Automatic Exposure Control System Research Articles

Performance evaluation of stationary and mobile radiography systems in Indonesia.

An analysis and evaluation has been carried out on each test parameter contained in the compliance test of 1016 stationary and 480 mobile radiography devices compiled by the Indonesian Nuclear Energy Regulatory Agency (Badan Pengawas Tenaga Nuklir, BAPETEN) from 2019 to 2020. The data were categorised and analysed based on the devices' age to observe the correlation of performance with the age of the X-ray machine. In addition, the implementation level of the Automatic Exposure Control (AEC) system test of the stationary radiography X-ray modality is also reviewed. The results of the evaluation showed that 89.9% of the stationary radiography devices unconditionally pass the test, 5.2% are in the status of 'conditional pass' and 4.9% fail the test. On the other hand, 84.8% of mobile radiography devices unconditionally pass the test, 2.1% are in the status of 'conditional pass' and 13.1% fail the test. From the evaluation conducted, there is no observable correlation between the age of the modality and the results of the compliance test. Overall, only 9.2% of stationary radiography X-ray compliance test reports have included the AEC test since it is not a mandatory requirement of the national protocol.

Microsievert Wide-Volume Versus Spiral Computed Tomography Using an Automatic Exposure Control System in the Diagnosis of Foreign Body Aspiration in Children.

Foreign body aspiration (FBA) in childhood is a life-threatening condition that necessitates prompt management to prevent devastating complications. Different imaging methods are used in the diagnosis of FBA. The aim of this study was to compare the diagnostic value and dose of microsievert wide-volume computed tomography (μSv-WV-CT) with multidetector computed tomography using an automatic exposure control system (MDCT-AEC) in children with FBA. In this single-center cross-sectional study, 102 cases diagnosed with FBA between September 2013 and September 2021 were retrospectively evaluated. The patients were divided into 2 groups according to the diagnostic modality used: group A, μSv-WV-CT (2016-2021) and group B, MDCT-AEC (2013-2021). The diagnostic performance and radiation dose of the 2 groups were statistically compared. The diagnostic performance (sensitivity, specificity, positive predictive value, negative predictive value, and accuracy) of the 2 groups was similar. The mean effective radiation dose of group A was 34.89 ± 0.01 μSv, which was significantly lower than that of group B (179.75 ± 114.88 μSv) ( P < 0.001). In children with suspected FBA, μSv-WV-CT at a lower radiation dose had similar diagnostic performance to MDCT-AEC.

Variations in signal-to-noise characteristics of tissue-equivalent attenuators for mammographic automatic exposure control system performance evaluation.

This work investigates the impact of tissue-equivalent attenuator choice on measured signal-to-noise ratio (SNR) for automatic exposure control (AEC) performance evaluation in digital mammography. It also investigates how the SNR changes for each material when used to evaluate AEC performance across different mammography systems. AEC performance was evaluated for four mammography systems using seven attenuator sets at two thicknesses (4 and 8 cm). All systems were evaluated in 2D imaging mode, and one system was evaluated in digital breast tomosynthesis (DBT) mode. The methodology followed the 2018 ACR digital mammography quality control (DMQC) manual. Each system-attenuator-thickness combination was evaluated using For Processing images in ImageJ with standard ROI size and location. The closest annual physicist testing results were used to explore the impact of varying measured AEC performance on image quality. The measured SNR varied by 44%-54% within each system across all attenuators at 4 cm thickness in 2D mode. The variation appeared to be largely due to changes in measured noise, with variations of 46%-67% within each system across all attenuators at 4 cm thickness in 2D mode. Two systems had failing SNR levels for two of the materials using the minimum SNR criterion specified in the ACR DMQC manual. Similar trends were seen in DBT mode and at 8 cm thickness. Within each material, there was 115%-131% variation at 4 cm and 82%-114% variation at 8 cm in the measured SNR across the four imaging systems. Variation in SNR did not correlate with system operating level based on visual image quality and average glandular dose (AGD). Choice of tissue-equivalent attenuator for AEC performance evaluation affects measured SNR values. Depending on the material, the difference may be enough to result in failure following the longitudinal and absolute thresholds specified in the ACR DMQC manual.

Method of determining technique from weight and height to achieve targeted detector exposures in portable chest and abdominal digital radiography.

This study presents a methodology to develop an X‐ray technique chart for portable chest and abdomen imaging which utilizes patient data available in the modality worklist (MWL) to reliably achieve a predetermined exposure index (EI) at the detector for any patient size. The method assumes a correlation between the patients’ tissue equivalent thickness and the square root of the ratio of the patient's weight to height. To assess variability in detector exposures, the EI statistics for 75 chest examinations and 99 abdominal portable X‐ray images acquired with the new technique chart were compared to those from a single portable unit (chest: 3877 images; abdomen: 200 images) using a conventional technique chart with three patient sizes, and to a stationary radiography room utilizing automatic exposure control (AEC) (chest: 360 images; abdomen: 112 images). The results showed that when using the new technique chart on a group of portable units, the variability in EI was significantly reduced (p < 0.01) for both AP chest and AP abdomen images compared to the single portable using a standard technique chart with three patient sizes. The variability in EI for the images acquired with the new chart was comparable to the stationary X‐ray room with an AEC system (p > 0.05). This method could be used to streamline the entire imaging chain by automatically selecting an X‐ray technique based on patient demographic information contained in the MWL to provide higher quality examinations to clinicians by eliminating outliers. In addition, patient height and weight can be used to estimate the patients’ tissue equivalent thickness.

From the use of exposure index in quality control testing to the use of exposure index for quality control of clinical images

AimThe exposure index (EI) is used in routine quality control (QC) tests performed in the radiographic equipment installed in our hospitals. This study aimed at investigating the factors affecting the calculation of EI in QC and clinical images, and the implementation of target EI (EIT) and deviation index (DI) in clinical practice. MethodsThe EI is 100 times the incident air kerma (IAK) in μGy on the image receptor, using the RQA-5 X-ray beam quality. Conformance to this relationship was investigated in QC images and clinical images acquired using anthropomorphic phantom body parts and different examination protocols, tube potential settings and radiation field sizes. Furthermore, a survey on EIT and DI data from clinical images was performed. ResultsThough automatic exposure control (AEC) systems have been adjusted for an IAK of 2.5 μGy, for most anthropomorphic phantom images the EIs were far from 250, depending on the manufacturer, the anatomy imaged, and the examination protocol. Regarding the survey results, DI calculation was feasible in only 38 % of the systems, since for the rest EIT values have not been set. However, the rationale based on which EIT have been selected is unclear. Some systems use only one while others many different EIT values. ConclusionBefore using EI for quality control of clinical images image all receptors and AEC systems should be properly calibrated. Then, the methodology of selecting appropriate EIT should be refined, since the EI calculation may vary, depending on the manufacturer, the anatomy imaged, and the examination protocol.

Radiation doses during computed tomography scan imaging in Hassan II Hospital, Agadir, Morocco.

Introductionthe aim of this study was to establish local Diagnostic Reference Levels (DRLs) for four adult Computed Tomography (CT) examinations in the radiology department, Hassan II hospital of Agadir.Methodsduring this survey, we have examined the data of 200 patients at an average of 50 per localization. A General Electric 16 CT with automatic exposure control system was used to perform all CT examinations. Scanner acquisition parameters, number of series, contrast medium use, rotation time plus slice thickness, the displayed Computed Tomography Dose Index (CTDIvol), and the Dose Length Product (DLP) were among the data collected for each diagnostic exam chosen. To evaluate the DRL and effective dose, the conversion factor and formalism of the International Commission on Radiological Protection (ICRP) were utilized.Resultsthe average effective dose (Eeff), the displayed CT dose index (CTDIvol), dose length product (DLP) were (7.28±2.35) mSv, (10.80±3.80) mGy and (428.35±138.26) mGy.cm respectively at chest CT. For abdomen-pelvis CT scan, there were (12.48±5.58) mSv, (9.30±2.99) mGy and (805.43±359.98) mGy. Those at chest abdomen-pelvic CT scan were (11.72±3.98) mSv, (10.82±2.53) mGy and (755.97±251.52) mGy.cm respectively. For lumbar CT, there were (12.12±2.32) mSv, (26.46±5.24) mGy and (787.00±149.37) mGy.cm respectively.Conclusionthe findings of this study shows that our values are slightly higher than those of developed countries. This first-ever CT practice evaluation at Agadir's Hassan II Hospital reinforced the need for further radiology training for computed tomography practitioners on parameters influencing image quality, dose, and protocols improvement.

Variation in digital breast tomosynthesis image quality at differing heights above the detector.

IntroductionThe aim of this preliminary work was to determine if image quality in digital breast tomosynthesis (DBT) changes when tomosynthesis image slices were obtained at differing heights above the detector and in differing breast thicknesses.MethodsA CIRS Model 020 BR3D breast imaging phantom was used to obtain the DBT images. The images were also acquired at different tube voltages, and each exposure was determined by the automatic exposure control system. Contrast‐to‐noise ratio (CNR) and figure‐of‐merit (FOM) values were obtained and compared.ResultsAt a phantom thickness of 5 cm or greater, there was a significant reduction (P ≤ 0.05) of image CNR values obtained from the images near the top of the phantom to those obtained near the bottom of the phantom. When the phantom thickness was 4 cm, there was no significant difference in CNR values between DBT images acquired at any height in the phantom. FOM values generally showed no difference when images were obtained at differing heights above the detector.ConclusionImage quality, as measured by the CNR, was reduced when tomosynthesis slice image heights were at the top of the phantom and when the thickness of the phantom was more than 4 cm. From this preliminary work, clinicians need to be aware that DBT images obtained near the top of the breast, when breast thickness is greater than 4 cm, may have reduced image quality. Further work is needed to fully assess any DBT image quality changes when images are obtained near the top of the breast.

European consensus on patient contact shielding

Patient contact shielding has been in use for many years in radiology departments in order to reduce the effects and risks of ionising radiation on certain organs. New technologies in projection imaging and CT scanning such as digital receptors and automatic exposure control (AEC) systems have reduced doses and improved image consistency. These changes and a greater understanding of both the benefits and the risks from the use of shielding have led to a review of shielding use in radiology. A number of professional bodies have already issued guidance in this regard. This paper represents the current consensus view of the main bodies involved in radiation safety and imaging in Europe: European Federation of Organisations for Medical Physics, European Federation of Radiographer Societies, European Society of Radiology, European Society of Paediatric Radiology, EuroSafe Imaging, European Radiation Dosimetry Group (EURADOS), and European Academy of DentoMaxilloFacial Radiology (EADMFR). It is based on the expert recommendations of the Gonad and Patient Shielding (GAPS) Group formed with the purpose of developing consensus in this area. The recommendations are intended to be clear and easy to use. They are intended as guidance, and they are developed using a multidisciplinary team approach. It is recognised that regulations, custom and practice vary widely on the use of patient shielding in Europe and it is hoped that these recommendations will inform a change management program that will benefit patients and staff.

European consensus on patient contact shielding

Patient contact shielding has been in use for many years in radiology departments in order to reduce the effects and risks of ionising radiation on certain organs. New technologies in projection imaging and CT scanning such as digital receptors and automatic exposure control (AEC) systems have reduced doses and improved image consistency. These changes and a greater understanding of both the benefits and the risks from the use of shielding have led to a review of shielding use in radiology. A number of professional bodies have already issued guidance in this regard. This paper represents the current consensus view of the main bodies involved in radiation safety and imaging in Europe: European Federation of Organisations for Medical Physics, European Federation of Radiographer Societies, European Society of Radiology, European Society of Paediatric Radiology, EuroSafe Imaging, European Radiation Dosimetry Group (EURADOS), and European Academy of DentoMaxilloFacial Radiology (EADMFR). It is based on the expert recommendations of the Gonad and Patient Shielding (GAPS) Group formed with the purpose of developing consensus in this area. The recommendations are intended to be clear and easy to use. They are intended as guidance, and they are developed using a multidisciplinary team approach. It is recognised that regulations, custom and practice vary widely on the use of patient shielding in Europe and it is hoped that these recommendations will inform a change management program that will benefit patients and staff.

MODELLING AUTOMATIC EXPOSURE CONTROL RESPONSE TO THE PRESENCE OF THE PATIENT SCANNING BED IN A HYBRID PET/CT SCANNER.

Automatic Exposure Control (AEC) systems optimise radiation dose to the patient while providing adequate image quality. This study examined the effect that the increased localiser region of interest of a hybrid PET/CT has on the CTDIvol, focussing on the role of extraneous objects and patient attenuation profiles. A Siemens Biograph™ 16 Horizon PET/CT system and a Siemens Somatom Sensation 64, both employing the Siemens CAREDose 4D AEC system, were used for acquisition of a range of phantoms. The effect of patient miscentring and effect of the patient bed impinging on the localiser was established and modelled. For PA localiser scans, a non-linear relationship between miscentring and CTDIvol was observed, attributable to the presence of the patient bed being misinterpreted as the patient width. The model identified how the presence of the patient bed led to an increase in the CTDIvol significantly larger than expected (~12%, or 1mSv), particularly prevalent for smaller patients.

Reader Performance as a Function of Patient Size for the Detection of Hepatic Metastases.

To investigate reader performance as a function of patient size for the detection of hepatic metastases when an automatic exposure control (AEC) system is used, which varies image noise as a function of patient size. Abdominal computed tomograhy examinations across 100, 120, 160, and 200 quality reference tube current-time product were collected, involving a cohort of 83 patients. Three radiologists identified hepatic metastases across all dose levels. Partial Spearman rank correlation and multivariate logistic regression were used to evaluate correlations between reader performance and patient size and lesion size/contrast while accounting for potential confounding effects. Analyses were repeated on an emulated less-variable noise AEC. No statistically significant correlation was observed between patient size and radiologist performance (for variable-noise AEC: range of partial Spearman ρ, -0.157 to -0.035]; range of adjusted odds ratios, 0.987, 1.006). Reader performance was independent of patient size, suggesting that variable-noise AEC provides better modulation for larger patients than constant-noise AEC.

A comparison of automatic and manual compensation methods for the calculation of tube currents during off-centered patient positioning with a noise-based automatic exposure control system in computed tomography.

Automatic exposure control (AEC) is used to optimize the X-ray tube output during computed tomography (CT) scans. However, calculation of the tube current by AEC can be affected when a patient is not aligned with the rotational center of the X-ray tube. An automatic couch height-positioning compensation mechanism provides a corrective function when the patient is off-center. In this study, we aimed to (a) evaluate the performance characteristics of the positioning compensation mechanism and (b) confirm whether our proposed compensation method can be properly applied to a noise-based AEC system even if the CT device is not equipped with a positioning compensation mechanism. An elliptical phantom was scanned at various table heights on systems without/with the positioning compensation mechanism. Expressions describing the offset from the gantry's isocenter and adjusted standard deviation settings were derived and used in our proposed compensation method. A phantom was scanned at various table heights with our proposed compensation method, and volume CT dose index (CTDIvol) and image noise levels were obtained. An anthropomorphic chest phantom was also scanned using the proposed compensation method to verify its accuracy. When the positioning compensation mechanism was used, it yielded a constant CTDIvol and image noise levels at various table heights tested. A comparison between our proposed method and the positioning compensation mechanism for both the elliptical and chest phantoms yielded similar CTDIvol. Therefore, both automatic and manual positioning compensation methods are useful for avoiding AEC miscalculations in off-centered patient positioning cases.

Radiographic and fluoroscopic X-ray systems: Quality control of the X-ray tube and automatic exposure control using theoretical spectra to determine air kerma and dose to a homogenous phantom.

PurposeTo develop a method to perform quality control (QC) of X‐ray tubes and automatic exposure control (AEC) as a part of the QC of the radiographic and fluoroscopic X‐ray system. Our aim is to verify the output from the X‐ray tube by comparing the measured radiation output, or air kerma, to the theoretical output given the applied exposure settings and geometry, in addition to comparing the measured kV to the nominal kV. The AEC system for fluoroscopic and conventional X‐ray systems is assessed by determining the absorbed dose to a homogenous phantom with different thicknesses.MethodThis study presents a model to verify the X‐ray tube measurement results and a method to determine the dose to a homogenous phantom (Dphantom). The following input is needed: a parameterized model of the X‐ray spectrum, the X‐ray tube measurements using a multifunctional X‐ray meter, the exposure parameters recorded via imaging of polymethyl methacrylate (PMMA) slabs of different thickness that simulate the patient using AEC, and a parameterized model for calculating the dose to water from Monte Carlo simulations. The output is the entrance surface dose (ESD) and absorbed dose in the phantom, Dphantom (µGy). In addition, the parameterized X‐ray spectrum is used to compare theoretical and measured air kerma as a part of the QC of the X‐ray tube. To verify the proposed method, the X‐ray spectrum provided in this study, SPECTRUM, was compared to two commercially available spectra, SpekCalc and Institute of Physics and Engineering in Medicine (IPEM) 78. The fraction of energy imparted to the homogenous phantom was compared to the imparted fraction calculated by PCXMC.ResultsThe spectrum provided in this study was in good agreement with two previously published X‐ray spectra. The absolute percentage differences of the spectra varied from 0.05% to 3.9%, with an average of 1.4%, compared to SpekCalc. Similarly, the deviation from IPEM report 78 varied from 0.02% to 2.3%, with an average of 0.74%. The SPECTRUM was parameterized for calculation of the imparted fraction for target angles of 10°, 12°, and 15°, kV (50–150 kV) with the materials Al (2.2–8 mm), Cu (0–1 mm), and any combination of the filters, PMMA and water. The deviation of energy imparted from the results by PCXMC was less than 8% for all measurements across different kV, filtration, and vendors, obtained by using PMMA to record the exposure parameters, while the dose was calculated based on water with same thicknesses as the PMMA.ConclusionThis study presents an accurate and suitable method to perform a part of the QC of fluoroscopic and conventional X‐ray systems with respect to the X‐ray tube and the associated AEC system. The method is suitable for comparing protocols within and between systems via the absorbed dose.

Proper Management of the Clinical Exposure Index Based on Body Thickness Using Dose Optimization Tools in Digital Chest Radiography: A Phantom Study.

In radiography, the exposure index (EI), as per the International Electrotechnical Commission standard, depends on the incident beam quality and exposure dose to the digital radiography system. Today automatic exposure control (AEC) systems are commonly employed to obtain the optimal image quality. An AEC system can maintain a constant incident exposure dose on the image receptor regardless of the patient thickness. In this study, we investigated the relationship between body thickness, entrance surface dose (ESD), EI, and the exposure indicator (S value) with the aim of using EI as the dose optimization tool in digital chest radiography (posterior–anterior and lateral projection). The exposure condition from the Korean national survey for determining diagnostic reference levels and two digital radiography systems (photostimulable phosphor plate and indirect flat panel detector) were used. As a result, ESD increased as the phantom became thicker with constant exposure indicator, which indicates similar settings to an AEC system, but the EI indicated comparatively constant values without following the tendency of ESD. Therefore, body thickness should be considered under the AEC system for introducing EI as the dose optimization tool in digital chest radiography.

3D Non-Rigid Alignment of Low-Dose Scans Allows to Correct for Saturation in Lower Extremity Cone-Beam CT.

Detector saturation in cone-beam computed tomography occurs when an object of highly varying shape and material composition is imaged using an automatic exposure control (AEC) system. When imaging a subject’s knees, high beam energy ensures the visibility of internal structures but leads to overexposure in less dense border regions. In this work, we propose to use an additional low-dose scan to correct the saturation artifacts of AEC scans. Overexposed pixels are identified in the projection images of the AEC scan using histogram-based thresholding. The saturation-free pixels from the AEC scan are combined with the skin border pixels of the low-dose scan prior to volumetric reconstruction. To compensate for patient motion between the two scans, a 3D non-rigid alignment of the projection images in a backward-forward-projection process based on fiducial marker positions is proposed. On numerical simulations, the projection combination improved the structural similarity index measure from 0.883 to 0.999. Further evaluations were performed on two in vivo subject knee acquisitions, one without and one with motion between the AEC and low-dose scans. Saturation-free reference images were acquired using a beam attenuator. The proposed method could qualitatively restore the information of peripheral tissue structures. Applying the 3D non-rigid alignment made it possible to use the projection images with inter-scan subject motion for projection image combination. The increase in radiation exposure due to the additional low-dose scan was found to be negligibly low. The presented methods allow simple but effective correction of saturation artifacts.

Inadequate object positioning and improvement of automatic exposure control system calculations based on an empirical algorithm.

When using automatic exposure control (AEC) systems in computed tomography (CT), miscalculation of tube current occurs when a patient is not aligned with the rotational center of the X-ray tube. A positioning compensation mechanism provides a corrective function when the patient is off-center; however, not all CT systems are equipped with this mechanism. AEC systems can broadly be divided into noise- and empirical-based. The authors studied empirical-based AEC systems to derive a compensation process to achieve an equivalent effect to that offered by the mechanism and to verify the accuracy of this process. A relational equation was derived to keep the tube current constant with variations in table height and quality reference milliampere-seconds (QRmAs), and this was adopted as the proposed compensation method. The radiation dose and image quality were evaluated for phantom imaging with and without the proposed compensation method using AEC and varying table heights. The output radiation dose and image quality were also evaluated for anthropomorphic chest phantom imaging to verify the compensatory effect of the proposed method. With the proposed compensation method, changes in the table height resulted in only small changes in the output radiation dose and noise level. Conversely, when the proposed compensation method was not used, changes in the table height resulted in widely varying output radiation dose and noise level. Imaging the anthropomorphic chest phantom with the proposed compensation method also yielded a stable output radiation dose.

CT-Dose Measurement of the Spinal Cord Region Using XR-QA2 Radiochromic Films and TLD 100H Dosimeters

The European Directive 2013/59/Euratom focuses on the radiation protection and patient dosimetry. In particular, the dose absorbed by serial organs such as the spinal cord due to diagnostic exams plays a crucial role in the appraisal of medical exposure. In this work, a comparison between dose measurements performed with GafchromicTM XR-QA2 and TLD 100H is presented. The dosimeters—after a calibration procedure through an X-ray tube—were placed within the thorax region of an anthropomorphic phantom corresponding to the spinal cord area exposed to a thoracic CT procedure. The mean-dose value was measured with GafchromicTM first, and it was then compared to the dose value obtained with TLDs, resulting in a good agreement between the two dosimetric methodologies. Additionally, the results showed that—due to the usage of the automatic exposure control (EC) system—the discrepancy between the two methods is proportional to the current output of the CT system.

Physical parameters affecting the distribution of X-ray dose during hysterosalpingography

Objective: Hysterosalpingography (HSG) is based on the administration of a shading agent to the uterine cavity and fallopian tubes using a Schulze apparatus. An X-ray beam (X) is then directed at the abdominal area of the patient and diagnostic images are obtained for evaluation. The radiation beam and its mode of administration have a decisive influence on the radiation dose to which the patient is exposed. The aim of this study was to determine the physical parameters of this exposure in such a way that the dose distribution during the HSG examination was the most beneficial for the patient. Materials and Methods: Measurements to evaluate the effect of exposure parameters on the quality of radiological images obtained during HSG in slim and obese patients were made in 216 repetitions of the standard HSG test. Additional research data was obtained from measurements made in the X-ray laboratory at the Clinical Hospital. Results: The comparison of all measurements made for experimental models simulating a slim and obese patient demonstrated that the dose distribution most advantageous for the patient is obtained for pulsations of an X-ray tube for PPS = 6, regardless of the thickness of the patient. Conclusions: The image quality and size of the radiation dose received during the HSG examination depends on the individual characteristics of the patient. During the measurements performed in order to compare the exposure conditions set by the automatic exposure control (AEC) system and the resulting dose, this study demonstrated that the dose distribution most advantageous for the patients is obtained for pulsations on an X-ray tube for PPS = 6, regardless of the thickness of the patient.

A suggested method for setting up GSI profiles on the GE Revolution CT scanner.

“GSI Assist” is the automatic exposure control (AEC) system for dual‐energy acquisitions on the GE Revolution CT scanner. This paper describes the user options of GSI Assist, and describes the method developed at UAB Medical Center to simplify the use of GSI Assist without adversely affecting the AEC Operation.

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

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.