Radiation dosimetry in digital breast tomosynthesis: Report of AAPM Tomosynthesis Subcommittee Task Group 223

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134828/1/mp2600.pd

Image processing methods to study the living hearing organ

In this thesis we are developing image processing methods allowing one to probe the structure and function of the mammalian hearing organ, an intricate cellular assembly with a highly specialized three-dimensional organization. Confocal as well as electron microscopy was used for image acquisition. Three-dimensional confocal imaging is hampered by noise and blur, and this is even more significant when working with deep biological imaging, such as our temporal bone preparation of the guinea pig cochlea. Blur is not only caused by the optical properties of the microscope, but by the scattering of light and distortions caused by the sample itself. Deconvolution is widely used in image processing to reverse these effects. If the system s point-spread function (PSF) is known, a deconvolution can be performed leading to increased image resolution. The idea of getting all the information about the PSF and deconvolution from the image itself is explored in this thesis. A set of tools were developed that screens the images for structures that can be used as PSF estimates. Using the extracted structures, a PSF model for deconvolution was designed, resulting in a significant improvement in deconvolutions of images acquired from the inner ear. To study functionally relevant movements inside the hearing organ, a wavelet-based threedimensional brightness-adjusted optical flow algorithm was designed. Numerical experiments show that the algorithm allows motion detection with less than 10% magnitude error over the range from 0.5 5 pixels under conditions of noise more severe than that typically found in real experiments. The angular error was less than 10° for the same range of motions. Accurate quantification of motion and deformation patterns in the hearing organ is therefore possible. The algorithm was applied to three-dimensional image sequences showing the sound-evoked motion of cochlearsensory cells. Motion directed perpendicular and parallel to the surface of the hearing organ were robust and displayed a linear relationship to each other, suggesting that they are governed by passive cellular properties such as stiffness, mass and damping. In contrast, components directed away from the center of the spiral-shaped cochlea showed much higher variability, and thesecomponents may be more tightly linked to the active, force-generating property of the outer hair cells. Outer hair cells are unique because of their capacity for high-frequency force generation, which requires specialized connections between molecular motors and the cell skeleton. Using electron tomography and three-dimensional reconstruction, we examined one such connecting structure, the pillars , which links the plasma membrane to the cell skeleton. Individual pillars show structural variability, which may have functional relevance. However, tissue processing and imperfect imaging conditions may cause a part of the variability. Information gained from these studies will be useful to develop a more detailed understanding of the three dimensional micromechanics of the cochlea, and to test existing models describing the mechanical vibrations of this organ

Measurement of breast-tissue x-ray attenuation by spectral mammography: first results on cyst fluid

Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to better characterize cysts at mammography screening would be highly desirable to reduce recalls, but the development is hampered by the lack of attenuation data for cysts. We have developed a method to measure x-ray attenuation of tissue samples using a prototype photon-counting spectral mammography unit. The method was applied to measure the attenuation of 50 samples of breast cyst fluid and 50 samples of water. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The attenuation of cyst fluid was found to be significantly different from water. There was a relatively large natural spread between different samples of cyst fluid, whereas the homogeneity of each individual sample was found to be good; the variation within samples did not reach above the quantum noise floor. The spectral method proved stable between several measurements on the same sample. Further, chemical analysis and elemental attenuation calculation were used to validate the spectral measurement on a subset of the samples. The two methods agreed within the precision of the elemental attenuation calculation over the mammographic energy range.QC 20210108</p