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Evaluation of Bone Contrast Enhanced MRI Sequences and Voxel Based SegmentationJohansson, Adam January 2010 (has links)
An ultra-short echo time (UTE) magnetic resonance imaging (MRI) sequence was used together with other MRI sequences to evaluate the possibility of segmenting air, soft tissues and bone. Three patients were imaged with the UTE sequence and other sequences as well as with computed tomography (CT). An algorithm using Gaussian mixture models was developed and applied to the problem of segmenting the MR images. A similar algorithm was developed and used to generate an artificial CT image from the MR data. The images of the first patient were used as training data for the algorithms and the images of the other two patients were used for validation. It was found that less than 20 percent of the volume inside the head was misclassified and that the root mean square error of the artificial CT image was less than 420 Hounsfield units. Finally a volunteer was imaged in the same way but with an additional UTE sequence with a larger flip angle. The results suggested that the additional image may improve segmentation further. / En sekevens för bildgivande magnetresonans (MRI) med ultrakort ekotid (UTE) användes tillsammans med andra MRI-sekvenser till att utvärdera möjligheten att segmentera luft, mjukvävnad och ben. Bilder togs av tre patienter med UTE-sekvensen och med övriga sekvenser samt med datortomografi (CT). En algoritm baserad på en blanding av normalfördelningar utvecklades och tillämpades på MR-segmenteringsproblemet.En likande algoritm utvecklades och användes till att skapa en konstgjord CT-bild utifrån MR-bilderna.Bilderna tagna av den första patienten användes till att träna algoritmerna medan bilderna av de två andra patienterna användes för validering. Mindre än 20 procent av volymen inuti huvudet felklassificerades och det kvadratiska medelvärdet av avvikelserna i den konstgjorda CT-bilden var mindre än 420 hounsfieldenheter. Slutligen togs bilder av en frivillig på samma sätt men med ytterligare en UTE-sekvens med en större flippvinkel. Resultatet antyder att den nya bilden kan bidra till en förbättrad segmentering.
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Aplicação das unidades Hounsfield em imagens de tomografia computadorizada de feixe cônico / Application of Hounsfield units in cone beam computed tomography imagesNadaes, Mariana Rocha 06 February 2015 (has links)
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Previous issue date: 2015-02-06 / FAPEMIG - Fundação de Amparo à Pesquisa do Estado de Minas Gerais / Apesar das muitas indicações da tomografia computadorizada de feixe cônico
(TCFC) na Odontologia, a avaliação da qualidade óssea, por meio das Unidades
Hounsfield (HU), não apresenta um consenso sobre sua precisão e confiabilidade. O
objetivo neste estudo foi avaliar, por meio de uma revisão sistemática da literatura,
os principais resultados de pesquisas que compararam diversos materiais em
exames de tomografia computadorizada multislice (TCMS) e TCFC, utilizando HU
como unidade de medida. Para isso, foi realizada uma busca na base de dados
Medline (PubMed) utilizando as palavras chaves “cone beam computed tomography”,
“cone beam tomography”, “cbct”, “Hounsfield unit” e “Hounsfield”. A exclusão dos
artigos foi realizada, inicialmente, por meio da leitura do título e resumo e,
posteriormente, após a leitura do texto completo. Os dados da amostra selecionada
(n=8) foram distribuídos em tabelas, possibilitando sua comparação. Os resultados
obtidos em relação à aplicação de HU em TCFC foram divergentes, com alguns
autores aplicando diretamente HU nesse exame, outros desenvolvendo fatores de
correção para essa comparação e outros ainda, invalidando a utilização dessa
unidade em exames de TCFC. Apenas um estudo concluiu que se pode aplicar
diretamente HU em TCFC, sem prejuízo para avaliação das densidades dos tecidos.
Assim, pode-se concluir que uma nova abordagem é necessária para o
desenvolvimento de futuros trabalhos nessa linha e que a tentativa de aplicar HU em
TCFC deveria ser abandonada. / Despite the many indications of cone beam computed tomography (CBCT) in
dentistry, there is no consensus regarding the accuracy and reliability of bone quality
assessment, through Hounsfield Units (HU). The aim of this study was to evaluate,
through a systematic review of the literature, the main results of studies comparing
various tissues in multislice CT (MSCT) and CBCT scans, using the HU as the unit of
measurement. To this end, a search was conducted in the Medline (PubMed)
database using the keywords "cone beam computed tomography", "cone beam
tomography", "CBCT", "Hounsfield unit", and "Hounsfield". Articles were initially
excluded by reading the title and abstract, and were later excluded after reading the
full text. The data from the selected sample (n = 8) were tabulated and compared.
The results obtained regarding the application of HU in CBCT were divergent, with
some authors directly applying HU in CBCT, others developing correction factors for
this comparison, and still others invalidating the use of this unit in CBCT. Only one
study concluded that is possible to directly apply HU in CBCT, without damaging the
evaluation of tissue densities. In this way, it’s possible to affirm that a new approach
is necessary for the development of future work in this line and that the attempt to
apply HU in CBCT should be abandoned.
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Auswirkungen einer akuten, intrakraniellen Druckerhöhung auf die computertomographisch bestimmte Lungenparenchymdichte und das extravaskuläre Lungenwasser in gesunden und geschädigten Schweinelungen / Auswirkungen einer akuten, intrakraniellen Druckerhöhung auf die computertomographisch bestimmte Lungenparenchymdichte und das extravaskuläre Lungenwasser in gesunden und geschädigten SchweinelungenSauter, Philip 31 January 2012 (has links)
No description available.
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