DWI: factores que influenciam a medição do coeficiente de difusão aparente (ADC) no estudo da mama

Mestrado em Radiações Aplicadas às Tecnologias da Saúde. Área de especialização: Ressonância Magnética

Quantificação por imagem ponderada em difusão (DWI) das lesões tumorais da mama

Introdução – A técnica de Difusão por Ressonância Magnética (RM), ao avaliar o movimento das moléculas de água nos tecidos, permite inferir sobre a arquitetura dos mesmos, em particular relativamente à celularidade, volume celular e permeabilidade das membranas. O Coeficiente de Difusão Aparente (ADC) é um parâmetro quantificável da imagem ponderada em difusão (DWI). A sua análise poderá fornecer informação clínica adicional sobre estas lesões, sobretudo em relação à sua caracterização histológica. Objetivos – Caracterizar e diferenciar tipos e alguns subtipos de lesões mamárias através da análise do ADC. Metodologia – 20 Mulheres com 23 lesões mamárias foram submetidas a RM mamária: 3 lesões benignas (3 Fibroadenomas-FA) e 20 malignas (16 Carcinomas Ductais Invasivos-CDI, 2 Carcinomas Ductais In Situ-CDIS e 2 Carcinomas Invasivos Lobulares-CLI). Num equipamento 1.5T aplicou-se uma sequência de Difusão (b=0,50,250,500,750,1000 s/mm2). Obteve-se o ADC através do ajuste exponencial da intensidade de sinal das lesões em função do valor de b, fazendo-se corresponder os valores de ADC à respetiva caracterização histológica e posterior comparação com a literatura. Resultados e Discussão – As lesões malignas apresentaram ADCs significativamente (p=0,014) inferiores [(0,94±0,22)x10-3 mm2/s] aos das benignas [(1,43±0,25)x10-3 mm2/s]. A justificação pode residir no aumento da celularidade e consequente restrição da Difusão que se observa nas lesões malignas. Os CDI apresentaram ADCs baixos [(0,88±0,17)x10-3 mm2/s], enquanto que os CDIS apresentaram ADCs mais elevados [(1,33±0,29)x10-3 mm2/s]. Estes resultados estão de acordo com o facto dos CDIS estarem limitados aos ductos mamários, mantendo-se menos alterada a estrutura do tecido adjacente e resultando numa menor restrição à difusão que nos CDI. Verificaram-se diferenças significativas entre FA e CDI (p=0,010) e entre CDI e CDIS (p=0,049). Conclusões – O ADC possibilita a diferenciação entre lesões mamárias benignas e malignas, bem como entre alguns tipos histológicos. O desenvolvimento deste conceito pode representar um avanço no papel da RM na avaliação destas neoplasias. ABSTRACT - Introduction – The Magnetic Resonance (MR) diffusion technique measures the movement of water molecules in tissues. Therefore, it provides useful information about tissue architecture, specially regarding tissue cellularity, cell volume and membrane permeability. The quantification of diffusion weighted imaging (DWI) data is done by measuring the so-called. Apparent Diffusion Coefficient (ADC). This parameter provides additional clinical information about breast lesions, and potentially allows for in-vivo histological characterization. Purpose – To characterize and differentiate breast lesions through ADC analysis. Methodology – The study comprised 20 women, with 23 breast lesions: 3 benign lesions - 3 Fibroadenomas (FA); and 20 malignant - 16 Invasive Ductal Carcinomas (CDI), 2 Ductal Carcinomas In Situ (CDIS), 2 Invasive Lobular Carcinoma (CLI). On a 1.5T equipment a diffusion-weighted sequence with 6 b-values (b=0,50,250,500,750,1000 s/mm2) was used to examine the patients. ADC was obtained by fitting an exponential to data of lesion signal intensity vs. b values. A correspondence of ADC values to histological lesion characterization was done and finally, the results were comparison with the literature. Results and Discussion – Malignant lesions showed inferior ADCs significantly (p=0.014) lower ((0.94±0.22)x10-3 mm2/s) than the benign lesions ((1.43±0.25)x10-3 mm2/s). This may be associated to increasead cellularity in malignant lesions, which result in higher tissue restriction to diffusion. CDI showed low ADC values ((0.88±0.17)x10-3 mm2/s), while the CDIS showed higher ADCs ((1.33±0.29)x10-3 mm2/s). These results agree with the fact that CDIS are limited to mammary ducts, maintaining a less altered neighboring tissue structure, which results in a lower restriction to diffusion than observed in CDI. Significant differences between FA and CDI (p=0.010) and between CDI and CDIS (p=0.049) were observed. Conclusion – The ADC parameter is able to differentiate between malignant and benign breast lesions, as well as between some histological types.

Lesões da substância branca por ressonância magnética: uma avaliação entre as ponderações DWI e T2 FLAIR

RESUMO: Objetivos – Determinar a sensibilidade e especificidade das ponderações Difusão (DWI) e T2 Fluid-Attenuated Inversion Recovery (FLAIR) na avaliação de lesões da substância branca (SB) e verificar em que medida se complementam, por forma a criar um conjunto de boas práticas na RM cranioencefálica de rotina. Metodologia – Recorrendo-se a uma metodologia quantitativa, efetuou-se uma análise retrospetiva da qual foram selecionados 30 pacientes, 10 sem patologia e 20 com patologia (2 com EM, 7 com Leucoencefalopatia, 6 com doença microangiopática e 5 com patologia da substância branca indefinida). Obteve-se uma amostra de 60 imagens, nomeadamente: 30 imagens ponderadas em DWI e 30 em T2 FLAIR. Recorrendo ao programa Viewdex®, três observadores avaliaram um conjunto de imagens segundo sete critérios: visibilidade, deteção, homogeneidade, localização, margens e dimensões da lesão e capacidade de diagnóstico. Com os resultados obtidos recorreu-se ao cálculo de sensibilidade e especificidade pelas Curvas ROC, bem como à análise estatística, nomeadamente, Teste-T, Índice de Concordância Kappa e coeficiente de correlação de Pearson entre as variáveis em estudo. Resultados – Os resultados de sensibilidade e de especificidade obtidos para a ponderação T2 FLAIR foram superiores (0,915 e 0,038, respetivamente) aos da ponderação DWI (0,08 e 0,100, respetivamente). Não se verificaram variâncias populacionais significativas. Obteve-se uma elevada correlação linear entre as variáveis com um valor r situado entre 0,8 e 0,99. Verificou-se também uma variabilidade considerável entre os observadores. Conclusões – Dados os baixos valores de sensibilidade e especificidade obtidos para a DWI, sugere-se que esta deva ser incluída no protocolo de rotina de crânio como auxiliar no diagnóstico diferencial com outras patologias.

Dependence of IVIM-DWI estimations on acquisition parameters

Dissertação para obtenção do Grau de Mestre em Engenharia Biomédica

Imagerie de diffusion (DWI) dans la caractérisation de l'échinococcose alvéolaire hépatique.

Objectifs: Etudier l'utilité de DWI dans l'échinococcose alveolaire (EA) hépatique. Matériels et méthodes: Dix-sept patients (10 hommes, âge moyen 64.3) avec 55 lésions hépatiques ont été examinés par IRM. La sémiologie des lésions a été étudiée après classification selon Kodama. Les coefficients apparent de diffusion (ADCmax, ADCmin, ADCtot) ont été mesurés. Résultats: Trois lésions de Kodama de type 1, 13 de type 2, 15 de type 3, 3 de type 4, et 21 de type 5. L'ADCtot des lésions mesurait 1.23±0.18 x 10-3 mm2/s. L'ADCtot de Kodama type 1, 2, 3, 4 et 5 mesuraient 1.97±0.27, 1.66±0.13, 1.73±0.12, 1.15±0.27 et 1.76±0.10 x 10-3 mm2/s, respectivement. Il n'y avait pas de différence significative de l'ADCtot entre les types (p=0.25) hormis le type 4 qui représente une lésion solide (p=0.035). Conclusion: Les valeurs d'ADC des lésions d'EA ne se révèlent pas utiles pour différencier les différents types selon Kodama, hormis pour le type 4 ce qui suggère la présence d'une composante solide. Celles-ci sont relativement basses comparées à d'autres lésions kystiques hépatiques, ce qui peut aider à suggérer le diagnostic.

Ultra-high Field (7 T) MRI and a Novel Robust Segmentation of Thalamic Nuclei on DWI for Gamma Knife Surgery Purposes: The Targeting of the Ventrointermediate Nucleus

Introduction: Gamma Knife surgery (GKS) is a noninvasive neurosurgical stereotactic procedure, increasingly used as an alternative to open functional procedures. This includes the targeting of the ventrointermediate nucleus of the thalamus (e.g., Vim) for tremor. Objective: To enhance anatomic imaging for Vim GKS using high-field (7 T) MRI and Diffusion Weighted Imaging (DWI). Methods: Five young healthy subjects and two patients were scanned both on 3 and 7 T MRI. The protocol was the same in all cases, and included: T1-weighted (T1w) and DWI at 3T; susceptibility weighted images (SWI) at 7T for the visualization of thalamic subparts. SWI was further integrated into the Gamma Plan Software® (LGP, Elekta Instruments, AB, Sweden) and co-registered with 3T images. A simulation of targeting of the Vim was done using the quadrilatere of Guyot. Furthermore, a correlation with the position of the found target on SWI and also on DWI (after clustering of the different thalamic nuclei) was performed. Results: For the 5 healthy subjects, there was a good correlation between the position of the Vim on SWI, DWI and the GKS targeting. For the patients, on the pretherapeutic acquisitions, SWI helped in positioning the target. For posttherapeutic sequences, SWI supposed position of the Vim matched the corresponding contrast enhancement seen at follow-up MRI. Additionally, on the patient's follow-up T1w images, we could observe a small area of contrast-enhancement corresponding to the target used in GKS (e.g., Vim), which belongs to the Ventral-Lateral-Ventral (VLV) nuclei group. Our clustering method resulted in seven thalamic groups. Conclusion: The use of SWI provided us with a superior resolution and an improved image contrast within the central gray matter, enabling us to directly visualize the Vim. We additionally propose a novel robust method for segmenting the thalamus in seven anatomical groups based on DWI. The localization of the GKS target on the follow-up T1w images, as well as the position of the Vim on 7 T, have been used as a gold standard for the validation of VLV cluster's emplacement. The contrast enhancement corresponding to the targeted area was always localized inside the expected cluster, providing strong evidence of the VLV segmentation accuracy. The anatomical correlation between the direct visualization on 7T and the current targeting methods on 3T (e.g., quadrilatere of Guyot, histological atlases, DWI) seems to show a very good anatomical matching.

DWI and complex brain network analysis predicts vascular cognitive impairment in spontaneous hypertensive rats undergoing executive function tests

The identification of biomarkers of vascular cognitive impairment is urgent for its early diagnosis. The aim of this study was to detect and monitor changes in brain structure and connectivity, and to correlate them with the decline in executive function. We examined the feasibility of early diagnostic magnetic resonance imaging (MRI) to predict cognitive impairment before onset in an animal model of chronic hypertension: Spontaneously Hypertensive Rats. Cognitive performance was tested in an operant conditioning paradigm that evaluated learning, memory, and behavioral flexibility skills. Behavioral tests were coupled with longitudinal diffusion weighted imaging acquired with 126 diffusion gradient directions and 0.3 mm(3) isometric resolution at 10, 14, 18, 22, 26, and 40 weeks after birth. Diffusion weighted imaging was analyzed in two different ways, by regional characterization of diffusion tensor imaging (DTI) indices, and by assessing changes in structural brain network organization based on Q-Ball tractography. Already at the first evaluated times, DTI scalar maps revealed significant differences in many regions, suggesting loss of integrity in white and gray matter of spontaneously hypertensive rats when compared to normotensive control rats. In addition, graph theory analysis of the structural brain network demonstrated a significant decrease of hierarchical modularity, global and local efficacy, with predictive value as shown by regional three-fold cross validation study. Moreover, these decreases were significantly correlated with the behavioral performance deficits observed at subsequent time points, suggesting that the diffusion weighted imaging and connectivity studies can unravel neuroimaging alterations even overt signs of cognitive impairment become apparent.

DWI sanctions: the law and the practice.

Mode of access: Internet.

Evaluation of a day reporting center for repeat DWI offenders.

National Highway Traffic Safety Administration, Office of Research and Traffic Records, Washington, D.C.

Examination of DWI conviction rate procedures.

National Highway Traffic Safety Administration, Washington, D.C.

Evaluation support for innovative alcohol projects: evaluation support for assessing the effectiveness of videotaping persons arrested for DWI. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Motivating anti-DWI behavior using existing values. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Development and field test of psychophysical tests for DWI arrest. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

Lessons learned from public health campaigns and applied to anti-DWI norms development. Final report.

National Highway Traffic Safety Administration, Washington, D.C.