Luces y sombras del tratamiento endoscópico del enfisema / Pros and Cons of Endoscopic Treatment of Emphysema

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How electron cryotomography is opening a new window onto prokaryotic ultrastructure.

Electron cryotomography is an emerging technology that enables thin samples, including small intact prokaryotic cells, to be imaged in three dimensions in a near-native 'frozen-hydrated' state to a resolution sufficient to recognize very large macromolecular complexes in situ. Following years of visionary technology development by a few key pioneers, several laboratories are now using the technique to produce biological results of major significance in the field of prokaryotic ultrastructure. Recent discoveries have included the surprising generality and complexity of the cytoskeleton, the connectivity of key membrane compartments, the location and architecture of large macromolecular machines such as the ribosome and flagellar motors, and the structure of some extraordinary external appendages. Through further technology development, identification of the most revealing model systems and sustained effort, electron cryotomography is poised to help resolve many fundamentally important questions about prokaryotic ultrastructure.

In search for the third dimension: from radiostereoscopy to three-dimensional imaging.

The radiographic image is the bidimensional projection of a tridimensional volume. Interpretation of such an image is sometimes uneasy as we cannot determine ot which level the shadows are located. To dissociate the superimposed shadows, the radiologist may rely on different techniques including fluoroscopy, profile view, radiosteoroscopy, conventional tomography, transverse axial tomography or really three-dimensional imaging techniques such as computer assisted (axial) tomography, ultrasound, and magnetic resonance imaging. This paper makes a short historical overview of these different techniques.

From radio-astronomy to medical imaging.

A common thread in much of the medical imaging that has developed over the past 20 years has been the Fourier transform. It was Richard Bates' interest in radio-interferometry, as well as his fascination with problems of medical imaging that prompted an initial interest in applying Fourier techniques to medical imaging in general and to Computed Tomography in particular. This resulted 20 years ago in one of the earliest technical papers advocating Fourier techniques for reconstructing cross-sections from radiographic projections (Bates and Peters, NZ J Science 14:883-896, 1971). Since those early days, medical imaging has explored into a multi-billion dollar industry. The CT scanner has become the workhorse imaging modality in the radiology department, while its more recent relative, the MR scanner, is rapidly gaining ground as a technique of even greater importance. Richard Bates, with his team of "Medical Imagers" was a very significant force in the development of the field of Medical Imaging as we know it today. This paper attempts to chronicle the genesis of this process from the personal perspective of the author.

Theory of image reconstruction in computed tomography.

Mathematical methods are of central importance in the new technologies of radiographic and radioisotopic image reconstruction. The most important procedures are classified as Back-projection, iterative, and analytical (Two-dimensional Fourier, Filtered Back-projection). Back-projection played an important historical role but is no longer used because of sizable artifacts. Analytical methods excel in speed and accuracy when a large number of projections are available and are extensively used in x-ray imaging. Iterative reconstruction is more attractive when the number of views is limited, if noise is significant, and if additional factors, e.g., gamma-ray attenuation, are present. For these reasons, iterative methods are widely used in radioisotope imaging.