Phantoms for diffusion-weighted imaging and diffusion tensor imaging quality control: a review and new perspectives

Abstract: Introduction Diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) combine magnetic resonance imaging (MRI) techniques and diffusion measures. In DWI, the contrast is defined by microscopic motion of water protons. Nowadays, DWI has become important for early diagnostic of acute stroke. DTI images are calculated from DWI images acquired in at least six directions, which give information of diffusion directionality, making it possible to reconstruct axonal or muscle fiber images. Both techniques have been applied to study body structures in healthy and pathological conditions. Currently, it is known that these images and derived parameters are quite sensitive to factors related to acquisition and processing. Magnetic field inhomogeneity, susceptibility, chemical shift, radiofrequency (RF) interference, eddy currents and low signal-to-noise ratio (SNR) can have a more harmful effect in diffusion data than in T1- or T2-weighted image data. However, even today there are not reference phantoms and guidelines for DWI or DTI quality control (QC). Review Proposals for construction and use of DWI and DTI QC phantoms can be found in literature. DWI have been evaluated using containers filled by gel or liquid with tissue-like MRI properties, as well as using microfabricated devices. DTI acquisitions also have been checked with these devices or using natural or artificial fiber structures. The head phantom from American College of Radiology (ACR) is also pointed out as an alternative for DTI QC. This article brings a discussion about proposed DWI and DTI phantoms, challenges involved and future perspectives for standardization of DWI and DTI QC.

ADHD and Cerebellar Vermis Tumor: DTI Analysis of an Incidental Finding

The increase in number of magnetic resonance imaging (MRI) scans for investigation of neurological diseases in childhood and adolescence leads to increase of incidental findings of central nervous system (CNS) tumors in these stages of life. Among MRI techniques, diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) have been increasingly used in brain studies. These images are based on random motion of water molecules in the body, which can change depending on constitution and geometry of biological tissues, as well as the existence of pathologies. This paper reports the use of DTI and DWI to evaluation of a CNS tumor incidentally detected in a patient diagnosed previously with Attention Deficit Hyperactivity Disorder (ADHD). He was diagnosed at age 9 and has been treated with medicines and psycho-pedagogical therapies. At age 15 a MRI detected a cerebellar vermis tumor with a volume of 2 cm3 . Due to parental decision, the patient did not undergo any surgical intervention. During the follow-up period we did not observe significant changes in tumor size or diffusion directions in the tumor and surrounding brain tissues. The main brain tracts presented normal diffusion patterns, both in terms of size and geometry. The DTI analysis showed that lesion was quite homogeneous and isotropic, with no significant restriction of diffusion. There also were no significant diffusion pattern changes in other regions of the brain which possibly could be related to ADHD. So, given the characteristics of lesion and the patient's clinical symptoms, it cannot be directly related to ADHD.

O maior número de exames de Ressonância Magnética (RM) para a investigação de doenças neurológicas na infância e adolescência leva a um aumento de achados incidentais de tumores do Sistema Nervoso Central (SNC) nessas fases da vida. Dentre as técnicas de RM, imagens ponderadas por difusão (DWI) e do tensor de difusão (DTI) vêm sendo cada vez mais empregadas em exames exploratórios. Essas imagens são baseadas no movimento randômico das moléculas de água no organismo, que varia em função da constituição e geometria dos tecidos biológicos, bem como da existência de patologias. Este trabalho relata o emprego das DWI e DTI para avaliação de um tumor no SNC detectado de forma incidental em um paciente com diagnóstico prévio de Transtorno do Déficit de Atenção (TDAH). Ele recebeu esse diagnóstico aos 9 anos, sendo tratado com medicações e suporte psicopedagógico. Aos 15 anos a RM apontou um tumor de 2 cm3 no vermis cerebelar. Por decisão dos pais, não houve qualquer intervenção cirúrgica. Durante o período de acompanhamento não foram observadas mudanças no tamanho do tumor ou direção de difusão na lesão e nas estruturas ao seu redor. Os principais tratos cerebrais apresentaram padrões de difusão normais, em termos de tamanho e geometria. A análise das DTI mostrou que a lesão era bastante homogênea e isotrópica, não apresentando restrição à difusão. Não foram encontradas alterações significantes na difusão em outras regiões do cérebro. Assim, dadas as características da lesão e as manifestações clínicas, não relacionamos o tumor diretamente ao TDAH.

Investigation of magnetic resonance imaging texture analysis as an aid tool for characterization of refractory epilepsies / Investigacao da analise de textura em imagem de ressonancia magnetica como auxilio para caracterizacao de epilepsias refratarias

Refractory epilepsies are syndromes for which therapies that employ two or more antiepileptic drugs, separately or in association, do not result in control of crisis. Patients may present focal cortical dysplasia or diffuse dysplasia and/or hippocampal atrophic alterations that may not be detectable by a simple visual analysis in magnetic resonance imaging. The aim of this study was to evaluate MRI texture in regions of interest located in the hippocampi, limbic association cortex and prefrontal cortex of 20 patients with refractory epilepsy and to compare them with the same areas in 20 healthy individuals, in order to find out if the texture parameters could be related to the presence of the disease. Of the 11 texture parameters calculated, three indicated the existence of statistically significant differences between the studied groups. Such findings suggest the possibility of this technique contributing to studies of refractory epilepsies.

Epilepsias refratárias compreendem síndromes para as quais as terapias que empregam duas ou mais drogas antiepilépticas, isoladamente ou em associação, não resultam no controle da frequência das crises. Portadores podem apresentar displasias corticais focais ou difusas e/ou alterações atróficas hipocampais que, em alguns casos, não são detectáveis por uma simples análise visual nas imagens de ressonância magnética. Nesse contexto, o objetivo deste estudo foi avaliar a textura de imagens de RM em regiões de interesse localizadas nos hipocampos, córtex de associação límbico e córtex pré-frontal de 20 pacientes com epilepsia refratária e compará-las às mesmas áreas de um grupo de 20 indivíduos sadios. Dos 11 parâmetros de textura calculados, três indicaram a existência de diferenças estatisticamente significantes entre os grupos estudados. Tais achados sugerem a possibilidade desta técnica contribuir para os estudos das epilepsias de difícil controle.