RESUMO
Multi-post-labeling-delay pseudo-continuous arterial spin labeling (multi-PLD PCASL) allows for absolute quantification of the cerebral blood flow (CBF) as well as the arterial transit time (ATT). Estimating these perfusion parameters from multi-PLD PCASL data is a non-linear inverse problem, which is commonly tackled by fitting the single-compartment model (SCM) for PCASL, with CBF and ATT as free parameters. The longitudinal relaxation time of tissue T1t is an important parameter in this model, as it governs the decay of the perfusion signal entirely upon entry in the imaging voxel. Conventionally, T1t is fixed to a population average. This approach can cause CBF quantification errors, as T1t can vary significantly inter- and intra-subject. This study compares the impact on CBF quantification, in terms of accuracy and precision, of either fixing T1t , the conventional approach, or estimating it alongside CBF and ATT. It is shown that the conventional approach can cause a significant bias in CBF. Indeed, simulation experiments reveal that if T1t is fixed to a value that is 10% off its true value, this may already result in a bias of 15% in CBF. On the other hand, as is shown by both simulation and real data experiments, estimating T1t along with CBF and ATT results in a loss of CBF precision of the same order, even if the experiment design is optimized for the latter estimation problem. Simulation experiments suggest that an optimal balance between accuracy and precision of CBF estimation from multi-PLD PCASL data can be expected when using the two-parameter estimator with a fixed T1t value between population averages of T1t and the longitudinal relaxation time of blood T1b .
Assuntos
Artérias/fisiologia , Circulação Cerebrovascular/fisiologia , Marcadores de Spin , Adulto , Simulação por Computador , Feminino , Substância Cinzenta/irrigação sanguínea , Substância Cinzenta/diagnóstico por imagem , Humanos , Imageamento por Ressonância Magnética , Masculino , Projetos de Pesquisa , Razão Sinal-Ruído , Adulto JovemRESUMO
Bone age is an essential measure of skeletal maturity in children with growth disorders. It is typically assessed by a trained physician using radiographs of the hand and a reference model. However, it has been described that the reference models leave room for interpretation leading to a large inter-observer and intra-observer variation. In this work, we explore a novel method for automated bone age assessment to assist physicians with their estimation. It consists of a powerful combination of deep learning and Gaussian process regression. Using this combination, sensitivity of the deep learning model to rotations and flips of the input images can be exploited to increase overall predictive performance compared to only using the deep learning network. We validate our approach retrospectively on a set of 12611 radiographs of patients between 0 and 19 years of age.
Assuntos
Determinação da Idade pelo Esqueleto , Aprendizado Profundo , Ossos da Mão/diagnóstico por imagem , Interpretação de Imagem Assistida por Computador , Adolescente , Criança , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Distribuição Normal , Variações Dependentes do Observador , Radiografia , Estudos Retrospectivos , Adulto JovemRESUMO
Purpose To assess the potential dose reduction to the thyroid and breasts in chest computed tomography (CT) with organ-based tube current modulation (OBTCM). Materials and Methods In this retrospective study (from January 2015 to December 2016), the location of the breasts with respect to the reduced tube current zone was determined. With Monte Carlo simulations, patient-specific dose distributions of chest CT scans were calculated for 50 female patients (mean age, 53.7 years ± 17.5; range, 20-80 years). The potential dose reduction with OBTCM was assessed. In addition, simulations of clinical OBTCM scans were made for 17 of the 50 female patients (mean age, 43.8 years ± 17.1; range, 20-69 years). Posterior organs in the field of view were analyzed and lifetime attributable risk (LAR) of cancer incidence and mortality was estimated. Image quality between standard CT and OBTCM scans was compared. Results No women had all breast tissue within the reduced tube current zone. Dose reductions of 18% in the thyroid and 9% in the breasts were observed, whereas the doses in lung, liver, and kidney were 17%, 11%, and 26% higher. Overall, the LAR for cancer incidence was not significantly different between conventional and OBTCM scanning (P = .06). Image quality improved with OBTCM (P < .002). Conclusion The potential benefit of OBTCM to the female breast in chest CT is overestimated because of a limited reduced tube current zone; despite a 9% dose reduction to the female breast, posterior organs will absorb up to 26% more radiation, resulting in no reduction in radiation-induced malignancies. © RSNA, 2018.
Assuntos
Mama/diagnóstico por imagem , Doses de Radiação , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Radiografia Torácica/métodos , Glândula Tireoide/diagnóstico por imagem , Tomografia Computadorizada por Raios X/métodos , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Pessoa de Meia-Idade , Método de Monte Carlo , Estudos Retrospectivos , Risco , Adulto JovemRESUMO
PURPOSE: The evaluation of clinical image quality (IQ) is important to optimize CT protocols and to keep patient doses as low as reasonably achievable. Considering the significant amount of effort needed for human observer studies, automatic IQ tools are a promising alternative. The purpose of this study was to evaluate automatic IQ assessment in chest CT using Thiel embalmed cadavers. METHODS: Chest CT's of Thiel embalmed cadavers were acquired at different exposures. Clinical IQ was determined by performing a visual grading analysis. Physical-technical IQ (noise, contrast-to-noise and contrast-detail) was assessed in a Catphan phantom. Soft and sharp reconstructions were made with filtered back projection and two strengths of iterative reconstruction. In addition to the classical IQ metrics, an automatic algorithm was used to calculate image quality scores (IQs). To be able to compare datasets reconstructed with different kernels, the IQs values were normalized. RESULTS: Good correlations were found between IQs and the measured physical-technical image quality: noise (ρ=-1.00), contrast-to-noise (ρ=1.00) and contrast-detail (ρ=0.96). The correlation coefficients between IQs and the observed clinical image quality of soft and sharp reconstructions were 0.88 and 0.93, respectively. CONCLUSIONS: The automatic scoring algorithm is a promising tool for the evaluation of thoracic CT scans in daily clinical practice. It allows monitoring of the image quality of a chest protocol over time, without human intervention. Different reconstruction kernels can be compared after normalization of the IQs.
Assuntos
Garantia da Qualidade dos Cuidados de Saúde/métodos , Radiografia Torácica , Tomografia Computadorizada por Raios X , Automação , Cadáver , Humanos , Imagens de Fantasmas , Doses de Radiação , Razão Sinal-RuídoRESUMO
OBJECTIVES: To develop a clinically applicable method to estimate patient-specific organ and blood doses and lifetime attributable risks (LAR) from paediatric torso CT examinations. METHODS: Individualized voxel models were created from full-body CT data of 10 paediatric patients (2-18 years). Patient-specific dose distributions of chest and abdominopelvic CT scans were simulated using Monte Carlo methods. Blood dose was calculated as a weighted sum of simulated organ doses. LAR of cancer incidence and mortality were estimated, according to BEIR-VII. A second simulation and blood dose calculation was performed using only the thoracic and abdominopelvic region of the original voxel models. For each simulation, the size-specific dose estimate (SSDE) was calculated. RESULTS: SSDE showed a significant strong linear correlation with organ dose (r > 0.8) and blood dose (r > 0.9) and LAR (r > 0.9). No significant differences were found between blood dose calculations with the full-body voxel models and the thoracic or abdominopelvic models. CONCLUSION: Even though clinical CT images mostly do not cover the whole body of the patient, they can be used as a voxel model for blood dose calculation. In addition, SSDE can estimate patient-specific organ and blood doses and LAR in paediatric torso CT examinations. KEY POINTS: ⢠Blood dose can be simulated using the patient's clinical CT images. ⢠SSDE estimates patient-specific organ/blood dose and LAR in paediatric CAP CT-examinations. ⢠SSDE makes on-the-spot dose and LAR estimations possible in routine clinical practice.
Assuntos
Abdome/diagnóstico por imagem , Neoplasias Induzidas por Radiação/epidemiologia , Órgãos em Risco , Pelve/diagnóstico por imagem , Doses de Radiação , Tórax/diagnóstico por imagem , Tomografia Computadorizada por Raios X/efeitos adversos , Adolescente , Criança , Pré-Escolar , Simulação por Computador , Feminino , Humanos , Masculino , Modelos Teóricos , Método de Monte Carlo , Neoplasias Induzidas por Radiação/etiologia , Tomografia Computadorizada por Raios X/métodosRESUMO
This work is the result of a health technology assessment for the Flemish regional government, Belgium, performed in 2006. A search of the available literature in the databases Medline and EMBASE was performed to find evidence for a rational choice between CT and MRI techniques in the work-up of patients with clinically isolated syndrome (CIS) with a suspicion for multiple sclerosis (MS), and in follow-up exams performed in such patients. From the presented evidence, in patients referred for CIS or MS, MR is superior to CT for detection and characterization of brain and spine lesions.
Assuntos
Imageamento por Ressonância Magnética , Esclerose Múltipla/diagnóstico , Avaliação da Tecnologia Biomédica , Tomografia Computadorizada por Raios X , Humanos , Esclerose Múltipla/diagnóstico por imagem , Sensibilidade e Especificidade , SíndromeRESUMO
Diffusion weighted magnetic resonance imaging enables the visualization of fibrous tissues such as brain white matter. The validation of this non-invasive technique requires phantoms with a well-known structure and diffusion behavior. This paper presents anisotropic diffusion phantoms consisting of parallel fibers. The diffusion properties of the fiber phantoms are measured using diffusion weighted magnetic resonance imaging and bulk NMR measurements. To enable quantitative evaluation of the measurements, the diffusion in the interstitial space between fibers is modeled using Monte Carlo simulations of random walkers. The time-dependent apparent diffusion coefficient and kurtosis, quantifying the deviation from a Gaussian diffusion profile, are simulated in 3D geometries of parallel fibers with varying packing geometries and packing densities. The simulated diffusion coefficients are compared to the theory of diffusion in porous media, showing a good agreement. Based on the correspondence between simulations and experimental measurements, the fiber phantoms are shown to be useful for the quantitative validation of diffusion imaging on clinical MRI-scanners.
Assuntos
Mapeamento Encefálico/métodos , Imagem de Difusão por Ressonância Magnética/métodos , Imagens de Fantasmas , Algoritmos , Anisotropia , Água Corporal/metabolismo , Simulação por Computador , Processamento de Imagem Assistida por Computador , Imageamento Tridimensional , Método de Monte Carlo , Fibras NervosasRESUMO
OBJECTIVES: Inflammation contributes to degeneration in Alzheimer's disease (AD), not simply as a secondary phenomenon, but primarily as a significant source of pathology. [(123)I]iodo-PK11195 is a single photon emission computed tomography (SPECT) ligand for the peripheral benzodiazepine receptor, the latter being expressed on microglia (brain resident macrophages) and upregulated under inflammatory circumstances. The objectives were to assess AD inflammation by detecting [(123)I]iodo-PK11195 uptake changes and investigate how uptake values relate with perfusion SPECT and neuropsychological findings. METHODS: Ten AD and 9 control subjects were included. [(123)I]iodo-PK11195 SPECT images were realigned into stereotactic space where binding indices, normalized on cerebellar uptake, were calculated. RESULTS: The mean [(123)I]iodo-PK11195 uptake was increased in AD patients compared with controls in nearly all neocortical regions; however, statistical significance was only reached in the frontal and right mesotemporal regions. Significant correlations were found between regional increased [(123)I]iodo-PK11195 uptake and cognitive deficits. CONCLUSIONS: [(123)I]iodo-PK11195 is a cellular disease activity marker and allows in vivo assessment of microglial inflammation in AD.
Assuntos
Doença de Alzheimer/diagnóstico por imagem , Encefalite/diagnóstico por imagem , Processamento de Imagem Assistida por Computador , Radioisótopos do Iodo , Isoquinolinas , Microglia/diagnóstico por imagem , Neocórtex/diagnóstico por imagem , Receptores de GABA-A/fisiologia , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Idoso , Idoso de 80 Anos ou mais , Doença de Alzheimer/imunologia , Doença de Alzheimer/patologia , Mapeamento Encefálico , Dominância Cerebral/fisiologia , Encefalite/imunologia , Encefalite/patologia , Feminino , Humanos , Masculino , Entrevista Psiquiátrica Padronizada , Microglia/imunologia , Microglia/patologia , Pessoa de Meia-Idade , Neocórtex/imunologia , Neocórtex/patologia , Projetos Piloto , Ensaio Radioligante , Valores de Referência , Regulação para Cima/fisiologiaRESUMO
BACKGROUND AND PURPOSE: When planning an intensity-modulated radiation therapy (IMRT) treatment in a heterogeneous region (e.g. the thorax), the dose computation algorithm of a treatment planning system may need to account for these inhomogeneities in order to obtain a reliable prediction of the dose distribution. An accurate dose verification technique such as monomer/polymer gel dosimetry is suggested to verify the outcome of the planning system. MATERIALS AND METHODS: The effects of low-density structures: (a) on narrow high-energy (18 MV) photon beams; and (b) on a class-solution IMRT treatment delivered to a thorax phantom have been examined using gel dosimetry. The used phantom contained air cavities that could be filled with water to simulate a homogeneous or heterogeneous configuration. The IMRT treatment for centrally located lung tumors was delivered on both cases, and gel derived dose maps were compared with computations by both the GRATIS and Helax-TMS planning system. RESULTS: Dose rebuildup due to electronic disequilibrium in a narrow photon beam is demonstrated. The gel measurements showed good agreement with diamond detector measurements. Agreement between measured IMRT dose maps and dose computations was demonstrated by several quantitative techniques. An underdosage of the planning target volume (PTV) was revealed. The homogeneity of the phantom had only a minor influence on the dose distribution in the PTV. An expansion of low-level isodoses in the lung volume was predicted by collapsed cone computations in the heterogeneous case. CONCLUSIONS: For the class-solution described, the dose in centrally located mediastinal tumors can be computed with sufficient accuracy, even when neglecting the lower lung density. Polymer gel dosimetry proved to be a valuable technique to verify dose calculation algorithms for IMRT in 3D in heterogeneous configurations.