CT History


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CT History

  1. 1. COMPUTED TOMOGRAPHY PROGRAM Professor E. Lobel Lesson 1 – CT:History CT: Process CT: Scanners Digital Image Processing Volume Scanning
  2. 2. Contributors to TOMOGRAPHY <ul><li>Stratigraphy </li></ul>Planigraphy Z. des Plantes Laminography Zonography
  3. 3. History <ul><li>NOBEL PRIZES </li></ul><ul><li>Roentgen (1901) </li></ul><ul><li>Hounsfield & Cormack (1979) Computed Tomography </li></ul>
  4. 4. Hounsfield <ul><li>Sir Godfrey N. Hounsfield , DSc, the father of computed tomography, died on August 12, 2004 at the age of 84. He was awarded the Nobel Prize in Physiology or Medicine for 1979 along with Allan M. Cormack , a South African-born naturalized American physicist, for the “development of computer assisted tomography, a revolutionary radiological method, particularly for the investigation of diseases of the nervous system.” </li></ul><ul><li>Hounsfield’s name is immortalised in the Hounsfield units , a quantitative scale used to describe the brightness of tomograms ( radiodensity ). He left his money to fund engineering research and scholarships. He died in August 2004 at the age of 84 from a chronic and progressive lung disease, spending his last years in a nursing home. He was unmarried and unattached, and had no children. </li></ul>
  5. 5. CONSTRUCTION OF FIRST CT <ul><li>RADIATION SOURCE – AMERICUM GAMMA SOURCE </li></ul><ul><li>SCAN—9 DAYS </li></ul><ul><li>COMPUTER PROCESSING—2.5 HOURS </li></ul><ul><li>PICTURE PRODUCTION 1 DAY </li></ul>http://en.wikipedia.org/wiki/Godfrey_Hounsfield
  6. 6. Prototype CT Scanner Hounsfield built a prototype head scanner and tested it first on a preserved human brain , then on a fresh cow brain from a butcher shop, and later on himself. In September 1971 , CT scanning was introduced into medical practice with a successful scan on a cerebral cyst patient at Atkinson Morley's Hospital in Wimbledon, London , United Kingdom . In 1975 , Hounsfield built a whole-body scanner.
  7. 7. EARLY EXPERIMENTS In his initial experiments, Hounsfield used a gamma source rather than an x-ray tube, because the energy distribution of gamma radiation was more uniform It took nine days to acquire image data and 2 and a half hours to reconstruct the image. Once he replaced the gamma ray with an x-ray tube the scan time was reduced to 9 hours.
  9. 9. 1974 <ul><li>Dr. Robert Ledley develops first whole body CT Scanner </li></ul>
  10. 10. SCANNING DEVELOPMENT <ul><li>5 MIN. –1972 </li></ul><ul><li>1 SEC – 1993 </li></ul><ul><ul><li>(now we are sub second) </li></ul></ul><ul><li>3 Lp/cm 1972 </li></ul><ul><li>15 Lp/cm 1993 </li></ul>
  11. 11. Tomography Tomography otherwise known as body section radiography, planigraphy, laminography or stratigraphy, is the process of using motion of the X-ray focal spot and image receptor (e.g. film) in generating radiographic images where object detail from only one plane or region remains in sharp focus
  12. 12. TOMOGRAPHY
  13. 13. Tomo Variations
  14. 14. ZONOGRAPHY –ANGLE <10 DEG Zonography - a form of tomography where the tomographic angle is small, on the order of 10, resulting in a thick plane of focus. The technique is sometimes used to better delineate suspected pathology.
  15. 15. PANTOMOGRAPHY- Panorex Panoramic radiography for obtaining radiographs of the maxillary and mandibular dental arches and their associated structures.
  16. 16. AUTOTOMOGRAPHY A method of body-section radiography involving movement of the patient instead of the x-ray tube.
  17. 17. CT Defined <ul><li>Computed tomography or CT is a diagnostic imaging modality which uses x-rays to image individual cross-sectional slices through the body. </li></ul>AKA <ul><li>COMPUTERIZED TRANSVERSE AXIAL TOMOGRAPHY </li></ul><ul><li>COMPUTER ASSISTED TOMOGRAPHY </li></ul><ul><li>COMPUTERIZED AXIAL TOMOGRAPHY </li></ul><ul><li>COMPUTED TOMOGRAPHY </li></ul>
  18. 18. CT Setup X-RAY EMMISSION
  19. 19. CT SETUP overview Responsible for slice thickness Can reduce dose 15%
  20. 20. Full System
  21. 21. CT
  23. 23. Instructional commands initiated by the technologist about pt. Specific imaging parameters, post processing & Archiving. Image Reconstruction Commands translated into machine language Timing/operation of table, gantry, high volt. Generator.These are electrical signals Digital to Analog (continuous, wave form) Attenuation Information In the form of tiny little electrical signals Amplified signals are sampled and then digitized by the analog-to-digital converter Image Creation
  24. 24. Image Reconstruction Has Volume Thickness
  25. 25. Data Acquisition System (DAS)
  26. 26. Reconstruction of What?
  27. 27. Image Reconstruction 2D views (projections) at angles all the way around the patient
  28. 28. Types of Image Reconstruction <ul><li>BACK-PROJECTION </li></ul><ul><li>ITERATIVE ALGORITHM ( not used ) </li></ul><ul><li>ANALYTIC RECONSTRUCTION ALGORITHM </li></ul><ul><ul><li>FILTERED BACK PROJECTION </li></ul></ul><ul><ul><li>FOURIER RECONSTRUCTION </li></ul></ul>The raw data collected from measured attenuation information must be further processed (reconstructed) in the scanners array processor. Most CT systems today use a reconstruction method called filtered back projection .
  29. 29. Back Projection BACK PROJECTION
  30. 30. Filtered Back Projection Steps <ul><li>Projection profiles are obtained </li></ul><ul><li>Logarithm of data is obtained </li></ul><ul><li>Logarithmic values are multiplied by digital filter or convolution filter to generate filtered profiles </li></ul><ul><li>Filtered profiles are now back-projected </li></ul><ul><li>Filtered projections are summed and the negative and positive components are therefore canceled providing an image free of blurring </li></ul>
  31. 32. ITERATIVE ALGORITHM <ul><li>In mathematics , computing , linguistics , and related disciplines, an algorithm is a finite list of well-defined instructions for accomplishing some task that, given an initial state, will proceed through a well-defined series of successive states, eventually terminating in an end-state. </li></ul>
  32. 33. ITERATIVE ALGORITHM <ul><li>Iterative algorithms use repetitive constructs like loops and sometimes additional data structures like stacks to solve the given problems. </li></ul>
  33. 34. Filtered Back Projection
  34. 35. FBB
  35. 36. FBB diag
  36. 37. FBB
  37. 38. Fourier Reconstruction <ul><li>This reconstruction process is used in MRI but not in modern CT scanners because it requires more complicated mathematics than the filtered back projection algorithm. </li></ul>
  38. 39. Convolution <ul><li>This process involves multiplication of overlapping portions of the filter function. </li></ul><ul><li>Convolution plays a partial role in reconstruction when combined with filtered back projection. </li></ul>
  39. 40. Image Display Specifications: • 3D volume rendering, real-time interactive performance (VP) • Real-time interactive MPR, Slab MIP, and curved MPR views • Independent masks with powerful cutting, editing, and segmentation tools • Cutplane and user defined slab thickness inspection
  40. 41. Communication
  41. 42. Communications
  42. 43. Image Storage <ul><li>With the multitude of studies and images a great deal of storage is necessary and can come in several forms. </li></ul><ul><li>Images are stored in 2D pixel arrays with each point representing a number of bits determining a gray level. </li></ul><ul><li>Typically floppy disks do not have enough memory for CT </li></ul>MOD
  43. 44. http://youtube.com/watch?v=3SFUzLBV9aA&feature=related
  44. 45. Scanner Types <ul><li>Conventional </li></ul><ul><li>High Speed (cardiovascular CT) </li></ul><ul><li>Spiral/Helical Scanners </li></ul><ul><li>Mobile Scanners </li></ul><ul><li>CT Fluoroscopy </li></ul>
  45. 46. Conventional Scanner <ul><li>Also known as Step by Step. Or Step and Shoot. </li></ul>
  46. 47. High Speed CT (cardiovascular CT) <ul><li>Speed 50, 100 ms </li></ul><ul><li>Thickness 1.5, 3, 6, 10 mm </li></ul><ul><li>ECG trigger Cardiac Images </li></ul>EBCT
  47. 48. EBCT To achieve shorter image acquisition times than conventional mechanical CT, especially for cardiac and pediatric imaging, Electron Beam CT (EBCT) was introduced in 1984 . EBCT provides image acquisition times down to 100msec that become possible with a non-mechanical movement of the X-ray source and a stationary detector array. For cardiac scanning, the heart is covered with prospectively ECG-triggered sequential scans. As EBCT is also restricted to single-slice acquisition for ECG-triggered scans examination times may still be beyond a single breath-hold. Typical scan times are 30 to 40 seconds for a 12cm volume.
  48. 49. EBCT ( SIEMENS)
  49. 50. MOBILE CT USE:
  50. 51. Spiral CT <ul><li>Spiral/Helical scanners use slip ring technology to allow the tube to make continuous rotations around the patient while the patient simultaneously moves into the gantry so a volume of tissue may be scanned in one breath hold </li></ul>                                                                                
  51. 52. CT Fluoroscopy (CTF) <ul><li>Display of constantly updated images produced by continuous rotation of CT tube </li></ul><ul><li>Couch position controlled by operator </li></ul><ul><li>Generally performed at same KV, but lower mA than conventional CT Scanning </li></ul><ul><ul><li>120KV, 50mA for CT Fluro </li></ul></ul><ul><ul><li>120KV, 200-300mA conventional </li></ul></ul>Picker 5000 Venue Helical CT scanner with C-arm fluoroscopy with integrated biopsy arm, 3-4D image reconstruction capability, as well as a radiation therapy planning package (VOXEL Q software).
  52. 53. CT Fluro <ul><li>Guidance in interventional procedures </li></ul><ul><ul><li>Tissue Biopsies </li></ul></ul><ul><ul><li>Drainage of fluid from lesions </li></ul></ul><ul><ul><li>Spinal nerve blocks </li></ul></ul><ul><li>Timing </li></ul><ul><ul><li>Optimizing start of helical CT run in contrast agent studies. Important in CTA where cardiac output can be variable </li></ul></ul>
  53. 54. CT Angio (CTA) <ul><li>Computerized tomographic angiography, also called CT angiography or CTA, is a test that combines the technology of a conventional CT scan with that of traditional angiography to create detailed images of the blood vessels in the body. </li></ul>
  54. 55. CT ENDOSCOPY (CTE) <ul><li>Based on a combination of spiral CT images and 3-D reconstruction techniques, virtual colonoscopy can detect most polyps of clinically significant size and differentiate between polyps and complex folds. </li></ul>
  55. 56. CTE
  56. 57. TRANSPARENCY <ul><li>Transparency can be used to enrich the visualization and investigate the relationship among several anatomical structures </li></ul>
  57. 58. PET/CT fusion <ul><li>A dual-purpose imaging device, PET/CT is literally the combination of PET (positron emission tomography) and CT (computed tomography) imaging techniques within a single machine. The individual scans, which are taken virtually simultaneously, can be presented separately or as a single, overlapping, or &quot;fused&quot; image. The two techniques present different types of information about the human body: PET shows metabolic or chemical activity in the body; CT shows the body's anatomical structures. For example, a PET scan would highlight a tumor's increased glucose consumption, while a CT scan would reveal its physical mass. </li></ul>                                                                                                                                  
  58. 59. ANIMAL SCANNING                                                                                                                                                                                             
  59. 60. Multi-Slice CT Scanners
  60. 61. A multislice scanner allows for less contrast and faster acquisition times. More slices per tube rotation.
  61. 62. First Generation <ul><ul><li>Single detector with parallel beam </li></ul></ul><ul><ul><li>Translate - rotate acquisition </li></ul></ul><ul><ul><ul><li>Translates across patient </li></ul></ul></ul><ul><ul><ul><li>Rotates around patient </li></ul></ul></ul><ul><ul><li>Very slow </li></ul></ul><ul><ul><ul><li>minutes per slice </li></ul></ul></ul>180 degree Rotation
  62. 63. Second Generation <ul><ul><li>Narrow fan beam (10°) </li></ul></ul><ul><ul><li>Multiple detectors </li></ul></ul><ul><ul><li>Multiple angle acquisition at each position </li></ul></ul><ul><ul><ul><li>Larger angle rotate </li></ul></ul></ul><ul><ul><ul><li>Translate still required </li></ul></ul></ul><ul><ul><li>Slow </li></ul></ul><ul><ul><ul><li>20s per slice </li></ul></ul></ul>
  63. 64. Third Generation <ul><ul><li>Fan beam </li></ul></ul><ul><ul><li>Multiple (500 - 1000) detectors </li></ul></ul><ul><ul><li>Rotation only </li></ul></ul><ul><ul><ul><li>no translation required </li></ul></ul></ul><ul><ul><li>Much faster </li></ul></ul><ul><ul><ul><li>as fast as 0.5 s per rotation </li></ul></ul></ul><ul><ul><li>Most common modern scanner design </li></ul></ul>Spiral Scanning is now possible
  64. 66. Fourth Generation <ul><ul><li>Cone Style Beam </li></ul></ul><ul><ul><li>Static detectors all round gantry (up to 4800 on a single ring) </li></ul></ul><ul><ul><li>Only tube rotates </li></ul></ul><ul><ul><li>Avoids ring artifact problems of 3rd generation scanners </li></ul></ul>
  65. 67. Comparison Schematic illustration of different generations of X-ray CT scan geometries. Solid arrows indicate movements during data collection, dashed arrows indicate movement between sequences of data collection. The solid lines passing from the sources to the detectors are ray paths, and each set of solid lines from a single angular orientation constitutes a view. These illustrations show the source and detectors moving around a stationary object, as is the case with medical scanners. The motion is relative, however, and in many industrial scanners the object moves while the source and detectors are stationary. In all cases, the axis of rotation is the center of the circle. A . First-generation, translate-rotate pencil beam geometry. B . Second-generation, translate-rotate fan beam geometry. C . Third-generation, rotate-only geometry. D . Third-generation offset-mode geometry.
  66. 68. Dose Reduction In CT <ul><li>PRE-PATIENT FILTERING—15% REDUCTION </li></ul><ul><li>ULTRAFAST CERAMIC DETECTORS-25% REDUCTION </li></ul><ul><li>DOSE ADAPTION –40% REDUCTION </li></ul>
  67. 69. Dose C.A.R.E ADAPTION Combined Applications to Reduce Exposure Fluro System
  68. 70. QC
  69. 71. QC
  70. 72. Other Uses - Archeology
  71. 73. Other Uses – Materials Testing
  74. 76. 3D Scanning
  75. 77. Thanks……