On the use of positioning aids to reduce misregistration in the head and neck in whole-body PET/CT studies.

UNLABELLED Involuntary patient motion from insufficient patient preparation may lead to local misregistration of PET/CT images and, thus, can invalidate the attempt to fuse the resulting images. We estimate the efficacy of selected patient support structures in reducing the likelihood of patient motion in the area of the head and neck during whole-body PET/CT studies. METHODS Motion of the head and neck was estimated in 51 healthy volunteers during simulated whole-body PET/CT studies using an infrared camera-based tracking system. Four patient positioning schemes (arms down) were studied, with the neck placed on a standard PET head holder with no support at the sides (setup A), on a special head holder fitted with a subject-specific mold from construction foam (setup B), on a vacuum-lock bag (setup C), and on a special head holder fitted with a vacuum-lock bag (setup D). We report the average motion of the head and neck as the difference in the position of a set of target points between the simulated CT image and PET image of the head and neck. To estimate the efficacy of additional patient support measures in clinical practice, we reviewed the misregistration of the head and neck in whole-body PET/CT studies of 10 patients each who were imaged using setups A and C by comparing the mean translational and rotational alignment parameters from a semiautomatic linear registration approach needed to realign the CT and PET images. RESULTS Average translational and rotational misalignment of the head and neck was highest for setup A, at 7 mm and 1 degrees , respectively. Misalignment was reduced to a minimum of 1.4 mm and 0.3 degrees for setup D. Setup B resulted in a similar reduction in patient motion of the head and neck: 2.4 mm and 0.4 degrees , whereas setup C provided only somewhat improved support, with a resulting average misalignment of 4.5 mm and 0.7 degrees. In clinical PET/CT, we found setup C to reduce translational misalignment of the CT and PET images of the head and neck to 2 mm, compared with 6 mm for setup A, whereas no significant reduction of rotational misalignment was observed. CONCLUSION Average motion of the head and neck in unrestrained subjects during whole-body PET/CT examinations can be reduced by use of rigid positioning aids, such as foam molds, or vacuum-lock bags. Vacuum-lock bags are reusable, quickly adaptable, and olfactory neutral and can be used routinely, either alone or in combination with a head holder, in whole-body PET/CT for high-quality examinations.