Research ArticleImaging

The Semicolon Sign: Dopamine Transporter Imaging Artifact from Head Tilt

Matthew F. Covington, Natalie A. McMillan, Ryan J. Avery and Phillip H. Kuo
Journal of Nuclear Medicine Technology June 2013, 41 (2) 105-107; DOI: https://doi.org/10.2967/jnmt.112.117184

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Figures

  • FIGURE 1.
    FIGURE 1.

    Effect of head positioning on axial imaging of caudate (gold) and putamen (blue). These images represent rough approximation of basal ganglia anatomy. (A) Abnormal forward head tilt results in slices (red lines) through caudate head that do not include putamen. Subsequent slices (white lines) demonstrate both caudate and putamen. (B) With correct head positioning, all slices through caudate head also include putamen (white lines).

  • FIGURE 2.
    FIGURE 2.

    Semicolon sign. Abnormal forward head tilt creates images in which caudate head is imaged in separate axial slices from putamen. (Images are obtained with filtered backprojection using Butterworth filter with cutoff of 0.6 and order of 8. No attenuation correction was applied. Matrix size of 128 × 128 was acquired at 1.23 zoom and was manually adjusted to zoom of 1.6. Axial images are presented at slice thickness of 2.5 mm. Images were acquired at 30 s/frame over 30-min acquisition time using dual-head camera. Circular orbit was used with radius of 13 cm. Stop-and-shoot setting was 3°. Bottom edge of field of view is positioned at level of patient’s nose). (A) Top 2 rows demonstrate normal appearance of properly aligned caudate heads and putamen with comma appearance. Bottom 2 rows demonstrate semicolon artifact in which caudate heads appear separate from putamen on isolated slices. (B) This graphic depicts separate axial images of caudate heads and putamen that have been superimposed to illustrate semicolon appearance.

  • FIGURE 3.
    FIGURE 3.

    Correct head positioning using head holder (Composites Horizons, Inc.). (A) Vertex of head should reach head holder’s superior edge (black line with arrow). Canthomeatal line should be oriented as vertically as possible (black line). Chin should rest in neutral position (connected arrowheads). (B) Incorrect positioning of head within head holder may result in head tilt artifact. Vertex of head does not reach head holder’s superior edge (black line with arrow). Canthomeatal line (black line) is slightly deflected forward, indicating abnormal forward head tilt. Chin is also deflected toward neck (connected arrowheads).

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