Wednesday, March 4, 2009
x-ray history
Wilhelm Conrad Roentgen, a German scientist, discovered x-ray on November 8, 1895 when he was working with cathode rays, light phenomena and electrical currents in highly evacuated glass tubes. That next month he presented a x-ray of his wife’s hand to the Wurzburg Physical-Medical Society. He discovered that x-rays (using the mathematical symbol “x” for the unknown quantity, he called his discovery x-ray) could be recorded on photographic film in order to make them permanent. By January 1896, x-rays were used in a hospital (Oden, 2004 and Lentle, 2003).
what is x-ray
X-ray belongs in the same category as visible light, radio waves, ultraviolet and microwave. All these are electromagnetic energy. One end of the spectrum has radio waves while the opposite end has gamma rays. Visible light is in the center of the scale. Only visible light can be seen with the eye. Radio waves has a longer wavelength, lower frequencies and lower energy than gamma rays. The gamma rays have short wavelengths, high frequency and high energy. X-Ray is on the gamma ray end. “Because of their short wave length, x-ray can penetrate materials that normally reflect or absorb visible light. Like light, x-rays can produce a visible image on photographic film
Thursday, January 1, 2009
X-RAY DETECTOR
X-RAY DETECTOR
With the advent of large semiconductor array detectors it has become possible to design detector systems using a scintillator screen to convert from X-rays to visible light which is then converted to electrical signals in an array detector. Indirect Flat Panel Detectors (FPDs) are in widespread use today in medical, dental, veterinary and industrial applications. A common form of these detectors is based on amorphous silicon TFT/photodiode arrays.The array technology is a variant on the amorphous silicon TFT arrays used in many flat panel displays, like the ones in computer laptops. The array consists of a sheet of glass covered with a thin layer of silicon that is in an amorphous or disordered state. At a microscopic scale, the silicon has been imprinted with millions of transistors arranged in a highly ordered array, like the grid on a sheet of graph paper. Each of these thin film transistors (TFTs) are attached to a light-absorbing photodiode making up an individual pixel (picture element). Photons striking the photodiode are converted into two carriers of electrical charge, called electron-hole pairs. Since the number of charge carriers produced will vary with the intensity of incoming light photons, an electrical pattern is created that can be swiftly converted to a voltage and then a digital signal, which is interpreted by a computer to produce a digital image. Although silicon has outstanding electronic properties, it is not a particularly good absorber of X-ray photons. For this reason, X-rays first impinge upon scintillators made from eg. gadolinium oxysulfide or caesium iodide. The scintillator absorbs the X-rays and converts them into visible light photons that then pass onto the photodiode array.
With the advent of large semiconductor array detectors it has become possible to design detector systems using a scintillator screen to convert from X-rays to visible light which is then converted to electrical signals in an array detector. Indirect Flat Panel Detectors (FPDs) are in widespread use today in medical, dental, veterinary and industrial applications. A common form of these detectors is based on amorphous silicon TFT/photodiode arrays.The array technology is a variant on the amorphous silicon TFT arrays used in many flat panel displays, like the ones in computer laptops. The array consists of a sheet of glass covered with a thin layer of silicon that is in an amorphous or disordered state. At a microscopic scale, the silicon has been imprinted with millions of transistors arranged in a highly ordered array, like the grid on a sheet of graph paper. Each of these thin film transistors (TFTs) are attached to a light-absorbing photodiode making up an individual pixel (picture element). Photons striking the photodiode are converted into two carriers of electrical charge, called electron-hole pairs. Since the number of charge carriers produced will vary with the intensity of incoming light photons, an electrical pattern is created that can be swiftly converted to a voltage and then a digital signal, which is interpreted by a computer to produce a digital image. Although silicon has outstanding electronic properties, it is not a particularly good absorber of X-ray photons. For this reason, X-rays first impinge upon scintillators made from eg. gadolinium oxysulfide or caesium iodide. The scintillator absorbs the X-rays and converts them into visible light photons that then pass onto the photodiode array.
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