Hard X-rays can penetrate solid objects, and their largest use is to take images of the inside of objects in diagnostic radiography and crystallography. The roentgen (R) is an obsolete traditional unit of exposure, which represented the amount of radiation required to create one electrostatic unit of charge of each polarity in one cubic centimeter of dry air. The rad is the (obsolete) corresponding traditional unit, equal to 10 millijoules of energy deposited per kilogram. The sievert (Sv) is the SI unit of equivalent dose, which for X-rays is numerically equal to the gray (Gy). X-rays are generated by an X-ray tube, a vacuum tube that uses a high voltage to accelerate the electrons released by a hot cathode to a high velocity.
In crystallography, a copper target is most common, with cobalt often being used when fluorescence from iron content in the sample might otherwise present a problem. X-ray fluorescence: If the electron has enough energy it can knock an orbital electron out of the inner electron shell of a metal atom, and as a result electrons from higher energy levels then fill up the vacancy and X-ray photons are emitted. So the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines.
In medical diagnostic applications, the low energy (soft) X-rays are unwanted, since they are totally absorbed by the body, increasing the dose.
To generate an image of the cardiovascular system, including the arteries and veins (angiography) an initial image is taken of the anatomical region of interest.
A specialized source of X-rays which is becoming widely used in research is synchrotron radiation, which is generated by particle accelerators. The most commonly known methods are photographic plates, photographic film in cassettes, and rare earth screens. Before the advent of the digital computer and before invention of digital imaging, photographic plates were used to produce most radiographic images. Since photographic plates are sensitive to X-rays, they provide a means of recording the image, but they also required much X-ray exposure (to the patient), hence intensifying screens were devised. Areas where the X-rays strike darken when developed, causing bones to appear lighter than the surrounding soft tissue. Contrast compounds containing barium or iodine, which are radiopaque, can be ingested in the gastrointestinal tract (barium) or injected in the artery or veins to highlight these vessels.
An increasingly common method is the use of photostimulated luminescence (PSL), pioneered by Fuji in the 1980s. The PSP plate can be reused, and existing X-ray equipment requires no modification to use them. For many applications, counters are not sealed but are constantly fed with purified gas, thus reducing problems of contamination or gas aging.
Some materials such as sodium iodide (NaI) can "convert" an X-ray photon to a visible photon; an electronic detector can be built by adding a photomultiplier. Chinese paintings, and may also be of some assistance even to the more sophisticated scholar or collector of Chinese paintings in bridging some of the diverse gaps that still exist in our collective assessment of individual works. Chinese ethnicity, and generally trained through the traditional private master-pupil relationship.
This approach to learning by copying was the standard method by which all Chinese artists learned to paint. Taipei Xiaozhong xianda album, does add some credence to the notion that the Taipei album may in fact be by Wang Shimin himself. Based on the theories of scholar painters of earlier periods, chiefly Su Shi (1036,1101) and Mi Fu (1051-1107) of the Song, Zhao Mengfu (125-1322) of the Yuan, and Dong Qichang (1555-1636) of the late Ming, the Qing dynasty literati painters, who generally were also connoisseurs and collectors, established an orthodoxy of correct models, techniques of painting, and most important, standards for brushwork. A A A  This approach to learning by copying was the standard method by which all Chinese artists learned to paint. A A A  In a remarkable set of twelve hanging scrolls, now in the Shanghai Museum, painted in 1670, Wang Jian transformed these compositions once again, but this time into full~size vertical scrolls of uniform dimensions.


A A A  Based on the theories of scholar painters of earlier periods, chiefly Su Shi (1036,1101) and Mi Fu (1051-1107) of the Song, Zhao Mengfu (125-1322) of the Yuan, and Dong Qichang (1555-1636) of the late Ming, the Qing dynasty literati painters, who generally were also connoisseurs and collectors, established an orthodoxy of correct models, techniques of painting, and most important, standards for brushwork.
This process produces an emission spectrum of X-ray frequencies, sometimes referred to as the spectral lines. The intensity of the X-rays increases linearly with decreasing frequency, from zero at the energy of the incident electrons, the voltage on the X-ray tube. A second image is then taken of the same region after iodinated contrast material has been injected into the blood vessels within this area. The contrast compounds have high atomic numbered elements in them that (like bone) essentially block the X-rays and hence the once hollow organ or vessel can be more readily seen.
In modern hospitals a photostimulable phosphor plate (PSP plate) is used in place of the photographic plate. Following the model of the calligrapher, the best painters sought to master the styles and techniques of a number of different artists and gradually to synthesize the results into an individual personal style.
4 In either case, the album embodies the attitudes of early 17th century literati towards the artistic process. The assumption was that a skilled artist was capable of capturing the essence of each large-format model and recreating the essential stylistic features and spirit of the original through his scaled-down copies. In the case of the literati scholar-painters, the student not only mastered the techniques of painting but also aligned himself, through the selection of appropriate models to copy, with the great masters of the past. 7 Wang ]ian probably painted this series, or other versions of the compositions depicted in this album, many times.
The same composition could be ascribed to different artists, even by the same copyist, but this did not lessen the value of either the original or the copy. Using calligraphy as a model, the Qing literati reinforced the notion that brushwork should be the principal criterion for judging quality in painting. It is crucial, therefore, that the visual templates themselves are accurate representations of the categories they purport to represent.
It is for this reason that it is useful to study copies and forgeries in addition to original works, using the former to chart the evolving image of early masters down through the subsequent ages.
Today, we fly all over the world to view blockbuster exhibitions in Shanghai, Beijing, Tokyo, New York, London, and Taipei. Wai-kam Ho, editor, The Century of Tung Ch'i.ch'ang 1555-1636, volume 2, Seattle and London, 1992, p. The spectral lines generated depend on the target (anode) element used and thus are called characteristic lines. These two images are then digitally subtracted, leaving an image of only the iodinated contrast outlining the blood vessels.
Photographic film largely replaced these plates, and it was used in X-ray laboratories to produce medical images.
In the pursuit of a non-toxic contrast material, many types of high atomic number elements were evaluated. After the plate is X-rayed, excited electrons in the phosphor material remain "trapped" in "colour centres" in the crystal lattice until stimulated by a laser beam passed over the plate surface.
Electrons accelerate toward the anode, in the process causing further ionization along their trajectory. They attempted to transform the methods of their predecessors and use them for their own creative ends. The copyist hoped to penetrate the internal essence of the original artist's creation and transmit the spirit of the large compositions through his small copies that duplicated the external forms of each composition. Many artists of the same aesthetic persuasion as Wang Shimin produced versions of the same compositions featured in the Xiaozhong xianda album. 13) is a highly attenuated version of the now-familiar composition elsewhere ascribed to either Wu Zhen or Juran.


Ming scholar painters, such as Shen Zhou (1427-1509) and Wen Zhengming (1470-1559) had modeled their styles primarily after Zhao Mengfu and the Four Yuan Masters. The connoisseur must constantly update his visual database as new discoveries are made and new evidence is revealed. Moreover, connoisseurship in general has been increasingly de-emphasized in art history programs worldwide, in favor of less object-oriented approaches to art. The radiologist or surgeon then compares the image obtained to normal anatomical images to determine if there is any damage or blockage of the vessel.
In more recent years, computerized and digital radiography has been replacing photographic film in medical and dental applications, though film technology remains in widespread use in industrial radiography processes (e.g. For example, the first time the forefathers used contrast it was chalk, and was used on a cadaver's vessels.
This process, known as a Townsend avalanche, is detected as a sudden current, called a "count" or "event". 960~980) and Wu Zhen i??(1280-1354) in the album on paper, but curiously assigned to Wu Zhen and Xu Ben (d. Although Wang had to manipulate the proportions of the landscape elements in order to fit the vertical format, he retains all of the basic forms and compositional relationships among forms. In other words, a painter's individual personality was discernible and significant, but only within the context of a relatively narrow range of acceptable conventions of brushwork techniques and compositional modes. By adapting large vertical compositions on silk to smaller, less vertical formats, often on paper, the early Qing literati were able to expand the pantheon of acceptable models to include a broad range of artists from remote antiquity who worked in styles as diverse as those of Fan Kuan (c.
We can exchange information twenty-four hours a day with colleagues halfway across the world by telephone, fax, and e-mail. 960~980) and Wu Zhen (1280-1354) in the album on paper, but curiously assigned to Wu Zhen and Xu Ben (d.
When the film is developed, the parts of the image corresponding to higher X-ray exposure are dark, leaving a white shadow of bones on the film.
1403) in the silk versions, were most likely part of a complete album on silk, or perhaps silk and paper. The harsh, raw strength of the brushstrokes and the intimidating angularity of the forms in the original are entirely lacking. Chinese paintings are sold at public auction and in galleries, and are available for study in museums throughout the world.
Photographic plates are mostly things of history, and their replacement, the "intensifying screen", is also fading into history. 6 In any case, Wang Hui's version reflects the same attitude of reverence towards the ancients and similarly attempts to faithfully convey the spirit and form of the original compositions. 1046-after 1100), and Gao Kegong (1248-1310), as well as the Four Yuan Masters and Zhao Mengfu. We have the tools to elevate connoisseurship to an unprecedented level of accuracy but, in order to do so, we must match the diligence, sensitivity, and passion of our predecessors. The metal silver (formerly necessary to the radiographic & photographic industries) is a non-renewable resource. Thus it is beneficial that this is now being replaced by digital (DR) and computed (CR) technology.
Where photographic films required wet processing facilities, these new technologies do not. Historical differences in scale, function, and artistic intent were subordinated to the promotion of a universal aesthetic based on brushwork.



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