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On the Use of Positioning Aids to Reduce Misregistration in the Head and Neck in Whole-Body PET/CT Studies

¹ Department of Nuclear Medicine, University Hospital Essen, Essen, Germany
² Institute of Medicine, Research Centre Jülich, Jülich, Germany
³ Department of Nuclear Medicine, Friedrich-Alexander-University Erlangen, Erlangen, Germany
⁴ Department of Physics, University of Wuppertal, Wuppertal, Germany

View larger version (27K): [in a new window]   FIGURE 1. (A) Limited coronal view of WB FDG PET/CT study with severe misalignment (arrows) in area of head and neck. (B and C) PET image after CT-based attenuation correction (B) demonstrates biased FDG uptake (arrow), which appears normal on uncorrected PET image (C). (D) Fused CT and uncorrected PET illustrate magnitude of misalignment.

View larger version (28K): [in a new window]   FIGURE 2. (A) Timeline of simulated WB PET/CT study and bed motion. Each plateau represents physically stationary bed position; connecting arrows indicate bed motion. (B) Drawing illustrates arrangement of motion-tracking device with coordinate system for monitoring misregistration of head and neck by means of 3 rotational and 3 translational parameters. IR = infrared.

View larger version (43K): [in a new window]   FIGURE 3. Supports for head and neck in simulated WB PET/CT studies: disposable cushion (A), head holder with disposable construction-foam insert (B), vacuum-lock bag (C), and smaller vacuum-lock bag (D) inside head holder shown in B. Photographs were taken from rear of PET tomograph used for simulations.

View larger version (22K): [in a new window]   FIGURE 4. Boxcar plots for PET/CT misregistration in the 3 translational (x, y, z) and 3 rotational (pi, pitch; ya, yaw; ro, roll) parameters for subjects in setup A, head holder (A); setup B, head holder with construction foam (B); setup C, vacuum-lock bag (C); and setup D, head holder with vacuum-lock bag (D).

View larger version (39K): [in a new window]   FIGURE 5. (A) Patient positioning in clinical PET/CT scanner with armrest to support arms above head during combined scanning. (B and C) Axial CT images (windowed) illustrate patient positioning with vacuum-lock bag (arrow) placed inside armrest (arrowhead) (B) and with head supported by cushion (arrow) placed in front of armrest (C). Measured CT attenuation values of cushion, armrest, and vacuum-lock bag were –970 HU, –900 HU, and –940 HU, respectively.

View larger version (51K): [in a new window]   FIGURE 6. (A) Boxcar plots of center-to-center misalignment of head and neck in WB PET/CT studies of patients with standard neck support (group 1) and with vacuum-lock support (group 2). (B and C) Examples of axial (left) and coronal (right) fusion images are shown before and after linear realignment for group 1 (B) and group 2 (C). Effect of realignment is significant in patients without head restraint (group 1) and less noticeable in group 2 because of better intrinsic patient positioning.