Novel Anterior Cranial Base Area for Voxel-Based Superimposition of Craniofacial CBCTs

Abstract

A standard method to assess changes in craniofacial morphology over time is through the superimposition of serial patient images. This study evaluated the reliability of a novel anterior cranial base reference area, principally including stable midline structures (EMACB) after an early age, and compared it to the total anterior cranial base (TACB) and an area including only midline structures (MACB). Fifteen pairs of pre-existing serial CBCT images acquired from growing patients were superimposed with all techniques by applying a best-fit registration algorithm of corresponding voxel intensities (Dolphin 3D software). The research outcomes were the reproducibility of each technique and the agreement between them in skeletal change detection, as well as their validity. The TACB and EMACB methods were valid, since the superimposed midline ACB structures consistently showed adequate overlap. They also presented perfect overall reproducibility (median error < 0.01 mm) and agreement (median difference < 0.01 mm). MACB showed reduced validity, higher errors, and a moderate agreement to the TACB. Thus, the EMACB method performed efficiently and mainly included the stable midline ACB structures during growth. Based on the technical, anatomical, and biological principles applied when superimposing serial 3D data to assess craniofacial changes, we recommend the EMACB method as the method of choice to fulfil this purpose.

Keywords: anterior cranial base; cone-beam computed tomography; imaging; three-dimensional; voxel-based superimposition.

Figure 1

Definition of the Total Anterior Cranial Base area (TACB) (in red) and the Extended Middle Anterior Cranial Base area (EMACB) (in yellow) depicted on T0–T1 volumes, following TACB superimposition. On the right image, the EMACB frame is not visible because it is identical to the one of TACB.

Figure 2

Box plots showing the intraoperator reproducibility of the TACB superimposition (Total Anterior Cranial Base), the MACB (Middle Anterior Cranial Base), and the EMACB (Extended Middle Anterior Cranial Base) on the detected T0–T1 changes in mm, for all measurement areas. Zero value, depicted by the continuous horizontal line, indicates perfect reproducibility, whereas any deviation from zero is considered error. The dashed lines indicate 0.5 mm and −0.5 mm. The upper limit of the black line represents the maximum value, the lower limit the minimum value, the box the interquartile range, and the horizontal black line the median value. Outliers are shown as black circles or stars in more extreme cases.

Figure 3

Bland–Altman plots on the T0–T1 changes (mm) detected through repeated EMACB superimpositions by the same operator. The continuous horizontal line shows the mean of the differences in the detected T0–T1 changes, and the dashed lines show the corresponding 95% Limits of Agreement. M1: Measurement 1; M2: Measurement 2.

Figure 4

Color coded distance maps showing the intraoperator differences on T1 surfaces obtained from repeated T0–T1 EMACB voxel-based superimpositions, with the T0 surface held constant as a reference. The samples that presented the least (left), average (middle), and largest (right) absolute differences on the seven measurement areas are shown.

Figure 5

Box plots showing the agreement between EMACB (Extended Middle Anterior Cranial Base) and MACB (Middle Anterior Cranial Base) with the TACB (Total Anterior Cranial Base) superimposition on the detected T0–T1 changes, for all measurement areas. Zero value, depicted by the continuous horizontal line, indicates perfect agreement, whereas any deviation from zero is considered disagreement. The dashed lines indicate 0.5 mm and −0.5 mm. The upper limit of the black line represents the maximum value, the lower limit the minimum value, the box the interquartile range, and the horizontal black line the median value. Outliers are shown as black circles or stars in more extreme cases.

Figure 6

Bland–Altman plots on the T0–T1 changes (mm) detected through the TACB and the EMACB superimpositions by the same operator. The continuous horizontal line shows the mean of the differences in the detected T0–T1 changes, and the dashed lines show the corresponding 95% Limits of Agreement. TACB: Total Anterior Cranial Base; EMACB: Extended Middle Anterior Cranial Base.

Figure 7

Color coded distance maps showing the differences of T1 surfaces obtained from T0–T1 TACB and EMACB voxel-based superimpositions, with the T0 surface held constant as a reference. The samples that presented the least (left), average (middle), and largest (right) absolute distances of the EMACB from the TACB T1 surface, on the seven measurement areas, are shown.