Superparamagnetic iron oxide nanoparticles are suitable contrast agents for magnetic resonance imaging due to their effect on proton relaxation times, and excellent biocompatibility and biodistribution in tissue. In the present study, a ferrofluid formed by dextrancoated iron oxide nanoparticles was prepared by the coprecipitation method and with subsequent steps of crosslinking and addition of functionalizations on the nanoparticle´s surface (amino groups and a fluorophore). The effect of differences in the synthesis route (ratio of dextran to iron salts and temperature of the reaction) on the physico-chemical characteristics of the nanoparticles and their performance as contrast agents for magnetic resonance imaging was investigated. Overall, the nuclear magnetic relaxation times of water protons in aqueous suspensions of the nanoparticles did not show major differences among different batches, with no significant effect due to the addition of the fluorophore or changes in the dextran fraction of up to 50%. Larger reductions in the ratio of dextran to iron salts resulted in particles with slightly larger sizes, higher saturation magnetization and distinct nuclear magnetic relaxation times.

Computed tomography is considered a high radiation dose modality, and therefore establishment of diagnostic reference levels is highly recommended. These levels are expected not to be exceeded for standard procedures, when good practice is applied. Most CT scanners display a dose index, CTDIvol. For pediatric studies, this dose index is measured using a standard phantom and an ionization chamber, and does not represent patient dose, but a reference measurement. The objective of this study was to investigate the CTDIvol dose descriptor in head CT scans of a sample of pediatric patients, comparing them with the DRL presented in the literature. Data of head CT without contrast of 40 pediatric patients were retrospectively collected. The acquisition parameters of each examination were extracted from DICOM header and analyzed to assess the protocols typically used by technicians. The mean values of CTDIvol of each group were compared with the DRL values from literature. The measurement of accuracy indicated a difference of 11,6% with the CTDIvol registered by the scan, which can be explained by six different protocols used by technicians for the same exam. The variation is specially critic for the youngers than 1 year. Some children were submitted to a protocol with 50% higher dose than others. This group has 4% higher mean CTDIvol than DRL in literature, while other groups have lower values. The results show the role of medical physicist, optimizing clinical protocols to guarantee the maximum image quality with minimum dose.

No abstract

Devido à dose de radiação na tomografia computadorizada (TC) ser relativamente alta, é importante que se tenha uma estimativa da dose a que o paciente é submetido, considerando parâmetros utilizados e fatores de correção, a fim de que o valor seja mais próximo do real. O objetivo deste estudo é relacionar a estimativa de dose em pacientes submetidos à TC do abdômen com os grupos IMC, considerando o tamanho específico da região anatômica. O trabalho desenvolveu-se em um hospital de Porto Alegre, utilizando equipamento Siemens Somaton Emotion 16.Foram coletados 30 indivíduos adultos que realizaram TC do abdômen em Janeiro de 2014. Destes, 17 realizaram aquisição utilizando mecanismo de redução de dose (Care Dose) (Amostra 1) e o restante sem este mecanismo (Amostra 2). Registrou-se peso, altura, CTDIvol e diâmetro lateral e ântero-posterior na altura do umbigo. Foram calculados valores de IMC e o fator de correção para a estimativa de dose, de acordo com o tamanho específico do abdômen. Determinou-se a variação percentual entre os valores de CTDIvol fornecidos pela TC e o valor do CTDIvol, após aplicação do fator de correção, além da variação percentual média para cada grupo IMC. A variação percentual média ficou entre 65% e 19% para a Amostra 1 e entre 35% e 10% para a Amostra 2, do menor para o maior valor do grupo IMC. Observou-se redução da variação percentual média com o aumento do grupo IMC, em ambas as amostras. É necessária uma amostra maior de indivíduos para verificação dos resultados encontrados.Palavras-chave: Tomografia Computadorizada; Dose de radiação; IMC.