Reproducibility of Frankfort horizontal plane on 3D multi-planar reconstructed MR images.

OBJECTIVE: The purpose of this study was to determine the accuracy and reliability of Frankfort horizontal plane identification using displays of multi-planar reconstructed MRI images, and propose it as a sufficiently stable and standardized reference plane for craniofacial structures. MATERIALS AND METHODS: MRI images of 43 subjects were obtained from the longitudinal population based cohort study SHIP-2 using a T1-weighted 3D sequence. Five examiners independently identified the three landmarks that form FH plane. Intra-examiner reproducibility and inter-examiner reliability, correlation coefficients (ICC), coefficient of variability and Bland-Altman plots were obtained for all landmarks coordinates to assess reproducibility. Intra-examiner reproducibility and inter-examiner reliability in terms of location and plane angulation were also assessed. RESULTS: Intra- and inter-examiner reliabilities for X, Y and Z coordinates of all three landmarks were excellent with ICC values ranging from 0.914 to 0.998. Differences among examiners were more in X and Z than in Y dimensions. The Bland-Altman analysis demonstrated excellent intra- as well as inter-examiner agreement between examiners in all coordinates for all landmarks. Intra-examiner reproducibility and inter-examiner reliability of the three landmarks in terms of distance showed mean differences between 1.3 to 2.9 mm, Mean differences in plane angulation were between 1.0° to 1.5° among examiners. CONCLUSION: This study revealed excellent intra-examiner reproducibility and inter-examiner reliability of Frankfort Horizontal plane through 3D landmark identification in MRI. Sufficiently stable landmark-based reference plane could be used for different treatments and studies

Axial head view, A. FH plane estimated prior scan on subjects head B. FH plane identified by landmarks on Images.

<p>(Note the differences in the muscles cross sectional area between both views).</p

Bland-Altman Plot for Examiner 1 vs. Examiner 5.

<p>a) in x coordinate of left Orbitale (the shown digit preference reflects the slice thickness of 1 mm) b) In y coordinate of left Orbitale.</p

Intra- Examiner Reproducibility and Inter-Examiner Reliability – Reader Differences in Dihedral Angle of FH Plane.

<p>Intra- Examiner Reproducibility and Inter-Examiner Reliability – Reader Differences in Dihedral Angle of FH Plane.</p

Inter-Examiner Reliability – Mean differences, Coefficients of Variability (CV) and Intra-class Correlation statistics.

<p>Inter-Examiner Reliability – Mean differences, Coefficients of Variability (CV) and Intra-class Correlation statistics.</p

Images were viewed using multi planar reconstruction (MPR) with coronal view as the center of orientation.

<p>a) Horizontal and vertical lines were adjusted until the standard trans-porionic axis was observed. b) Balance between axial, coronal and sagittal axis adjusted to connect trans-porionic axis (purple) with Orbitale through a coronal axis (blue). c) Axial view through FH after connecting the 3 axes.</p

Plotted landmarks on 3D rendered images with MPR view.

<p>Plotted landmarks on 3D rendered images with MPR view.</p