J. Richard Rahn

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.

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.

Dual-mode optical projection tomography microscope using gold nanorods and hematoxylin-stained cancer cells

An optical projection tomography microscope (OPTM) can improve axial resolution by viewing a sample from different perspectives. Here, we report a dual-mode OPTM that can generate 3D images of single cancer cells in both absorption mode and polarization mode. Cancer cells were labeled with hematoxylin for absorption imaging and nanorods for polarization imaging. Absorption images can provide morphologic information, and polarization images can provide molecular information. The combination of molecular detection and 3D cytological cell analysis may help with early cancer diagnosis.

Simultaneous 3D imaging of morphology and nanoparticle distribution in single cells with the Cell-CT™ technology

The Cell-CT™ is an optical projection tomography microscope (OPTM) developed for high resolution 3D imaging of single cells based on absorption stains and brightfield microscopy. In this study we demonstrate the use of the Cell-CT™ in multi-color mode for simultaneous imaging of cellular 3D morphology and the 3D distribution of nanoparticle clusters in the cytoplasm. The ability to image cellular processes in relation to cellular compartments with a non-fluorescence 3D technology opens new perspectives for molecular research.

Development of micro-optical projection tomography for 3D analysis of single cells

The Micro-Optical Projection Tomographic Microscope (μOPTM) is an instrument that is being developed for three-dimensional (3D) imaging of cells and subcellular components. The target application for the μOPTM is the early detection of lung cancer by revealing the complex 3D information about chromatin redistribution in the nucleus. The µOPTM employs a scanning objective lens (100x, N.A.=1.25) to create an extended depth-of-field image, similar to a shadowgram or projection, that we call a pseudo-projection. A large number of pseudo-projections (90+) are acquired, from which a tomographically reconstructed 3D image is computed using a filtered backprojection algorithm. The prototype μOPTM uses a single objective lens, so the object (cell) must be rotated for each new pseudo-projection. A custom microtube stage minimizes the lateral and axial motion of the sample tube during scanning and rotation so that registration between successive pseudo-projections is maintained. Image processing methods are used to correct any remaining registration errors. The media inside and outside the tube are refractive index-matched to each other and to the tube (Δnavg < 0.02). The index-matched materials are pressed between two flat parallel windows, providing a nearly distortion-free image. Custom phantoms using microspheres have been constructed and images of these 3D test targets acquired. The minimum resolvable feature size is better than 3 microns. The first 3D image of a cell using μOPTM is also shown.

Multimodal three-dimensional imaging with isometric high resolution using optical projection tomography

The optical projection tomography microscope (OPTM) is an optical microscope that acquires focus-invariant images from multiple views of single cells. Although the depth of field of the objective is short, it can be extended by scanning the objectives focal plane. This extended depth of field image is similar to a projection in conventional X-ray CT. Samples flow through a microcapillary tube filled with optical gel. Optical distortion is minimized by matching refractive index of optical gel and tube. Multiple projection images are taken by rotating the microcapillary tube with sub-micron mechanical precision. After these pseudoprojection images are further aligned, computed tomography methods are then applied to the images to create a 3D reconstruction with isometric resolution of 0.35 microns. Three-dimensional reconstructed images of fluorescent microspheres and cells are shown.

Dual Modal Three-Dimensional Imaging of Single Cell Using Optical Projection Tomography Microscope

The optical projection tomography microscope (OPTM) acquires three-dimensional images with isometric high resolution both in absorption and fluorescence modes, employing computed tomographic image reconstruction. The three-dimensional chromosome structure of a female muntjac cell is shown.