A carregar...
Projeto de investigação
Institute of Biophysics and Biomedical Engineering (IBEB)
Financiador
Autores
Publicações
Microwave Imaging to Improve Breast Cancer Diagnosis
Publication . Godinho, Daniela M.; Conceição, Raquel Cruz da; Fernandes, Carlos António Cardoso
Breast cancer is the most prevalent type of cancer worldwide. The correct diagnosis of Axillary Lymph Nodes (ALNs) is important for an accurate staging of breast cancer. The performance of current imaging modalities for both breast cancer detection and staging is still unsatisfactory. Microwave Imaging (MWI) has been studied to aid breast cancer diagnosis. This thesis addresses several novel aspects of the development of air-operated MWI systems for both breast cancer detection and staging.
Firstly, refraction effects in air-operated setups are evaluated to understand whether refraction calculation should be included in image reconstruction algorithms. Then, the research completed towards the development of a MWI system to detect the ALNs is presented. Anthropomorphic numerical phantoms of the axillary region are created, and the dielectric properties of ALNs are estimated from Magnetic Resonance Imaging exams. The first pre-clinical MWI setup tailored to detect ALNs is numerically and experimentally tested. To complement MWI results, the feasibility of using machine learning algorithms to classify healthy and metastasised ALNs using microwave signals is analysed. Finally, an additional study towards breast cancer detection is presented by proposing a prototype which uses a focal system to focus the energy into the breast and decrease the coupling between antennas.
The results show refraction calculation may be neglected in low to moderate permittivity media. Moreover, MWI has the potential as an imaging technique to assess ALN diagnosis as estimation of dielectric properties indicate there is sufficient contrast between healthy and metastasised ALNs, and the imaging results obtained in this thesis are promising for ALN detection. The performance of classification models shows these models may potentially give complementary information to imaging results. The proposed breast imaging prototype also shows promising results for breast cancer detection.
Diffusion-Weighted Imaging in Breast Magnetic Resonance
Publication . Borlinhas, Filipa; Ferreira, Hugo Alexandre; Conceição, Raquel Cruz da
Breast cancer is the most frequent, prevalent and mortal cancer affecting women. An earlier and more accurate diagnosis may change this scenario. Different methods are being explored to improve MRI diagnosis of this disease, namely through Diffusion-Weighted Imaging (DWI) and its different diffusion models. The diffusion models studied in this thesis were: the monoexponential, IntraVoxel Incoherent Motion (IVIM), Diffusion Kurtosis Imaging (DKI), IVIM+DKI, stretched exponential, truncated or statistical, and Gamma Distribution (GD). This work aimed to characterize different groups of breast lesions, establish differences among these groups using diffusion models, and compare their diagnostic performances. Additionally, this thesis aimed to study the optimal b-value combination in the DKI model for usage in clinical practice.
Women with breast lesions were scanned with MRI and an additional diffusion-weighted sequence was acquired. Lesions were classified in types and subgroups through histology, and the corresponding diffusion models parameters were obtained. Statistical analysis investigated the differences of these parameters and their diagnostic performances were assessed. For the study of optimal b-value combination, the available b-values were exhaustively combined and tested in terms of diagnostic performance for the DKI model. In this optimization study, some principles were depicted and should be considered in DKI studies to minimize the DWI standardization issues.
The GD and the statistical model were applied to breast lesions for the first time in this thesis, showing the capability to characterize and to significantly differentiate groups of lesions. The results showed that it is possible to characterize breast lesions using DWI in a robust way, with Gaussian and non-Gaussian diffusion models. These diffusion models also provided differentiation among different groups of lesions. Some non-Gaussian diffusion models surpassed the performance of the monoexponential model for breast cancer diagnosis.
This work strongly supports the DWI use to improve the MRI role in breast cancer diagnosis.
Transcutaneous spinal direct current stimulation of the lumbar and sacral spinal cord: a modelling study
Publication . Fernandes, Sofia Rita; Salvador, Ricardo; Wenger, Cornelia; Carvalho, Mamede; Miranda, Pedro Cavaleiro
Objective: Our aim was to perform a computational study of the electric field (E-field) generated by transcutaneous spinal direct current stimulation (tsDCS) applied over the thoracic, lumbar and sacral spinal cord, in order to assess possible neuromodulatory effects on spinal cord circuitry related with lower limb functions.
Approach: A realistic volume conductor model of the human body consisting of 14 tissues was obtained from available databases. Rubber pad electrodes with a metallic connector and a conductive gel layer were modelled. The finite element (FE) method was used to calculate the E-field when a current of 2.5 mA was passed between two electrodes. The main characteristics of the E-field distributions in the spinal grey matter (spinal-GM) and spinal white matter (spinal-WM) were compared for seven montages, with the anode placed either over T10, T8 or L2 spinous processes (s.p.), and the cathode placed over right deltoid (rD), umbilicus (U) and right iliac crest (rIC) areas or T8 s.p. Anisotropic conductivity of spinal-WM and of a group of dorsal muscles near the vertebral column was considered.
Main results: The average E-field magnitude was predicted to be above 0.15 V m-1 in spinal cord regions located between the electrodes. L2-T8 and T8-rIC montages resulted in the highest E-field magnitudes in lumbar and sacral spinal segments (>0.30 V m-1). E-field longitudinal component is 3 to 6 times higher than the ventral-dorsal and right-left components in both the spinal-GM and WM. Anatomical features such as CSF narrowing due to vertebrae bony edges or disks intrusions in the spinal canal correlate with local maxima positions.
Significance: Computational modelling studies can provide detailed information regarding the electric field in the spinal cord during tsDCS. They are important to guide the design of clinical tsDCS protocols that optimize stimulation of application-specific spinal targets.
Unidades organizacionais
Descrição
Palavras-chave
Contribuidores
Financiadores
Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/BIO/00645/2013