K-edge & K shell

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K-edge describes a sudden increase in the attenuation coefficient of photons occurring at a photon energy just above the binding energy of the K shell electron of the atoms interacting with the photons. The sudden increase in attenuation is due to photoelectric absorption of the photons. For this interaction to occur, the photons must have more energy than the binding energy of the K shell electrons. A photon having an energy just above the binding energy of the electron is therefore more likely to be absorbed than a photon having an energy just below this binding energy.

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The two X-ray contrast media iodine and barium have ideal K shell binding energies for absorption of X-rays, 33.2 keV and 37.4 keV, respectively, which is close to the mean energy of most diagnostic X-ray beams. Similar sudden increases in attenuation may also be found for other inner shells than the K shell; the general term for the phenomenon is absorption edge.

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    X-RAY BEAM QUANTITY AND QUALITY said:
    December 3, 2011 at 2:58 pm

    Patient protection. It is the responsibility of the x-ray technician to useall available protective measures to reduce exposure to the patient. Only thoseradiographs requested by the dental officer will be taken. Be sure that a good qualityx-ray is produced each time a request is made. Wrong exposures, improper exposures,and faulty processing techniques must be avoided. These mistakes result in retakesand unnecessary patient exposure. Also, the lead apron must be used for everyexposure.
    NOTE:Lead aprons are stored flat or hung unfolded. Do not fold or bend lead apronsThese safety devices significantly reduce patient exposure.
    ALARA. ALARA stands for “as low as reasonably achievable.” It refersto taking every reasonable effort to maintain exposures to radiation as far belowprevailing dose limits as practical.
    1-11. X-RAY BEAM QUANTITY AND QUALITYThe quality of the x-ray beam is controlled by the voltage while the milliamperescontrol the quantity. An increase in the voltage and milliamperes reduces exposuretime for the patient.
    a. X-ray Beam Quality. The quality of the x-ray beam is controlled by theamount of voltage. Voltage provides contrast to the film. The desired contrast appearsas various shades of gray, black, and white in the x-ray negative (radiograph).Increased voltage provides less contrast (or more shades of gray). However, the beamhas more penetrating power. Decreased voltage, on the other hand, provides morecontrast (fewer shades of gray and more black and white shades). However, there isless penetrating power in the low voltage exposure. The technique most commonlyused to expose periapical and bite-wing X-rays is a 75 kilovolt peak and 15milliamperes.
    b. X-ray Beam Quantity. The x-ray beam quantity is controlled by themilliamperes. The more x-rays (photons) in the x-ray beam, the more dense (dark) thex-ray negative (radiograph) becomes. By increasing the milliamperes, we increase thenumber of available electrons at the cathode filament. When electrical current (voltage)is applied to the x-ray tube, the electrons cross the gap. When they impact on theanode (tungsten target), a greater number of x-rays (photons) are also produced. Themore x-rays that are available to penetrate an object, the more dense (dark) is the x-raynegative (radiograph).

    Heterogeneous clinical databases can assist clinical association awareness said:
    November 30, 2011 at 7:02 pm

    Researchers from Columbia University determined that, if examined properly, information contained in large, heterogeneous clinical databases can provide detailed illustrations of the temporal patterns of clinical associations and of the types of clinical associations that are made.

    The study, the results of which were published Nov. 28 in the Journal of the American Medical Informatics Association, builds off of past research regarding the relationships among clinical variables with a slightly different angle in comparison: the exploitation of time.

    Using the New York-Presbyterian Hospitals’ clinical database, which contains 22 years worth of EHR data on 3 million patients, the researchers calculated linear correlation between seven clinical laboratory values and 30 clinical concepts that included diseases, medications and symptoms.

    “A relatively simple method, which we use in this study, is to measure linear correlation between co-occurrences of pairs of variables, lagging one variable with respect to the other to assess the change in correlation as variables are shifted in time,” George Hripcsak, MD, of Columbia University, New York City, and his fellow researchers wrote.

    The study’s goal was to show that clinical databases can be used to reveal temporal associations, show different types of associations and determine any value associated with the exploitation of time.

    The study’s authors believe that large clinical databases will prove to be useful tools in the future because the aggregate data that they provide offer reflections of the healthcare process and the recording process, but that healthcare professionals must develop an understanding of EHRs’ inherent biases when conducting analyses of data.

    “We classified associations into three types — definitional, physiologic, and intentional — and showed that care must be taken in interpreting the associations because the health record represents the clinical workflow and not just patient physiology,” Hripcsak concluded. “We found that fully exploiting time in the record revealed the most detailed and reliable information.“

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