Alan C. Nelson

Imaging radio frequency electron‐spin‐resonance spectrometer with high resolution and sensitivity for in vivo measurements

We report the development of a novel radio frequency electron‐spin‐resonance spectrometer designed to provide measurements with high molar sensitivity and resolution in vivo. Radio frequency (250 MHz) is chosen to obtain good penetration in animal tissue and large aqueous samples with modest sacrifice of sensitivity. The spectrometer has a lumped component resonator and operates in continuous‐wave mode. The spectrometer is capable of two‐dimensional imaging, and with a modest addition should be capable of three‐dimensional imaging. We demonstrate 3‐mm spatial resolution for DPPH samples. For 10‐ml samples of aqueous nitroxide, we demonstrate sensitivity (normalized to spectral width of 1 G) to 3×10−8‐M concentrations and spectral resolution of 0.1 G. Spectra from nitroxide spin label injected into a live mouse are shown.

Three-dimensional imaging of single isolated cell nuclei using optical projection tomography

A method is presented for imaging single isolated cell nuclei in 3D, employing computed tomographic image reconstruction. The system uses a scanning objective lens to create an extended depth-of-field (DOF) image similar to a projection or shadowgram. A microfabricated inverted v-groove allows a microcapillary tube to be rotated with sub-micron precision, and refractive index matching within 0.02 both inside and outside the tube keeps optical distortion low. Cells or bare cell nuclei are injected into the tube and imaged in 250 angular increments from 0 to 180 degrees to collect 250 extended DOF images. After these images are further aligned, the filtered backprojection algorithm is applied to compute the 3D image. To estimate the cutoff spatial frequency in the projection image, a spatial frequency ratio function is calculated by comparing the extended depth-of-field image of a typical cell nucleus to the fixed focus image. To assess loss of resolution from fixed focus image to extended DOF image to 3D reconstructed image, the 10-90% rise distance is measured for a dyed microsphere. The resolution is found to be 0.9 microm for both extended DOF images and 3D reconstructed images. Surface and translucent volume renderings and cross-sectional slices of the 3D images are shown of a stained nucleus from fibroblast and cancer cell cultures with added color histogram mapping to highlight 3D chromatin structure.

HANDX: a model-based system for automatic segmentation of bones from digital hand radiographs

The authors detail the design and implementation of HANDX, a model-based computer vision system used in the domain of medical image processing. Given a digitized hand radiograph, HANDX segments out specific bones and measures particular parameters of the bones, without requiring specific characterization of noise variations in background contrast and anatomical differences which arise from patient variation. Observer variability is reduced by the system, and the resulting measurement may be useful for detecting short-term skeletal growth abnormalities in children and may additional clinical applications. The overall system is modularized into three stages: preprocessing, segmentation, and measurement. In the preprocessing state model-based histogram modification is used to normalize the radiograph. The histogram model is based on the physics of the imaging process. The segmentation stage finds and outlines specific bones using domain-dependent and domain-independent knowledge of hand anatomy and physiology and image edges. The measurement stage obtains clinically useful quantitative parameters from the segmented image.

Semi-automatic segmentation of vascular network images using a rotating structuring element (ROSE) with mathematical morphology and dual feature thresholding

A method for measuring the spatial concentration of specific categories of vessels in a vascular network consisting of vessels of several diameters, lengths, and orientations is demonstrated. It is shown that a combination of the mathematical morphology operation, opening, with a linear rotating structuring element (ROSE) and dual feature thresholding can semi-automatically segment categories of vessels in a vascular network. Capillaries and larger vessels (arterioles and venules) are segmented here in order to assess their spatial concentrations. The ROSE algorithm generates the initial segmentation, and dual feature thresholding provides a means of eliminating the nonedge artifact pixels. The subsequent gray-scale histogram of only the edge pixels yields the correct segmentation threshold value. This image processing strategy is demonstrated on micrographs of vascular casts. By adjusting the structuring element and rotation angles, it could be applied to other network structures where a segmentation by network component categories is advantageous, but where the objects can have any orientation.

Automated cell analysis in 2D and 3D: A comparative study

Optical projection tomographic microscopy is a technique that allows 3D analysis of individual cells. Theoretically, 3D morphometry would more accurately capture cellular features than 2D morphometry. To evaluate this thesis, classifiers based on 3D reconstructions of cell nuclei were compared with 2D images from the same nuclei. Human adenocarcinoma and normal lung epithelium cells were used. Testing demonstrated a three-fold reduction in the false negative rate for adenocarcinoma detection in 3D versus 2D at the same high specificity. We conclude that 3D imaging will potentially expand the horizon for automated cell analysis with broad applications in the biological sciences.

Dual-modal three-dimensional imaging of single cells with isometric high resolution using an optical projection tomography microscope

The practice of clinical cytology relies on bright-field microscopy using absorption dyes like hematoxylin and eosin in the transmission mode, while the practice of research microscopy relies on fluorescence microscopy in the epi-illumination mode. The optical projection tomography microscope is an optical microscope that can generate 3-D images of single cells with isometric high resolution both in absorption and fluorescence mode. Although the depth of field of the microscope objective is in the submicron range, it can be extended by scanning the objectives focal plane. The extended depth of field image is similar to a projection in a conventional x-ray computed tomography. Cells suspended in optical gel flow through a custom-designed microcapillary. Multiple pseudoprojection images are taken by rotating the microcapillary. After these pseudoprojection images are further aligned, computed tomography methods are applied to create 3-D reconstruction. 3-D reconstructed images of single cells are shown in both absorption and fluorescence mode. Fluorescence spatial resolution is measured at 0.35 microm in both axial and lateral dimensions. Since fluorescence and absorption images are taken in two different rotations, mechanical error may cause misalignment of 3-D images. This mechanical error is estimated to be within the resolution of the system.

Three-Dimensional Display from Cross-Sectional Tomographic Images: An Application to Magnetic Resonance Imaging

A system has been developed to facilitate three-dimensional visualizations of tomographic image data. Tomographic techniques yield parallel planes of data at discrete locations; thus, a series of images comprises a three-dimensional database. From this database, a system has been developed to perform three-dimensional calculations, measurements, and display. The system consists of a conventional two-dimensional video monitor, a digitizing tablet for user interaction and region-of-interest (ROI) definition, application-oriented computational software, and an image display system for true three-dimensional database visualization. The three-dimensional display makes use of a varifocal mirror system with vector graphics capability. Through the use of specialized contouring software, we illustrate the utility of this system in the specific examples of displays prepared from magnetic resonance (MR) images of the brain and carotid arteries. It can be concluded that this system will provide valuable diagnostic and physiologic information that will provide added insight into normal and abnormal structure and its relationship to function.

Simulation studies of biomagnetic computed tomography (current flow identification)

Simulation studies were performed on phantom models of electrical sources. As a first step toward the development of an imaging algorithm, the simplified problem of identifying the shape and direction of current flow in a planar surface was addressed. The problem was formulated by identifying a space in which the image was to be reconstructed. The space was segmented into a grid. Each grid space represented a current element. The magnetic field at a sampling point due to the current elements was computed using the Biot-Savart law. Since there were many more current elements than sample points, the problem was underdetermined and had an uncountable number of solutions. The projection theorem was used to define an analytic solution for the magnitude and orientation of the current elements in the grid space. The accuracy of the resulting image was determined by comparing it with the known location of the sources shows that shape of the filamentary current flow can be imaged with this technique. The resolution of images based on the sampling of the field, number of voxels in the reconstruction space, and noise is also analyzed.<<ETX>>

Computed tomography from optical projections for three-dimensional reconstruction of thick objects

An optical tomography system is developed for generating three-dimensional reconstructions of thick objects from projections. The system is useful for studying transparent structures that are 1-10 mm in diameter. Evaluation of the reconstruction system with a test object demonstrates 98% geometric accuracy, 90% accuracy in the detection of boundaries, and 90% accuracy in the measurement of absorbance. Reconstructions are computed from 96 parallel projections spaced evenly within 180 degrees . Accurate alignment of the projections is achieved with a cross-correlation method following data acquisition. Application of the optical tomography reconstruction technique to an intact cochlea permits measurement of internal structures with 16-microm pixels and a diffraction-limited resolution of 24 microm.

Automated 3-Dimensional Morphologic Analysis of Sputum Specimens for Lung Cancer Detection: Performance Characteristics Support Use in Lung Cancer Screening

The LuCED Lung Test comprises an automated 3‐dimensional morphologic analysis of epithelial cells in sputum. For each cell, 594 morphology‐based features are measured to drive algorithmic classifiers that quantitatively assess whether neoplastic cells are present. The current interim clinical study involves sputum samples from patients with known benign and malignant outcomes to assess the feasibility of LuCED as an adjunctive test after suspicious low‐dose computed tomography (LDCT) results or as an independent screening test for lung cancer.