Assessment of phantom dosimetry and image quality of i-CAT FLX cone-beam computed tomography

Abstract

Introduction: The increasing use of cone-beam computed tomography in orthodontics has been coupled with heightened concern about the long-term risks of x-ray exposure in orthodontic populations. An industry response to this has been to offer low-exposure alternative scanning options in newer cone-beam computed tomography models.

Methods: Effective doses resulting from various combinations of field of view size and field location comparing child and adult anthropomorphic phantoms with the recently introduced i-CAT FLX cone-beam computed tomography unit (Imaging Sciences, Hatfield, Pa) were measured with optical stimulated dosimetry using previously validated protocols. Scan protocols included high resolution (360° rotation, 600 image frames, 120 kV[p], 5 mA, 7.4 seconds), standard (360°, 300 frames, 120 kV[p], 5 mA, 3.7 seconds), QuickScan (180°, 160 frames, 120 kV[p], 5 mA, 2 seconds), and QuickScan+ (180°, 160 frames, 90 kV[p], 3 mA, 2 seconds). Contrast-to-noise ratio was calculated as a quantitative measure of image quality for the various exposure options using the QUART DVT phantom.

Results: Child phantom doses were on average 36% greater than adult phantom doses. QuickScan+ protocols resulted in significantly lower doses than standard protocols for the child (P = 0.0167) and adult (P = 0.0055) phantoms. The 13 × 16-cm cephalometric fields of view ranged from 11 to 85 μSv in the adult phantom and 18 to 120 μSv in the child phantom for the QuickScan+ and standard protocols, respectively. The contrast-to-noise ratio was reduced by approximately two thirds when comparing QuickScan+ with standard exposure parameters.

Conclusions: QuickScan+ effective doses are comparable with conventional panoramic examinations. Significant dose reductions are accompanied by significant reductions in image quality. However, this trade-off might be acceptable for certain diagnostic tasks such as interim assessment of treatment results.

Copyright © 2013 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Figures

Figure 1

Locations of optically stimulated luminescent dosimeters (OSLD) in adult Atom Max Model 711 phantom

Figure 2

Adult phantom demonstrating positioning principles for phantom scanning: A) lower border of volume is 5 mm below bony chin; anterior border of volume is 5 mm anterior to central incisors. This positioning was used on dental (8×8 cm High resolution scan seen here), mandible, both arches, and arches + TMJ scans. B) lower border of volume is 5 mm below central incisal edge; anterior border of volume is 5 mm anterior to central incisors. This positioning was used on maxilla volumes (6×16 cm High resolution scan seen here). C) tip of the nose and lower soft tissue border of the chin are included in the field of view for standard cephalometric volumes (13×16 cm High resolution scan seen here) and extended field of view (EFOV) volumes.

Figure 3

CIRS 10 year-old child phantom dosimeter locations

Figure 4

Child phantom demonstrating positioning principles for phantom scanning: A) lower border of volume is 5 mm below bony chin; anterior border of volume is 5 mm anterior to central incisors. This positioning was used on dental (8×8 cm High resolution scan seen here), mandible, and both arches. B) lower border of volume is 5 mm below central incisal edge; anterior border of volume is 5 mm anterior to central incisors. This positioning was used on maxilla volumes (6×16 cm High resolution scan seen here). C) tip of the nose and lower soft tissue border of the chin are included in the field of view for standard cephalometric volumes (13×16 cm High resolution scan seen here) and arches + TMJ scans.

Figure 5

Quart DVT_AP CBCT image quality system: A) phantom, B) Sample axial images of aluminum and air elements (top) and plexiglass layer (bottom), C) analysis software window for calculation of Nyquist frequency, D) analysis software window for calculating Homogeneity

Figure 6

Comparison of adult RANDO and ATOM phantoms, TLD and OSL dosimeter, Standard cephalometric and Extended FOVs

Figure 7

Adult phantom effective dose by scan type and FOV

Figure 8

Alternate depiction of Child phantom effective dose by exposure protocol and FOV

Figure 9

Comparison of thyroid level in child and adult. Red line denotes lower edge of volume.