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Previous issue date: 2017-01-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / It has been shown that the use of contrast media in PET/CT (positron emission tomography/ computed tomography) studies is beneficial when compared to an unenhanced CT scan. This is due to the fact that contrast media generates better contrast regarding adjacent structures, allows better characterization of abnormalities, and also allows visualizing alterations that do not present abnormal metabolic behavior. However, contrast agents generate more absorption of CT photons in relation to those of PET potentially giving rise to errors in attenuation correction of PET images. Errors converting the attenuation map from the CT to the PET scan may lead to inaccurate quantification of PET images. The occurrence of SUV (Standardized uptake value) modifications in lesions when PET images are corrected with either contrast-enhanced or unenhanced CT scans has already been studied. Our goal, however, was to study the occurrence of such alterations in relation with lesion size, and distance from the lesion to areas of high contrast concentration, such as high caliber vases and focal areas of the gastrointestinal tract (GIT). Methods: We obtained the SUVmax of 149 lesions, from 26 patients who underwent a PET/CT scan in which images were corrected using both an unenhanced computed tomography (PETCTUE) and a contrast-enhanced computed tomography (PETCTCE). In addition, we measured lesion sizes (smallest and largest diameter, and area) and their distance to large vessels and the GIT. Size measures were not taken when the lesion could not be visualized in the CT image. For lesions in which the distance to high contrast concentration areas was too large or too small, and could not be accurately estimated, the median distance of similar lesions was used to replace the measures. Following the repeated measures principle, we obtained Lin's concordance correlation coefficient and its confidence interval. A Bland-Altman analysis was performed using the absolute difference values and ratio, between PETCTCE and PETCTUE with concordance limits. Results: A total of 149 lesions could be visualized in PET. Eleven of them could not be identified in the CT, and so their measurements were not taken. For 16 lesions, the distance to high contrast concentration areas could not be obtained. The concordance level between the methods, by Lin's concordance correlation coefficient, was 0.99 (CCC: 0.99), and the confidence interval was 95% of 0.98 ? 0.99 (IC95%: 0.98 ? 0.99). The mean absolute difference between the methods was approximately zero and the relative difference was +3.37% (concordance limits of 95% between -2.72 and +2.72, and between -15.73 and +22.48%, respectively). Eighty-two lesions had their larger diameter below 17mm and the other 56 had a larger diameter above or equal to 17mm, with mean percent variation of SUVmax from PETCTCE to PECCTUE of 3.85% and 2.83%, respectively (p=0.54). Sixty-six lesions had a smaller diameter below 17mm and the remaining 72 had a smaller diameter equal to or above 17mm. The mean percent SUVmax variation from PETCTCE to PECCTUE was 2.71%?1,74 and 3.80% ?1,60, respectively (p=0.41). Eighty-two lesions had an area larger than 2.27 cm2 and the other 57 had an area equal to or larger than 2.27 cm2. The mean percent variation of the SUVmax obtained for PETCTCE and PETCTUE was 2.81%?1.64 e 3,83%?1.70, respectively (p=0.48). Sixty-seven lesions were more than 1.82 cm distant from large vessels/ GIT, and 82 were at a less than 1cm distance. The mean SUVmax variation between the methods (PETCTCE versus PETCTUE) was 0.57?1.65% e 4.98?1.61% respectively (p < 0.005). Conclusions: For the totality of studied lesions (149), as well as for the analysis regarding the factors size (non significant p) and distance (significant p), the medium SUVmax variation we identified it not clinically relevant. Thus, both contrast-enhanced and unenhanced PET/CT can be used for attenuation correction. / Nos estudos de PET/CT (tomografia por emiss?o de p?sitrons/ tomografia computadorizada), o uso de material contrastado endovenoso na CT mostra benef?cios diagn?sticos em rela??o a CT n?o contrastada. Isto ocorre pois o material contrastado al?m de gerar maior contraste entre as les?es em rela??o ?s estruturas adjacentes, e melhor caracterizar as anormalidades, tamb?m permite a visualiza??o de altera??es que n?o demonstram comportamento metab?lico anormal. Entretanto, os meios de contraste geram maior absor??o dos f?tons da CT em rela??o aos do PET, e isto tende a gerar erros na corre??o de atenua??o das imagens do PET. Esses erros na convers?o do mapa de atenua??o da CT para o do PET podem levar a inacur?cias na quantifica??o das imagens do PET. A ocorr?ncia de altera??es do SUV das les?es entre as imagens de PET corrigidas para atenua??o com o CT sem contraste e com o CT contrastado j? foi amplamente estudada. Nosso objetivo foi estudar essa ocorr?ncia em fun??o do tamanho das les?es e das dist?ncias entre elas e zonas de maior concentra??o de contraste, como ? o caso de vasos calibrosos e ?reas focais em trato gastrintestinal (TGI). M?todos: Mensuramos o SUVmax de 149 les?es em 26 pacientes cujos exames de PET/CT foram corrigidos tanto utilizando tomografia n?o-contrastada (PETCTSC) quanto tomografia contrastada (PETCTCC). Al?m disso, medimos as dimens?es das les?es (maior e menor di?metro e ?rea) e suas dist?ncias para vasos calibrosos e TGI. Medidas de tamanho n?o foram feitas quando n?o foram visualizadas na CT. Em les?es cujas dist?ncias de ?reas de maior contraste n?o puderam ser feitas com seguran?a por serem muito pr?ximas ou muito grandes, suas medidas foram repostas pela mediana de les?es similares quanto a este aspecto. Seguindo o princ?pio de medidas repetidas, obteve-se o n?vel de concord?ncia dos m?todos atrav?s do coeficiente de correla??o de concord?ncia de Lin e seu respectivo intervalo de confian?a. Realizou-se uma an?lise de Bland-Altman cruzando os valores de diferen?a absoluta e de raz?o entre o PETCTCC versus o PETCTSC com os limites de concord?ncia. Resultados: Das 149 les?es visualiz?veis no PET, 11 n?o demonstraram correspond?ncia na CT, n?o sendo mensuradas suas dimens?es. Dezesseis les?es n?o tiveram calculadas as suas dist?ncias para alguma ?rea de maior concentra??o de contraste e seus valores foram repostos. O n?vel de concord?ncia dos m?todos, pelo coeficiente de correla??o de concord?ncia de Lin, foi de 0.99 (CCC: 0.99) com intervalo de confian?a de 95% de 0.98 ? 0.99 (IC95%: 0.98 ? 0.99). A diferen?a m?dia absoluta entre os m?todos foi de aproximadamente zero e relativa de +3.37% (limites de concord?ncia de 95% entre -2.72 e +2.72 e entre -15.73 e +22.48% respectivamente). Oitenta e duas les?es apresentaram maior di?metro abaixo de 17mm e as outras 56, igual ou acima de 17mm, com diferen?a m?dia percentual dos SUVmax medida nos PETCTCC e PETCTSC igual a 3,85%?1,65 e 2,83%?1,80 respectivamente (p = 0,54). Sessenta e seis les?es apresentaram menor di?metro abaixo do que 17mm e as demais 72, di?metro igual ou acima de 17mm. A diferen?a m?dia percentual dos SUVmax medida nos PETCTCC e PETCTSC foi igual a 2,71%?1,74 e 3,80% ?1,60 respectivamente (p = 0,41). Oitenta e uma les?es apresentaram ?rea menor que 2,27 cm2 e as outras 57, ?rea igual ou maior que 2,27 cm2. A diferen?a m?dia percentual dos SUVmax medida nos PETCTCC e PETCTSC foi igual a 2,81%?1,64 e 3,83%?1,70 respectivamente (p = 0,48). Sessenta e sete les?es tinham dist?ncia de vasos calibrosos/ TGI acima de 1cm, e 82, igual ou menor que 1cm. A diferen?a m?dia percentual entre os m?todos (PETCTCC versus PETCTSC) foi igual a 0,57?1,65% e 4,98?1,61% respectivamente (p < 0,005). Conclus?es: Mesmo para o grupo total de les?es (149) bem como para os grupos de les?es separados em fun??o dos fatores ?tamanho? (p n?o significativo) e ?dist?ncia? (p significativo), a varia??o m?dia do SUVmax visualizada n?o tem relev?ncia cl?nica, tornando intercambi?vel a corre??o do PET pelo CT sem e com contraste.
| Identifer | oai:union.ndltd.org:IBICT/oai:tede2.pucrs.br:tede/7363 |
| Date | 20 January 2017 |
| Creators | Berdichevski, Eduardo Herz |
| Contributors | Baldisserotto, Matteo |
| Publisher | Pontif?cia Universidade Cat?lica do Rio Grande do Sul, Programa de P?s-Gradua??o em Medicina/Pediatria e Sa?de da Crian?a, PUCRS, Brasil, Escola de Medicina |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da PUC_RS, instname:Pontifícia Universidade Católica do Rio Grande do Sul, instacron:PUC_RS |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | 3098206005268432148, 600, 600, 600, 600, -224747486637135387, -969369452308786627, 2075167498588264571 |
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