Computed tomography basics

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Basic and Conceptual information about Computed Tomography.

Text of Computed tomography basics

  • 1.Maulik R. Shah B. E. (Inst & Control Engg.) M. S. (Biomed Engg., USA) PGDHA (Apollo Hospital) Consultant Biomedical Engineer Medical Equipment Planner Hospital Project Consultant Mobile : 9824019971 Email :

2. Basic & Conceptual Information about Computed Tomography. 3. Equipment Arrangement Radiography v/s Tomography 4. Tomo = image // to long axis of the body CT = image is transverse to the body 5. Basic C T Principles Computed Tomography has the x- ray tube move across the so the image is called a transverse image or one perpendicular to the long axis of the body. 6. Computed Tomography Development Computed tomography has gone through five major design advancements since 1970 Each development improved both scan time and resolution or image quality. Scan time have been reduced from 5 minutes to 50 ms. First scanner used a very tightly collimated pencil beam. 7. Generations First Generation Scanners Translation/Rotation Tube produced a finely collimated beam or pencil beam 1 to 3 detectors were placed opposite the tube for radiation detection 4.5 minutes to gather enough information for one slice Tube was only able to rotate 180 degrees 8. First Generation 1971 Pencil Thin Beam of Radiation Translate and Rotate X-ray source and detector fixed relative position One degree of rotation possible Scan Time (Single Image) 5 min 128 x 128 images Patient X-ray tube Detector 9. First Generation CT Scanner Pencil Beam Translate-Rotate Design 180 one degree images or translations. One or two detectors. 5 minutes scan time 10. Second Generation Fan-shaped x-ray beam 30 or more detectors 20 seconds per slice or 10 minutes for a 40 slice exam 180 degree rotation Long data reconstruction time 11. Second Generation 1974 X-rays Multiple Pencil Fan Shaped 3 - 26 degrees Still Translate and Rotate X-ray source and detector still fixed relative position Rotation increased from one to three degrees Scan time (Single Image) 3.5 min Eventually 5.3 sec X-ray tube Detectors 12. Second Generation CT Scanner Translate-Rotate Fan beam collimation so there is more scatter radiation. 5 to 30 detectors 10 degrees /translation 18 per scan. 30 second scan times Faster scan time 13. Third Generation Fan-shaped x-ray beam 960 detectors opposite the x-ray tube Complete 360 degree rotation Rotate/Rotate movement One rotation = one slice Second data acquisition could be made as the tube and detectors move in the opposite direction. Time reduced to 1 sec per slice 14. 3rd generation configuration 15. Third Generation 1977 X-ray Fan Shaped 21 - 45 degrees Rotation Only Array of Detectors Scan Time (Single Image) 4.8 sec Eventually reduced to 2.5 seconds Detectors X-ray tube 16. Third Generation CT Scanner Rotate-Rotate Fan shaped beam of 30 to 60 for full patient coverage. Constant Source to detector distance due to curvilinear detector array. 17. Third Generation CT Scanner If one detector fails, a ring artifact appears. 1 second scan times Superior reconstruction and resolution. 18. Fourth Generation Developed in 1980s Fixed ring of as many as 4800 detectors, completely surrounding the patient, Rotate only movement Rotating x-ray tube provides short bursts of radiation Detectors collect the remnant radiation to reconstruct into an image 1 minute for multiple slices 19. 4th generation configuration 20. Fourth Generation 1980 X-ray Wide Fan 48 - 120 degrees Rotation Only Full Ring of Detectors Scan Time (Single Image) 5 Sec Eventually reduced to ~1 sec X-ray tube Ring of Detectors 21. Fourth Generation CT Scanner The tube rotates around a stationary ring of detectors. Fan beam Variable slice thickness with pre and post patient collimation. 22. Fourth Generation CT Scanner As many as 8000 detectors. 1 second scan time. Auto-detector calibration so no ring artifact. High radiation dose compared to earlier scanners. 23. Fifth Generation CT Scanner This is the latest generation of CT. Allows for continuous rotation of the tube for spiral CT. 5th Generation also includes two novel designs: