Korean J Orthod.  2009 Oct;39(5):289-299.

Use of Head Posture Aligner to improve accuracy of frontal cephalograms generated from cone-beam CT scans

• Sun MK
• Uhm GS
• Cho JH
• Hwang HS

Abstract

OBJECTIVE
The purpose of the present study was to evaluate the effectiveness of the use of Head Posture Aligner (HPA) during cone-beam computed tomography (CBCT) scan in generation of frontal cephalograms using 3D CBCT images.
METHODS
CBCT scans and frontal cephalograms were made in 30 adult individuals. While a couple of CBCT scan was made for one subject, one was made with conventional method, without use of HPA, the other was acquired with the use of HPA. After creation of virtual frontal cephalogram from each 3D CBCT image, it was traced and compared with the tracing of real frontal cephalogram.
RESULTS
In the comparison of the measurements, the virtual cephalograms with the use of HPA did not show statistically significant differences with the real cephalograms whereas the virtual cephalograms without the use of HPA presented significant differences with real cephalograms in many measurements. In the correlation analysis with the measurements of the real cephalograms, the virtual cephalograms with the use of HPA showed higher correlations in all measurements than the virtual cephalograms without the use of HPA.
CONCLUSIONS
Measurements from CBCT-generated cephalograms become similar to those from real cephalograms with the use of HPA during CBCT scan. Thus, the use of HPA is suggested during the CBCT scan in order to construct accurate virtual frontal cephalograms using 3D CBCT images.

Keyword

Cone-beam CT; Virtual frontal cephalogram; Head Posture Aligner

MeSH Terms

Adult
Cone-Beam Computed Tomography
Head
Humans
Posture

Figure

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  Fig. 1 Image acquisition to compare accuracy of CBCT-generated frontal cephalograms between with and without the use of Head Posture Aligner (HPA). The real frontal cephalograms serve as the gold standard in this study.

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  Fig. 2 A, Head Posture Aligner: straight wire indicator is attached in parallel with fluid spirit level equalizer; B, Reference ear plug: titanium ball marker is located in the center of ear plug; C, A subject with the HPA on one side and a couple of ear plugs positioned in both sides of the ear. A couple of ball markers in the ear plugs are represented on volume rendering image to simulate ear rods in conventional cephalometric apparatus.

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  Fig. 3 This window shows procedure of virtual frontal cephalogram generated from 3D volume rendering image. Virtual central ray is geometrized by using right and left ball markers of the reference ear plug (top left and right). Then the vertical head rotation is determined with the help of the HPA; The image is rotated upward or downward on the axis of virtual central ray so the wire indicator in the HPA is leveled horizontally (bottom left). Using the function of the program, virtual frontal cephalogram is created (bottom right).

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  Fig. 4 Anatomic landmarks used in this study. Cg, crista galli; ANS, anterior nasal spine; NC, right nasal cavity; NC', left nasal cavity; Mx, right maxillare; Mx', left maxillare; UM, upper right first molar; UM', upper left first molar; LM, lower right first molar; LM', lower left first molar; Ag, right antegonion; Ag', left antegonion; Me, menton.

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  Fig. 5 A, Height measurements: 1, total facial height (Cg-Me); 2, upper facial height (Cg-ANS); 3, lower facial height (ANS-Me); 4, right maxillary height (Mx to HR); 5, left maxillary height (Mx' to HR); 6, right ramus height (Ag to HR); 7, left ramus height (Ag' to HR). B, Width measurements: 1, nasal width (NC-NC'); 2, maxillary width (Mx-Mx'); 3, maxillary intermolar width (UM-UM'); 4, mandibular intermolar width (LM-LM'); 5, mandibular width (Ag-Ag'). C, Angular measurements: 1, ∠Cg-Me to MSR; 2, ∠ANS-Me to MSR; 3, ∠Cg-Mx to HR; 4, ∠Cg-Mx' to HR; 5, ∠Cg-Ag to HR; 6, ∠Cg-Ag' to HR (the same abbreviation as Fig 4).

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