Comparison of physical quality assurance between Scanora 3D and 3D Accuitomo 80 dental CT scanners

Abstract

Background: The use of cone beam computed tomography (CBCT) in dentistry has proven to be useful in the diagnosis and treatment planning of several oral and maxillofacial diseases. The quality of the resulting image is dictated by many factors related to the patient, unit, and operator.

Materials and methods: In this work, two dental CBCT units, namely Scanora 3D and 3D Accuitomo 80, were assessed and compared in terms of quantitative effective dose delivered to specific locations in a dosimetry phantom. Resolution and contrast were evaluated in only 3D Accuitomo 80 using special quality assurance phantoms.

Results: Scanora 3D, with less radiation time, showed less dosing values compared to 3D Accuitomo 80 (mean 0.33 mSv, SD±0.16 vs. 0.18 mSv, SD±0.1). Using paired t-test, no significant difference was found in Accuitomo two scan sessions (p>0.05), while it was highly significant in Scanora (p>0.05). The modulation transfer function value (at 2 lp/mm), in both measurements, was found to be 4.4%. The contrast assessment of 3D Accuitomo 80 in the two measurements showed few differences, for example, the grayscale values were the same (SD=0) while the noise level was slightly different (SD=0 and 0.67, respectively).

Conclusions: The radiation dose values in these two CBCT units are significantly less than those encountered in systemic CT scans. However, the dose seems to be affected more by changing the field of view rather than the voltage or amperage. The low doses were at the expense of the image quality produced, which was still acceptable. Although the spatial resolution and contrast were inferior to the medical images produced in systemic CT units, the present results recommend adopting CBCTs in maxillofacial imaging because of low radiation dose and adequate image quality.

Keywords: CBCT; contrast; image quality; radiation dose; resolution.

Fig. 1

A CBCT unit with a variable FOV (1).

Fig. 2

A wire phantom, with the wire appearing vertical in the middle of the cylinder (arrow).

Fig. 3

The TLD chips inserted in their holes (from 1 to 6) in the slice, which was then fitted into the RANDO phantom.

Fig. 4

MTF graph in 3D Accuitomo 80 (60×60, 90 kv, 6 mA) to be 4.4% when set at 2 lp/mm (upper left panel). The object on which MTF value was assessed had a spatial frequency of 3 lp/mm (upper right panel) in the space inside the phantom (lower left panel). Axial slices of the object show the luminance intensity after receiving the X-ray signal; no artifacts were noticed (lower right panel).

Fig. 5

MTF in 3D Accuitomo (60×60, 80 kv, 7 mA) to be 4.4% when set at 2 lp/mm (upper left panel). The object on which MTF value was assessed had a spatial frequency of 3 lp/mm (upper right panel) in the space inside the phantom (lower left panel). Axial slices of the object show the luminance intensity after receiving the X-ray signal; no artifacts were noticed (lower right panel).

Fig. 6

A graph illustrating the means of grayscale values and SD value of the central region (for noise) in both measurements. The SD is shown as small vertical bars on the smaller columns, while the SD of longer columns was zero: 90=90 kV, 6=6 mA, 80=80 kV, 7=7 mA.

Fig. 7

Contrast measurement in 3D Accuitomo 80 (60×60, 90 kV, 6 mA) showing the uniformity/grayscale of five selected regions in the phantom (upper left panel), and the SD value of their five means besides the SD of the noise at the central region (upper right panel). The contrast resolution using four different materials in the phantom (lower left panel) was tested and the values are shown in the graph (lower right panel).

Fig. 8

Contrast measurement in 3D Accuitomo 80 (60×60, 80 kv, 7 mA) showing uniformity/grayscale of five selected regions in the phantom (upper left panel), and the SD value of their five means besides the SD of the noise at the central region (upper right panel). The contrast resolution using four different materials in the phantom (lower left panel) was tested and the values are shown in the graph (lower right panel).

Fig. 9

The graphic distribution of the radiation doses in the two scans of 3D Accuitomo 80. It can be seen that the values in the two scans are generally similar and, using paired t-test, no significant differences were found (p>0.05).

Fig. 10

The graphic distribution of the radiation dose value of the Scanora 3D in the two sessions of changing FOVs. It is obvious that the values of the wider FOV (75×100) tend to be higher than the 60×60 FOV (p<0.05).