Radiographic applications of spatial frequency multiplexing

The application of spacial frequency encoding techniques which allow different regions of the X-ray spectrum to be encoded on conventional radiographs was studied. Clinical considerations were reviewed, as were experimental studies involving the encoding and decoding of X-ray images at different energies and the subsequent processing of the data to produce images of specific materials in the body

Books in Pieces: Granger, History, and the Collection

This article analyzes the influence of James Granger's Biographical His­tory of England (1769), a volume that spearheaded a remarkable praxis of collecting, interleaving, and rebinding during the eighteenth and nineteenth centuries. This praxis reflects not only radical changes in concepts of col­lecting during this period, but also three central dimensions of book his­tory. These include the era's passion for artefactual collections; its propen­sity for annotative forms, such as marginalia and prefaces; and its burgeon­ing publication of compilatory, systematized texts—such as catalogues, al­manacs, encyclopedias, and other compendium forms. The article goes on to suggest that grangerized texts extend beyond simple, stochastic gather­ings to reveal key precepts of historiographic continuity, serialized succes­sion, ekphrastic reproduction, and synoptic collectivity

Object-Based 3-D Reconstruction of Arterial Trees from Magnetic Resonance Angiograms

By exploiting a priori knowledge of arterial shape and smoothness, subpixel accuracy reconstructions are achieved from only four noisy projection images. The method incorporates a priori knowledge of the structure of branching arteries into a natural optimality criterion that encompasses the entire arterial tree. An efficient optimization algorithm for object estimation is presented, and its performance on simulated, phantom, and in vivo magnetic resonance angiograms is demonstrated. It is shown that accurate reconstruction of bifurcations is achievable with parametric models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85841/1/Fessler111.pd

Model-Based Estimation Techniques for 3-D Reconstruction from Projections

A parametric estimation approach to reconstruction from projections with incomplete and very noisy data is described. Embedding prior knowledge about "objects" in the probed domain and about the data acquisition process into stochastic dynamic models, we transform the reconstruction problem into a computationally ,challenging nonlinear state-estimation problem, where the objects' parametrized descriptions are to be directly estimated from the projection data. This paper is a review in a common framework and a comparative study of two distinct algorithms which were developed recently for the solution of this problem. The first, is an approximate, globally optimal minimum-meansquare- error recursive algorithm. The second is a hierarchical suboptimal Bayesian algorithm. Simulation examples demonstrate accurate reconstructions with as few as four views in a 135 ~ sector, at an average signal to noise ratio of 0.6.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85941/1/Fessler114.pd

Model-Based 3-D Reconstruction of Branching Vessels

This paper describes a new approach to the problem of reconstructing a 3-D arterial tree model from a few angiographic projections. We first develop a natural optimality criterion that defines the globally best reconstruction, and then outline an algorithm that maximizes this criterion. The criterion is a compromise between the conflicting goals of measurement likelihood and object smoothness. Our approach uses a parametric model for the arterial tree, with a new, more accurate model for bifurcations. The algorithm is demonstrated on simulated projections and on magnetic resonance (MR) images.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85823/1/Fessler116.pd

Anomalous scaling law for noise variance and spatial resolution in differential phase contrast computed tomography

In conventional absorption based x-ray computed tomography (CT), the noise variance in reconstructed CT images scales with spatial resolution following an inverse cubic relationship. Without reconstruction, in x-ray absorption radiography, the noise variance scales as an inverse square with spatial resolution. In this letter we report that while the inverse square relationship holds for differential phase contrast projection imaging, there exists an anomalous scaling law in differential phase contrast CT, where the noise variance scales with spatial resolution following an inverse linear relationship. The anomalous scaling law is theoretically derived and subsequently validated with phantom results from an experimental Talbot-Lau interferometer system

Microtesla MRI of the human brain combined with MEG

One of the challenges in functional brain imaging is integration of complementary imaging modalities, such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). MEG, which uses highly sensitive superconducting quantum interference devices (SQUIDs) to directly measure magnetic fields of neuronal currents, cannot be combined with conventional high-field MRI in a single instrument. Indirect matching of MEG and MRI data leads to significant co-registration errors. A recently proposed imaging method - SQUID-based microtesla MRI - can be naturally combined with MEG in the same system to directly provide structural maps for MEG-localized sources. It enables easy and accurate integration of MEG and MRI/fMRI, because microtesla MR images can be precisely matched to structural images provided by high-field MRI and other techniques. Here we report the first images of the human brain by microtesla MRI, together with auditory MEG (functional) data, recorded using the same seven-channel SQUID system during the same imaging session. The images were acquired at 46 microtesla measurement field with pre-polarization at 30 mT. We also estimated transverse relaxation times for different tissues at microtesla fields. Our results demonstrate feasibility and potential of human brain imaging by microtesla MRI. They also show that two new types of imaging equipment - low-cost systems for anatomical MRI of the human brain at microtesla fields, and more advanced instruments for combined functional (MEG) and structural (microtesla MRI) brain imaging - are practical.Comment: 8 pages, 5 figures - accepted by JM

Presence of time-dependent diffusion in the brachial plexus

Purpose This work describes the development of a method to measure the variation of apparent diffusion coefficient (ADC) with diffusion time (Δ) in the brachial plexus, as a potential method of probing microstructure. Methods Diffusion-weighted MRI with body signal suppression was used to highlight the nerves from surrounding tissues, and sequence parameters were optimized for sensitivity to change with diffusion time. A porous media-restricted diffusion model based on the Latour-Mitra equation was fitted to the diffusion time-dependent ADC data from the brachial plexus nerves and cord. Results The ADC was observed to reduce at long diffusion times, confirming that diffusion was restricted in the nerves and cord in healthy subjects. T2 of the nerves was measured to be 80 ± 5 ms, the diffusion coefficient was found to vary from (1.5 ± 0.1) × 10−3 mm2/s at a diffusion time of 18.3 ms to (1.0 ± 0.2) × 10−3 mm2/s at a diffusion time of 81.3 ms. Conclusion A novel method of probing restricted diffusion in the brachial plexus was developed. Resulting parameters were comparable with values obtained previously on biological systems

從中文作文看學生的情意表達能力: 個案研究

本文是一個追蹤研究，首先收集研究對象中一至中三的作文103篇，並採用現象學研究法（Phenomenological Research ）的意念進行研究。現象學研究法的重點在於深入了解人類自然的生活，把沒有虛飾的生活體驗和意義呈現出來。本文主要運用兩種分析工具：威堅遜模式（Wilkinson， 1980）及內容分析（text analysis）。論文研究的目的：分析受試者初中情意表達能力的層次。 This article is a longitudinal research which monitors 103 essays of a student from F.1 to F.3 by adopting 'phenomenological research'. Phenomenological research is based on the deep understanding of human life, presenting us with the truest life experiences without disguise. The ability to express emotion of a student as reflected from his Chinese composition. Two models are employed in this research: Wilkinson’s (1980) and text analysis. The objectives of this research is to analyse the abilities of junior secondary school students to express emotions.link_to_OA_fulltex