Original article
Three-dimensional accuracy of measurements made with software on cone-beam computed tomography images

https://doi.org/10.1016/j.ajodo.2006.08.024Get rights and content

Introduction: The purpose of this article was to evaluate the accuracy of measurements made on 9- and 12-in cone-beam computed tomography (CBCT) images compared with measurements made on a coordinate measuring machine (CMM), which is the gold standard. Methods: Ten markers were placed on a synthetic mandible, and landmark coordinates and linear and angular measurements were determined with the CMM. Three-dimensional CBCT images, measuring 9 and 12 in, were taken of the mandible with a CBCT machine (NewTom 3G, Aperio Services, Verona, Italy), and landmark coordinates and linear and angular measurements were obtained with AMIRA (Mercury Computer Systems, Berlin, Germany) software. Results: The coordinate intrareliability correlation coefficient was almost perfect between the 3-dimensional CBCT images and the CMM measurements. With the Student t test, we found no significant statistical difference between linear and angular measurements from the CMM and the NewTom 3G images, which differed less than 1 mm and 1°, respectively. Conclusions: The NewTom 3G produces a 1-to-1 image-to-reality ratio.

Section snippets

Material and methods

Ten titanium markers (6 mm diameter × 3 mm height) with a hollow cone for which the deepest point marks the center of gravity were placed on a rapid prototype mandible (Fig 1).8 The CMM with a point stylus tip was used as the gold standard to obtain the 3D coordinates of 10 ten markers (Fig 2). All markers faced upward because the CMM could only access marks vertically. Three arbitrary markers were used to standardize the mandible in the coordinate axial system. M1 was assigned as x = 0, y = 0,

Results

Coordinates of the 10 markers obtained from the CMM were registered in a data sheet as the x, y, and z dimensions. The ICC for each of the 3 axes (x, y, and z) was obtained. The intrareliability value was 1.000 for each axis.

Coordinates of the 10 markers were also obtained from the DICOM 9- and 12-in images and placed in a data sheet as the x, y, and z dimensions. The ICC for each of the 3 axes was determined for both images separately. For the 9-in image, the intrareliability values were 1.000

Discussion

In orthodontics, cephalometric analysis has been an important tool in the diagnosis and treatment planning of patients as well as for the assessment of changes over time. Many types of measurements or norms have been made to analyze oral relationships of teeth, jaws, and cranial base.10 A major problem associated with cephalometry is projection errors. Projection errors that have an effect on linear and angular measurements are caused by magnification and distortion and are compounded by

Conclusions

NewTom 9- and 12-in 3D images have a 1-to-1 ratio with real coordinates and with the linear and angular distances obtained by the CMM.

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