Low-exposure Images Research Articles

Cephalometric analysis with digital storage phosphor images: Extreme low-exposure images with and without postprocessing noise reduction

This study evaluated extreme exposure reduction in cephalography with monitor-displayed DICOM (Digital Imaging and Communication in Medicine, Rosslyn, Va) images. The purposes were to investigate to what extent exposure can be reduced without losing diagnostic information for tracing analysis, whether postprocessing noise reduction could benefit localization of anatomic landmarks in extreme low-exposure images, and the quality of the images. Three images (optimal, extreme low exposure, and noise-reduced extreme low exposure) were obtained from 24 volunteers. Three orthodontists traced 18 landmarks and subjectively judged the quality of the images. Sixteen of the landmarks were well identified on the extreme low-exposure images when they were compared with the optimal images. Apex inferius and apex superius were not well identified. The evaluation of image quality on a visual analogue scale showed that the optimal images were given the highest scores, extreme low-exposure images with postprocessing noise reduction the second highest scores, and extreme low-exposure images the lowest scores. Monitor-based tracing analysis on storage phosphor cephalographic images with a 94% exposure reduction, compared with conventional exposure, can be performed with only 2 of 18 landmarks not well identified. The landmarks were better identified on the low-exposure images with standard postprocessing than on the images with post-processing noise reduction, although the subjective evaluation of the image quality indicated the opposite.

CCD detectors in high-resolution biological electron microscopy.

1. Introduction 11.1 The ‘band gap’ in silicon 22. Principles of CCD detector operation 32.1 Direct detection 32.2 Electron energy conversion into light 42.3 Optical coupling: lens or fibre optics? 62.4 Readout speed and comparison with film 83. Practical considerations for electron microscopic applications 93.1 Sources of noise 93.1.1 Dark current noise 93.1.2 Readout noise 93.1.3 Spurious events due to X-rays or cosmic rays 103.2 Efficiency of detection 113.3 Spatial resolution and modulation transfer function 123.4 Interface to electron microscope 143.5 Electron diffraction applications 154. Prospects for high-resolution imaging with CCD detectors 185. Alternative technologies for electronic detection 235.1 Image plates 235.2 Hybrid pixel detectors 246. References 26During the past decade charge-coupled device (CCD) detectors have increasingly become the preferred choice of medium for recording data in the electron microscope. The CCD detector itself can be likened to a new type of television camera with superior properties, which makes it an ideal detector for recording very low exposure images. The success of CCD detectors for electron microscopy, however, also relies on a number of other factors, which include its fast response, low noise electronics, the ease of interfacing them to the electron microscope, and the improvements in computing that have made possible the storage and processing of large images.CCD detectors have already begun to be routinely used in a number of important biological applications such as tomography of cellular organelles (reviewed by Baumeister, 1999), where the resolution requirements are relatively modest. However, in most high- resolution microscopic applications, especially where the goal of the microscopy is to obtain structural information at near-atomic resolution, photographic film has continued to remain the medium of choice. With the increasing interest and demand for high-throughput structure determination of important macromolecular assemblies, it is clearly important to have tools for electronic data collection that bypass the slow and tedious process of processing images recorded on photographic film.In this review, we present an analysis of the potential of CCD-based detectors to fully replace photographic film for high-resolution electron crystallographic applications.

Time-resolved low-dose microscopy of glutamine synthetase molecules

Time sequences of low-exposure images from the enzyme molecules of glutamine synthetase have been recorded digitally using an on-line recording system. Processing the images results in a time sequence of averaged molecule images which, in the very beginning, exhibit the molecule structure still undamaged by electron irradiation. Different sources of the noise which obscures structural details, such as shot noise, stain embedding and radiation damage, are investigated.

Detection and correction of geometrical distortion in X-ray fluoroscopic images

The use of X-ray fluoroscopy with the image intensifier in radiological work has become routine in most departments of radiology in Britain. The problem of image distortion is rarely highlighted. A method has been devised to identify and correct distorted images using a computer programme after digitisation of the bony outline. The programme re-plots each digitised point, allows good correction of pin-cushion, barrel, trapezoidal and non-linear distortion and permits accurate measurements to be made from the images produced by a low X-ray exposure image intensifier. The method has been used successfully in a study of biplanar radiography of the moving shoulder girdle.