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1.
Phys Med ; 88: 193-217, 2021 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-34284332

RESUMO

Cone beam computed tomography (CBCT) is a diverse 3D x-ray imaging technique that has gained significant popularity in dental radiology in the last two decades. CBCT overcomes the limitations of traditional two-dimensional dental imaging and enables accurate depiction of multiplanar details of maxillofacial bony structures and surrounding soft tissues. In this review article, we provide an updated status on dental CBCT imaging and summarise the technical features of currently used CBCT scanner models, extending to recent developments in scanner technology, clinical aspects, and regulatory perspectives on dose optimisation, dosimetry, and diagnostic reference levels. We also consider the outlook of potential techniques along with issues that should be resolved in providing clinically more effective CBCT examinations that are optimised for the benefit of the patient.


Assuntos
Tomografia Computadorizada de Feixe Cônico , Radiometria , Humanos , Imageamento Tridimensional , Doses de Radiação , Raios X
2.
J Radiol Prot ; 41(2)2021 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-33461178

RESUMO

Cone beam computed tomography (CBCT) has been available since the late 1990s for use in dentistry. European legislation requires optimisation of protection and the use of diagnostic reference levels (DRLs) as well as regular quality control (QC) of the imaging devices, which is well outlined in existing international recommendations. Nevertheless, the level of application is not known. Earlier studies have indicated that few European countries have established DRLs and that patient doses (exposure parameters) have not been properly optimised. The EURADOS Working Group 12-Dosimetry in Medical Imaging undertook a survey to identify existing practices in Member States. Questionnaires were developed to identify equipment types, clinical procedures performed, and exposure settings used. The surveys were circulated to 22 countries resulting in 28 responses from 13 countries. Variations were identified in the exposure factors and in the doses delivered to patients for similar clinical indicators. Results confirm that patient doses are still not properly optimised and DRLs are largely not established. There is a need to promote the importance of performing QC testing of dental CBCT equipment and to further optimise patient exposure by establishment and use of DRLs as a part of a continuous optimisation process.


Assuntos
Tomografia Computadorizada de Feixe Cônico , Níveis de Referência de Diagnóstico , Humanos , Controle de Qualidade , Doses de Radiação , Radiometria
3.
BMC Med Imaging ; 21(1): 2, 2021 01 06.
Artigo em Inglês | MEDLINE | ID: mdl-33407232

RESUMO

BACKGROUND: Cone-beam computed tomography (CBCT) has become an increasingly important medical imaging modality in orthopedic operating rooms. Metal implants and related image artifacts create challenges for image quality optimization in CBCT. The purpose of this study was to develop a robust and quantitative method for the comprehensive determination of metal artifacts in novel CBCT applications. METHODS: The image quality of an O-arm CBCT device was assessed with an anthropomorphic pelvis phantom in the presence of metal implants. Three different kilovoltage and two different exposure settings were used to scan the phantom both with and without the presence of metal rods. RESULTS: The amount of metal artifact was related to the applied CBCT imaging protocol parameters. The size of the artifact was moderate with all imaging settings. The highest applied kilovoltage and exposure level distinctly increased artifact severity. CONCLUSIONS: The developed method offers a practical and robust way to quantify metal artifacts in CBCT. Changes in imaging parameters may have nonlinear effects on image quality which are not anticipated based on physics.

4.
Eur Radiol ; 30(12): 6937-6939, 2020 12.
Artigo em Inglês | MEDLINE | ID: mdl-32621240
5.
Radiat Prot Dosimetry ; 189(4): 466-474, 2020 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-32424394

RESUMO

PURPOSE: Occupational radiation exposure for medical workers in radiology and cardiology was analyzed in nine hospitals in the UAE between 2002 and 2016. The purpose of the study was to determine the time trend and the differences in occupational radiation exposure among worker groups and hospitals in the country. METHODS: Readings of 5700 thermoluminescence dosimeters (TLDs) were obtained from 1011 medical workers and grouped into 5 worker groups (radiographers, diagnostic radiologists, nurses, cardiologists and physicians). RESULTS: The mean annual effective dose was from 0.38 to 0.62 mSv per worker. Even though an increase in the collective effective dose has been noticed during the study period, no significant time trend was observed in the mean effective dose. Furthermore, cardiologists received higher mean and maximum effective doses than the other worker groups. CONCLUSION: The annual effective doses were below the limits set by national legislation and international standards, and for the average worker, the likelihood of high exposure is small. However, improvements in radiation protection practices could be implemented to reduce occupational radiation dose to cardiologists, who were the most exposed worker group in this study.


Assuntos
Cardiologia , Exposição Ocupacional , Lesões por Radiação , Monitoramento de Radiação , Radiologia , Hospitais , Humanos , Exposição Ocupacional/análise , Doses de Radiação , Emirados Árabes Unidos
6.
Eur J Radiol Open ; 6: 24-32, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30619916

RESUMO

Purpose: To determine the effect of patient's vertical off-centering and scout direction on the function of automatic tube voltage selection (ATVS) and tube current modulation (TCM) in chest computed tomography (CT). Methods: Chest phantom was scanned with Siemens and GE CT systems using three clinical chest CT protocols exploiting ATVS and a fixed 120 kVp chest protocol. The scans were performed at five vertical positions of the phantom (-6 to +6 cm from the scanner isocenter). The effects of scout direction (posterior-to-anterior, anterior-to-posterior, and lateral) and vertical off-centering on the function of ATVS and TCM were studied by examining changes in selected voltage, radiation dose (volume CT dose index, CTDIvol), and image noise and contrast. Results: Both scout direction and vertical off-centering affected ATVS. The effect differed between the vendors for the studied geometry, demonstrating differences in technical approaches. The greatest observed increase in CTDIvol due to off-centering was 91%. Anterior-to-posterior scout produced highest doses at the uppermost table position, whereas posterior-to-anterior scout produced highest doses at the lowermost table position. Dose varied least using lateral scouts. Vertical off-centering impacted image noise and contrast due to the combined effect of ATVS, TCM, structural noise, and bowtie filters. Conclusions: Patient vertical off-centering and scout direction affected substantially the CTDIvol and image quality in chest CT examinations. Vertical off-centering caused variation also in the selected tube voltage. The function of ATVS and TCM methods differ significantly between the CT vendors, resulting in differences in CTDIvol and image noise characteristics.

7.
Acad Radiol ; 26(1): 50-61, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-29724675

RESUMO

RATIONALE AND OBJECTIVES: This phantom study aimed to evaluate low-dose (LD) chest computed tomography (CT) protocols using model-based iterative reconstruction (MBIR) for diagnosing lung metastases in patients with sarcoma. MATERIALS AND METHODS: An adult female anthropomorphic phantom was scanned with a 64-slice CT using four LD protocols and a standard-dose protocol. Absorbed organ doses were measured with 10 metal-oxide-semiconductor field-effect transistor dosimeters. Furthermore, Monte Carlo simulations were performed to estimate organ and effective doses. Image quality in terms of image noise, contrast, and resolution was measured from the CT images reconstructed with conventional filtered back projection, adaptive statistical iterative reconstruction, and MBIR algorithms. All the results were compared to the performance of the standard-dose protocol. RESULTS: Mean absorbed organ and effective doses were reduced by approximately 95% with the LD protocol (100-kVp tube voltage and a fixed 10-mA tube current) compared to the standard-dose protocol (120-kVp tube voltage and tube current modulation) while yielding an acceptable image quality for diagnosing round-shaped lung metastases. The effective doses ranged from 0.16 to 2.83 mSv in the studied protocols. The image noise, contrast, and resolution were maintained or improved when comparing the image quality of LD protocols using MBIR to the performance of the standard-dose chest CT protocol using filtered back projection. The small round-shaped lung metastases were delineated at levels comparable to the used protocols. CONCLUSIONS: Radiation exposure in patients can be reduced significantly by using LD chest CT protocols and MBIR algorithm while maintaining image quality for detecting round-shaped lung metastases.


Assuntos
Processamento de Imagem Assistida por Computador/métodos , Neoplasias Pulmonares/diagnóstico por imagem , Tomografia Computadorizada Multidetectores/métodos , Sarcoma/diagnóstico por imagem , Adulto , Algoritmos , Feminino , Humanos , Neoplasias Pulmonares/secundário , Imagens de Fantasmas , Doses de Radiação , Interpretação de Imagem Radiográfica Assistida por Computador , Radiografia Torácica/métodos , Sarcoma/secundário
8.
Acta Radiol ; 60(1): 68-77, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29665709

RESUMO

BACKGROUND: Radiation worker categorization and exposure monitoring practices must be proportional to the current working environment. PURPOSE: To analyze exposure data of Finnish radiological workers and to estimate the magnitude and frequency of their potential occupational radiation exposure, and to propose appropriate radiation worker categorization. MATERIAL AND METHODS: Estimates of the probabilities of annual effective doses exceeding certain levels were obtained by calculating the survival function of a lognormal probability density function (PDF) fitted in the measured occupational exposure data. RESULTS: The estimated probabilities of exceeding annual effective dose limits of 1 mSv, 6 mSv, and 20 mSv were in the order of 1:200, 1:10,000, and 1:500,000 per person, respectively. CONCLUSION: It is very unlikely that the Category B annual effective dose limit of 6 mSv could even potentially be exceeded using modern equipment and appropriate working methods. Therefore, in terms of estimated effective dose, workers in diagnostic and interventional radiology could be placed into Category B in Finland. Current national personal monitoring practice could be replaced or supplemented using active personal dosimeters, which offer more effective means for optimizing working methods.


Assuntos
Pessoal de Saúde/estatística & dados numéricos , Modelos Estatísticos , Exposição Ocupacional/estatística & dados numéricos , Doses de Radiação , Radiologia Intervencionista/estatística & dados numéricos , Sistema de Registros/estatística & dados numéricos , Finlândia , Humanos , Proteção Radiológica
9.
Phys Med ; 56: 90-93, 2018 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30449653

RESUMO

Big data and deep learning will profoundly change various areas of professions and research in the future. This will also happen in medicine and medical imaging in particular. As medical physicists, we should pursue beyond the concept of technical quality to extend our methodology and competence towards measuring and optimising the diagnostic value in terms of how it is connected to care outcome. Functional implementation of such methodology requires data processing utilities starting from data collection and management and culminating in the data analysis methods. Data quality control and validation are prerequisites for the deep learning application in order to provide reliable further analysis, classification, interpretation, probabilistic and predictive modelling from the vast heterogeneous big data. Challenges in practical data analytics relate to both horizontal and longitudinal analysis aspects. Quantitative aspects of data validation, quality control, physically meaningful measures, parameter connections and system modelling for the future artificial intelligence (AI) methods are positioned firmly in the field of Medical Physics profession. It is our interest to ensure that our professional education, continuous training and competence will follow this significant global development.


Assuntos
Big Data , Aprendizado Profundo , Diagnóstico por Imagem/métodos , Física Médica/métodos , Europa (Continente) , Pessoal de Saúde , Humanos , Sociedades Médicas
10.
J Radiol Prot ; 38(3): 967-989, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-29769433

RESUMO

As in any medical intervention, there is either a known or an anticipated benefit to the patient from undergoing a medical imaging procedure. This benefit is generally significant, as demonstrated by the manner in which medical imaging has transformed clinical medicine. At the same time, when it comes to imaging that deploys ionising radiation, there is a potential associated risk from radiation. Radiation risk has been recognised as a key liability in the practice of medical imaging, creating a motivation for radiation dose optimisation. The level of radiation dose and risk in imaging varies but is generally low. Thus, from the epidemiological perspective, this makes the estimation of the precise level of associated risk highly uncertain. However, in spite of the low magnitude and high uncertainty of this risk, its possibility cannot easily be refuted. Therefore, given the moral obligation of healthcare providers, 'first, do no harm,' there is an ethical obligation to mitigate this risk. Precisely how to achieve this goal scientifically and practically within a coherent system has been an open question. To address this need, in 2016, the International Atomic Energy Agency (IAEA) organised a summit to clarify the role of Diagnostic Reference Levels to optimise imaging dose, summarised into an initial report (Järvinen et al 2017 Journal of Medical Imaging 4 031214). Through a consensus building exercise, the summit further concluded that the imaging optimisation goal goes beyond dose alone, and should include image quality as a means to include both the benefit and the safety of the exam. The present, second report details the deliberation of the summit on imaging optimisation.


Assuntos
Diagnóstico por Imagem , Doses de Radiação , Diagnóstico por Imagem/efeitos adversos , Humanos , Agências Internacionais , Guias de Prática Clínica como Assunto , Risco
11.
Radiat Prot Dosimetry ; 174(1): 141-146, 2017 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-27103644

RESUMO

Radiation worker categorization and exposure monitoring are principal functions of occupational radiation safety. The aim of this study was to use the actual occupational exposure data in a large university hospital to estimate the frequency and magnitude of potential exposures in radiology. The additional aim was to propose a revised categorization and exposure monitoring practice based on the potential exposures. The cumulative probability distribution was calculated from the normalized integral of the probability density function fitted to the exposure data. Conformity of the probabilistic model was checked against 16 years of national monitoring data. The estimated probabilities to exceed annual effective dose limits of 1 mSv, 6 mSv and 20 mSv were 1:1000, 1:20 000 and 1:200 000, respectively. Thus, it is very unlikely that the class A categorization limit of 6 mSv could be exceeded, even in interventional procedures, with modern equipment and appropriate working methods. Therefore, all workers in diagnostic and interventional radiology could be systematically categorized into class B. Furthermore, current personal monitoring practice could be replaced by use of active personal dosemeters that offer more effective and flexible means to optimize working methods.


Assuntos
Exposição Ocupacional , Doses de Radiação , Exposição à Radiação , Humanos , Monitoramento de Radiação , Proteção Radiológica , Intensificação de Imagem Radiográfica , Radiologia Intervencionista
12.
Dentomaxillofac Radiol ; 46(2): 20160261, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27786546

RESUMO

OBJECTIVES: This study aimed to determine the optimal post-operative CT imaging method that enables best visualization of facial bony structures in the vicinity of osteosynthesis material. METHODS: Conducted at Töölö Hospital (Helsinki, Finland), this study relied on scanning a phantom with CBCT, 64-slice CT and high-definition multislice CT with dual-energy scan (providing monochromatic images of 70-, 100-, 120- and 140-keV energy levels) and iterative reconstruction (IR) methods. Two radiologists assessed the image quality, and the assessments were analyzed. In addition, a physicist performed a semi-quantitative analysis of the metal-induced artefacts. RESULTS: The three subjects most easily assessed were the loose screw and both the bone structure and the fracture further away from the screw and the plate. Soft tissues adjacent to the screw and the plate remained more difficult for assessment. Both image interpreters agreed that the artefacts disturbed their assessments under dual energy. Metal artefacts disturbed the least under multislice CT with IR [adaptive statistical iterative reconstruction (ASiR) and VEO]. Neither interpreter found metal suppression helpful in CBCT. CONCLUSIONS: CBCT with or without a metal artefact reduction algorithm was not optimal for post-operative facial imaging compared with multislice CT with IR. Multislice CT with ASiR filtering offered good image quality performance with fast image volume reconstruction, representing the current sweet spot in post-operative maxillofacial imaging.


Assuntos
Fixação de Fratura , Fraturas Cranianas/diagnóstico por imagem , Tomografia Computadorizada por Raios X , Artefatos , Placas Ósseas , Parafusos Ósseos , Humanos , Fraturas Cranianas/cirurgia
13.
Radiology ; 280(3): 663-73, 2016 09.
Artigo em Inglês | MEDLINE | ID: mdl-27533027

RESUMO

Rising concerns of radiation exposure from computed tomography have caused various advances in dose reduction technologies. While proper justification and optimization of scans has been the main focus to address increasing doses, the value of dose management has been largely overlooked. The purpose of this article is to explain the importance of dose management, provide an overview of the available options for dose tracking, and discuss the importance of a dedicated dose team. The authors also describe how a digital radiation tracking software can be used for analyzing the big data on doses for auditing patient safety, scanner utilization, and productivity, all of which have enormous personal and institutional implications. (©) RSNA, 2016.


Assuntos
Segurança do Paciente , Doses de Radiação , Proteção Radiológica/métodos , Tomografia Computadorizada por Raios X , Humanos , Modelos Organizacionais , Melhoria de Qualidade , Radiometria
14.
Dentomaxillofac Radiol ; 45(1): 20150095, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-26313308

RESUMO

OBJECTIVES: Dental radiography may involve situations where the patient is known to be pregnant or the pregnancy is noticed after the X-ray procedure. In such cases, the radiation dose to the foetus, though low, needs to be estimated. Uniform and widely used guidance on dental X-ray procedures during pregnancy are presently lacking, the usefulness of lead shields is unclear and practices vary. METHODS: Upper estimates of radiation doses to the foetus and breasts of the pregnant patient were estimated with an anthropomorphic female phantom in intraoral, panoramic, cephalometric and CBCT dental modalities with and without lead shields. RESULTS: The upper estimates of foetal doses varied from 0.009 to 6.9 µGy, and doses at the breast level varied from 0.602 to 75.4 µGy. With lead shields, the foetal doses varied from 0.005 to 2.1 µGy, and breast doses varied from 0.002 to 10.4 µGy. CONCLUSIONS: The foetal dose levels without lead shielding were <1% of the annual dose limit of 1 mSv for a member of the public. Albeit the relative shielding effect, the exposure-induced increase in the risk of breast cancer death for the pregnant patient (based on the breast dose only) and the exposure-induced increase in the risk of childhood cancer death for the unborn child are minimal, and therefore, need for foetal and breast lead shielding was considered irrelevant. Most important is that pregnancy is never a reason to avoid or to postpone a clinically justified dental radiographic examination.


Assuntos
Mama/efeitos da radiação , Feto/efeitos da radiação , Doses de Radiação , Proteção Radiológica/instrumentação , Radiografia Dentária/métodos , Cefalometria/métodos , Tomografia Computadorizada de Feixe Cônico/métodos , Feminino , Humanos , Concentração Máxima Permitida , Imagens de Fantasmas , Gravidez/efeitos da radiação , Radiografia Interproximal/métodos , Radiografia Panorâmica/métodos
15.
Phys Med ; 31(8): 844-860, 2015 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-26481816

RESUMO

For the maxillofacial region, there are various indications that cannot be interpreted from 2D images and will benefit from multiplanar viewing. Dental cone beam CT (CBCT) utilises a cone- or pyramid-shaped X-ray beam using mostly flat-panel detectors for 3D image reconstruction with high spatial resolution. The vast increase in availability and amount of these CBCT devices offers many clinical benefits, and their ongoing development has potential to bring various new clinical applications for medical imaging. Additionally, there is also a need for high quality research and education. European guidelines promote the use of a medical physics expert for advice on radiation protection, patient dose optimisation, and equipment testing. In this review article, we perform a comparison of technical equipment based on manufacturer data, including scanner specific X-ray spectra, and describe issues concerning CBCT image reconstruction and image quality, and also address radiation dose issues, dosimetry, and optimisation. We also discuss clinical needs and what type of education users should have in order to operate CBCT systems safely. We will also take a look into the future and discuss the issues that still need to be solved.


Assuntos
Tomografia Computadorizada de Feixe Cônico/métodos , Odontologia/métodos , Tomografia Computadorizada de Feixe Cônico/instrumentação , Humanos , Guias de Prática Clínica como Assunto , Radiometria
16.
Duodecim ; 131(1): 42-8, 2015.
Artigo em Finlandês | MEDLINE | ID: mdl-26245054

RESUMO

The same CT imaging program should not be applied to all patients, because the required image quality and dose of radiation vary according to the indications and regions. The programs should be optimized on the basis of indication, size of the patient and usage of intravenously administered iodine contrast agent. New technical options are available for reducing the radiation exposure. Additional means of optimization include proper definition of the region being imaged, avoidance of redundant series of images, selection of correct image quality, tube current and voltage, and new methods of calculating images. Patients' radiation exposure and clinical image quality should also be monitored.


Assuntos
Seleção de Pacientes , Tomografia Computadorizada por Raios X/métodos , Meios de Contraste , Humanos , Doses de Radiação , Proteção Radiológica , Radiometria
17.
J Appl Clin Med Phys ; 16(4): 266­278, 2015 07 08.
Artigo em Inglês | MEDLINE | ID: mdl-26219008

RESUMO

The aims of this study were to characterize reinforced metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters to assess the measurement uncertainty, single exposure low-dose limit with acceptable accuracy, and the number of exposures required to attain the corresponding limit of the thermoluminescent dosimeters (TLD). The second aim was to characterize MOSFET dosimeter sensitivities for two dental photon energy ranges, dose dependency, dose rate dependency, and accumulated dose dependency. A further aim was to compare the performance of MOSFETs with those of TLDs in an anthropomorphic phantom head using a dentomaxillofacial CBCT device. The uncertainty was assessed by exposing 20 MOSFETs and a Barracuda MPD reference dosimeter. The MOSFET dosimeter sensitivities were evaluated for two photon energy ranges (50-90 kVp) using a constant dose and polymethylmethacrylate backscatter material. MOSFET and TLD comparative point-dose measurements were performed on an anthropomorphic phantom that was exposed with a clinical CBCT protocol. The MOSFET single exposure low dose limit (25% uncertainty, k = 2) was 1.69 mGy. An averaging of eight MOSFET exposures was required to attain the corresponding TLD (0.3 mGy) low-dose limit. The sensitivity was 3.09 ± 0.13 mV/mGy independently of the photon energy used. The MOSFET dosimeters did not present dose or dose rate sensitivity but, however, presented a 1% decrease of sensitivity per 1000 mV for accumulated threshold voltages between 8300 mV and 17500 mV. The point doses in an anthropomorphic phantom ranged for MOSFETs between 0.24 mGy and 2.29 mGy and for TLDs between 0.25 and 2.09 mGy, respectively. The mean difference was -8%. The MOSFET dosimeters presented statistically insignificant energy dependency. By averaging multiple exposures, the MOSFET dosimeters can achieve a TLD-comparable low-dose limit and constitute a feasible method for diagnostic dosimetry using anthropomorphic phantoms. However, for single in vivo measurements (<1.7 mGy) the sensitivity is too low.


Assuntos
Antropometria , Anormalidades Maxilofaciais/radioterapia , Imagens de Fantasmas , Fótons , Semicondutores , Dosimetria Termoluminescente/instrumentação , Dosimetria Termoluminescente/métodos , Cabeça/diagnóstico por imagem , Humanos , Doses de Radiação , Radiografia , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador/métodos , Radioterapia de Intensidade Modulada/métodos
18.
Pediatr Radiol ; 45(10): 1544-53, 2015 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-25939873

RESUMO

BACKGROUND: Medical professionals need to exercise particular caution when developing CT scanning protocols for children who require multiple CT studies, such as those with craniosynostosis. OBJECTIVE: To evaluate the utility of ultra-low-dose CT protocols with model-based iterative reconstruction techniques for craniosynostosis imaging. MATERIALS AND METHODS: We scanned two pediatric anthropomorphic phantoms with a 64-slice CT scanner using different low-dose protocols for craniosynostosis. We measured organ doses in the head region with metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters. Numerical simulations served to estimate organ and effective doses. We objectively and subjectively evaluated the quality of images produced by adaptive statistical iterative reconstruction (ASiR) 30%, ASiR 50% and Veo (all by GE Healthcare, Waukesha, WI). Image noise and contrast were determined for different tissues. RESULTS: Mean organ dose with the newborn phantom was decreased up to 83% compared to the routine protocol when using ultra-low-dose scanning settings. Similarly, for the 5-year phantom the greatest radiation dose reduction was 88%. The numerical simulations supported the findings with MOSFET measurements. The image quality remained adequate with Veo reconstruction, even at the lowest dose level. CONCLUSION: Craniosynostosis CT with model-based iterative reconstruction could be performed with a 20-µSv effective dose, corresponding to the radiation exposure of plain skull radiography, without compromising required image quality.


Assuntos
Craniossinostoses/diagnóstico por imagem , Imagens de Fantasmas , Doses de Radiação , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Tomografia Computadorizada por Raios X/métodos , Artefatos , Pré-Escolar , Humanos , Recém-Nascido , Razão Sinal-Ruído
19.
Radiat Prot Dosimetry ; 165(1-4): 226-30, 2015 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-25836690

RESUMO

The connection between recorded volumetric CT dose index (CTDI vol) and determined mean fetal dose (Df) was examined from metal-oxide-semiconductor field-effect transistor dose measurements on an anthropomorphic female phantom in four stages of pregnancy in a 64-slice CT scanner. Automated tube current modulation kept the mean Df fairly constant through all pregnancy stages in trauma (4.4-4.9 mGy) and abdomino-pelvic (2.1-2.4 mGy) protocols. In pulmonary angiography protocol, the mean Df increased exponentially as the distance from the end of the scan range decreased (0.01-0.09 mGy). For trauma protocol, the relative mean Df as a function of gestational age were in the range 0.80-0.97 compared with the mean CTDI vol. For abdomino-pelvic protocol, the relative mean Df was 0.57-0.79 and for pulmonary angiography protocol, 0.01-0.05 compared with the mean CTDI vol, respectively. In conclusion, if the fetus is in the primary beam, the CTDI vol can be used as an upper estimate of the fetal dose. If the fetus is not in the primary beam, the fetal dose can be estimated by considering also the distance of the fetus from the scan range.


Assuntos
Feto/diagnóstico por imagem , Exposição Materna , Doses de Radiação , Tomografia Computadorizada por Raios X/efeitos adversos , Angiografia/efeitos adversos , Antropometria , Calibragem , Simulação por Computador , Feminino , Idade Gestacional , Humanos , Pulmão/diagnóstico por imagem , Metais/química , Método de Monte Carlo , Óxidos/química , Imagens de Fantasmas , Gravidez , Exposição à Radiação , Semicondutores , Tomógrafos Computadorizados
20.
AJR Am J Roentgenol ; 204(1): 117-23, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25539246

RESUMO

OBJECTIVE: The purpose of this study was to study different optimization methods for reducing eye lens dose in head CT. MATERIALS AND METHODS: Two anthropomorphic phantoms were scanned with a routine head CT protocol for evaluation of the brain that included bismuth shielding, gantry tilting, organ-based tube current modulation, or combinations of these techniques. Highsensitivity metal oxide semiconductor field effect transistor dosimeters were used to measure local equivalent doses in the head region. The relative changes in image noise and contrast were determined by ROI analysis. RESULTS: The mean absorbed lens doses varied from 4.9 to 19.7 mGy and from 10.8 to 16.9 mGy in the two phantoms. The most efficient method for reducing lens dose was gantry tilting, which left the lenses outside the primary radiation beam, resulting in an approximately 75% decrease in lens dose. Image noise decreased, especially in the anterior part of the brain. The use of organ-based tube current modulation resulted in an approximately 30% decrease in lens dose. However, image noise increased as much as 30% in the posterior and central parts of the brain. With bismuth shields, it was possible to reduce lens dose as much as 25%. CONCLUSION: Our results indicate that gantry tilt, when possible, is an effective method for reducing exposure of the eye lenses in CT of the brain without compromising image quality. Measurements in two different phantoms showed how patient geometry affects the optimization. When lenses can only partially be cropped outside the primary beam, organ-based tube current modulation or bismuth shields can be useful in lens dose reduction.


Assuntos
Absorção de Radiação , Cabeça/diagnóstico por imagem , Cristalino/efeitos da radiação , Doses de Radiação , Proteção Radiológica/métodos , Intensificação de Imagem Radiográfica/métodos , Tomografia Computadorizada por Raios X/métodos , Testes Diagnósticos de Rotina , Humanos , Imagens de Fantasmas , Intensificação de Imagem Radiográfica/instrumentação , Radiometria , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Tomografia Computadorizada por Raios X/instrumentação
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