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Collimators for Gamma Ray Imaging
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
A pinhole is, as applied in the camera obscura, a very natural way of projecting (and mirroring) a large object (e.g. the outside world) to a small surface (e.g. a wall in a dark room). In nuclear medicine, pinhole collimators were used from the very beginning to make projections of small regions of interest to a larger detector surface. As opposed to the camera obscura, where objects are mapped to a minified projection image, a pinhole collimator exhibits the magnification effect by placing the object close to the pinhole. This magnification effect will again – as with converging hole collimators – minimize the effect of intrinsic detector resolution. This property, together with the high sensitivity in the near field, make collimation with pinholes an attractive alternative when imaging small organs like the thyroid [13], parathyroids [14], joints [15] or kidneys [16]. The magnification m of a pinhole collimator is defined as:
The Seventeenth Century
Published in Arturo Castiglioni, A History of Medicine, 2019
At this time when new ideas frequently arose from the violent shock of minds and events, there was an ever increasing appreciation of the correlation between human problems and the possibilities of human knowledge. The philosophies.of Campanella, Sarpi, and Galileo took this specially into account. Among the medical philosophers, of the time and a pioneer in optics was Giambattista della Porta (1540–1615), the inventor of the camera obscura (1563) and the opera glass (1590). Having discovered the principle of the former as a boy of fifteen, according to his own account, he became convinced that vision was due, not to rays leaving the eye, but to something that entered the eye. The Accademia dei Segreti that he founded about 1560 furnished him with observations for his work on Magia Naturalis (1589). Fortunius Licetus of Rapallo (1577–1657) developed the Aristotelian doctrine of the activity of the senses, dominated, however, by the power of the spirit. Licetus, one of the less effective opponents of Harvey’s doctrine, was a prolific writer who enjoyed a popularity even in northern Europe that is hard to explain today. The fact that it was in the ranks of medicine that philosophy found some of its most outstanding representatives is a good indication of the close connection that existed between philosophic and medical studies at this time.
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Published in Anton Sebastian, A Dictionary of the History of Medicine, 2018
Porta, Giovanni Batista della (1535–1615) Italian natural philosopher, born in Naples. He wrote on natural magic, occult sciences, crystallography and physiognomy. He demonstrated the camera obscura and was a member of the Academia dei Lincei in Rome 1610. He is also considered the father of physiognomy, because of his De Humana Physiognomia of 1586. He wrote a botanical work, Phytognomonica in 1583.
Why did Donders, after describing pseudotorsion, deny the existence of ocular counterrolling together with Ruete, Volkmann, von Graefe and von Helmholtz, until Javal reconfirmed its existence?
Published in Strabismus, 2018
Ruete did not employ a gimbal suspension in a second version of his ophthalmotrope.13 This kind of globe suspension will not bring the eye in a tertiary position that complies with Listing’s Law. Pseudotorsion occurs in tertiary positions of gaze in accordance with Donders’ Law. Ruete wrote that the ring with screws supporting the model eye represented the “fat pad behind the eye, the nutshell in which the eye was suspended”, quite a modern concept for his time. Donders, 14, 15 (Figure 5) later presented his own ophthalmotrope to illustrate Donders’ Law. In this model he used gimbal suspension on purpose, to make pseudotorsion visible. This ophthalmotrope was equipped with a camera obscura, to obtain an image of, for instance, the left upper hand corner of the wall in front of us. This image was to be compared with the retinal meridians, which were represented by four copper bars surrounding the camera obscura.
Evolution of the myth of the human rete mirabile traced through text and illustrations in printed books: The case of Vesalius and his plagiarists
Published in Journal of the History of the Neurosciences, 2022
The fine details of the Geminus (1545) figure are, in fact, more regular in arrangement, with smoother lines, reflecting at least in part the differences in line creation in woodcuts and copperplate engravings: With woodcut, fine details, like lines, are created by the relatively difficult process of removing material to either side of an intended line, creating a “relief” that will transmit the ink to paper, whereas with copperplate engravings, lines can simply be scratched onto the plate using a hardened steel tool (i.e., a burin or graver). It is possible to make copies of the same orientation (i.e., not right–left reversed) by tracing, at least in outline and preserving some of the largest details, if the tracing itself is flipped to transfer the tracing ink to the copper plate before engraving (e.g., by rubbing).40As the variation in copies of the Vesalian originals attests, several different techniques were used; likely, some that were destructive (damaging the original) and some that were not destructive (e.g., use of transparent transfer paper, carta lucida; Landau and Parshall 1994). To avoid reversing a copied image (of the same size as the original), the original print could be traced onto a sheet of transparent paper, which could then be reversed and the copied image transferred to the copper plate that had been prepared with a thin layer of wax. There is no evidence that optical devices (e.g., the camera lucida, use of a mirror, or camera obscura) were used for the purpose of copying woodcuts or engravings in the sixteenth century. However, the original Vesalian figure was not simply traced for Geminus (1545), because the figures are not the same size; furthermore, for some of the other plagiarized images it is clear that there is poor fidelity even with many of the larger features (Lanska and Lanska 2013c).