Current Issue : April - June Volume : 2013 Issue Number : 2 Articles : 5 Articles
A critical need exists for new imaging tools to more accurately characterize bone quality beyond the conventional modalities of\r\ndual energy X-ray absorptiometry (DXA), ultrasound speed of sound, and broadband attenuation measurements. In this paper\r\nwe investigate the microwave dielectric properties of ex vivo trabecular bone with respect to bulk density measures. We exploit\r\na variation in our tomographic imaging system in conjunction with a new soft prior regularization scheme that allows us to\r\naccurately recover the dielectric properties of small, regularly shaped and previously spatially defined volumes. We studied six\r\nexcised porcine bone samples from which we extracted cylindrically shaped trabecular specimens from the femoral heads and\r\ncarefully demarrowed each preparation. The samples were subsequently treated in an acid bath to incrementally remove volumes\r\nof hydroxyapatite, and we tested them with both the microwave measurement system and a micro-CT scanner. The measurements\r\nwere performed at five density levels for each sample. The results show a strong correlation between both the permittivity and\r\nconductivity and bone volume fraction and suggest that microwave imaging may be a good candidate for evaluating overall bone\r\nhealth...
Intravascular ultrasound (IVUS) imaging is a catheter-based medical methodology establishing itself as a useful modality for\r\nstudying atherosclerosis. The detection of lumen and media-adventitia boundaries in IVUS images constitutes an essential step\r\ntowards the reliable quantitative diagnosis of atherosclerosis. In this paper, a novel scheme is proposed to automatically detect\r\nlumen and media-adventitia borders. This segmentation method is based on the level-set model and the contourletmultiresolution\r\nanalysis. The contourlet transform decomposes the original image into low-pass components and band-pass directional bands.\r\nThe circular hough transform (CHT) is adopted in low-pass bands to yield the initial lumen and media-adventitia contours.\r\nThe anisotropic diffusion filtering is then used in band-pass subbands to suppress noise and preserve arterial edges. Finally, the\r\ncurve evolution in the level-set functions is used to obtain final contours. The proposed method is experimentally evaluated via\r\n20 simulated images and 30 real images from human coronary arteries. It is demonstrated that the mean distance error and the\r\nrelative mean distance error have increased by 5.30 pixels and 7.45%, respectively, as compared with those of a recently traditional\r\nlevel-set model. These results reveal that the proposed method can automatically and accurately extract two vascular boundaries....
We developed and evaluated an algorithm for enumerating fluorescently labeled cells (e.g., stem and cancer cells) in mouse-sized,\r\nmicroscopic-resolution, cryo-image volumes. Fluorescent cell clusters were detected, segmented, and then fit with a model which\r\nincorporated a priori information about cell size, shape, and intensity. The robust algorithm performed well in phantom and tissue\r\nimaging tests, including accurate (<2% error) counting of cells in mouse. Preliminary experiments demonstrate that cryo-imaging\r\nand software can uniquely analyze delivery, homing to an organ and tissue distribution of stem cell therapeutics....
The increasing number of experimental microwave breast imaging systems and the need to properly model them have motivated\r\nour development of an integrated numerical characterization technique. We use Ansoft HFSS and a formalism we developed\r\npreviously to numerically characterize an S-parameter- based breast imaging system and link it to an inverse scattering algorithm.\r\nWe show successful reconstructions of simple test objects using synthetic and experimental data. We demonstrate the sensitivity\r\nof image reconstructions to knowledge of the background dielectric properties and show the limits of the current model....
Microwave imaging techniques are prone to signal corruption from unwanted multipath signals. Near-field systems are especially\r\nvulnerable because signals can scatter and reflect from structural objects within or on the boundary of the imaging zone. These\r\nissues are further exacerbated when surface waves are generated with the potential of propagating along the transmitting and\r\nreceiving antenna feed lines and other low-loss paths. In this paper, we analyze the contributions ofmulti-path signals arising from\r\nsurface wave effects. Specifically, experiments were conducted with a near-field microwave imaging array positioned at variable\r\nheights from the floor of a coupling fluid tank. Antenna arrays with different feed line lengths in the fluid were also evaluated.\r\nThe results show that surface waves corrupt the received signals over the longest transmission distances across the measurement\r\narray. However, the surface wave effects can be eliminated provided the feed line lengths are sufficiently long independently of the\r\ndistance of the transmitting/receiving antenna tips from the imaging tank floor. Theoretical predictions confirm the experimental\r\nobservations....
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