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BACKGROUND: Computed tomography (CT) scans are routinely performed in positron emission tomography (PET) and single photon emission computed tomography (SPECT) examinations globally, yet few surveys have been conducted to gather national diagnostic reference level (NDRL) data for CT radiation doses in positron emission tomography/computed tomography (PET/CT) and single photon emission computed tomography/computed tomography (SPECT/CT). In this first Nordic-wide study of CT doses in hybrid imaging, Nordic NDRL CT doses are suggested for PET/CT and SPECT/CT examinations specific to the clinical purpose of CT, and the scope for optimisation is evaluated. Data on hybrid imaging CT exposures and clinical purpose of CT were gathered for 5 PET/CT and 8 SPECT/CT examinations via designed booklet. For each included dataset for a given facility and scanner type, the computed tomography dose index by volume (CTDIvol) and dose length product (DLP) was interpolated for a 75-kg person (referred to as CTDIvol,75kg and DLP75kg). Suggested NDRL (75th percentile) and achievable doses (50th percentile) were determined for CTDIvol,75kg and DLP75kg according to clinical purpose of CT. Differences in maximum and minimum doses (derived for a 75-kg patient) between facilities were also calculated for each examination and clinical purpose. RESULTS: Data were processed from 83 scanners from 43 facilities. Data were sufficient to suggest Nordic NDRL CT doses for the following: PET/CT oncology (localisation/characterisation, 15 systems); infection/inflammation (localisation/characterisation, 13 systems); brain (attenuation correction (AC) only, 11 systems); cardiac PET/CT and SPECT/CT (AC only, 30 systems); SPECT/CT lung (localisation/characterisation, 12 systems); bone (localisation/characterisation, 30 systems); and parathyroid (localisation/characterisation, 13 systems). Great variations in dose were seen for all aforementioned examinations. Greatest differences in DLP75kg for each examination, specific to clinical purpose, were as follows: SPECT/CT lung AC only (27.4); PET/CT and SPECT/CT cardiac AC only (19.6); infection/inflammation AC only (18.1); PET/CT brain localisation/characterisation (16.8); SPECT/CT bone localisation/characterisation (10.0); PET/CT oncology AC only (9.0); and SPECT/CT parathyroid localisation/characterisation (7.8). CONCLUSIONS: Suggested Nordic NDRL CT doses are presented according to clinical purpose of CT for PET/CT oncology, infection/inflammation, brain, PET/CT and SPECT/CT cardiac, and SPECT/CT lung, bone, and parathyroid. The large variation in doses suggests great scope for optimisation in all 8 examinations.
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BACKGROUND: Follow-up with computed tomographic angiography is recommended after endovascular aneurysm repair, exposing patients to significant levels of radiation and iodine contrast medium. Dual-energy computed tomography allows virtual noncontrast (VNC) images to be reconstructed from contrast-enhanced images using a software algorithm. If the VNC images are a good-enough approximation of true noncontrast (TNC) images, a reduction in radiation dose can be ensured through omitting a TNC scan. PURPOSE: To compare image quality of VNC images reconstructed from arterial phase and venous phase dual-energy computed tomographic angiography to TNC images and to assess which one is more suitable to replace TNC images. METHODS: Sixty-three consecutive patients were examined using a dual-energy computed tomography as elective follow-up after endovascular aneurysm repair. The examination protocol included 1 unenhanced and 2 contrast-enhanced scans (80 kV/Sn140 kV) of the aorta. Virtual noncontrast data sets were reconstructed from the arterial (A-VNC) and venous (V-VNC) phase scans, respectively. Mean attenuation and image noise were measured for TNC, A-VNC, and V-VNC images within regions of interest at 2 levels in the aorta, the liver, retroperitoneal fat, and psoas muscle. Subjective image quality was assessed on a 4-point scale by 2 blinded readers. RESULTS: The differences between A-VNC and TNC, and between A-VNC and V-VNC, were substantial aorta at the level of diaphragm and aorta at the level of renal arteries. The difference between V-VNC and TNC was, on the other hand, very small and not statistically significant for the renal artery aorta. For liver, fat, and muscle tissue, there were significant differences between both A-VNC and V-VNC compared with TNC, but findings were similar between A-VNC and V-VNC. CONCLUSIONS: Virtual noncontrast images based on venous-phase scans appear to be a more accurate representation of TNC scans than VNC images based on arterial-phase scans.
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Aneurisma Aórtico/diagnóstico por imagem , Angiografia por Tomografia Computadorizada/métodos , Imagem Radiográfica a Partir de Emissão de Duplo Fóton/métodos , Idoso , Algoritmos , Aneurisma Aórtico/cirurgia , Meios de Contraste , Procedimentos Endovasculares , Feminino , Humanos , Iohexol , Masculino , Estudos Prospectivos , Interpretação de Imagem Radiográfica Assistida por ComputadorRESUMO
OBJECTIVE: Previous studies have shown the possibility to reduce radiation dose in abdominal CT by 25-50% without negatively affecting detection of liver lesions. How radiation dose reduction affects characterization of liver metastases is not as well known. The objective of this study was to investigate how different levels of simulated dose reduction affect the detection and characterization of liver lesions, primarily hypovascular metastases. A secondary objective was to analyze the relationship between the lesion size and contrast-to-noise ratio (CNR) and the detection rate. MATERIALS AND METHODS: Thirty-nine patients (19 with metastases and 20 without) were retrospectively selected. The following radiation dose levels (DLs) were simulated: 100% (reference level), 75%, 50%, and 25%. Five readers were asked to mark liver lesions and rate the probability of malignancy on a 5-grade Likert scale. Noninferiority analysis using the jackknife free-response ROC (JAFROC) method was performed as well as direct comparison of detection rates and grades. RESULTS: JAFROC analysis showed noninferior detection and characterization of metastases at DL75 as compared with DL100. However, the number of benign lesions and false-positive localizations rated as "suspected malignancy" was significantly higher at DL75. CONCLUSION: Radiation dose can be reduced by 25% without negatively affecting diagnosis of hypovascular liver metastases. Characterization of benign lesions, however, is impaired at DL75, which may lead to unnecessary follow-up examinations. Finally, increased image noise seems to affect the detection of small lesions to a degree that cannot be explained solely by the reduction in CNR.
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Neoplasias Hepáticas/diagnóstico por imagem , Doses de Radiação , Radiografia Abdominal/métodos , Tomografia Computadorizada por Raios X/métodos , Idoso , Meios de Contraste , Feminino , Humanos , Neoplasias Hepáticas/secundário , Masculino , Pessoa de Meia-Idade , Gradação de Tumores , Imagens de Fantasmas , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Padrões de Referência , Reprodutibilidade dos Testes , Estudos RetrospectivosRESUMO
Background In pediatric patients, computed tomography (CT) is important in the medical chain of diagnosing and monitoring various diseases. Because children are more radiosensitive than adults, they require minimal radiation exposure. One way to achieve this goal is to implement new technical solutions, like iterative reconstruction. Purpose To evaluate the potential of a new, iterative, model-based method for reconstructing (IMR) pediatric abdominal CT at a low radiation dose and determine whether it maintains or improves image quality, compared to the current reconstruction method. Material and Methods Forty pediatric patients underwent abdominal CT. Twenty patients were examined with the standard dose settings and 20 patients were examined with a 32% lower radiation dose. Images from the standard examination were reconstructed with a hybrid iterative reconstruction method (iDose4), and images from the low-dose examinations were reconstructed with both iDose4 and IMR. Image quality was evaluated subjectively by three observers, according to modified EU image quality criteria, and evaluated objectively based on the noise observed in liver images. Results Visual grading characteristics analyses showed no difference in image quality between the standard dose examination reconstructed with iDose4 and the low dose examination reconstructed with IMR. IMR showed lower image noise in the liver compared to iDose4 images. Inter- and intra-observer variance was low: the intraclass coefficient was 0.66 (95% confidence interval = 0.60-0.71) for the three observers. Conclusion IMR provided image quality equivalent or superior to the standard iDose4 method for evaluating pediatric abdominal CT, even with a 32% dose reduction.
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Abdome/diagnóstico por imagem , Processamento de Imagem Assistida por Computador , Tomografia Computadorizada por Raios X , Adolescente , Criança , Pré-Escolar , Humanos , Lactente , Doses de Radiação , Tomografia Computadorizada por Raios X/métodosRESUMO
Background Dual-energy computed tomography (DECT) has conceptually been known since the late 1970s and commercially available as dual-source CT (DSCT) systems since 2006; however, the technique has not yet seen widespread implementation in routine protocols. Part of the cause for this is likely due to misconceptions about radiation dose and/or image quality when using DECT. Purpose To compare image quality and radiation dose of single-energy CT (SECT) and DECT abdominal examinations obtained in clinical practice on a second generation DSCT. Material and Methods A total of 495 included patients (mean age = 70.9 years) were retrospectively analyzed after undergoing either SECT (120 kVp and age-based mAs) or DECT examinations (80/Sn140 kVp and age-based mAs). The patients were divided into two groups based on examination type (247 SECT, 248 DECT), which were then subdivided into two groups, each based on age. Image noise was measured in the liver and image quality was subjectively assessed in 100 randomly selected patients. Results Noise levels were significantly lower in DECT (13.9 HU) compared with SECT (14.7 HU) ( P < 0.05). No significant differences in subjective image quality were found between DECT and SECT, except for one criterion in the 50-74-year age group. The mean dose-length product (DLP) (376 mGy-cm) and effective dose (6.1 mSv) of DECT were significantly lower than the DLP (513 mGy-cm) and effective dose (8.4 mSv) of SECT ( P < 0.05). Conclusion DECT can be implemented in routine clinical use without negatively impacting image quality while lowering radiation dose to the patient.
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Doses de Radiação , Radiografia Abdominal/métodos , Tomografia Computadorizada por Raios X/métodos , Idoso , Meios de Contraste , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Intensificação de Imagem Radiográfica/métodos , Imagem Radiográfica a Partir de Emissão de Duplo Fóton/métodos , Estudos RetrospectivosRESUMO
BACKGROUND: The number of computed tomography (CT) examinations is increasing and leading to an increase in total patient exposure. It is therefore important to optimize CT scan imaging conditions in order to reduce the radiation dose. The introduction of iterative reconstruction methods has enabled an improvement in image quality and a reduction in radiation dose. PURPOSE: To investigate how image quality depends on reconstruction method and to discuss patient dose reduction resulting from the use of hybrid and model-based iterative reconstruction. MATERIAL AND METHODS: An image quality phantom (Catphan® 600) and an anthropomorphic torso phantom were examined on a Philips Brilliance iCT. The image quality was evaluated in terms of CT numbers, noise, noise power spectra (NPS), contrast-to-noise ratio (CNR), low-contrast resolution, and spatial resolution for different scan parameters and dose levels. The images were reconstructed using filtered back projection (FBP) and different settings of hybrid (iDose4) and model-based (IMR) iterative reconstruction methods. RESULTS: iDose4 decreased the noise by 15-45% compared with FBP depending on the level of iDose4. The IMR reduced the noise even further, by 60-75% compared to FBP. The results are independent of dose. The NPS showed changes in the noise distribution for different reconstruction methods. The low-contrast resolution and CNR were improved with iDose4, and the improvement was even greater with IMR. CONCLUSION: There is great potential to reduce noise and thereby improve image quality by using hybrid or, in particular, model-based iterative reconstruction methods, or to lower radiation dose and maintain image quality.
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Algoritmos , Exposição à Radiação/análise , Exposição à Radiação/prevenção & controle , Proteção Radiológica/métodos , Intensificação de Imagem Radiográfica/métodos , Tomografia Computadorizada por Raios X/métodos , Humanos , Imagens de Fantasmas , Doses de Radiação , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Tomografia Computadorizada por Raios X/instrumentação , Tronco/diagnóstico por imagemRESUMO
BACKGROUND: Follow-up of endovascular aneurysm repair (EVAR) with life-long computed tomography angiography (CTA) surveillance exposes patients with impaired renal function to repeated risks of contrast medium-induced nephropathy (CIN). PURPOSE: To retrospectively compare vascular attenuation, image noise, contrast-to-noise ratio (CNR), subjective image quality and effective radiation dose (mSv) for CTA with a 16-multirow detector CT (MDCT) equipment at 80 kVp after EVAR using a contrast medium (CM) dose that is half of that used at 120 kVp. MATERIAL AND METHODS: Forty patients with estimated glomerular filtration rate (eGFR) <45 mL/min underwent 80-kVp CTA with 160 mg I/kg, and 40 patients with eGFR ≥45 mL/min 120-kVp CTA with 320 mg I/kg (maximum dose weight, 80 kg). Arterial phase analysis included vascular attenuation, image noise and CNR, and calculated effective dose. Subjective image quality was assessed on a 4-point scale by two blinded readers at three different levels as well as overall. RESULTS: Median values in the 80/120 kVp cohorts were: age, 74-75 years; body weight, 77/80 kg; BMI 24/27 kg/m(2); CM dose, 13/25 gram-iodine; gram-iodine/GFR ratio, 0.35/0.38; mean aortic attenuation, 313/326 HU; image noise, 26/32 HU; CNR 10-11; subjective image quality score, 3.0-3.5 (Reader 1) and 3.0-3.3 (Reader 2); number of non-diagnostic examinations, 0/1; and effective dose, 4.5/5.1 mSv. There was no statistically significant difference in aortic CNR and effective dose between the 80 and 120 kVp cohorts. CONCLUSION: 80 kVp 16-MDCT with halved CM dose tailored to body weight for CTA follow-up of EVAR may provide satisfactory diagnostic results compared to common standards and be beneficial for patients at risk of CIN, though the present CT equipment may limit the use of the method to patients below 90 kg or with a BMI below 35 kg/m(2).
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Aneurisma/diagnóstico por imagem , Meios de Contraste , Procedimentos Endovasculares , Complicações Pós-Operatórias/diagnóstico por imagem , Intensificação de Imagem Radiográfica , Tomografia Computadorizada por Raios X , Idoso , Idoso de 80 Anos ou mais , Aneurisma/cirurgia , Feminino , Seguimentos , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Estudos RetrospectivosRESUMO
Today, computed tomography (CT) systems routinely use automatic exposure control (AEC), which modulates the tube current. However, for optimal use, there are several aspects of an AEC system that need to be considered. The purpose of this study was to provide an overview of the Siemens CARE Dose 4D AEC system, discuss practical tips and demonstrate potential pitfalls. Two adult anthropomorphic phantoms were examined using two different Siemens CT systems. When optimising the CT radiation dose and image quality, the projection angle of the localiser, patient centring, protocol selection, scanning direction and the use of protective devices requires special attention.
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Imageamento Tridimensional/instrumentação , Exposição à Radiação/análise , Exposição à Radiação/prevenção & controle , Monitoramento de Radiação/instrumentação , Proteção Radiológica/instrumentação , Tomografia Computadorizada por Raios X/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Retroalimentação , Humanos , Imagens de Fantasmas , Proteção Radiológica/métodos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
Computed tomography (CT) is one of the most important modalities in a radiological department. This technique not only produces images that enable radiological reports with high diagnostic confidence, but it may also provide an elevated radiation dose to the patient. The radiation dose can be reduced by using advanced image reconstruction algorithms. This study was performed on a Brilliance iCT, equipped with iDose(4) iterative reconstruction and an iterative model-based reconstruction (IMR) method. The purpose was to investigate the effect of reduced slice thickness combined with an IMR method on image quality compared with standard slice thickness with iDose(4) reconstruction. The results of objective and subjective image quality evaluations showed that a thinner slice combined with IMR can improve the image quality and reduce partial volume artefacts compared with the standard slice thickness with iDose(4) In conclusion, IMR enables reduction of the slice thickness while maintaining or even improving image quality versus iDose(4).
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Modelos Estatísticos , Exposição à Radiação/prevenção & controle , Proteção Radiológica/métodos , Intensificação de Imagem Radiográfica/métodos , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Tomografia Computadorizada por Raios X/métodos , Simulação por Computador , Interpretação Estatística de Dados , Variações Dependentes do Observador , Imagens de Fantasmas , Doses de Radiação , Exposição à Radiação/análise , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Razão Sinal-Ruído , Tomografia Computadorizada por Raios X/instrumentaçãoRESUMO
OBJECTIVE: The purpose of this study was to evaluate an abdominal CT protocol in which radiation dose was reduced and i.v. contrast dose increased for young patients and radiation dose was increased and i.v. medium dose decreased for elderly patients. The hypothesis was that these adjustments would result in constant image quality and a reduction in age-specific risk. MATERIALS AND METHODS: Patients were divided into four age groups of 25 patients each: group 1, 16-25 years; group 2, 26-50 years; group 3, 51-75 years; and group 4, older than 75 years. The quality reference tube load ranged from 100 to 300 mAs, and the i.v. contrast dose ranged from 600 to 350 mg I/kg. Group 3 was the reference group. Signal-to-noise and contrast-to-noise ratios for a hypothetical hypovascular liver metastatic lesion were calculated. Subjective image quality was evaluated by visual grading characteristic analysis in which four readers assessed the reproduction of seven image-quality criteria. RESULTS: Radiation dose was reduced 57% in the youngest group, and the i.v. contrast dose was reduced 18% in elderly patients. There were no statistically significant differences between the groups with respect to signal-to-noise and contrast-to-noise ratios. Subjective image quality was graded significantly lower for four criteria in group 1 compared with group 3. No significant difference was found in comparisons of groups 2 (except for one criterion) and 4 with group 3. CONCLUSION: It is possible to balance radiation dose and contrast dose against each other and maintain signal-to-noise and contrast-to-noise ratios. Subjective image quality was affected by increased noise level on the images but was judged acceptable in all groups except the one with the lowest radiation dose.
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Doses de Radiação , Radiografia Abdominal/métodos , Tomografia Computadorizada por Raios X/métodos , Adolescente , Adulto , Fatores Etários , Idoso , Meios de Contraste/administração & dosagem , Feminino , Humanos , Injeções Intravenosas , Masculino , Pessoa de Meia-Idade , Modelos Teóricos , Interpretação de Imagem Radiográfica Assistida por Computador , Estudos Retrospectivos , Razão Sinal-RuídoRESUMO
UNLABELLED: PET with (18)F-choline ((18)F-FCH) is used in the diagnosis of prostate cancer and its recurrences. In this work, biodistribution data from a recent study conducted at Skåne University Hospital Malmö were used for the development of a biokinetic and dosimetric model. METHODS: The biodistribution of (18)F-FCH was followed for 10 patients using PET up to 4 h after administration. Activity concentrations in blood and urine samples were also determined. A compartmental model structure was developed, and values of the model parameters were obtained for each single patient and for a reference patient using a population kinetic approach. Radiation doses to the organs were determined using computational (voxel) phantoms for the determination of the S factors. RESULTS: The model structure consists of a central exchange compartment (blood), 2 compartments each for the liver and kidneys, 1 for spleen, 1 for urinary bladder, and 1 generic compartment accounting for the remaining material. The model can successfully describe the individual patients' data. The parameters showing the greatest interindividual variations are the blood volume (the clearance process is rapid, and early blood data are not available for several patients) and the transfer out from liver (the physical half-life of (18)F is too short to follow this long-term process with the necessary accuracy). The organs receiving the highest doses are the kidneys (reference patient, 0.079 mGy/MBq; individual values, 0.033-0.105 mGy/MBq) and the liver (reference patient, 0.062 mGy/MBq; individual values, 0.036-0.082 mGy/MBq). The dose to the urinary bladder wall of the reference patient varies between 0.017 and 0.030 mGy/MBq, depending on the assumptions on bladder voiding. CONCLUSION: The model gives a satisfactory description of the biodistribution of (18)F-FCH and realistic estimates of the radiation dose received by the patients.
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Colina/farmacocinética , Radioisótopos de Flúor , Neoplasias da Próstata/diagnóstico por imagem , Idoso , Humanos , Cinética , Masculino , Pessoa de Meia-Idade , Modelos Biológicos , Neoplasias da Próstata/metabolismo , Radiometria , Cintilografia , Distribuição Tecidual , Bexiga Urinária/efeitos da radiaçãoRESUMO
STUDY DESIGN: Retrospective study. OBJECTIVES: To optimize the radiation doses and image quality for the cone-beam O-arm surgical imaging system in spinal surgery. SUMMARY OF BACKGROUND: Neurovascular compromise has been reported after screw misplacement during thoracic pedicle screw insertion. The use of O-arm with or without navigation system during spinal surgery has been shown to lower the rate of screw misplacement. The main drawback of such imaging surgical systems is the high radiation exposure. METHODS: Chest phantom and cadaveric pig spine were examined on the O-arm with different scan settings: 2 were recommended by the O-arm manufacturer (120 kV/320 mAs, and 120 kV/128 mAs), and 3 low-dose settings (80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs). The radiation doses were estimated by Monte Carlo calculations. Objective evaluation of image quality included interobserver agreement in the measurement of pedicular width in chest phantom and assessment of screw placement in cadaveric pig spine. RESULTS: The effective dose/cm for 120 kV/320 mAs scan was 13, 26, and 69 times higher than those delivered with 80 kV/80 mAs, 80 kV/40 mAs, and 60 kV/40 mAs scans, respectively. Images with 60 kV/40 mAs were unreliable. Images with 80 kV/80 mAs were considered reliable with good interobserver agreement when measuring the pedicular width (random error 0.38 mm and intraclass correlation coefficient 0.979) and almost perfect agreement when evaluating the screw placement (κ value 0.86). CONCLUSIONS: The radiation doses of the O-arm system can be reduced 5 to 13 times without negative impact on image quality with regard to information required for spinal surgery.
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Parafusos Ósseos , Tomografia Computadorizada de Feixe Cônico/métodos , Monitorização Intraoperatória/métodos , Imagens de Fantasmas , Doses de Radiação , Adulto , Animais , Parafusos Ósseos/normas , Humanos , Imagens de Fantasmas/normas , Estudos Retrospectivos , Coluna Vertebral/diagnóstico por imagem , Coluna Vertebral/cirurgia , SuínosRESUMO
New imaging technologies utilising X rays and radiopharmaceuticals are continuously under development. The benefit of computed tomography (CT) has been so dramatic that there is a tendency to overuse it and not to place enough efforts into optimisation of the technique. It is also now more and more common to combine two imaging techniques into a single investigation, such as PET/CT and SPECT/CT--the so-called 'hybrid imaging'. The increasing radiation exposure from CT has been of concern for some years and is now receiving increased attention from health professionals, authorities, manufacturers and patient groups. The relatively high radiation doses from PET and SPECT investigations have only recently been discussed. The aim of this article is to provide information on developing technologies and clinical techniques for 3D imaging using ionising radiation and their associated radiation dose to patients and staff. Tools for improved dose management are also discussed.
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Tomografia por Emissão de Pósitrons , Doses de Radiação , Lesões por Radiação/diagnóstico , Lesões por Radiação/prevenção & controle , Tomografia Computadorizada de Emissão de Fóton Único , Tomografia Computadorizada por Raios X , Fluordesoxiglucose F18 , Humanos , Compostos RadiofarmacêuticosRESUMO
The purpose of this study was to evaluate the effect of different choices of adaptation strengths on image quality and radiation exposure to the patient with Siemens automatic exposure control system called CARE Dose 4D. An anthropomorphic chest phantom was used to simulate the patient and computed tomography scans were performed with a Siemens SOMATOM Sensation 16 and 64. Owing to adaptation strengths, a considerable reduction (26.6-51.5 % and 27.5-49.5 % for Sensation 16 and Sensation 64, respectively) in the radiation dose was found when compared with using a fixed tube current. There was a substantial difference in the image quality (image noise) between the adaptation strengths. Independent of selected adaptation strengths, the level of image noise throughout the chest phantom increased when CARE Dose 4D was used (p < 0.0001). We conclude that the adaptation strengths can be used to obtain user-specified modifications to image quality or radiation exposure to the patient.