ADC PRE-PATIENT COLLIMATION POST-PATIENT COLLIMATION

 The Restriction of X-Radiation to the Area being Examined or Treated by Confining the Beam with Metal Diaphragms or Shutters made of Lead which Completely Absorb the Photons; With High Radiation - Absorption Power.  In addition to Protecting the Patient and Others From Scatter Radiation.  Beam Collimation Reduces Radiographic Density.  Collimator Reduces Scatter Radiation that Reaches the Detector Array.  Improving the Image Contrast.  Determines the Slice Thickness.  In CT Imaging, Two Collimators are used.  One Collimator is Mounted on the X-Ray Tube Housing or Adjacent to it.  This is Called Prepatient Collimator that Determines Patient Dose.  Second Collimator is Called Predetector Collimator.

 Remove the Soft, Low - Energy X - Rays, which Contribute Strongly to the Patient Dose and Scatter Radiation but Less to the Detected Signal.  Make the Beam Harder and More Monoenergetic.  The Inherent Filtration of the X - ray - Tube, Typically 3 mm Aluminum Equivalent Thickness, is the First Filter.  In addition, Flat or Shaped Filters Made of Copper or Aluminum, are placed between the X - Ray Source and the Patient.

 CT Imaging system have Multiple Detectors in an Array that Numbers Up to Tens of Thousands.  The Detector is the System for Quantitative Recording of the Incident Ionizing Radiation. It Acts in Two Steps; The Reception of the Incident X - Ray Photon, and The Transformation of the X - Ray Photon into a Corresponding Electrical Signal, that is then Amplified and Converted from an Analog to a Digital Form.  Previously Gas – Filled Detectors were used: Ionization Chambers, mostly Filled with the Noble Gas Xenon Under High Pressure. Gas Detectors have become Obsolete Due to their Limited Detection Efficiency and the Difficulty in Manufacturing them for Multi - Row Design, but now, all are Scintillation, Solid State Detectors.  Early Scintillation Detector Arrays contained Scintillation Crystal in Photodiode such as Cesium Iodide or Cadmium Tungstate, and Ceramic Materials such as Gadolinium Oxysulfide. Photodiodes Convert the Light into an Electronic Signal.  The Combination of a Scintillation Crystals and the Light Detectors is Called a Scintillation Detectors.