1 / 46

CT Scanner

CT Scanner. Presented by: Dr M A Oghabian Medical Physics Department, Tehran University of Medical Sciences. Computed Tomography. CT uses a rotating x-ray tube, with the beam in the form of a thin slice (about 1 - 10 mm)

alaqua
Télécharger la présentation

CT Scanner

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CT Scanner Presented by: Dr M A Oghabian Medical Physics Department, Tehran University of Medical Sciences

  2. Computed Tomography • CT uses a rotating x-ray tube, with the beam in the form of a thin slice (about 1 - 10 mm) • The “image” is a simple array of x-ray intensity (Projections), and many hundreds of these are used to make the CT image, which is a “slice” through the patient

  3. Third generation CT Scanners(Rotate/Rotate , Wide fan beam) • Wide fan beam • More than 800 detectors • No translational motion • Scan time ~ 0.5 Sec.

  4. A look inside a rotate/rotate CT Detector Array and Collimator X-Ray Tube

  5. 4th Generation CT ScannersRotate/Stationary • Fan beam geometry • More than 4800 detectors

  6. 5th generation: Electron Beam CT (EBCT) - x-ray source is not x-ray tube but a focused, steered, microwave-accelerated EB incident on a tungsten target. - It has no moving parts . - Target covers one-half of the imaging circle; detector array covers the other half. • Images in • less than • 50ms.

  7. Electron Beam CT (EBCT)

  8. EBCT(CONT’D) • There are 4 targets and 4 detector arrays resulting in 4 contiguous images simultaneously. • Each solid -state detector consists of a luminescent crystal and cadmium tungstate • coupled with silicon photodiodes. • Heat dissipation is no problem in EBCT. • Developed for fast imaging. • Used for cardiac imaging

  9. EBCT(CONT’D)

  10. A Look Inside a Slip Ring CT Note: how most of the electronics is placed on the rotating gantry X-Ray Tube Detector Array Slip Ring

  11. Reciprocating rotation (A) versus fast continuous rotation using slip-ring technology (B)

  12. Comparison of data acquisition for axial and helical technologies.

  13. (A) Pitch =1 (B) Pitch = 2

  14. Comparison of the accuracy of 3D reconstruction for conventional (A) and spiral/helical (B) CT scanning.

  15. Multislice Scanning

  16. MULTISLICE SPIRAL CT • Introduced at the 1998. • They are based multiple detector. rows ranging between 8, 16, 24, 32 and 64 depending on the manufacturer. • The overall goal is to improve the volume coverage speed performance. • Complete x-ray tube/detector array rotation in less than 1s. • Partial scan images can be obtained in approximately 100ms.

  17. Multislice CT, where up to 64 variable thickness slices can be collected simultaneously • CT fluoroscopy, where the patient is stationary, but the tube continues to rotate • 3-dimensional CT and CT endoscopy

  18. Detector Configurations X-ray Tube Focal Spot X-ray Beam Collimator a • 4 x 1.25 mm Detector Configuration 16-row Mosaic Detector Flex Connector A Flex Connector B Diode FET Switching Array

  19. Detector Configurations X-ray Tube Focal Spot X-ray Beam Collimator 4 x 2.5 mm Detector Configuration 16-row Mosaic Detector Flex Connector A Flex Connector B Diode FET Switching Array

  20. Detector Configurations X-ray Tube Focal Spot X-ray Beam Collimator 4 x 3.75 mm Detector Configuration 16-row Mosaic Detector Flex Connector A Flex Connector B Diode FET Switching Array

  21. Detector Configurations X-ray Tube Focal Spot X-ray Beam Collimator 4 x 5.0 mm Detector Configuration 16-row Mosaic Detector Flex Connector A Flex Connector B Diode FET Switching Array

  22. Multi slice CT collimation 5mm 2,5mm 1mm 0,5mm

  23. Speed: Single vs. 4 Slice Single Slice 235 mm 5 mm 31 240 255 mm 5 mm 34 300 65 17,720 4 slice Chest Coverage Thickness Time (s) mA Abdomen/Pelvis Coverage Thickness Time (s) mA Scan Time (s) Tube Load (mAs) 235 mm 5 mm 8 240 255 mm 5 mm 9 300 17 4,725

  24. MULTISLICE IMAGING(CONT’D) ADVANTAGES • Improved spatial resolution this advantage improved MPR,3D images. • Reduction of radiation exposure. • Motion artifacts are greatly reduced. • Patient breathhold is much less demanding. • Imaging larger z-axis volume in less time is possible with MI. • Less contrast medium required. • Because of imaging speed, coronary artery is comparable with EBCT. • Improved accuracy in needle placement CT fluoroscopy.

  25. Clinical Benefits Of Multi-Slice Multi-phase Organ Studies • Liver – Pancreas Arterial, Renal Nephrogram Arterial Phase Scanning • Hypervascular Tumors CT Angiography • Multi-Plane Reconstructions, Contrast Enhancement New CT Applications • CT fluoroscopy • CT Colonography • Cardiac: morphology, function • Advanced Lung Analysis

  26. CT Fluoroscopy • Real Time Guidance • Great Image Quality • Low Risk • Faster Procedures

  27. REAL-TIME CT FLUOLOROSCOPY • CT fluoroscopy acquire dynamic images in real time. • Fast continuous imaging, fast image reconstruction & continuous image display. • Patient movement is low during Tube rotation. • Fast image Reconstruction algorithm is required.

  28. CT ANGIOGRAPHY (CTA) • CTA allows maximum visualization of the pulmonary artery and its segmental braches. • CTA requires low kVp and MA, for example 90Kvp/100mA. • CTA employs MIP and MPR to maximum advantage.

  29. CT ANGIOGRAPHY (CTA)

  30. 3D Stereo Imaging

  31. Enhanced 3D

  32. CT Endoscopy

  33. CT VIRTUAL REALITY IAMAGING • The use of virtual reality is the creation the inner views of tubular structures. • Offers both endoluminal and extra luminal information. • It reduces complication (eg. infection and perforation). • Four requirements: • data acquisition • image processing • 3D rendering • image display and analysis.

  34. CT Scanner • Generator • High frequency, 30 - 70 kW • X-ray tube • Rotating anode, high thermal capacity: 3-7 MHU • Dual focal spot sizes: about 0.8 and 1.4 • Gantry • Aperture: > 70 cm of diameter • Detectors: gas or solid state; > 600 detectors • Scanning time: <1 s, 1 - 4 s • Slice thickness: 0.5 - 10 mm • Spiral scanning: up to 1400 mm

  35. Gas detector (xenon) • Fast detection response • High Sensitivity • Stability against Radiation damage • Stability against Temperature & Humidity • Higher Dynamic range • But less Quantum efficiency • Inherent collimation • Total DQE(Detective Quantum Efficiency) • = 60 percent

  36. Solid detectors (Ultra Fast Ceramics) UF • Godalinium OxiSulphade has uniform sensitivity and fast response time • Need collimation so: • Less Geometric Detection Efficiency (GDE) • Total DQE(Detective Quantum Efficiency) • = 80 percent

  37. MTF of CT detectors • MTF depends on: • Geometric characteristics and size of detector • Time response of the detectors • Cross Talk from adjacent projections or Slices due to long Decay time • Decay time is about 3 s • Afterglow is about 10-4 after 3mS • Design type and construction of detector arrays, (detector separation and distance)

  38. number=1000×(mpixel-mwater)/mwaterDetector Calibration CT CT Projections and Reconstruction

  39. CT scanner Image processing: • Reconstruction time: • 0.5 - 5 s/slice • Reconstruction matrix: 256x256 – 1024x1024 • Reconstruction algorithms: • Bone, Standard, High resolution, etc • Special image processing software: • 3D reconstruction • Angio CT with MIP • Virtual endoscopy • CT fluoroscopy

  40. Window width & window level

More Related