OtherClinical Investigations

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

Thomas Beyer, Lutz Tellmann, Ingo Nickel and Uwe Pietrzyk
Journal of Nuclear Medicine April 2005, 46 (4) 596-602;

Article Figures & Data

Figures

  • FIGURE 1.
    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.

  • FIGURE 2.
    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.

  • FIGURE 3.
    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.

  • FIGURE 4.
    FIGURE 4.

    Boxcar plots for PET/CT misregistration in the 3 translational (Δx, Δy, Δz) 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).

  • FIGURE 5.
    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.

  • FIGURE 6.
    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.

Tables

  • TABLE 1

    Average (±SD) Absolute Displacement (Rotation [Pitch, Yaw, Roll] and Translation [Δx, Δy, Δz]) of Reference Markers for Subjects in Groups A–D

    ParameterGroup
    ABCD
    Rotation (degrees)
        Pitch0.8 ± 0.50.3 ± 0.1(0.6 ± 0.4)0.3 ± 0.3
        Yaw1.1 ± 0.8(0.6 ± 0.6)(1.2 ± 0.6)(0.5 ± 0.4)
        Roll1.1 ± 0.90.3 ± 0.30.2 ± 0.20.2 ± 0.1
        〈rot〉1.0 ± 0.20.4 ± 0.1(0.7 ± 0.5)0.3 ± 0.2
    Translation (mm)
        Δx4 ± 21 ± 1(4 ± 2)0.4 ± 0.3
        Δy4 ± 31 ± 11.0 ± 0.80.6 ± 0.5
        Δz3 ± 1(1 ± 1)(2 ± 1)1.1 ± 0.5
        〈Δr〉7 ± 32 ± 2(4 ± 2)1.4 ± 0.5

    • Mean (±SD) of average absolute rotational displacement (<rot>) and mean (±SD) of individual translational displacements Δr (<Δr>) are listed also. Numbers in parentheses indicate no statistically significant difference with respect to group A for Student t test (2-tailed, P < 0.05).

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