Microwave Breast Models Through T1-weighted 3-d Mri Data

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2013Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2013Son yıllarda, meme kanserinin erken teşhisi konusunda mikrodalga görüntüleme alanında yapılan çalışmalar popülerlik kazanmıştır. Bu bağlamda, insan memesinin elektromanyetik sayısal modelleri bu konuda çalışan araştırmacılara, hızlı deneysel analizler yaparak yeni teknolojilerin fizibilitesinin artırılması ve böylece daha iyi görüntüleme tekniklerinin ve aygıtlarının geliştirilmesi konularında yardımcı olmaktadır. Literatürde özel olarak sayısal mikrodalga meme modellerini konu alan bu ilk çalışmada arzu edilen türde bir model üretilebilmesi için 3 ana adım içeren bir yöntem öne sürülmüştür. Bu yöntemin alt adımları kısaca: MRI verisindeki gürültünün homomorfik filtreleme ile giderilmesi, dokuların Gauss Karışım Modeli (GMM) ile segmentasyonu ve elektromanyetik özelliklerin parçalı-doğrusal eşleme fonksiyonları ile eşlenmesi olarak tarif edilebilir. Bu çalışmada, mikrodalga meme görüntülemesi çalışmalarında kullanılmak üzere değişik şekil, ebat ve radyografik yoğunluklarda 3-boyutlu sayısal mikrodalga meme modelleri üretilmesi için etkin ve kendi kendine işleyebilen bir yöntem sunulmuştur. Memenin heterojen yapısının mekânsal bilgisi, memelerinde bir anomaliye rastlanmayan değişik hastaların yüz üstü pozisyonda alınmış T1-ağırlıklı 3-boyutlu MRI verileri kullanılarak elde edilmiştir. Dokulara ait her bir sınıf ile elektromanyetik özellikler arasında tekdüze parçalı kübik Hermitte interpolasyon yöntemi kullanılarak doğrusal olmayan bir ilişki kurulmuştur. İlgili meme dokularının elektromanyetik özellikleri Debye and Cole-Cole dağılım modelleri üzerinden tercih edilen çalışma frekansına göre belirlenmiş, böylece MRI verisindeki her bir voksel değeri uygun bağıl geçirgenlik ve iletkenlik değerleri ile eşlenmiştir. Bağıl geçirgenlik ve iletkenlik dağılımlarına dönüştürülen MRI kesitleri, doğrusal interpolasyon ile 3-boyutlu ve gerçekçi bir yapıya dönüştürülmüştür.Recent years, early detection of breast cancer in the field of electromagnetic imaging has gained high popularity. In this context, computational electromagnetic models of the human breast are used to help researchers develope better techniques and instruments for imaging, increasing the feasibility of new technologies, and doing fast experimental analysis. In this study, an effective and automated methodology for realistic numerical 3-D breast phantom development of different shapes, size and radiographic density in order to be used for different electromagnetic simulation models in microwave breast imaging research is presented. The spatial information of heterogeneity of the breast structure is collected from T1-weighted MRI slices of different patients’ in prone position with normal breast tissue (not malignant or abnormal). Each voxel in MRI data was mapped to the appropriate dielectric properties using several steps. First, bias field appears on each slice in MRI data was estimated and eliminated. After filtering of all slices, voxels belong to adipose and glandular tissues were classified into four categories. Then those tissue categories were related to electromagnetic properties of relative permittivity and conductivity by monotone piecewise polynomial cubic Hermite interpolation. Electromagnetic properties of the breast tissue are expanded to desired frequency using Debye dispersion models. Each voxel intensity value is nonlinearly mapped to the appropriate electromagnetic properties of the corresponding breast tissue. Later, the resultant slices of permittivity and conductivity are linearly interpolated to form a proper 3-D breast structure.Yüksek LisansM.Sc

Anniversary Paper: Evolution of ultrasound physics and the role of medical physicists and the AAPM and its journal in that evolution

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134810/1/mp2048.pd

Visible Optical Coherence Tomography based Multimodal Imaging for Quantification of Retinal Lipofuscin

Retinal degeneration is the leading cause of irreversible low vision and blindness in the world, that describes conditions characterized by progressive loss of photoreceptors. Retinal Pigment Epithelium (RPE) is located under photoreceptors’ outer segments and plays an important role in the maintenance of photoreceptors by completing the visual cycle and phagocytosis of shed photoreceptor outer segments. Lipofuscin, a byproduct of the visual cycle, is a nondegradable compound that accumulates in the RPE cells and eventually damages the RPE cells and inevitably causes photoreceptor degeneration. Lipofuscin is the major cause of fundus fluorescence that can be detected by Fundus Autofluorescent (FAF) imaging systems. Reliable and quantified FAF values are necessary for lipofuscin quantification which can be a significant tool in the diagnosis of retinal degenerative disease in early stages and provide a better opportunity for treatment before the loss of vision stage. However, FAF is attenuated by the ocular media prior to the RPE, including cornea, lens, vitreous body, retinal layers in front of the RPE, and the melanin granules within the RPE cells that migrate to the apical region upon light exposure. This attenuation varies among people and for an individual over time and cannot be measured directly, thus hurdles measurement of the true FAF values. Further, differences in acquisition systems such as illumination power and detector sensitivity, directly affect the measured FAF. This issue has been addressed by implementing a reference target in the FAF imaging system. Normalizing the FAF signal to that of the target eliminates the dependency on the acquisition parameters. However, the issue of pre-RPE and RPE melanin attenuation remains unresolved. Further, the fluorescence characteristics of the commercially available fluorescent reference are quite different than retinal lipofuscin that challenges the quantification of the absolute amount of lipofuscin in the RPE. In this dissertation, we propose a new multimodal imaging system based on visible-light optical coherence tomography (VIS-OCT) that provides a three-dimensional image. The technology simultaneously acquires VIS-OCT and FAF with a single broadband visible light source. Since both images are originated from the same group of photons and travel through the same ocular media at the same time, the attenuation factor is similar in both modalities. Therefore, by normalizing FAF by VIS-OCT of the RPE layer, the attenuation of the pre_RPE media can be eliminated. Further, we implemented two reference targets to quantify VIS-OCT and FAF and eliminate the dependency on acquisition parameters. These references were later substituted by a single customized reference that consists of the major lipofuscin fluorophore, called A2E. The quantitative imaging independent of system fluctuation, and attenuation of pre-RPE and RPE melanin was successfully tested on retinal simulating phantoms, in vivo on the animal retina, and human subjects. The in vivo quantification in small animals linearly correlates with A2E content measured by mass spectrometry. Quantitative imaging of human retinas is consistent with the linear accumulation of lipofuscin with age. The VIS-OCT-FAF has the potential for clinical diagnosis

Application-Specific Broadband Antennas for Microwave Medical Imaging

The goal of this work is the introduction of efficient antenna structures on the basis of the requirement of different microwave imaging methods; i.e. quantitative and qualitative microwave imaging techniques. Several criteria are proposed for the evaluation of single element antenna structures for application in microwave imaging systems. The performance of the proposed antennas are evaluated in simulation and measurement scenarios

Multispectral three-dimensional optical coherence tomography

A spectral-domain OCT system operating at 1300 nm wavelength region, capable of acquiring 47,000 A-lines/s, was designed and developed. Its axial and transverse resolutions were 6 micro and 15 &micro respectively. OCT images of human skin were obtained in vivo using three OCT systems, in order to find the optimal wavelength region for dermal imaging. 800 nm OCT system provided better image contrast over other two wavelength regions. Meanwhile, 1300 nm wavelength region was needed to obtain information from deeper dermal layers. To determine the effect of melanin pigmentation on OCT, images were taken from subjects with different ethnic origins. Interestingly, melanin pigmentation was found to have little effect on penetration depth in OCT. In vitro tumour samples, comprising samples with different degrees of dysplasia, were imaged at 800 nm, 1060 nm and 1300 nm wavelength regions to find the capability of OCT to diagnose microstructural changes occurring during tumour progression. 800 nm OCT system was capable to detect the malignant changes with higher contrast than other wavelength regions. However, higher wavelength regions were required to penetrate deeper in densely scattering tumour samples at advanced stages. OCT system operating at 1060 nm was combined with a photoacoustic imaging (PAT) system to obtain complementary information from biological tissues. This multimodal OCT/PAT system demonstrated its potential to deliver microstructural information based on optical scattering and vascular information based on optical absorption in living mice and human skin. The results indicate OCT as a promising imaging modality that can have profound applications in several areas of clinical diagnostic imaging

Evaluation of a diffraction-enhanced imaging (DEI) prototype and exploration of novel applications for clinical implementation of DEI

Conventional mammographic image contrast is derived from x-ray absorption, resulting in breast structure visualization due to density gradients that attenuate radiation without distinction between transmitted, scattered, or refracted x-rays. Diffraction-enhanced imaging (DEI) allows for increased contrast with decreased radiation dose compared to conventional mammographic imaging due to monochromatic x-rays, its unique refraction-based contrast mechanism, and excellent scatter rejection. Although laboratory breast imaging studies have demonstrated excellent breast imaging, important clinical translation and application studies are needed before the DEI system can be established as a useful breast imaging modality. This dissertation focuses on several important studies toward the development of a clinical DEI system. First, contrast-enhanced DEI was explored using commercially available contrast agents. Phantoms were imaged at a range of x-ray energies and relevant contrast agent concentrations. Second, we performed a reader study to determine if superior DEI contrast mechanisms preserve image quality as tissue thickness increases. Breast specimens were imaged at several thicknesses, and radiologist perception of lesion visibility was recorded. Lastly, a prototype DEI system utilizing an x-ray tube source was evaluated through a reader study. Breast tissue specimens were imaged on the traditional and prototype DEI systems, and expert radiologists evaluated image quality and pathology correlation. This dissertation will demonstrate proof-of-principle for contrast-enhanced DEI, establishing the feasibility of contrast-enhanced DEI using commercially available contrast agents. Further, it will show that DEI might be able to reduce breast compression, and thus the perception of pain during mammography, without significantly decreasing breast lesion visibility. Finally, this research shows the successful implementation of a DEI prototype, displaying breast features with approximately statistically equivalent visibility to the traditional DEI system. Together, this research is an important step toward the clinical translation of DEI, a technology with the potential to facilitate early breast cancer detection and diagnosis