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CT detector technology
- 1. Taman kumar BRIT 4rd sem 190528027
- 2. CT detector capture the radiation beam from the patient and convert it into electrical signal which then is converted into binary coded information It measure the intensity of radiation transmitted through the patient
- 3. High efficiency:- refers to the ability to capture, and convert x-ray photons to electrical signal Less Response time:- refers to the speed with which the detector can detect x-rays High Dynamic range:- refers to the ratio of the largest signal to be measured to the smallest signal.
- 4. No After glow:- refers to the persistence of the image even after the radiation has been turned off Small size :-size should be small but resolution should be good
- 5. Solid state detector (semiconductor Radiation Detector) –use semiconductor material as detecting medium. • Scintillation Detectors 1 • Gas Ionization detectors 2
- 6. 1. Scintillation detectors Convert x-ray energy into light then electrical signal 2. Gas ionization detector Convert x-ray energy directly into electrical signal
- 7. X-rays come in contact with scintillator NaI(Erlier) CsI Gets converted into light photons Light photon falls on photocatode Solar cell
- 9. 1. Photomultiplier tube(not enough signal) 2. Dinodes 3. Dinode curve shape 4. maintained at diff. potential(acceleration) 5. Secondary photoelectrons 6. Leads to the amplification of photoeletrons
- 10. Used in multislice ct scan Size 1.0 x 1.5mm QDE (quantum detection efficiency)is 90% Sensitivity about 90-99%
- 11. high pressure ( about 25 atm) non radioactive xenon gas Based on the principle of ionization used for 3rd generation scanner only
- 12. A series of individual gas chamber, usually separated by tungsten plate Electrodes are positioned to collect electrons Xe is used as gas Aprox 1000 chambers When x-ray interact with these chamber Formation of ions occur Run to wards electrodes , lead to moving charge .(small current)
- 13. Not used anymore QDE is 50%-60% Sensitivity is 50 %
- 14. Faster image Improve image quality Patient dose is less Low SNR Less afterglow
- 15. Problem with single slice is time duration Single slice has one detector for imaging Introduction of multi-row detector for 360 degree rotation imaging Collimated Beam Thickness Collimated Beam Thickness Z-Axis Z-Axis
- 16. SINGLE SLICE VS. MULTISLICE DETECTOR Z-Axis Collimated Beam Thickness Single slice detector Multislice detector
- 17. In 1992, Elscint introduced the first solid state detector special x-ray tube based on a double dynamic focus system Focal spot is switched by a computer controlled electron optic system results in the simultaneous scan of two contiguous slices with excellent resolution
- 18. Acquire 4 to 64 to 320 slices per 360 degree rotation Open collimators in “Z” direction 1 2 3 4
- 19. Detector signals can be used Individually In groups 1 2 3 4 Four thin slices 1 2 3 4 Four thicker slices “z” direction •Physical Detectors not necessarily equal to of possible Slices •Thickness is controlled by 1.Digital Acquisition System (DAS) channels 2.collimators
- 20. MULTI-SLICE DETECTOR EXAMPLE 16 DETECTOR ROWS, 4 CHANNELS
- 21. DETECTORS VS. CHANNELS 4 X 1.25 MM Beam collimated to 4 detector rows 1 detector row per DAS channel Effective Detector
- 22. DETECTORS VS. CHANNELS 4 X 2.5 MM Beam collimated to 8 detector rows 2 detector rows per DAS channel Effective Detector
- 23. DETECTORS VS. CHANNELS 4 X 3.75 MM Beam collimated to 12 detector rows 3 detector rows per DAS channel Effective Detector
- 24. DETECTORS VS. CHANNELS 4 X 5 MM Beam collimated to 16 detector rows 4 detector rows per DAS channel Effective Detector
- 25. A . MATRIX ARRAY DETECTOR(isotropic) channels or cells that are equal in all dimensions B . ADAPTIVE ARRAY DETECTORS(anisotropic) cells have different sizes
- 26. DISTRIBUTION OF DETECTORS IN AXIAL DIRECTION VARIES WITH MANUFACTURER All detectors same width “Z” Direction Variable widths
- 27. MULTI-SLICE CT “ADAPTIVE ARRAY DETECTORS” Some scanners use detectors of various widths Post-collimators used to partially block wider elements for thinner slices “z” direction 1 2 3 Three thicker slices 1 2 4 Four thinner slices 3 Post- collimators
- 28. Currently undergoing testing 256 slice ct scannerprototype flat panel Ct scanner Philips 256 Slicer Toshiba 320 Slicer
- 29. A.The 256-slice CT 912 channels, 256 segments and a beam width of 128 mm Possible to scan entire heart in a single rotation
- 30. B.Flat panel detectors •based on the CsI indirect conversion DR
- 31. •Recently used in breast CT •used in DR and in7th gen