while axial (X) movement translates farther than the input amount. Vertical (Z) directional movement follows a quadratic shift with a small dc component with or without added weight on the table. A variety of patient imaging conditions along with x-ray image data are evaluated to demonstrate the reproducibility of positioning accuracy. Individual directional repositioning accuracy is found to be better than multiple, combined directional repositioning accuracy. Imaging results indicate a reproducibility (error) of less than 1mm, which may be suitable for SPECT imaging but perhaps not for higher resolution dedicated breast CT. However, for the independent SPECT system, bed motion is not necessary because the detector's line of sight can already acquire data at the chest wall.
