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  1. 1. COMPUTED TOMOGRAPHY<br />Saint Petersburg Electrotechnical University “LETI”<br />Student Alla Shorokhova<br />5104 group<br />Head Professor Alexander Mikerov<br />
  2. 2. Introduction<br />The term "tomography“comes from two Greek words: τομοσ - section and γραφοσ– write<br />(layer-by-layer study of the structure of variousobjects)<br />Typesof imaging<br />Essence: on the summary information it is necessary to define the local information (the matter density at each section)<br />Application<br />The first and most famous application of imaging is computerized X-ray reconstructive tomography (CT)<br />Shorokhova Alla, 5104<br />2<br />
  3. 3. History<br />Shorokhova Alla, 5104<br />3<br /><ul><li> 1917, Johann Radon, created a mathematical foundation </li></ul> tomography<br /><ul><li> 1963, Allan Cormack
  4. 4. 1969, GodfreyHounsfield </li></ul>EMI-scanner<br />a<br />b<br /><ul><li>1979, Cormack and </li></ul>Hounsfield were <br />awarded <br />the Nobel Prize<br />"for the development <br />of computed <br />tomography"<br />The first CT scanner (a) and the first tomography <br />of the brain (b)<br />
  5. 5. Schemes of imaging<br />Shorokhova Alla, 5104<br />4<br />2 generation<br />Several <br />detectors;<br />Imaging – <br />20 sec.<br />1 generation<br />1973;<br />incremental;<br />1 image – <br />4 minutes.<br />3 generation<br />Spiral CT<br />4 generation<br />1,088 fluorescent <br />sensors;<br />Rotates only <br />X-ray tube;<br />0.7 seconds<br />4 generations of CT scanners<br />
  6. 6. Construction<br />Shorokhova Alla, 5104<br />5<br />1. X-ray tube and <br /> a collimator<br />2. Detectors and data<br /> acquisition system<br />3. Tube controller<br />4. High-frequency <br /> generator<br />5. Built-in microcomputer<br />6. Computer <br /> that provides data <br /> exchange with <br /> the console<br />
  7. 7. Construction (2)<br />X-ray tube with the collimation system creates a narrow fan-shaped light beam, whose divergence angle is 30 ° -50 °<br />Attenuation of X-ray beam -> recorded by detectors -> electrical signals. These analog signals ->converted into digital pulses<br />In the CT ceramic, fluorescent and gas detectors are used<br />Extensive software package<br />Shorokhova Alla, 5104<br />6<br />
  8. 8. Scan Modes<br />Shorokhova Alla, 5104<br />7<br />Conventional (incremental) CT<br />(short pause , several minutes)<br />Spiral (helical) CT<br />(helical motion of X-ray tube, <br />reducing time and radiation exposure)<br />
  9. 9. Multiple-Row Detector Spiral CT<br />MDCT, 1992: two or more series of detectors located around the circumference gantry<br />width of the detector<br /> increases from center <br /> to edge<br />1998: 4-row unit<br />2004-2005: <br /> 32-, 64-,128-row units<br />Shorokhova Alla, 5104<br />8<br />
  10. 10. Image reconstruction<br />Shorokhova Alla, 5104<br />9<br />The HU of common substances:<br /><ul><li> The pixel itself is displayed according to the mean attenuation </li></ul> of the tissue(s) that it corresponds to on a scale from +3071 <br /> (most attenuating) to -1024 (least attenuating) on the Hounsfield scale<br /><ul><li> Voxel is a volumetric pixel</li></li></ul><li>Three-dimensional reconstruction<br />Maximal Intensity Projection, MIP<br /> (consists of voxels having the maximum density)<br />Multiplanar Reconstruction, MPR<br /> (makes it possible to reconstruct<br /> images in any projection)<br />Surface Shaded Display, SSD<br /> (threshold value in units of HU)<br />Volume Rendering<br /> (combination)<br />Shorokhova Alla, 5104<br />10<br />Figure: Typical screen layout for <br />diagnostic software, showing <br />one 3D and three MPR views<br />
  11. 11. Example of Volume Rendering (1)<br />Some slices of a cranial CT scan are shown below<br />A volume rendering of this volume clearly shows the high density bones.<br />Shorokhova Alla, 5104<br />11<br />Figures: <br />Computed tomography <br />of human brain, <br />from base of the skull <br />to top. Taken with <br />intravenous <br />contrast medium.<br />
  12. 12. Example of Volume Rendering (2)<br />After using a segmentation tool to remove the bone, the previously concealed vessels can now be demonstrated.<br />Shorokhova Alla, 5104<br />12<br />Bone reconstructed in 3D<br />Brain vessels reconstructed in 3D after <br />bone has been removed by segmentation<br />
  13. 13. Conclusions<br />CT - an important component of inpatient and outpatient care.<br /> The result of CT - a combination of powerful computer processing with the knowledge and skills of a trained human operator.<br />Modern CT scanners are able to emit and collect data about the 1400 positions of the detector tube on the circle 360 °, or about 4 positions in degrees.<br />Technical merits of the spiral CT and volumetric reconstruction open up new prospects for medical imaging.<br />In 2010, so-called 4-dimensional electron tomography was created - visualization techniquesof the dynamics of 3-dimensional objects in time. <br />Shorokhova Alla, 5104<br />13<br />
  14. 14. Thank you for your attention! <br />