A new brain CT reference line: the lower eyelid to the inner occipital base line closely parallels the Talairach–Tournoux line

Abstract

Background: There is no standardized brain computed tomography (CT) reference line that can be determined on both scout and reformatted sagittal CT images. Here, a tangential line from the anterior edge of the lower eyelid to the inner table of the occipital base (LEL/O line) appears nearly parallel to the Talairach-Tournoux (T/T) line, which shows a consistent intracranial anatomical relationship among subjects, and acts as a standard reference line for magnetic resonance (MR) imaging. Purpose: To quantitatively validate the LEL/O line as a new standard brain CT reference line. Material and Methods: We measured: angle 1 ¼ the LEL/O line on scout images from the LEL/O line on parasagittal CT images (n¼93); and angle 2 ¼ the LEL/O line on scout images from the T/T line on high resolution midsagittal MR images (n¼97). Angles in a clockwise direction were defined as positive and were expressed as meanAESD with the 95% confidence interval (CI) of the SD. Angle 2 was measured independently by two observers and intraclass correlation coefficients (ICCs) were calculated. Results: Angle 1 was-0.4 AE1.2 (95% CI of SD 1.1-1.5); angle 2 was-0.4 AE2.0 (95% CI of SD, 1.8-2.4). The ICC in the angle 2 measurement was 0.780 (P<0.001), which indicated high inter-observer reliability. Conclusion: The LEL/O lines on scout and parasagittal CT images show practically the same gradient, and these LEL/O lines are almost parallel to the T/T line. Use of the LEL/O line either for direct scanning or reformation can minimize intra-and inter-subject variations on CT images and mismatch between CT and MR images.