This is a presentation that i did as part of my neurology residency programme.

1. Computerised Tomography: Basics

2. WC Roentgen Allan Cormack History

3. Sir Godfrey Newbold Hounsfield. 1919-2004. CT for brain: 1972-73. CT for whole body: 1975. Worked on NMR. EMIDEC 1100. Magnetic films for information storage. Nobel prize in 1979. Knighted in 1981.

5. Initial sketch of the CT machine by GN Hounsefield

6. Experimental CT machine in the lab of GN Hounsefield

7. GN Hounsfield with his initial working prototype CT machine

9. Structure of a standard CT machine Generator Generator Array of Array of detectors Patient table a Aperture Gantry X-ray tube Scan frame

10. CT apparatus

16. Io= incident ray I=transmitted ray µ=100 µ=50 Tissue X-ray film 6x 4x 2x 6x X-ray source µ=100

17. Conventional radiography Vs CT µ1 µ2 µ3 µ2 µ2 µ2 Io I= x I= x Io

19. 8 4 4 4 4 4 4 8 2 2 6 6 6 6 6 6 6 6 4 4 4 4 8 8 8 8 Attenuation measurements are added Numerical representation of the object (matrix) 4 4 2 2 2 2

20. A. Applying grey scale B. Perfect representation C. Imperfect representation Pixel 8 6 4 6 8 4 6

22. 3 step process of CT imaging

23. Data Acquisition

24. A ray is the pathway of a portion of the x-ray beam from one specific focal-spot position to a specific detector position. A view is made-up of many individual rays.

26. As the x-ray beam is scanned around the body, forming many views, the data recorded by the detectors are stored in computer memory for later image reconstruction.

29. 2 types of motions of the x-ray beam relative to the patient's body. 1. Movement of the beam around the body. 2. Movement of the beam along the length of the body. This is achieved by moving the body through the beam as it is rotating. 2 types of beam motion

32. Spiral CT: X ray tube rotation and table movement 3 rd gen Slip ring technology

39. A major advantage of spiral scanning is that the thickness, position, and orientation of image slices can be adjusted during the reconstruction phase. Images of overlapping slices can be created. The reconstruction can be repeated to produce images with different spatial characteristics.

40. The radiation detectors are very small elements that are arranged in rows that span and intercept one view. A specific CT machine can be designed to have either a single row of detectors or multiple rows. There are advantages in having multiple rows. MDCT

41. A body section can be scanned faster with a multiple row detector system with multiple fan beams scanning simultaneously. Crucial for covering a large body section with thin beams for producing thin, high-detail slice images or 3-D volume images. MDCT

43. Reconstruction

49. Display

55. Improving picture quality: 1. Reducing pitch. 2. Small detector size and therefore small ray size. 3. Small voxel size.

56. Small voxel size increases the noise because fewer protons are absorbed or captured in each voxel. Noise can be decreased by increasing the dose to the patient. Selected filter algorithms can decrease or increase the noise.

57. Decreasing Slice Thickness (To Improve Detail)- small voxels- more noise- will require increased dose to reduce noise level. Hence, thin slices should be requested only when necessary. Effect of Slice thickness on Noise and Dose Voxel + Voxel -

58. Increasing pitch: 1. Faster scanning 2. Reduced dose (the radiation is less concentrated) 3. Limiting factor is reduced image detail.

60. Metal artifact

61. Ring artifacts

62. Eg of artifacts

72. Wide angle fan beam geometry 50-55 degree

74. Electron beam CT (modified 4 th generation CT) Calcium tungstate crystal with silicon photodiode 216 deg 210 deg