scholarly journals Thyroid shielding in cone beam computed tomography: recommendations towards appropriate use

2019 ◽  
Vol 48 (7) ◽  
pp. 20190014 ◽  
Author(s):  
Ruben Pauwels ◽  
Keith Horner ◽  
Jenia Vassileva ◽  
Madan M. Rehani
Keyword(s):  
Cone Beam Ct ◽  
Cone Beam ◽  
Current Evidence ◽  
Appropriate Use ◽  
Risk Models ◽  
Equivalent Thickness ◽  
Metal Artefacts ◽  
Current Trends ◽  
Dosimetric Data ◽  
Tube Current

The objective of this paper is to provide recommendations towards the appropriate use of thyroid shielding in dental cone beam CT (CBCT). Based on current evidence of thyroid radiosensitivity, dosimetric data in the presence and absence of shielding, and a depiction of potential adverse effects of thyroid shielding, a concise set of recommendations was prepared. According to current risk models, thyroid sensitivity is particularly high at a young age, and much higher for females. In the literature, involving adult male, female and paediatric reference phantoms, the use of a tightly fitted thyroid collar with a lead-equivalent thickness of at least 0.25 mm has consistently shown a significant reduction (average: 45.9%) of the equivalent dose to the thyroid. It can therefore be recommended that thyroid shielding should be routinely used for children undergoing CBCT scanning and is recommended for adults up to the age of 50. The increase of the X-ray tube current from automatic exposure control systems due to thyroid shielding can be avoided by placing the shielding collar after acquiring the scout images. Should real-time tube current modulation be implemented in dental CBCT imaging in the future, perspectives regarding the appropriate use of shielding may change according to current trends in CT. In view of the manifestation of metal artefacts, shielding is best avoided if radiological evaluation of tissues below the lower border of the mandible is needed.

Influence of the exomass on the detection of simulated root fracture in cone-beam ct – an ex-vivo study

2020 ◽  
pp. 20200450
Author(s):  
Amanda Pelegrin Candemil ◽  
Francesca Mangione ◽  
Karla Farias Vasconcelos ◽  
Anne Caroline Oenning ◽  
Reinhilde Jacobs ◽  
...  
Keyword(s):  
Ex Vivo ◽  
Cone Beam Ct ◽  
Receiver Operating Curve ◽  
Cone Beam ◽  
Metallic Materials ◽  
Root Fracture ◽  
Vertical Root Fracture ◽  
Metal Artefacts ◽  
Sensitivity Specificity ◽  
Ex Vivo Study

Objectives: To evaluate the influence of exomass-related metal artefacts on the detection of simulated vertical root fracture (VRF) in cone-beam computed tomography (CBCT). Methods: Twenty teeth were endodontically instrumented and VRF was induced in half of them. All teeth were individually placed in an empty socket of a human mandible. Metallic materials were differently arranged in the exomass [zone outside of the field of view (FOV) but between the X-ray source and the receptor] and/or endomass (zone inside of the FOV), and CBCT scans were obtained. Four radiologists evaluated the presence of VRF using a 5-point scale. Sensitivity, specificity, and area under the receiver operating curve (AUC) were compared using ANOVA. Also, the tooth of interest was replaced with a tube filled with a radiopaque solution and all CBCT scans were repeated to analyse the data objectively. Mean grey and noise values were obtained from the tube and compared using ANOVA followed by Tukey’s test (α = 0.05). Results: Mean grey values were significantly lower and noise was significantly higher when metallic materials were present in the endomass or both the exomass and endomass. Sensitivity, specificity, and AUC were not influenced by the artefacts from the metallic materials irrespective of the arrangement condition. Conclusions: Exomass-related metal artefacts did not influence the diagnosis of simulated VRF in CBCT.

SU-E-J-19: A Feasility Study: Tube Current Modulation as a Dose Savings Technique for Cone-Beam CT-Based IGRT

2011 ◽  
Vol 38 (6Part7) ◽  
pp. 3445-3446
Author(s):  
A Doemer ◽  
Y Huang ◽  
B Miller ◽  
T Nurushev ◽  
I Chetty
Keyword(s):  
Cone Beam Ct ◽  
Cone Beam ◽  
Tube Current Modulation ◽  
Current Modulation ◽  
Tube Current

scholarly journals Evaluation of metal artefacts for two CBCT devices with a new dental arch phantom

2020 ◽  
Vol 49 (5) ◽  
pp. 20190385
Author(s):  
Luciano Augusto Cano Martins ◽  
Polyane Mazucatto Queiroz ◽  
Yuri Nejaim ◽  
Karla de Faria Vasconcelos ◽  
Francisco Carlos Groppo ◽  
...  
Keyword(s):  
Cone Beam Ct ◽  
Cone Beam ◽  
Dental Arch ◽  
Adjacent Area ◽  
Significance Level ◽  
Metal Artefacts ◽  
Metal Artefact ◽  
Bone Structures ◽  
The Impact ◽  
Phantom Design

Objectives: To create a new phantom design to evaluate the real impact of artefacts caused by titanium on bone structures in cone beam CT images considering different positions and quantity of metals in the dental arch, with and without metal artefact reduction (MAR). Methods: A three cylindrical polymethyl methacrylate (PMMA) plate phantom was designed containing eight perforations arranged to simulate the lower dental arch in the intermediate plate. Three titanium cylinders were positioned in different locations and quantities to test different clinical conditions and to quantify the impact of the metal artefact around five bone cylinders. Scans were carried out in seven different protocols (Control, A-F) in two cone beam CT devices (OP300 Maxio and Picasso Trio). Eight regions of interest around each cortical and trabecular bone were used to measure the grey value standard deviation corresponding the artefact expression in the Image J software. Both the artefact expression and the MAR effect were assessed using the Wilcoxon, Friedman (Dunn) and Kruskal–Wallis tests (significance level of 5%). Results: For both devices, MAR was statistically efficient only for the protocols E, and F. Protocol F (three metals on the adjacent area of the analysis region) showed higher artefact expression when compared to the others. Conclusion: In conclusion, the new phantom design allowed the quantification of the metal artefact expression caused by titanium. The metal artefact expression is higher when more metal objects are positioned in the adjacent bone structures. MAR may not be effective to reduce artefact expression on the adjacencies of those objects for the devices studied.

scholarly journals Registration accuracy with the low dose kilovoltage cone-beam CT: A phantom study

BJR|Open ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 20190028
Author(s):  
Yoshiki Takei ◽  
Hajime Monzen ◽  
Kenji Matsumoto ◽  
Kohei Hanaoka ◽  
Mikoto Tamura ◽  
...  
Keyword(s):  
Soft Tissue ◽  
Image Quality ◽  
Image Registration ◽  
Low Dose ◽  
Cone Beam Ct ◽  
Cone Beam ◽  
Registration Accuracy ◽  
Tube Current ◽  
Quality Aspect ◽  
Imaging Dose

Objective: The aim of this study was to investigate low-dose kilovoltage cone-beam CT (kV-CBCT) for image-guided radiotherapy, with a particular focus on the accuracy of image registration with low-dose protocols. Methods: Imaging doses were measured with a NOMEX semiconductor detector positioned at the front of head, thorax, and pelvis human body phantoms while kV-CBCT scans were acquired at different tube currents. Aspects of image quality (spatial resolution, noise, uniformity, contrast, geometric distortion, and Hounsfield unit sensitivity) and image registration accuracy using bone and soft tissue were evaluated. Results: With preset and the lowest tube currents, the imaging doses were 0.16 and 0.08 mGy, 5.29 and 2.80 mGy, and 18.23 and 2.69 mGy for head, thorax, and pelvis, respectively. Noise was the only quality aspect directly dependent on tube current, being increased by 1.5 times with a tube current half that of the preset in head and thorax, and by 2.2 times with a tube current 1/8 of the preset in the pelvis. Accurate auto-bone matching was performed within 1 mm at the lowest tube current. The auto-soft tissue matching could not be performed with the lowest tube current; however, manual-soft tissue matching could still be performed within 2 mm or less. Conclusion: Noise was the only image quality aspect dependent on the imaging dose. Auto-bone and manual-soft tissue matching could still be performed at the lowest imaging dose. Advances in knowledge: When optimizing kV-CBCT imaging dose, the impact on bone and soft tissue image registration accuracy should be evaluated.

scholarly journals Optimal dose reduction algorithm using an attenuation-based tube current modulation method for cone-beam CT imaging

PLoS ONE ◽  
2018 ◽  
Vol 13 (2) ◽  
pp. e0192933 ◽  
Author(s):  
Kihong Son ◽  
Jieun Chang ◽  
Hoyeon Lee ◽  
Changhwan Kim ◽  
Taewon Lee ◽  
...  
Keyword(s):  
Dose Reduction ◽  
Cone Beam Ct ◽  
Optimal Dose ◽  
Ct Imaging ◽  
Cone Beam ◽  
Modulation Method ◽  
Tube Current Modulation ◽  
Reduction Algorithm ◽  
Current Modulation ◽  
Tube Current
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